- Email: [email protected]
Effects of fish size at harvest, initial stocking density and tank lighting conditions on the habituation of pond-reared yellow perch (Perca flavescens) to intensive culture conditions
Aquaculture, IO4 ( 1992) 67-78
67
Elsevier Science Publishers B.V., Amsterdam
Jeffrey A. Malison and James A. Held Universityqf WisconsinAquaculture Program, Universityof Wisconsin-Madison,Madison, WI, VS.4
(Accepted 12 September 1991) ABSTRACT
Malison, J.A. and Held, J.A., 1992. Effects of fish size at harvest, initial stocking density and tank lighting conditions on the habituation of pond-reared yellow perch (Percaflavescens) to intensive culture conditions. Aquaculrw, IO4: 67-18. Groups of age-0 pond-reared yellow perch (Percajbvescens) fingerlings were harvested and habituated to intensive culture conditions and formulated feeds under various treatment regimes. The habituation intervals for the different fish groups lasted from 19 to 5 1 days, until the number of dead fish recovered daily for each group became insignificant and all remaining fish were actively feeding. End points measured included ( 1) habituation, defined as the percentage of fish that survived the transition to intensive culture conditions; (2 ) starvation, defined as the percentage of fish that died and were recovered; and (3) cannibalism, defined as the percentage of fish that could not be accounted for at the end of the habituation intervals. The habituation of perch harvested at mean total lengths (TLs) of 16.9, 32.5, or 42.6 mm did not differ (53.3255, 68.326.3, and 55.7+4.5%, respectively), but habituation occurred faster and over a shorter interval in smaller perch. Perch harvested at 16.9 mm 1’L grew to a larger ultimate size than those harvested at 42.6 mm TL. Fingerlings harvested at 16-20 mm TL and initially stocked into 750-l tanks at 13.7 fish/l had improved habituation (53.3 + 5.5W) and reduced cannibalism (20 .S f 11.01) compared to those stocked at 37.4 fish/l (28.Ok3.2 and 50.5f 3.2Oh,respectively). Perch reared using internal tank lighting had improved habituation compared to those reared overhead lighting (54.5 f 3.2 vs. 42.7 f 2.2%). Our results show that pond-reared perch fingerlings can be successfully habituated to intensive culture conditions at a mean size as small as 16.9 mm TL. and that fingerling production can be greatly improved by using a strategy of early pond harvest in combination with appropriate tank stocking densities and internal tank lighting.
INTRODUCTION
The yellow perch (fercaflavescens) is a highly valued food fish in the North Central region of the United States, and as such is a potentially important Correspondence to: Dr. Jeffrey A. Malison, University of Wisconsin Aquaculture Program, Department of Food Science, 103 Babcock Hall, University of Wisconsin-Madison, Madison, WI 53706, USA. 00448486/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved,
68
J.A. MALISON AND J.A. HELD
species for commercial aquaculture. The Industry Advisory Council and the Technical Committees for Extension and Research of the North Central Regional Aquaculture Center identified yellow perch as a species that merits the highest priority for aquaculture research in the region. One major constraint on the development of yellow perch aquaculture is the lack of available information on fingerling production. The larvae of yellow perch, like those of many other fishes characterized by small eggs and fry (e.g., walleye [Stizostedion vitreum] and striped bass [ Morone saxatih] ), are difficult to rear intensively using formulated feeds (Mansuetti, 1964; Nickum, 1978; Best, 198 1; Eldridge et al., 198 1). Successful methods for intensively rearing larval perch currently rely on feeding large amounts of live zooplankton during the first few weeks of culture (Hale and Carlson, 1972; F.P. Binkowski, personal communication, 199 1) . An alternative and perhaps less costly strategy for producing perch fingerlings is to initially culture perch extensively in ponds for 4-8 weeks, and then harvest and habituate the fingerlings to intensive conditions .and formulated feeds (Heidinger and Kayes, 1986). Using this strategy, the production of habituated fingerlings will ultimately be determined by the number of fingerlings harvested from ponds as well as their habituation, defined as the percentage of fish surviving the transition from extensive to intensive culture conditions. The number of fingerlings that can be reared in production ponds is dependent on many factors including food availability, cannibalism and water quality (Li and Mathias, 1982; Keast and Eadie, 1985; Swanson and Ward, 1985; Colsante et al., 1986; McIntyre et al., 1987). Under most conditions, fingerling production for coolwater species such as perch and walleye normally ranges from 50 000 to 135 000 fish/ha of pond surface area when fish are harvested at 35-65 mm total length (TL, see e.g., Dobie, 1956; Buttner, 1989). Implicitly, the number of fingerlings produced will be maximized by harvesting fish at a small size and early age. The degree to which such an early pond harvest strategy can improve fingerling production is illustrated by the observation of Manci et al. ( 1983) that over 300 000 perch fingerlings/ha can be produced if the fingerlings are harvested at less than 20 mm TL. Habituation, on the other hand, will be reduced if the fingerlings are harvested at too small a size. Our experiences over the last 10 years suggest that 75-85% habituation can be expected when pond-reared yellow perch fingerlings are harvested at 35-45 mm TL. Little information is available regarding the habituation of perch at smaller sizes. In one study, Best ( 198 1) showed that habituation was lower than 50% for perch harvested at sizes smaller than 15 mm TL, and increased substantially (to 70-95%) for perch harvested at ul I L. ~~wt:u’c~~, Best’s ( 1Y6 1) sdy WASGUIIUUCL~Uursing very low initial stocking densities and small aquaria, and his results may not be applicable on a scale feasible for commercial aquaculture.
HABITUATION OF YELLOW PERCH TO INTENSIVECULTURE CONDITIONS
69
Optimal initial tank stocking densities for habituating perch to intensive culture conditions are unknown. In our laboratory, habituation has typically ranged from 75 to 85% when pond-reared perch fingerlings have been stocked into tanks at densities of l-4 fish/l. igher densities may have negative impacts on habituation. In walleyes, Cheshire and Steele ( 1972) showed that survival decreased substantially as stocking density was increased from 16 to 64 fish/l. The habituation of fingerlings to intensive. conditions can be affc;:ted by factors other than fish size at harvest and initial tank stocking density. These include such environmental factors as temperature (Hokanson and Koenst, 1986), water quality (Lewis and Morris, 1986), and rearing tank illumination (Stuiber, 1975; Colsante et al., 1986). Howey et al. ( 1980) su.ggested that light could be used to concentrate walleye fry under automatic feeders and reduce the length of time required for fish to begin actively feeding. Observations made by ourselves and others (e.g., Nagel, 1978 ) indicate that many species of pond-reared fingerlings, including yellow perch, are easily disturbed by shadows and movement. Nagel ( 1985) suggested that the use of internal tank lighting can minimize such disturbances. The over+ goal of this research effort is to develop strategies the production of pond-reared yellow perch fingerlings habituate sive culture conditions and formulated feed. In the studies report evaluated the effects of ( 1) fish size at harvest, (2) initial tank stocking density, and (3) internal tank lighting. MATERIALS AND METHODS
Generalprocedures All yellow perch used in these studies were the offspring of wild brood fish captured during the spawning season from Lakes Mendota and Cherokee, Dane County, WI. Following capture, the brood fish were transported to our ills (WI) State Fish main wet laboratory located at the Lak Perch eggs were stripped and fertili using the dry metho and Kayes, 1986 ). Subsequently, the egg ribbons were suspended from wire hangers in aerated, 750-l flow-through tanks, and water temperatures were increased from 11 OC to 15“C over an 8-day period. One or two days prior to hatch, approximately 500 000 eggs were moved into a wire-mesh cage submerged in a 0.4-ha fertilized production pond. We estimated that over 90% of the eggs hatched in the pond. At 34 and 40 days post-hatch, yellow perch Iingerlings were harveste ng a light trap system similar to that described by anti et al. ( 1983 1. ays post-hatch, fingerlings were harvested usin ap nets set overnight. At 77 days post-hatch, the pond was drained and fish were removed from the harvest basin using dip nets.
