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Survival and growth of sea bass (Dicentrarchus labrax) larvae as influenced by temperature, salinity, and delayed initial feeding
AquacuEture, 52 (1986) 11-19 Elsevier Science Publishers B.V., Amsterdam -Printed
11 in The Netherlands
SURVIVAL AND GROWTH OF SEA BASS (DICENTRARCHUS LARVAE AS INFLUENCED BY TEMPERATURE, SALINITY, AND DELAYED INITIAL FEEDING
LABRAX)
DONALD W. JOHNSON’ and IVAN KATAVIC Institute of Oceanography and Fisheries, Split (Yugoslavia) Present addresses: ‘Natural Resource Consultants, 304 N lath, Pocatello, ID 83201 (U.S.A.) a Ecological Research Center, Biology Department, Memphis State University, Memphis, TN 38152 (U.S.A.) and Southeastern Fish Cultural Laboratory, U.S. Fish and Wildlife Service, Marion, AL 36756 (U.S.A.) (Accepted
12 October 1985)
ABSTRACT Johnson, D.W. and Katavic, I., 1986. Survival and growth of sea bass (Dicentramhus Zabrux) larvae as influenced by temperature, salinity, and delayed initial feeding. Aquaculture, 52: 11-19. The determination of the optimum time and environmental conditions for initial feeding of sea bass larvae will contribute to the feasibility of their profitable culturing. Survival and growth of larvae were increased when ambient salinity (38”/00) was reduced (10”/0, and 20’/00). Intermediate salinity (26’100) produced consistently better growth. Although increased temperatures (18 and 21°C) improved growth rates, survival was decreased below that at ambient (15” C). Feeding of cultured sea bass larvae has commonly begun at initiation of mouth opening (4 days after hatching). At reduced salinity (13’/00 and 26’/00) delaying initial feeding until the fifth day resulted in survival equal to that of those fed on the fist day after mouth opening. Initial feeding can be delayed 2-4 days without adversely affecting survival or growth of sea bass larvae if they are held at ambient temperature in dilute sea water.
INTRODUCTION
The aquaculture potential of many species is limited by their live food requirement as larvae. Minimal use of live food will increase economic feasibility, while decreasing the possibility of a catastrophic loss resulting from disruption of the supply of live food. The effect of different feeding periods and levels on survival and growth of’larvae has been investigated for many species, including sea bass (Barahona-Fernandes and Girin, 1977). The determination of the optimum time and environmental conditions for initial feeding of larvae is critical to raising the maximum number of larvae with the minimum use of live food.
0044-8486/86/$03.50
0 1986 Elsevier Science Publishers B.V.
12
Feeding of sea bass larvae has commonly begun at initiation of mouth opening (4 days after hatching). To avoid overfeeding resulting in accumulation of less nutritious feed and degradation of water quality (Paffenhofer, 1967), as well as the waste of expensive feed, feeding should be delayed until the latest practical time. The most desirable day of initial feeding will be when the total population is capable of feeding and prior to any significant inhibition of growth or “point of no return” when “irreversible starvation” will have begun (Blaxter and Hempel, 1963; Lasker et al., 1970; Hunter, 1980; Iwai, 1980). Determination of environmental conditions for sea bass larval growth and survival with the most efficient use of available live food was the objective of this research. If feeding can be delayed without a major impact on survival or later growth, there would be water quality and economic benefits. MATERIALS
AND METHODS
Origin of brood stock and routine handling of larvae are described in an earlier report (Johnson and Katavic, 1984). One-day-old larvae for these experiments were from induced spawning in January 1983. Eggs were incubated at 16 ?I 0.3”C and 38’/00 salinity. Experiments were carried out under natural light and photoperiod. During the first week larvae were fed on rotifers (.BrachionuspZicatilis) at densities of lo/ml. On the fifth day after hatching Artemia nauplii (origin Great Salt Lake, Utah, U.S.A.) were added gradually with the rotifers. Dead larvae were removed when they became opaque and failed to respond to the jar-cleaning pipette when residue was removed after each feeding period. Statistical treatment included a G-test of independence of temperature and salinity, together with survival (Y?) which were followed by a priori tests of partitions. Differences in growth rate were determined by two-way analysis of variance (Sokal and Rohlf, 1969). Effects
of salinity and temperature
on survival and growth
of larvae
Differences in survival and growth of larvae held in a range of salinities and temperatures were analyzed to confirm earlier findings (Johnson and Katavic, 1984). Each of 36 two-liter jars were stocked with 55-66 larvae. Triplicate tests were made at 15, 18, and 21°C in 10,20, 30 and 38O/0o. Jars were held in water baths to maintain temperature. Salinity was maintained by replacing evaporative loss with distilled water. Dissolved oxygen was maintained at near saturation with compressed air through air stones. Growth in length (total) was determined by measuring 10 specimens per treatment each week using an ocular micrometer. Effects of delayed initial feeding varied salinities and temperatures
on survival and growth
of larvae held at
Investigations were completed delaying initial feeding until the second,
13
third or fifth days after mouth opening together with the common culture practice of presenting live food on the first day mouth opening was initiated. These experiments were performed at ambient temperatures (15°C) and salinities of 38, 26, and 16 or 13O/o0. RESULTS
Effects of salinity and temperature on survival and growth of larvae Survival was consistently increased by reduction of salinity from ambient to 20’/00 or 10°/oo at temperatures of 15 (ambient), 18, 21°C (Table 1). At 10°/oo there was no difference in survival between larvae held at 15, 18, and 21°C. At 20’/00 survival was greater at 15°C. Mortality also increased with elevated temperatures at 30’/00 and 38’/00 (Table 1). Reduced salinity also tended to improve larval growth, especially at elevated temperatures; no significant differences were seen between 38O/o0and 30’/00. Larvae held in lower salinities (20’/00 and 10°/oo) and higher temperatures (18 and 21°C) tended to have greater total lengths (Table 2). (38’/00)
Effects of delayed initial feeding on survival and growth of larvae held at varied salinities and tempemtures At ambient salinity (38O/o0) larval survival was not decreased by delaying the initial feeding until the third day after the mouth opened. At 26’/00 mortality of larvae was increased when initial feeding was delayed until the second day after the mouth opened. Although at 16’/00 delaying feeding until the third day after the mouth opened increased mortality, delay until the second day did not affect larval survival (Table 3). TABLE 1 Survival (%) of laboratory-reared sea bass larvae at ambient (15°C and with decreased salinities and elevated temperatures Temp. (“C)
Age (days)
Rearing salinity (O/W) 38
30
20
10
15
4 11 19
87.9a 65.2~ 24.2e
7o.oc 43.3d 18.3e
84.5ab 75.9b 46.6d
90.7a 83.7ab 41.9d
18
4 11 19
71.oc 25.8e 6.4f
65.5~ 54.5d 21.8e
80.6ab 51.6d 25.8e
91.5a 68.lbcd 31.9de
21
4 11 19
57.9cd 26.3e 7.9f
58.2cd 25.3e 6.3f
73.7b 54.4d 19.3ef
82.lab 76.813 35.7d
38”/00) conditions
G-test of independence was used to determine significant differences in mortality among salinities (values followed by different letters are significantly different, P < 0.05).
14 TABLE 2 Growth (mm TL) of laboratory-reared sea bass larvae at decreased salinities and increased temperatures Salinity (o/o0)
Temp. (“C)
7 days
38
15 18 21
5.23a 5.34a 5.42a
11.30e
20
15 18 21
5.26a 5.56ab 5.75b
8.45~ 10.18d 12.13e
10
15 18 21
5.34a 5.34a 5.7713
9.05c 9.48c 12.38e
21 days
7.9oc 9.37c
Variation between groups subjected to a-way analysis of variance with differences tested using Student-Newman-Keuls procedure (values followed by different letters are significantly different, P < 0.05). TABLE 3 Survival (%) of laboratory-reared sea bass larvae fed on the first day after their mouths opened and with delayed initial feeding when held at ambient and decreased salinities Day feeding initiated after mouth opened
Age (days)
1st
Salinity -38’/00
26’/00
16’/00
8 17
50.4bc 18.5e
90.7a 59.413
87.4a 46.1~
2nd
8 17
44.4c 16.9e
49.6c 30.2d
85.3a 45.6~
3rd
8 17
56.613 22.0e
66.4b 26.7de
52.8~ 11.4f
G-test for significant differences significantly different, P < 0.05).