J.A. MALISON AND J.A. HELD
70
After each harvest, the perch were immediately stocked into three to six O-1flow-through fiberglass tanks provided with tempered water (2 1 If:0.5 “C at s flow rate of 12 l/min) and airstone aeration. Each group of perch was stocked at the densities depicted in Table 1, and in all cases loading rates (kg of fish l- 1 min- 1 ) were low enough to maintain good water quality (e.g., dissolved oxygen concentrations were never lower than 6.0 mg/l ) . Except for the very high density of the fish harvested on day 40 (see Experiment 2 below), the initial densities were high enough to be feasible for commercial aquaculture, but low enough to expect good habituation (50-90%). During their first 2 days in the laboratory, the fingerlings were treated prophylactically to minimize bacterial disease outbreaks with a daily, 4-h static bath of NaCl (7 g/l) and furacin (5 mg/l using Nitrofurazone 9.3%, Argent Chemical Laboratories, Redmond, WA). For the duration all studies, the fish were fed continuously throughout the day with automatic feeders, as well as several times daily by hand, using Ziegler Salmon Starter (Ziegler Bros. Inc., Gardner, PA). The tanks were cleaned and dead fish were removed and counted on a daily basis. The tanks in all experiments were continually illuminated with either internal or external lights. For internal illumination, tanks were kept in a dark room with no overhead lighting. Each tank was provided with a single 12-V lamp sealed in an opaque plastic tube with a clear plastic bottom, and submerged 10 cm below the water surface. The light was positioned next to the feeder to attract the fish to the feed, and adjusted to illuminate approximately
of
TABLE I Stocking densities of pond-reared yellow perch (Pcwu jlavcxens) sizes and habituated to intensive culture conditions Mean fish size at harvest (mm total length )
Day of harvest (post-hatch )
16.9 16.9 19.8 32.5 42.6 42.6
34 34 40 62 77 77
Lighting conditionsb
Stocking densities“ Fish/l
Internal External Internal Internal Internal External
fingerlings harvested at different
Density indexC
g/l
Initial
Final
Initial
Final
Initial
Final
13.7 13.7 37.4 5.1 3.6 3.6
8.3 6.3 8.6 3.5 2.0 1.6
0.65 0.65 2.35 2.01 2.90 2.90
2.23 1.72 4.33 4.23 6.00 5.54
0.06 1 0.058 0.188 0.098 0.108 0.107
0.119 0.094 0.194 0.138 0.157 0.136
“Data represent the mean of three or four tanks at the beginning and end of experiments. bFish tanks were provided with either internal or external (overhead) lighting as described under Materials and Methods. ‘Density index= total fish weight (g ) x 1.S8/ (tank volume [I] x average fish length [mm] ), origina!ly calculated as pounds/ (cubic feet x inches) by Piper et al. ( 1982).
HABITUATION OF YELLOW PERCH TO INTENSIVE CULTURE CONDITIONS
71
one-half of the tank. The light intensity in these tanks was I .O lux in the darkest regions, 7.5 lux in the center of the lighted region, and 12.5 lux in the vicinity of the feeder. For external illumination, tanks were kept in a room provided with a single, overhead 25- incandescent bulb fitted with a translucent diffuser, located 2 m above the water surface. Tanks provided with external illumination had wooden covers to shade one-half of each tank, and the feeders were located over the lighted region of each tank. The illumination in these tanks was 1.0 lux in the shaded region, 7.0 lux in the center of the lighted regions, and 8.0 lux at the surface of the lighted regions. The end points measured in each of these studies included: ( I ) habituation, defined as the percenfage of fish that survived the transition to intensive culture conditions; ( 2 ) starvation, defined as the percentage of fish that died and were recovered; and ( 3) cannibalism, defined as the percentage of fish that could not be accounted for at the end of the habituation intervals Our definition of starvation is substantiated by observations that virtually all dead fish recovered were extremely emaciated, and losses which could be attributed to disease or other causes (e.g., mechanical injury) were negligible. Our definition of cannibalism is substantiated by observations of cannibalistic behavior and the fact that fish could not escape from the tanks through the standpipe screens or by any other means. Fingerlings were not size-graded prior to stocking into rearing tanks, and cannibals were not removed during the experiments. Eack habituation interval lasted from 19 to 5 1 days, and was terminated when the number of dead fish recovered daily dropped to less than 0.05% of the total initial stocking number, and all remaining fish were actively feeding. Experiment
1
To evaluate the influence of fish size at harvest on habituation, yellow perch were tar~&ed from tire ponii ai iYlt;dz: 1 T?.9 of 16.9, 32.5, and 42.6 mm (days 34, 62, and 77 post-hatch, respectively ), and fish from each size-group were s?ocked into three internally lighted tanks at the densities shown in Table 1. Fish were reared as described under General procedures for 19, 34, and 5 1 days, respectively. At the conclusion of the habituation intervals, approximately 100 randomly selected fish from the groups harvested at 16.9 and 42.6 mm TL were stocked into separate 110-i tanks and reared under opti.mal environmental and feeding conditions until day 2 15 post-hatch. These fish were individually weighed on days 131 and 2 15 post-hatch. Experiment 2 To evaluate the influence of initial stocking density on habituation, perch
harvested at 16-20 mm TL were stocked into three or four internally lighted tanks each at 13.7 or 37.4 fish/l. Fish were reared as described under General procedures for 19-24 days.