in mortality (values followed
by different letters are
When larvae were initially fed on the first day after their mouths opened survival was consistently higher at reduced salinity and was best at 26’/00. When feeding was delayed by 1 day, mortality was reduced to levels seen with the first day feeding if fish were held at 16’/00. The advantage of 16’/00 over 26O/o0 was lost when feeding of larvae was delayed an additional day (Table 3). Growth was not adversely affected by delaying the initial feeding of larvae in 38O/o0 or 16O/o0 until the second or third day after the mouth opened (Ta-
15
ble 5). In 26’100 salinity, delaying initial feeding reduced growth at 17 days, but that difference was no longer present at 24 days. Growth was greatest at reduced salinity regardless of when feeding was initiated and by 24 days after hatching was best at 26’/00 (Table 5). The above evaluations were repeated at 38’/00, 26’100 and 13’/00 salinity with feeding initiated on the first, third, and fifth day after mouth opening. Although at reduced salinity delayed feeding until the third day after mouth opening decreased survival, an additional 2 day delay did not increase mortality and survival was close to that seen in larvae fed on the first day after mouth opening (Table 4). These tests confirmed the value of decreasing salinity of culture water to increase larval survival and suggest that in dilute sea water initial feeding can be delayed from the first to the fifth day after mouths open without decreasing early survival (Table 4). Delayed initial TABLE4 Survival (%) of laboratory-reared sea bass larvae fed on the first day after mouths opened and with delayed initial feeding when held at am,bient and decreased salinities Day feeding initiated after mouth opened
Age (days)
Salinity 380100
26°/00
13°/00
1st
9 17
94.8a 18.2e
89.8a 13.0e
93.la 15.le
3rd
9 17
83.913 12.6e
75.4bc 6.6e
82.lb 0.9ef
5th
9 17
66.9d Of
85.813 11.0e
96.9a 13.9e
G-test for significant differences in mortality (values followed significantly different, P < 0.05).
by different letters are
TABLE5 Growth of sea bass larvae as influenced by delayed initial feeding and salinity ,( 28 Jan18 Feb; initial size 5.31 mm TL; a-way ANOVA analysis; values followed by different letters are significantly different, P < 0.05)
Age
(days)
Salinity 38°/00
26”/00
16”/00
Feeding initiated - days after mouth opened
10 17 24
1
2
3
1
2
3
1
2
6.22b 5.65a -
6.15b 5.88a -
6.OOab 5.93a 5.87a
6.20b 6.48~ 6.81d
6.15b 6.05ab 7.27d
6.00ab 6.12ab 6.97d
6.2813 6.02ab 6.08b 6.13b 6.18b 5.84a
3 6.25b 6.40~ 6.58~
16 TABLE 6 Growth of sea bass larvae as influenced by delayed initial feeding and salinity (14 Feb28 Feb; Z-way ANOVA analysis; values followed hy different letters are significantly different, P < 0.05) Age (days)
Salinity 38’100
26’/00
13°/oo
Feeding initiated - days after mouth opened 1 12 18
3
5
5.5713 5.42b 5.23ab 5.5813 5.4513 -
1
3
5
1
3
5.57b 6.20~
5.50b 6.20~
5.4213 5.60bc
5.6413 5.23ab 5.18a 5.30ab
5 5.3813 5.27ab
feeding had no effect on growth by day 18 (Table 6), but those held at 26’100 salinity were consistently larger than those held at 3ES”/00 or 13O/0o (Table 6). DISCUSSION
Although it is possible that other experimental conditions (e.g., container size) may have interacted with treatments to affect larval response, evaluation can only be based on the variables to which the larvae were exposed. Effects
of salinity and temperature
on survival and growth
of larvae
Larval survival was consistently increased by reduction of salinity below ambient levels. At salinities greater than 10°/oo mortality was increased at water temperatures (18 and 21°C) which exceeded ambient (15°C). These 1983 results confirmed similar findings in 1982 (Johnson and Katavic, 1984). Larvae at the lowest salinity (lO”/oo) were commonly observed inactive at the bottom of the aquaria. Holliday (1965) and Houde (1973) observed increased survival at lower salinities which they associated with reduced activity and metabolic demand. As in 1982, sea bass larval growth was enhanced by increasing temperatures (which reduced survival) or decreasing salinity (which increased survival). Alliot et al. (1983) found that sea bass larvae at high water temperature (22°C) grew better in high (37’/00) and low (~O/OO) salinities than at intermediate salinities, while at ambient temperature (15°C) growth was best at intermediate salinities (11’1 oo and 24’/00). We observed no beneficial effects of ambient (38’100) salinity and did not use hyposmotic salinities. A substantial metabolic expenditure for hydromineral balance has been demonstrated in rainbow trout; 27% of total oxygen consumption at 30’/00 (Rao, 1968). Beneficial effects of isosmotic salinities to teleost larvae include en-
17
hanced swimming ability, reduced metabolic activity, and increased growth rate (Holliday, 1969). Temperature and salinity have also been shown to affect the toxicity of ammonia to young (20-93 mm TL) striped bass; toxicity is greatest at elevated temperature (23 vs. 15°C) and in ambient sea water, compared to fresh water or 33% sea water (Hazel et al., 1971). The results of May (1975) with Bairdiellu icistia demonstrated that development at high salinities was best at low temperatures. Present findings with sea bass larvae are in agreement with the above observations of other teleost larvae. Effects of delayed initial feeding varied salinities and temperature
on survival and growth
of larvae held at
Early feeding of sea bass larvae requires cultured rotifers fed cultured phytoplankton followed by cultured brine shrimp before artificial (nonliving) diets can be successfully used. Larvae fed at the initiation of mouth opening have a low predator efficiency and many may not yet be capable of feeding. Accumulation of uneaten food may produce water quality problems and increase mortality. Although high early feeding levels have prqduced better growth at 15 days, that difference was not seen after 30 days (BarahonaFernandes and Girin, 1977). Temperatures above ambient also increase growth, but decrease survival. Delayed initial -feeding investigations were designed to determine any effect on survival and growth and were carried out only at ambient temperature (15°C). Alderdice and Velsen (1971) have shown that mortality of unfed herring larvae increased at higher temperatures, with maximum survival at intermediate temperatures and salinity. Others have also demonstrated that higher temperatures reduce the period larvae can survive without food (Qasim, 1959; Houde, 1974). Before delayed initial feeding could be suggested as a potential sea bass culture practice research which established an allowable, without reaching the “point of no return”, delay period had to be completed. When food is scarce or if it must be withheld, environmental conditions should be altered to reduce energy required and increase survival (Bardach et al., 1972). Grunion (Leuresthes tenuis) larvae have gone without food for as long as 3 weeks at 18°C and when fed, growth proceeded at the same rate as those fed from the first day. Unfed larvae were inactive and percent survival was inversely related to day of initial feeding (May, 1971). Theilacker and Dorsey (1980) also observed that unfed larvae were inactive and that each day of starvation required 2 days of tissue (pancreas, liver, gut) repair without growth. In the present study, delaying initial feeding beyond the first day to the second, third, or fifth either enhanced or had no effect on survival. Survival of larvae with delayed feeding was enhanced by reducing culture water salinity. Improved survival in dilute sea water when feeding was delayed beyond the third to the fifth day after mouth opening, suggests that develop-
18
mental change in larval hydromineral balance may occur during this period. Growth at 18 days was not depressed by delaying initial feeding until the second, third or fifth day after mouth opening was initiated. Although growth during the first week after feeding was initiated was best at the lowest salinities tested (13’/00 and 16’/00), after an additional week growth was consistently best at 26O/oo. Larval sea bass survival can be increased and their growth enhanced by culturing them in dilute sea water. Initial feeding of sea bass larvae can be delayed as long as 5 days without affecting growth or survival if they are held in dilute sea water. ACKNOWLEDGEMENTS The production of larvae and their maintenance resulted from the conscientious work of A. Majic (phytoplankton culture), M. Karljevic and M. Kozuh (tank maintenance and zooplankton production), and M. Tonkovic (chemical analyses). Partial support was provided by Natural Resource Consultants, as well as U.S. International Communication Agency and the Commission for Educational Exchange Between the U.S.A. and Yugoslavia through a Fulbright Scholar award to D.W. Johnson.
REFERENCES Alderdice, D.F. and Velsen, F.P.J., 1971. Some effects of salinity and temperature on early development of Pacific herring (Clupea pallasi). J. Fish. Res. Board Can., 28: 1545-1562. Alliot, E., Pastoureaud, A. and Thebault, H., 1983. Influence de la temperature et de la saliniti! sur la croissance et la composition corporelle d’alevins de Dicentrarchus labrax. Aquaculture, 31: 181-194. Barahona-Fernandes, M.H. and Girin, M., 1977. Effect of different food levels on the growth and survival of laboratory-reared sea bass larvae (Dicentrarchus Zabrax (L.)). Actes Colloq. CNEXO, 4: 69-84. Bardach, J.E., Ryther, J.J. and McLarney, W.O., 1972. Aquaculture - The Farming and Husbandry of Freshwater and Marine Organisms. Wiley-Inter Science, New York, NY, 868 pp. Blaxter, J.H.S. and Hempel, G., 1963. The influence of egg size on herring larvae. J. Cons., Cons. Int. Explor. Mer, 28: 211-240. Hazel, C.R., Thompsen, W. and Meith, S.J., 1971. Sensitivity of striped bass and stickleback to ammonia in relation to temperature and salinity. Calif. Fish Game, 57: 138153. Holliday, F.G.T., 1965. Osmoregulation in marine teleost eggs and larvae. Calif. Coop. Oceanic Fish. Invest. Rep., 10: 89-95. Holliday, F.G.T., 1969. The effects of salinity on the eggs and larvae of teleosts. In: W.S. Hoar and D.J. Randall (Editors), Fish physiology, Vol. I. Excretion, Ionic Regulation, and Metabolism. Academic Press, New York, NY, pp. 293-311. Houde, E.D., 1973. Some recent advances and unsolved problems in the culture of marine fish larvae. Proc. World Maricult. Sot., 3: 83-112. Houde, E.D., 1974. Effects of temperature and delayed feeding on growth and survival of larvae of three species of sub-tropical marine fishes. Mar. Biol., 26: 271-285.