72
J.A. MALISON AND J.A. HELD
Experiment 3 To evaluate the effect of lighting conditions on habituation, perch harvested at mean TLs of 16.9 and 42.6 mm (days 34 and 77 post-hatch, respectively) were stocked into three tanks each that were illuminated with internal or external lights. Fish were reared as described under General procedures for 19 or 5 1 days (for the fish harvested at 16.9 and 42.6 mm TL, respectively). Statisticalanalyses For Experiment 1, differences in habituation, starvation, and cannibalism, as well as the median day of starvation and the span of days over which 90% of the starvation occurred, were determined using a one-way analysis of variance (ANOVA ) followed by appropriate preplanned orthogonal comparisons. Differences in mean total weight of the fish on days 13 1 and 2 15 posthatch were determined using Student’s t-tests. Differences in habituation, starvation, and cannibalism in Experiments 2 and 3 were determined using Student’s t-test and a two-way factorial ANOVA (initial fish sizexlighting condition), respectively. All analyses were done with the SAS/STAT program (SAS, 1988 ) on a UNIX computer system. Arcsin transformation was used for all percentage data as suggested by Zar ( 1974 ). Unless otherwise indicated, differences were significant at PC 0.05. RESULTS
Experiment I There were no differences in habituation, starvation or cannibalism of yellow perch fingerlings harvested at mean TLs of 16.9,32.5 and 42.6 mm (Fig. ! ). Perch harvested at 16.9 mm TL starved earlier and over a shorter span of days than the other two groups, and perch harvested at 32.5 mm TL starved earlier than those harvested at 42.6 mm TL (Fig. 2). Subsequent to the habituation interval, perch harvested at 16.9 mm TL were heavier than those harvested at 42.6 mm TL. The mean total weights (g) + s.e.m. (n = 98 fish/ group) of these fish on days 13 1 and 215 post-hatch were S.OOLt0.15 vs. 3.91+0.45, and20.2220.51 vs. 18.2820.73, respectively. Experiment 2 Yellow perch fingerlings initially stocked at 13.7 fish/l had improved habituation and reduced cannibalism compared to fingerlings stocked at 37.4 fish/l (Fig. 3). Experiment 3 Fingerling yellow perch reared using internal tank lights had improved habituation compared to those reared using external overhead lights (Fig. 4). As a group, fingerlings harvested at 16.9 mm TL exhibited more frequent
HABITUATION
OF YELLCIW PERCH TO INTENSIVE
CULTURE
CONDITIONS
73
HABITUATION 80
STARVATION CANNIBALISM
60
0
32.5
16.9
MEAN TOTAL
42.6
LENGTH (mm)
AT HARVEST
Fig. 1. Habituation, starva’ion and cannibalism of pond-reared yellow perch fingerlings harvested at different sizes and reared under intensive culture conditions. Each bar represents the mean + s.e.m. of three tanks/treatment. A MEW TOTAL LENGTH AT HARVEST “..“.““....“.... 16.9mm 32.Smm . ... .... .... 416 mm
50
60
DAY AFTER WARWST
Fig. 2. Daily starvation rate of yellow perch fingerlings harvested at different sizes and reared under intensive culture conditions. Each curve represents the mean of three tanks, and the vertical and horizontal lines above the curves represent, respectively, the median day of starvation and the span of days over which 90°Aof the s
60
13.7
INITIAL STOCKING
37.4
DENSITY
(Fish/l ) Fig. 3. Habituation, starvation and cannibalism of yellow perch fingerlings harvested at 16-20 mm total length and reared under intensive culture conditions at two initial stocking densities. Each bar represents the mean ?Is.e.m. of three or four tanks/treatment.
J.A. MALISON AND J.A. HELD
74
0-i
HABITUATION
kl 2
@
STARVATlON
il
0
CANNIBALISM
7
INTERNALLIGHT
EXTERNALLIGHT
Fig. 4.Habituation, starvation, and cannibalism of yellow perch fingerlings harvested at two different sizes and reared under intensive culture conditions using either internal or external illumination, Each bar represents the mean I s.c,m. of three tankr&reatment,
starvation than those harvested at 42.6 mm TL, bul: differences in habituation and cannibalism between the harvest sizes were not significant. DISCUSSION
Our results demonstrate that pond-reared yellow perch fingerlings harvested at a mean size of 16.9 mm TL can be habituated to intensive culture conditions as successfully as perch harvested at much larger sizes. These findings show that a strategy of harvesting perch at a relatively small size and early age can be used to greatly improve the production of fingerlings in ponds without having a deleterious effect on subsequent habituation. The extent to which early pond harvest can improve production wz1.sfirst illustrated by Manci et al. ( 1983)) who used such a strategy to produce more than 300 000 fingerlings/ha of pond surface area. In the present study we harvested at total of 500 000 fish/ha. Together, these two findings suggest that a production
HABITUATION
OF YELLOW
PERCH TO INTENSIVE
CULTURE
CONDITIONS
75
increase of 240~800% can result from harvesting perch at less than 20 mm TL as compared to 35-65 mm TL. elieve that the production of fingerling perch in ponds can be substanproved even beyond 500 000 fish/ha. Over the last 10 years we have observed that the number of perch in heavily stocked ponds seems to decrease markedly between days 40 and 60 post-hatch (i.e., as perch grow from about 20 to 40 mm TL). Such decreases are probably due to starvation and cannibalism that result from a steadily declining zooplankton forage base in heavily stocked ponds. In the present study, our experimental designs necessitated that we rear fingerlings in our production pond to sizes larger than 20 mm TL. We estimate that our total production could have approached 1 000 000 fish/ha if we had harvested all of the fish at a size of less than 20 mm TL. Even further improvements in pond fingerling production may be achievable if perch can be successfully harvested and habi:uated at a mean size of less than 16.9 mm TL. To determine what level of production can be sustained on a regular basis will, however, require further studies using replicate ponds. Additional advantag.es to the early pond harvest strategy described here result from the fact that habituation to intensive culture conditions occurs faster in perch harvested at small sizes (Fig. 2). The interval during which pondreared fingerlings are habituated is characterized by slow fish growth and low feed conversion, both of which are due primarily to poor feed acceptance. Accordingly, a short habituation interval should result in an overall improvement of fish growth and feed conversion. Supporting this hypothesis is our finding that on days 13 1 and 2 15 post-hatch, fingerlings which had been harvested on day 34 were substantially larger than those harvested on day 77. A short habituation interval also minimizes the extensive manpower needed during this time for fish husbandry and tank cleaning. In Experiment 1, the standard errors associated with the mean fish weights on days 131 and 215 suggest that fingerlings harvested on day 77 exhibit a greater variation in size than those h;hrvested on day 34. This apparent difference may have resulted from greater competition for food among the fish reared in the pond from days 34-77 than among the fish reared in tanks which were fed to satiation. It may also have been related to the long habituation interval observed in fish harvested at large sizes (see Fig. 2). Such a long habituation interval was probably characterized by differences in when individual fish first began to accept and readily consume formulated feed, with early acceptance resulting in greater overall growth. Regardless of cause, the greater size uniformity of fish harvested at a small size offers the benefits of less frequent size-grading being required to control cannibalism, an a more easily managed crop for subsequent growout and processing ( Schwedler et al., 1989). The results of Experiment 2 show that an extremely high initial stocking density (37.4 fish/l) reduces habituation in perch by increasing cannibalism.