19
Hunter, J.R., 1980. The feeding behavior and ecology of marine fish larvae. In: J.E. Bardach, J.J. Magnuson, R.C. May and J.M. Reinhart (Editors), Fish Behavior and Its Use In Capture and Culture of Fishes. ICLARM Conference Proceedings 5. International Center for Living Aquatic Resources Management, Manila, Philippines, pp. 287-330. Iwai, T., 1980. Sensory anatomy and feeding of larvae. In: J.E. Bardach, J.J. Magnuson, R.C. May and J.M. Reinhart (Editors), Fish Behavior and Its Use In Capture and Culture of Fishes. ICLARM Conference Proceedings 5. International Center for Living Aquatic Resources Management, Manila, Philippines, pp. 124-145. Johnson, D.W. and Katavic, I., 1984. Mortality, growth and swim bladder stress syndrome of sea bass (Dicentrarchus Zabrux) larvae under varied environmental conditions. Aquaculture, 38: 67-78. Lasker, R., Feder, H.M., Theilacker, G.H. and May, R.C., 1970. Feeding, growth, and survival of Engraulis mordox larvae reared in the laboratory. Mar. Biol., 5: 345-353. May, R.C., 1971. Effects of delayed initial feeding on larvae of the grunion, Leuresfhes tenuis (Ayres). Fish. Bull., U.S., 69: 411-425. May, R.C., 1975. Effects of temperature and salinity in fertilization, embryonic development, and hatching in Bairdiella icistia (Pisces:Sciaenidae), and the effect of parental salinity acclimation on embryonic and larval salinity tolerance. Fish. Bull., U.S., 73: l-22. Paffenhofer, C.A., 1967. Caloric content of larvae of the brine shrimp Artemia salina. Helgol. Wiss. Meeresunters., 16: 130-135. Qasim, S.Z., 1959. Laboratory experiments on some factors affecting the survival of marine teleost larvae. J. Mar. Biol. Assoc. India, 1: 13-25. Rao, B.M.M., 1968. Oxygen consumption of rainbow trout (Salmo guirdneri) in relation to activity and salinity. Can. J. Zool., 46: 781-786. Sokal, R.R. and Rohlf, F.J., 1969. Biometry. W.H. Freeman and Company, London, 776 pp. Theilacker, G. and Dorsey, K., 1980. Larval fish diversity, a summary of laboratory and field research. In: Workshop On The Effects Of Environmental Variation On The Survival Of Larval Pelagic Fishes. IOC Workshop Report No. 28, pp. 105-142.
11 in The Netherlands
SURVIVAL AND GROWTH OF SEA BASS (DICENTRARCHUS LARVAE AS INFLUENCED BY TEMPERATURE, SALINITY, AND DELAYED INITIAL FEEDING
LABRAX)
DONALD W. JOHNSON’ and IVAN KATAVIC Institute of Oceanography and Fisheries, Split (Yugoslavia) Present addresses: ‘Natural Resource Consultants, 304 N lath, Pocatello, ID 83201 (U.S.A.) a Ecological Research Center, Biology Department, Memphis State University, Memphis, TN 38152 (U.S.A.) and Southeastern Fish Cultural Laboratory, U.S. Fish and Wildlife Service, Marion, AL 36756 (U.S.A.) (Accepted
12 October 1985)
ABSTRACT Johnson, D.W. and Katavic, I., 1986. Survival and growth of sea bass (Dicentramhus Zabrux) larvae as influenced by temperature, salinity, and delayed initial feeding. Aquaculture, 52: 11-19. The determination of the optimum time and environmental conditions for initial feeding of sea bass larvae will contribute to the feasibility of their profitable culturing. Survival and growth of larvae were increased when ambient salinity (38”/00) was reduced (10”/0, and 20’/00). Intermediate salinity (26’100) produced consistently better growth. Although increased temperatures (18 and 21°C) improved growth rates, survival was decreased below that at ambient (15” C). Feeding of cultured sea bass larvae has commonly begun at initiation of mouth opening (4 days after hatching). At reduced salinity (13’/00 and 26’/00) delaying initial feeding until the fifth day resulted in survival equal to that of those fed on the fist day after mouth opening. Initial feeding can be delayed 2-4 days without adversely affecting survival or growth of sea bass larvae if they are held at ambient temperature in dilute sea water.
INTRODUCTION
The aquaculture potential of many species is limited by their live food requirement as larvae. Minimal use of live food will increase economic feasibility, while decreasing the possibility of a catastrophic loss resulting from disruption of the supply of live food. The effect of different feeding periods and levels on survival and growth of’larvae has been investigated for many species, including sea bass (Barahona-Fernandes and Girin, 1977). The determination of the optimum time and environmental conditions for initial feeding of larvae is critical to raising the maximum number of larvae with the minimum use of live food.
0044-8486/86/$03.50
0 1986 Elsevier Science Publishers B.V.
12
Feeding of sea bass larvae has commonly begun at initiation of mouth opening (4 days after hatching). To avoid overfeeding resulting in accumulation of less nutritious feed and degradation of water quality (Paffenhofer, 1967), as well as the waste of expensive feed, feeding should be delayed until the latest practical time. The most desirable day of initial feeding will be when the total population is capable of feeding and prior to any significant inhibition of growth or “point of no return” when “irreversible starvation” will have begun (Blaxter and Hempel, 1963; Lasker et al., 1970; Hunter, 1980; Iwai, 1980). Determination of environmental conditions for sea bass larval growth and survival with the most efficient use of available live food was the objective of this research. If feeding can be delayed without a major impact on survival or later growth, there would be water quality and economic benefits. MATERIALS
AND METHODS
Origin of brood stock and routine handling of larvae are described in an earlier report (Johnson and Katavic, 1984). One-day-old larvae for these experiments were from induced spawning in January 1983. Eggs were incubated at 16 ?I 0.3”C and 38’/00 salinity. Experiments were carried out under natural light and photoperiod. During the first week larvae were fed on rotifers (.BrachionuspZicatilis) at densities of lo/ml. On the fifth day after hatching Artemia nauplii (origin Great Salt Lake, Utah, U.S.A.) were added gradually with the rotifers. Dead larvae were removed when they became opaque and failed to respond to the jar-cleaning pipette when residue was removed after each feeding period. Statistical treatment included a G-test of independence of temperature and salinity, together with survival (Y?) which were followed by a priori tests of partitions. Differences in growth rate were determined by two-way analysis of variance (Sokal and Rohlf, 1969). Effects
of salinity and temperature
on survival and growth
of larvae
Differences in survival and growth of larvae held in a range of salinities and temperatures were analyzed to confirm earlier findings (Johnson and Katavic, 1984). Each of 36 two-liter jars were stocked with 55-66 larvae. Triplicate tests were made at 15, 18, and 21°C in 10,20, 30 and 38O/0o. Jars were held in water baths to maintain temperature. Salinity was maintained by replacing evaporative loss with distilled water. Dissolved oxygen was maintained at near saturation with compressed air through air stones. Growth in length (total) was determined by measuring 10 specimens per treatment each week using an ocular micrometer. Effects of delayed initial feeding varied salinities and temperatures
on survival and growth
of larvae held at
Investigations were completed delaying initial feeding until the second,
13
third or fifth days after mouth opening together with the common culture practice of presenting live food on the first day mouth opening was initiated. These experiments were performed at ambient temperatures (15°C) and salinities of 38, 26, and 16 or 13O/o0. RESULTS
Effects of salinity and temperature on survival and growth of larvae Survival was consistently increased by reduction of salinity from ambient to 20’/00 or 10°/oo at temperatures of 15 (ambient), 18, 21°C (Table 1). At 10°/oo there was no difference in survival between larvae held at 15, 18, and 21°C. At 20’/00 survival was greater at 15°C. Mortality also increased with elevated temperatures at 30’/00 and 38’/00 (Table 1). Reduced salinity also tended to improve larval growth, especially at elevated temperatures; no significant differences were seen between 38O/o0and 30’/00. Larvae held in lower salinities (20’/00 and 10°/oo) and higher temperatures (18 and 21°C) tended to have greater total lengths (Table 2). (38’/00)
Effects of delayed initial feeding on survival and growth of larvae held at varied salinities and tempemtures At ambient salinity (38O/o0) larval survival was not decreased by delaying the initial feeding until the third day after the mouth opened. At 26’/00 mortality of larvae was increased when initial feeding was delayed until the second day after the mouth opened. Although at 16’/00 delaying feeding until the third day after the mouth opened increased mortality, delay until the second day did not affect larval survival (Table 3). TABLE 1 Survival (%) of laboratory-reared sea bass larvae at ambient (15°C and with decreased salinities and elevated temperatures Temp. (“C)
Age (days)
Rearing salinity (O/W) 38
30
20
10
15
4 11 19
87.9a 65.2~ 24.2e
7o.oc 43.3d 18.3e
84.5ab 75.9b 46.6d
90.7a 83.7ab 41.9d
18
4 11 19
71.oc 25.8e 6.4f
65.5~ 54.5d 21.8e
80.6ab 51.6d 25.8e
91.5a 68.lbcd 31.9de
21
4 11 19
57.9cd 26.3e 7.9f
58.2cd 25.3e 6.3f
73.7b 54.4d 19.3ef
82.lab 76.813 35.7d
38”/00) conditions
G-test of independence was used to determine significant differences in mortality among salinities (values followed by different letters are significantly different, P < 0.05).