76
J.A.MALISONAND J.A.HELD
Taken together, the facts that perch stocked at 37.4 fish/l exhibited more frequent cannibalism but similar starvation compared to perch stocked at 13.7 fish/l suggest that the increased cannibalism of perch at the high density did not result from competition for food. These findings support the idea of other investigators (e.g., Cuff, 1977; Polis, 198 1; Li and Mathias, 1982) that frequent cohort cannibalism is directly related to population density. In order to quantify and compare cannibalism between treatments, we did not remove obvious cannibals. This procedure was probably respolrsible for the overall reduction in habituation that we observed in these studies as compared to previous years (50-70 vs. 75-85%) in which we attempted to minimize cannibalism. The three units of measure that describe fish densities in Table 1 each have characteristics making it the most appropriate for use under certain circumstances. The measure of fish/l is best used when differences in fish size are not very great, or with juvenile fish that are difficult to weigh. Accordingly, we used this measure in the design of Experiment 2, in which different stocking densities of similar sized fish were compared. The measure of g/l accounts for differences in t&h size, but does not take into account the principle that, under tinny intensive culture conditions, density can be increased as fish size increases. The density index described by Piper et al. ( 1982 ) accounts for this concept, but appropriate values are not widely known for many species of fish. Piper et al. ( 1982) suggested rearing rainbow trout (Oncorhynchusmykiss) at a maximum density index of 0.5. Our results of Experiment 2 demonstrate that an initial density index of 0.188 yielded poor habituation (28.0%) in yellow perch fingerlings. In contrast, the initial density indices of 0.06-O. 1I used in Experiments 1 and 2 resulted in 50-70% habituation, and may have resulted in near-optimal habituation if cannibalism had been controlled. The use of internal tank lighting improved habituation, an effect that was probably related to the noticeably different behaviors observed in fish reared under the two lighting conditions. Fingerlings in internally lighted tanks were attracted to and constantly crowded around the light, and were frequently exposed to food as it dropped from the automatic feeders (located immediately above the light). In contrast, fingerlings in the externally lighted tanks were usually dispersed throughout the tank, and may have less frequently observed the food as it dropped through the water column. We also observed that fingerlings reared under internal illumination were much less disturbed by routine husbandry and maintenance activities such as hand feeding and tank cleaning. Shadows and movements in the vicinity of the externally illuminated tanks alarmed the fingerlings and caused an excited swimming behavior not usually observed in fish reared under internal lighting, Our studies show that the production of yellow perch fingerlings can be
HABITUATION OF YELLOW PERCH TO INTENSIVE CULTURE CONDITIONS
77
greatly increased by using a strategy of early pond harvest combined with techniques that improve habituation, such as appropriate initial stocking densities and internal tank lighting. Similar methods are probably applicable to the culture of other coolwater fishes such as walleye. To maximize perch fingerling production, further studies are needed to determine ( 1) the extent to which early harvest improves pond production, (2) the smallest size at which fingerlings can be successfully harvested and habituated, and ( 3 ) optimal tank stocking densi ties. ACKNOWLEDGMENTS
We thank Tom Kuczynski and the entire staff of the University of Wisconsin Aquaculture Program for their invaluable assistance. This work was supported in part by the University of Wisconsin-Madison College of Agricultural and Life Sciences; the Wisconsin Department of Natural esources; and the University of Wisconsin Sea Grant College Program under grants from the National Sea Grant College Program, National Oceanic and Atmospheric Administration, US Department of Commerce, and the State of Wisconsin (federal grant [email protected],4-D-SG469, Project No. R/AQ-20) and by the North Central Regional Aquaculture Center under a grant from the United States Department of Agriculture (federai grant 90-38500-5008) to Michigan State University (agreement 6 1-4050G between Michigan State University and the University of Wisconsin-
REFERENCES Best, CD., 198 1. Initiation of artificial feeding and the control of sex differentiation in yellow perch, Percu j?czve.xens. Masters Thesis, University of Wisconsin-Madison, Madison, WI, pp. 3 l-67. Buttner, J.K., 1989. Culture of fingerling walleye in earthen ponds. Aquaculture Magazine, M/ A: 37-46. Cheshire, W.F. and Steele, K.L., 1972. Hatchery rearing of walleyes using artificial food. Prog. Fish-Cult., 34: 96-99. Colsante, R.T., Youmans, N.B. and Ziolkoski, B., 1986. Intensive culture of walleye fry with live food and formulated diets, Prog. Fish-Cult., 48: 33-37. Cuff, W.R., 1977. Inttiation and control of cannibalism in larval walleyes. Prog. Fish-Cult., 39: 29-3’ Dobie, J., 1956. Walleye pond management in Minnesota. Prog. Fish-Cult., 18: 5 l-57. Eldridge, M.B., Whipple, J.A., Eng, D., Bowers, M.J. and Jarvis, B.M., 198 1. Effects of food and feeding factors on laboratory-reared striped bass larvae. Trans. Am. Fish. Sot., 110: 111-820. Hale, J.G. and Carlson, A.R., 19512.Culture of the yellow perch in the laboratory. Prog. FishCult., 34: 195-198. Heidinger, R.C. and Kayes, T.B., 1986. Yellow perch. In: R.R. Stickney (Editor), Culture of Nonsalmonid Freshwater Fishes. CRC Press, Boca Raton, FL, pp. 103-J 13. l
78
J.A. MALISON AND J.A. HELD
Hokanson, K.E.F. and Koenst, W.M., 1986. Revised estimates of growth requirements and lethal temperature limits ofjuvenile walleyes. Prog. Fish-Cult., 48: 90-94. Howey, R.G., Theis, G.L. and Haines, P.B., 1980. Intensive culture of walleye (Stizostedion vilreum). US Fish and Wildlife Service, Lamar Information Leaflet SO-05 Lamar, PA. Keast, A. and Eadie, J.M., 1985. Growth depensation in year-0 largemouth bass: the influence of diet. Trans. Am. Fish. Sot., 114: 204-2 13. Lewis, W.M. and Morris, D.P., 1986. Toxicity of nitrite to fish: a review. Trans. Am. Fish. Sot., 115: 183-195. Li, S. and Mathias, J.A., 1982. Causes of high mortality among cultured larval walleye. Trans. Am. Fish. Sot., 111: 7 1O-72 1. Manci, W.E., Malison, J.A., Kayes, T.B. and Kuczynski, T.E., 1983. Harvesting photopositive juvenile fish from a pond using a lift net and light. Aquaculture, 34: 157- 164. Mansuetti, A.J., 1964. Early development of yellow perch, PercaJlavescens. Chesapeake Sci., 5: 46-66. McIntyre, D.B., Ward, F.J. and Swanson, G.M., 1987. Factors affecting cannibalism by pondreared juvenile wallryes. Prog. Fish-Cult., 49: 264-269. Nagel, T.G., 1978. Walleye production in controlled environments. Ohio Department of Natural Resources Division of Wildlife, In-service Note 386 (unpublished), 6 pp. Nagel, T.O., 1985. Development of a domestic walleye broodstock. Prog. Fish-Cult., 47: 12 l122. Nickum, J., 1978. Intensive culture of walleyes: the state of the art. Am. Fish. Sot. Spec. Publ., 11: 187-194. Piper, R.G., McElwain, I.B., Orme, L.E., McCraren, J.P., Fowler, L.G. ar,d Leonard, J.R. (Editors), 1982. Fish Hatchery Management. United States Department ofthe Interior Fish and Wildlife Service, Washington, DC, pp. 7 I-74. Polis, G.A., 198 1. The evolution and dynamics of intraspecific predation. Annu. Rev. Ecol. Syst., 12: 225-251. SAS, 1988. SAS/STAT User’s Guide, release 6.03 edition. SAS Institute, Cary, NC. Schwedler, T.E., Tomasso, J.R. and Collier, J.A., 1989. Production characteristics and size variability of channel catfish reared in cages and open ponds. J. World Aquacult. Sot., 20: 158161. Stuiber, D.A., 1975. Aquaculture: facilities for the raising of yellow perch (~‘~~~~~u.ila~~~~~~c~ns) in a controlled environment system. In: Aquaculture: Raising Perch for the Midwest Market. University of Wisconsin Sea Grant College Program, Advisory report #13, Madison, WI, pp. 15-28. Swanson, G.M. and Ward, F.J., 1985. Growth ofjuvenile walleye, Srizostedion vitreurn vitreurn (Mitchill), in two man-made ponds in Winnipeg, Canada. Int. Vereinig. Angew. Limnol. Verhandl., 22: 2502-2507. Zar, J.H., 1974. Biostatistical Analysis. Prentice-Hall, Inc., Englewood Cliffs, NJ, 25 1 pp.