14 TABLE 2 Growth (mm TL) of laboratory-reared sea bass larvae at decreased salinities and increased temperatures Salinity (o/o0)
Temp. (“C)
7 days
38
15 18 21
5.23a 5.34a 5.42a
11.30e
20
15 18 21
5.26a 5.56ab 5.75b
8.45~ 10.18d 12.13e
10
15 18 21
5.34a 5.34a 5.7713
9.05c 9.48c 12.38e
21 days
7.9oc 9.37c
Variation between groups subjected to a-way analysis of variance with differences tested using Student-Newman-Keuls procedure (values followed by different letters are significantly different, P < 0.05). TABLE 3 Survival (%) of laboratory-reared sea bass larvae fed on the first day after their mouths opened and with delayed initial feeding when held at ambient and decreased salinities Day feeding initiated after mouth opened
Age (days)
1st
Salinity -38’/00
26’/00
16’/00
8 17
50.4bc 18.5e
90.7a 59.413
87.4a 46.1~
2nd
8 17
44.4c 16.9e
49.6c 30.2d
85.3a 45.6~
3rd
8 17
56.613 22.0e
66.4b 26.7de
52.8~ 11.4f
G-test for significant differences significantly different, P < 0.05).
in mortality (values followed
by different letters are
When larvae were initially fed on the first day after their mouths opened survival was consistently higher at reduced salinity and was best at 26’/00. When feeding was delayed by 1 day, mortality was reduced to levels seen with the first day feeding if fish were held at 16’/00. The advantage of 16’/00 over 26O/o0 was lost when feeding of larvae was delayed an additional day (Table 3). Growth was not adversely affected by delaying the initial feeding of larvae in 38O/o0 or 16O/o0 until the second or third day after the mouth opened (Ta-
15
ble 5). In 26’100 salinity, delaying initial feeding reduced growth at 17 days, but that difference was no longer present at 24 days. Growth was greatest at reduced salinity regardless of when feeding was initiated and by 24 days after hatching was best at 26’/00 (Table 5). The above evaluations were repeated at 38’/00, 26’100 and 13’/00 salinity with feeding initiated on the first, third, and fifth day after mouth opening. Although at reduced salinity delayed feeding until the third day after mouth opening decreased survival, an additional 2 day delay did not increase mortality and survival was close to that seen in larvae fed on the first day after mouth opening (Table 4). These tests confirmed the value of decreasing salinity of culture water to increase larval survival and suggest that in dilute sea water initial feeding can be delayed from the first to the fifth day after mouths open without decreasing early survival (Table 4). Delayed initial TABLE4 Survival (%) of laboratory-reared sea bass larvae fed on the first day after mouths opened and with delayed initial feeding when held at am,bient and decreased salinities Day feeding initiated after mouth opened
Age (days)
Salinity 380100
26°/00
13°/00
1st
9 17
94.8a 18.2e
89.8a 13.0e
93.la 15.le
3rd
9 17
83.913 12.6e
75.4bc 6.6e
82.lb 0.9ef
5th
9 17
66.9d Of
85.813 11.0e
96.9a 13.9e
G-test for significant differences in mortality (values followed significantly different, P < 0.05).