67
Elsevier Science Publishers B.V., Amsterdam
Jeffrey A. Malison and James A. Held Universityqf WisconsinAquaculture Program, Universityof Wisconsin-Madison,Madison, WI, VS.4
(Accepted 12 September 1991) ABSTRACT
Malison, J.A. and Held, J.A., 1992. Effects of fish size at harvest, initial stocking density and tank lighting conditions on the habituation of pond-reared yellow perch (Percaflavescens) to intensive culture conditions. Aquaculrw, IO4: 67-18. Groups of age-0 pond-reared yellow perch (Percajbvescens) fingerlings were harvested and habituated to intensive culture conditions and formulated feeds under various treatment regimes. The habituation intervals for the different fish groups lasted from 19 to 5 1 days, until the number of dead fish recovered daily for each group became insignificant and all remaining fish were actively feeding. End points measured included ( 1) habituation, defined as the percentage of fish that survived the transition to intensive culture conditions; (2 ) starvation, defined as the percentage of fish that died and were recovered; and (3) cannibalism, defined as the percentage of fish that could not be accounted for at the end of the habituation intervals. The habituation of perch harvested at mean total lengths (TLs) of 16.9, 32.5, or 42.6 mm did not differ (53.3255, 68.326.3, and 55.7+4.5%, respectively), but habituation occurred faster and over a shorter interval in smaller perch. Perch harvested at 16.9 mm 1’L grew to a larger ultimate size than those harvested at 42.6 mm TL. Fingerlings harvested at 16-20 mm TL and initially stocked into 750-l tanks at 13.7 fish/l had improved habituation (53.3 + 5.5W) and reduced cannibalism (20 .S f 11.01) compared to those stocked at 37.4 fish/l (28.Ok3.2 and 50.5f 3.2Oh,respectively). Perch reared using internal tank lighting had improved habituation compared to those reared overhead lighting (54.5 f 3.2 vs. 42.7 f 2.2%). Our results show that pond-reared perch fingerlings can be successfully habituated to intensive culture conditions at a mean size as small as 16.9 mm TL. and that fingerling production can be greatly improved by using a strategy of early pond harvest in combination with appropriate tank stocking densities and internal tank lighting.
INTRODUCTION
The yellow perch (fercaflavescens) is a highly valued food fish in the North Central region of the United States, and as such is a potentially important Correspondence to: Dr. Jeffrey A. Malison, University of Wisconsin Aquaculture Program, Department of Food Science, 103 Babcock Hall, University of Wisconsin-Madison, Madison, WI 53706, USA. 00448486/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved,
68
J.A. MALISON AND J.A. HELD
species for commercial aquaculture. The Industry Advisory Council and the Technical Committees for Extension and Research of the North Central Regional Aquaculture Center identified yellow perch as a species that merits the highest priority for aquaculture research in the region. One major constraint on the development of yellow perch aquaculture is the lack of available information on fingerling production. The larvae of yellow perch, like those of many other fishes characterized by small eggs and fry (e.g., walleye [Stizostedion vitreum] and striped bass [ Morone saxatih] ), are difficult to rear intensively using formulated feeds (Mansuetti, 1964; Nickum, 1978; Best, 198 1; Eldridge et al., 198 1). Successful methods for intensively rearing larval perch currently rely on feeding large amounts of live zooplankton during the first few weeks of culture (Hale and Carlson, 1972; F.P. Binkowski, personal communication, 199 1) . An alternative and perhaps less costly strategy for producing perch fingerlings is to initially culture perch extensively in ponds for 4-8 weeks, and then harvest and habituate the fingerlings to intensive conditions .and formulated feeds (Heidinger and Kayes, 1986). Using this strategy, the production of habituated fingerlings will ultimately be determined by the number of fingerlings harvested from ponds as well as their habituation, defined as the percentage of fish surviving the transition from extensive to intensive culture conditions. The number of fingerlings that can be reared in production ponds is dependent on many factors including food availability, cannibalism and water quality (Li and Mathias, 1982; Keast and Eadie, 1985; Swanson and Ward, 1985; Colsante et al., 1986; McIntyre et al., 1987). Under most conditions, fingerling production for coolwater species such as perch and walleye normally ranges from 50 000 to 135 000 fish/ha of pond surface area when fish are harvested at 35-65 mm total length (TL, see e.g., Dobie, 1956; Buttner, 1989). Implicitly, the number of fingerlings produced will be maximized by harvesting fish at a small size and early age. The degree to which such an early pond harvest strategy can improve fingerling production is illustrated by the observation of Manci et al. ( 1983) that over 300 000 perch fingerlings/ha can be produced if the fingerlings are harvested at less than 20 mm TL. Habituation, on the other hand, will be reduced if the fingerlings are harvested at too small a size. Our experiences over the last 10 years suggest that 75-85% habituation can be expected when pond-reared yellow perch fingerlings are harvested at 35-45 mm TL. Little information is available regarding the habituation of perch at smaller sizes. In one study, Best ( 198 1) showed that habituation was lower than 50% for perch harvested at sizes smaller than 15 mm TL, and increased substantially (to 70-95%) for perch harvested at ul I L. ~~wt:u’c~~, Best’s ( 1Y6 1) sdy WASGUIIUUCL~Uursing very low initial stocking densities and small aquaria, and his results may not be applicable on a scale feasible for commercial aquaculture.
HABITUATION OF YELLOW PERCH TO INTENSIVECULTURE CONDITIONS
69
Optimal initial tank stocking densities for habituating perch to intensive culture conditions are unknown. In our laboratory, habituation has typically ranged from 75 to 85% when pond-reared perch fingerlings have been stocked into tanks at densities of l-4 fish/l. igher densities may have negative impacts on habituation. In walleyes, Cheshire and Steele ( 1972) showed that survival decreased substantially as stocking density was increased from 16 to 64 fish/l. The habituation of fingerlings to intensive. conditions can be affc;:ted by factors other than fish size at harvest and initial tank stocking density. These include such environmental factors as temperature (Hokanson and Koenst, 1986), water quality (Lewis and Morris, 1986), and rearing tank illumination (Stuiber, 1975; Colsante et al., 1986). Howey et al. ( 1980) su.ggested that light could be used to concentrate walleye fry under automatic feeders and reduce the length of time required for fish to begin actively feeding. Observations made by ourselves and others (e.g., Nagel, 1978 ) indicate that many species of pond-reared fingerlings, including yellow perch, are easily disturbed by shadows and movement. Nagel ( 1985) suggested that the use of internal tank lighting can minimize such disturbances. The over+ goal of this research effort is to develop strategies the production of pond-reared yellow perch fingerlings habituate sive culture conditions and formulated feed. In the studies report evaluated the effects of ( 1) fish size at harvest, (2) initial tank stocking density, and (3) internal tank lighting. MATERIALS AND METHODS
Generalprocedures All yellow perch used in these studies were the offspring of wild brood fish captured during the spawning season from Lakes Mendota and Cherokee, Dane County, WI. Following capture, the brood fish were transported to our ills (WI) State Fish main wet laboratory located at the Lak Perch eggs were stripped and fertili using the dry metho and Kayes, 1986 ). Subsequently, the egg ribbons were suspended from wire hangers in aerated, 750-l flow-through tanks, and water temperatures were increased from 11 OC to 15“C over an 8-day period. One or two days prior to hatch, approximately 500 000 eggs were moved into a wire-mesh cage submerged in a 0.4-ha fertilized production pond. We estimated that over 90% of the eggs hatched in the pond. At 34 and 40 days post-hatch, yellow perch Iingerlings were harveste ng a light trap system similar to that described by anti et al. ( 1983 1. ays post-hatch, fingerlings were harvested usin ap nets set overnight. At 77 days post-hatch, the pond was drained and fish were removed from the harvest basin using dip nets.
J.A. MALISON AND J.A. HELD
70
After each harvest, the perch were immediately stocked into three to six O-1flow-through fiberglass tanks provided with tempered water (2 1 If:0.5 “C at s flow rate of 12 l/min) and airstone aeration. Each group of perch was stocked at the densities depicted in Table 1, and in all cases loading rates (kg of fish l- 1 min- 1 ) were low enough to maintain good water quality (e.g., dissolved oxygen concentrations were never lower than 6.0 mg/l ) . Except for the very high density of the fish harvested on day 40 (see Experiment 2 below), the initial densities were high enough to be feasible for commercial aquaculture, but low enough to expect good habituation (50-90%). During their first 2 days in the laboratory, the fingerlings were treated prophylactically to minimize bacterial disease outbreaks with a daily, 4-h static bath of NaCl (7 g/l) and furacin (5 mg/l using Nitrofurazone 9.3%, Argent Chemical Laboratories, Redmond, WA). For the duration all studies, the fish were fed continuously throughout the day with automatic feeders, as well as several times daily by hand, using Ziegler Salmon Starter (Ziegler Bros. Inc., Gardner, PA). The tanks were cleaned and dead fish were removed and counted on a daily basis. The tanks in all experiments were continually illuminated with either internal or external lights. For internal illumination, tanks were kept in a dark room with no overhead lighting. Each tank was provided with a single 12-V lamp sealed in an opaque plastic tube with a clear plastic bottom, and submerged 10 cm below the water surface. The light was positioned next to the feeder to attract the fish to the feed, and adjusted to illuminate approximately
of
TABLE I Stocking densities of pond-reared yellow perch (Pcwu jlavcxens) sizes and habituated to intensive culture conditions Mean fish size at harvest (mm total length )
Day of harvest (post-hatch )
16.9 16.9 19.8 32.5 42.6 42.6
34 34 40 62 77 77
Lighting conditionsb
Stocking densities“ Fish/l
Internal External Internal Internal Internal External
fingerlings harvested at different
Density indexC
g/l
Initial
Final
Initial
Final
Initial
Final
13.7 13.7 37.4 5.1 3.6 3.6
8.3 6.3 8.6 3.5 2.0 1.6
0.65 0.65 2.35 2.01 2.90 2.90
2.23 1.72 4.33 4.23 6.00 5.54
0.06 1 0.058 0.188 0.098 0.108 0.107
0.119 0.094 0.194 0.138 0.157 0.136
“Data represent the mean of three or four tanks at the beginning and end of experiments. bFish tanks were provided with either internal or external (overhead) lighting as described under Materials and Methods. ‘Density index= total fish weight (g ) x 1.S8/ (tank volume [I] x average fish length [mm] ), origina!ly calculated as pounds/ (cubic feet x inches) by Piper et al. ( 1982).
HABITUATION OF YELLOW PERCH TO INTENSIVE CULTURE CONDITIONS
71
one-half of the tank. The light intensity in these tanks was I .O lux in the darkest regions, 7.5 lux in the center of the lighted region, and 12.5 lux in the vicinity of the feeder. For external illumination, tanks were kept in a room provided with a single, overhead 25- incandescent bulb fitted with a translucent diffuser, located 2 m above the water surface. Tanks provided with external illumination had wooden covers to shade one-half of each tank, and the feeders were located over the lighted region of each tank. The illumination in these tanks was 1.0 lux in the shaded region, 7.0 lux in the center of the lighted regions, and 8.0 lux at the surface of the lighted regions. The end points measured in each of these studies included: ( I ) habituation, defined as the percenfage of fish that survived the transition to intensive culture conditions; ( 2 ) starvation, defined as the percentage of fish that died and were recovered; and ( 3) cannibalism, defined as the percentage of fish that could not be accounted for at the end of the habituation intervals Our definition of starvation is substantiated by observations that virtually all dead fish recovered were extremely emaciated, and losses which could be attributed to disease or other causes (e.g., mechanical injury) were negligible. Our definition of cannibalism is substantiated by observations of cannibalistic behavior and the fact that fish could not escape from the tanks through the standpipe screens or by any other means. Fingerlings were not size-graded prior to stocking into rearing tanks, and cannibals were not removed during the experiments. Eack habituation interval lasted from 19 to 5 1 days, and was terminated when the number of dead fish recovered daily dropped to less than 0.05% of the total initial stocking number, and all remaining fish were actively feeding. Experiment
1
To evaluate the influence of fish size at harvest on habituation, yellow perch were tar~&ed from tire ponii ai iYlt;dz: 1 T?.9 of 16.9, 32.5, and 42.6 mm (days 34, 62, and 77 post-hatch, respectively ), and fish from each size-group were s?ocked into three internally lighted tanks at the densities shown in Table 1. Fish were reared as described under General procedures for 19, 34, and 5 1 days, respectively. At the conclusion of the habituation intervals, approximately 100 randomly selected fish from the groups harvested at 16.9 and 42.6 mm TL were stocked into separate 110-i tanks and reared under opti.mal environmental and feeding conditions until day 2 15 post-hatch. These fish were individually weighed on days 131 and 2 15 post-hatch. Experiment 2 To evaluate the influence of initial stocking density on habituation, perch
harvested at 16-20 mm TL were stocked into three or four internally lighted tanks each at 13.7 or 37.4 fish/l. Fish were reared as described under General procedures for 19-24 days.
72
J.A. MALISON AND J.A. HELD
Experiment 3 To evaluate the effect of lighting conditions on habituation, perch harvested at mean TLs of 16.9 and 42.6 mm (days 34 and 77 post-hatch, respectively) were stocked into three tanks each that were illuminated with internal or external lights. Fish were reared as described under General procedures for 19 or 5 1 days (for the fish harvested at 16.9 and 42.6 mm TL, respectively). Statisticalanalyses For Experiment 1, differences in habituation, starvation, and cannibalism, as well as the median day of starvation and the span of days over which 90% of the starvation occurred, were determined using a one-way analysis of variance (ANOVA ) followed by appropriate preplanned orthogonal comparisons. Differences in mean total weight of the fish on days 13 1 and 2 15 posthatch were determined using Student’s t-tests. Differences in habituation, starvation, and cannibalism in Experiments 2 and 3 were determined using Student’s t-test and a two-way factorial ANOVA (initial fish sizexlighting condition), respectively. All analyses were done with the SAS/STAT program (SAS, 1988 ) on a UNIX computer system. Arcsin transformation was used for all percentage data as suggested by Zar ( 1974 ). Unless otherwise indicated, differences were significant at PC 0.05. RESULTS
Experiment I There were no differences in habituation, starvation or cannibalism of yellow perch fingerlings harvested at mean TLs of 16.9,32.5 and 42.6 mm (Fig. ! ). Perch harvested at 16.9 mm TL starved earlier and over a shorter span of days than the other two groups, and perch harvested at 32.5 mm TL starved earlier than those harvested at 42.6 mm TL (Fig. 2). Subsequent to the habituation interval, perch harvested at 16.9 mm TL were heavier than those harvested at 42.6 mm TL. The mean total weights (g) + s.e.m. (n = 98 fish/ group) of these fish on days 13 1 and 215 post-hatch were S.OOLt0.15 vs. 3.91+0.45, and20.2220.51 vs. 18.2820.73, respectively. Experiment 2 Yellow perch fingerlings initially stocked at 13.7 fish/l had improved habituation and reduced cannibalism compared to fingerlings stocked at 37.4 fish/l (Fig. 3). Experiment 3 Fingerling yellow perch reared using internal tank lights had improved habituation compared to those reared using external overhead lights (Fig. 4). As a group, fingerlings harvested at 16.9 mm TL exhibited more frequent
HABITUATION
OF YELLCIW PERCH TO INTENSIVE
CULTURE
CONDITIONS
73
HABITUATION 80
STARVATION CANNIBALISM
60
0
32.5
16.9
MEAN TOTAL
42.6
LENGTH (mm)
AT HARVEST
Fig. 1. Habituation, starva’ion and cannibalism of pond-reared yellow perch fingerlings harvested at different sizes and reared under intensive culture conditions. Each bar represents the mean + s.e.m. of three tanks/treatment. A MEW TOTAL LENGTH AT HARVEST “..“.““....“.... 16.9mm 32.Smm . ... .... .... 416 mm
50
60
DAY AFTER WARWST
Fig. 2. Daily starvation rate of yellow perch fingerlings harvested at different sizes and reared under intensive culture conditions. Each curve represents the mean of three tanks, and the vertical and horizontal lines above the curves represent, respectively, the median day of starvation and the span of days over which 90°Aof the s
60
13.7
INITIAL STOCKING
37.4
DENSITY
(Fish/l ) Fig. 3. Habituation, starvation and cannibalism of yellow perch fingerlings harvested at 16-20 mm total length and reared under intensive culture conditions at two initial stocking densities. Each bar represents the mean ?Is.e.m. of three or four tanks/treatment.
J.A. MALISON AND J.A. HELD
74
0-i
HABITUATION
kl 2
@
STARVATlON
il
0
CANNIBALISM
7
INTERNALLIGHT
EXTERNALLIGHT
Fig. 4.Habituation, starvation, and cannibalism of yellow perch fingerlings harvested at two different sizes and reared under intensive culture conditions using either internal or external illumination, Each bar represents the mean I s.c,m. of three tankr&reatment,
starvation than those harvested at 42.6 mm TL, bul: differences in habituation and cannibalism between the harvest sizes were not significant. DISCUSSION
Our results demonstrate that pond-reared yellow perch fingerlings harvested at a mean size of 16.9 mm TL can be habituated to intensive culture conditions as successfully as perch harvested at much larger sizes. These findings show that a strategy of harvesting perch at a relatively small size and early age can be used to greatly improve the production of fingerlings in ponds without having a deleterious effect on subsequent habituation. The extent to which early pond harvest can improve production wz1.sfirst illustrated by Manci et al. ( 1983)) who used such a strategy to produce more than 300 000 fingerlings/ha of pond surface area. In the present study we harvested at total of 500 000 fish/ha. Together, these two findings suggest that a production
HABITUATION
OF YELLOW
PERCH TO INTENSIVE
CULTURE
CONDITIONS
75
increase of 240~800% can result from harvesting perch at less than 20 mm TL as compared to 35-65 mm TL. elieve that the production of fingerling perch in ponds can be substanproved even beyond 500 000 fish/ha. Over the last 10 years we have observed that the number of perch in heavily stocked ponds seems to decrease markedly between days 40 and 60 post-hatch (i.e., as perch grow from about 20 to 40 mm TL). Such decreases are probably due to starvation and cannibalism that result from a steadily declining zooplankton forage base in heavily stocked ponds. In the present study, our experimental designs necessitated that we rear fingerlings in our production pond to sizes larger than 20 mm TL. We estimate that our total production could have approached 1 000 000 fish/ha if we had harvested all of the fish at a size of less than 20 mm TL. Even further improvements in pond fingerling production may be achievable if perch can be successfully harvested and habi:uated at a mean size of less than 16.9 mm TL. To determine what level of production can be sustained on a regular basis will, however, require further studies using replicate ponds. Additional advantag.es to the early pond harvest strategy described here result from the fact that habituation to intensive culture conditions occurs faster in perch harvested at small sizes (Fig. 2). The interval during which pondreared fingerlings are habituated is characterized by slow fish growth and low feed conversion, both of which are due primarily to poor feed acceptance. Accordingly, a short habituation interval should result in an overall improvement of fish growth and feed conversion. Supporting this hypothesis is our finding that on days 13 1 and 2 15 post-hatch, fingerlings which had been harvested on day 34 were substantially larger than those harvested on day 77. A short habituation interval also minimizes the extensive manpower needed during this time for fish husbandry and tank cleaning. In Experiment 1, the standard errors associated with the mean fish weights on days 131 and 215 suggest that fingerlings harvested on day 77 exhibit a greater variation in size than those h;hrvested on day 34. This apparent difference may have resulted from greater competition for food among the fish reared in the pond from days 34-77 than among the fish reared in tanks which were fed to satiation. It may also have been related to the long habituation interval observed in fish harvested at large sizes (see Fig. 2). Such a long habituation interval was probably characterized by differences in when individual fish first began to accept and readily consume formulated feed, with early acceptance resulting in greater overall growth. Regardless of cause, the greater size uniformity of fish harvested at a small size offers the benefits of less frequent size-grading being required to control cannibalism, an a more easily managed crop for subsequent growout and processing ( Schwedler et al., 1989). The results of Experiment 2 show that an extremely high initial stocking density (37.4 fish/l) reduces habituation in perch by increasing cannibalism.
76
J.A.MALISONAND J.A.HELD
Taken together, the facts that perch stocked at 37.4 fish/l exhibited more frequent cannibalism but similar starvation compared to perch stocked at 13.7 fish/l suggest that the increased cannibalism of perch at the high density did not result from competition for food. These findings support the idea of other investigators (e.g., Cuff, 1977; Polis, 198 1; Li and Mathias, 1982) that frequent cohort cannibalism is directly related to population density. In order to quantify and compare cannibalism between treatments, we did not remove obvious cannibals. This procedure was probably respolrsible for the overall reduction in habituation that we observed in these studies as compared to previous years (50-70 vs. 75-85%) in which we attempted to minimize cannibalism. The three units of measure that describe fish densities in Table 1 each have characteristics making it the most appropriate for use under certain circumstances. The measure of fish/l is best used when differences in fish size are not very great, or with juvenile fish that are difficult to weigh. Accordingly, we used this measure in the design of Experiment 2, in which different stocking densities of similar sized fish were compared. The measure of g/l accounts for differences in t&h size, but does not take into account the principle that, under tinny intensive culture conditions, density can be increased as fish size increases. The density index described by Piper et al. ( 1982 ) accounts for this concept, but appropriate values are not widely known for many species of fish. Piper et al. ( 1982) suggested rearing rainbow trout (Oncorhynchusmykiss) at a maximum density index of 0.5. Our results of Experiment 2 demonstrate that an initial density index of 0.188 yielded poor habituation (28.0%) in yellow perch fingerlings. In contrast, the initial density indices of 0.06-O. 1I used in Experiments 1 and 2 resulted in 50-70% habituation, and may have resulted in near-optimal habituation if cannibalism had been controlled. The use of internal tank lighting improved habituation, an effect that was probably related to the noticeably different behaviors observed in fish reared under the two lighting conditions. Fingerlings in internally lighted tanks were attracted to and constantly crowded around the light, and were frequently exposed to food as it dropped from the automatic feeders (located immediately above the light). In contrast, fingerlings in the externally lighted tanks were usually dispersed throughout the tank, and may have less frequently observed the food as it dropped through the water column. We also observed that fingerlings reared under internal illumination were much less disturbed by routine husbandry and maintenance activities such as hand feeding and tank cleaning. Shadows and movements in the vicinity of the externally illuminated tanks alarmed the fingerlings and caused an excited swimming behavior not usually observed in fish reared under internal lighting, Our studies show that the production of yellow perch fingerlings can be
HABITUATION OF YELLOW PERCH TO INTENSIVE CULTURE CONDITIONS
77
greatly increased by using a strategy of early pond harvest combined with techniques that improve habituation, such as appropriate initial stocking densities and internal tank lighting. Similar methods are probably applicable to the culture of other coolwater fishes such as walleye. To maximize perch fingerling production, further studies are needed to determine ( 1) the extent to which early harvest improves pond production, (2) the smallest size at which fingerlings can be successfully harvested and habituated, and ( 3 ) optimal tank stocking densi ties. ACKNOWLEDGMENTS
We thank Tom Kuczynski and the entire staff of the University of Wisconsin Aquaculture Program for their invaluable assistance. This work was supported in part by the University of Wisconsin-Madison College of Agricultural and Life Sciences; the Wisconsin Department of Natural esources; and the University of Wisconsin Sea Grant College Program under grants from the National Sea Grant College Program, National Oceanic and Atmospheric Administration, US Department of Commerce, and the State of Wisconsin (federal grant [email protected],4-D-SG469, Project No. R/AQ-20) and by the North Central Regional Aquaculture Center under a grant from the United States Department of Agriculture (federai grant 90-38500-5008) to Michigan State University (agreement 6 1-4050G between Michigan State University and the University of Wisconsin-
REFERENCES Best, CD., 198 1. Initiation of artificial feeding and the control of sex differentiation in yellow perch, Percu j?czve.xens. Masters Thesis, University of Wisconsin-Madison, Madison, WI, pp. 3 l-67. Buttner, J.K., 1989. Culture of fingerling walleye in earthen ponds. Aquaculture Magazine, M/ A: 37-46. Cheshire, W.F. and Steele, K.L., 1972. Hatchery rearing of walleyes using artificial food. Prog. Fish-Cult., 34: 96-99. Colsante, R.T., Youmans, N.B. and Ziolkoski, B., 1986. Intensive culture of walleye fry with live food and formulated diets, Prog. Fish-Cult., 48: 33-37. Cuff, W.R., 1977. Inttiation and control of cannibalism in larval walleyes. Prog. Fish-Cult., 39: 29-3’ Dobie, J., 1956. Walleye pond management in Minnesota. Prog. Fish-Cult., 18: 5 l-57. Eldridge, M.B., Whipple, J.A., Eng, D., Bowers, M.J. and Jarvis, B.M., 198 1. Effects of food and feeding factors on laboratory-reared striped bass larvae. Trans. Am. Fish. Sot., 110: 111-820. Hale, J.G. and Carlson, A.R., 19512.Culture of the yellow perch in the laboratory. Prog. FishCult., 34: 195-198. Heidinger, R.C. and Kayes, T.B., 1986. Yellow perch. In: R.R. Stickney (Editor), Culture of Nonsalmonid Freshwater Fishes. CRC Press, Boca Raton, FL, pp. 103-J 13. l
78
J.A. MALISON AND J.A. HELD
Hokanson, K.E.F. and Koenst, W.M., 1986. Revised estimates of growth requirements and lethal temperature limits ofjuvenile walleyes. Prog. Fish-Cult., 48: 90-94. Howey, R.G., Theis, G.L. and Haines, P.B., 1980. Intensive culture of walleye (Stizostedion vilreum). US Fish and Wildlife Service, Lamar Information Leaflet SO-05 Lamar, PA. Keast, A. and Eadie, J.M., 1985. Growth depensation in year-0 largemouth bass: the influence of diet. Trans. Am. Fish. Sot., 114: 204-2 13. Lewis, W.M. and Morris, D.P., 1986. Toxicity of nitrite to fish: a review. Trans. Am. Fish. Sot., 115: 183-195. Li, S. and Mathias, J.A., 1982. Causes of high mortality among cultured larval walleye. Trans. Am. Fish. Sot., 111: 7 1O-72 1. Manci, W.E., Malison, J.A., Kayes, T.B. and Kuczynski, T.E., 1983. Harvesting photopositive juvenile fish from a pond using a lift net and light. Aquaculture, 34: 157- 164. Mansuetti, A.J., 1964. Early development of yellow perch, PercaJlavescens. Chesapeake Sci., 5: 46-66. McIntyre, D.B., Ward, F.J. and Swanson, G.M., 1987. Factors affecting cannibalism by pondreared juvenile wallryes. Prog. Fish-Cult., 49: 264-269. Nagel, T.G., 1978. Walleye production in controlled environments. Ohio Department of Natural Resources Division of Wildlife, In-service Note 386 (unpublished), 6 pp. Nagel, T.O., 1985. Development of a domestic walleye broodstock. Prog. Fish-Cult., 47: 12 l122. Nickum, J., 1978. Intensive culture of walleyes: the state of the art. Am. Fish. Sot. Spec. Publ., 11: 187-194. Piper, R.G., McElwain, I.B., Orme, L.E., McCraren, J.P., Fowler, L.G. ar,d Leonard, J.R. (Editors), 1982. Fish Hatchery Management. United States Department ofthe Interior Fish and Wildlife Service, Washington, DC, pp. 7 I-74. Polis, G.A., 198 1. The evolution and dynamics of intraspecific predation. Annu. Rev. Ecol. Syst., 12: 225-251. SAS, 1988. SAS/STAT User’s Guide, release 6.03 edition. SAS Institute, Cary, NC. Schwedler, T.E., Tomasso, J.R. and Collier, J.A., 1989. Production characteristics and size variability of channel catfish reared in cages and open ponds. J. World Aquacult. Sot., 20: 158161. Stuiber, D.A., 1975. Aquaculture: facilities for the raising of yellow perch (~‘~~~~~u.ila~~~~~~c~ns) in a controlled environment system. In: Aquaculture: Raising Perch for the Midwest Market. University of Wisconsin Sea Grant College Program, Advisory report #13, Madison, WI, pp. 15-28. Swanson, G.M. and Ward, F.J., 1985. Growth ofjuvenile walleye, Srizostedion vitreurn vitreurn (Mitchill), in two man-made ponds in Winnipeg, Canada. Int. Vereinig. Angew. Limnol. Verhandl., 22: 2502-2507. Zar, J.H., 1974. Biostatistical Analysis. Prentice-Hall, Inc., Englewood Cliffs, NJ, 25 1 pp.