by different letters are
TABLE5 Growth of sea bass larvae as influenced by delayed initial feeding and salinity ,( 28 Jan18 Feb; initial size 5.31 mm TL; a-way ANOVA analysis; values followed by different letters are significantly different, P < 0.05)
Age
(days)
Salinity 38°/00
26”/00
16”/00
Feeding initiated - days after mouth opened
10 17 24
1
2
3
1
2
3
1
2
6.22b 5.65a -
6.15b 5.88a -
6.OOab 5.93a 5.87a
6.20b 6.48~ 6.81d
6.15b 6.05ab 7.27d
6.00ab 6.12ab 6.97d
6.2813 6.02ab 6.08b 6.13b 6.18b 5.84a
3 6.25b 6.40~ 6.58~
16 TABLE 6 Growth of sea bass larvae as influenced by delayed initial feeding and salinity (14 Feb28 Feb; Z-way ANOVA analysis; values followed hy different letters are significantly different, P < 0.05) Age (days)
Salinity 38’100
26’/00
13°/oo
Feeding initiated - days after mouth opened 1 12 18
3
5
5.5713 5.42b 5.23ab 5.5813 5.4513 -
1
3
5
1
3
5.57b 6.20~
5.50b 6.20~
5.4213 5.60bc
5.6413 5.23ab 5.18a 5.30ab
5 5.3813 5.27ab
feeding had no effect on growth by day 18 (Table 6), but those held at 26’100 salinity were consistently larger than those held at 3ES”/00 or 13O/0o (Table 6). DISCUSSION
Although it is possible that other experimental conditions (e.g., container size) may have interacted with treatments to affect larval response, evaluation can only be based on the variables to which the larvae were exposed. Effects
of salinity and temperature
on survival and growth
of larvae
Larval survival was consistently increased by reduction of salinity below ambient levels. At salinities greater than 10°/oo mortality was increased at water temperatures (18 and 21°C) which exceeded ambient (15°C). These 1983 results confirmed similar findings in 1982 (Johnson and Katavic, 1984). Larvae at the lowest salinity (lO”/oo) were commonly observed inactive at the bottom of the aquaria. Holliday (1965) and Houde (1973) observed increased survival at lower salinities which they associated with reduced activity and metabolic demand. As in 1982, sea bass larval growth was enhanced by increasing temperatures (which reduced survival) or decreasing salinity (which increased survival). Alliot et al. (1983) found that sea bass larvae at high water temperature (22°C) grew better in high (37’/00) and low (~O/OO) salinities than at intermediate salinities, while at ambient temperature (15°C) growth was best at intermediate salinities (11’1 oo and 24’/00). We observed no beneficial effects of ambient (38’100) salinity and did not use hyposmotic salinities. A substantial metabolic expenditure for hydromineral balance has been demonstrated in rainbow trout; 27% of total oxygen consumption at 30’/00 (Rao, 1968). Beneficial effects of isosmotic salinities to teleost larvae include en-
17
hanced swimming ability, reduced metabolic activity, and increased growth rate (Holliday, 1969). Temperature and salinity have also been shown to affect the toxicity of ammonia to young (20-93 mm TL) striped bass; toxicity is greatest at elevated temperature (23 vs. 15°C) and in ambient sea water, compared to fresh water or 33% sea water (Hazel et al., 1971). The results of May (1975) with Bairdiellu icistia demonstrated that development at high salinities was best at low temperatures. Present findings with sea bass larvae are in agreement with the above observations of other teleost larvae. Effects of delayed initial feeding varied salinities and temperature
on survival and growth
of larvae held at
Early feeding of sea bass larvae requires cultured rotifers fed cultured phytoplankton followed by cultured brine shrimp before artificial (nonliving) diets can be successfully used. Larvae fed at the initiation of mouth opening have a low predator efficiency and many may not yet be capable of feeding. Accumulation of uneaten food may produce water quality problems and increase mortality. Although high early feeding levels have prqduced better growth at 15 days, that difference was not seen after 30 days (BarahonaFernandes and Girin, 1977). Temperatures above ambient also increase growth, but decrease survival. Delayed initial -feeding investigations were designed to determine any effect on survival and growth and were carried out only at ambient temperature (15°C). Alderdice and Velsen (1971) have shown that mortality of unfed herring larvae increased at higher temperatures, with maximum survival at intermediate temperatures and salinity. Others have also demonstrated that higher temperatures reduce the period larvae can survive without food (Qasim, 1959; Houde, 1974). Before delayed initial feeding could be suggested as a potential sea bass culture practice research which established an allowable, without reaching the “point of no return”, delay period had to be completed. When food is scarce or if it must be withheld, environmental conditions should be altered to reduce energy required and increase survival (Bardach et al., 1972). Grunion (Leuresthes tenuis) larvae have gone without food for as long as 3 weeks at 18°C and when fed, growth proceeded at the same rate as those fed from the first day. Unfed larvae were inactive and percent survival was inversely related to day of initial feeding (May, 1971). Theilacker and Dorsey (1980) also observed that unfed larvae were inactive and that each day of starvation required 2 days of tissue (pancreas, liver, gut) repair without growth. In the present study, delaying initial feeding beyond the first day to the second, third, or fifth either enhanced or had no effect on survival. Survival of larvae with delayed feeding was enhanced by reducing culture water salinity. Improved survival in dilute sea water when feeding was delayed beyond the third to the fifth day after mouth opening, suggests that develop-
18
mental change in larval hydromineral balance may occur during this period. Growth at 18 days was not depressed by delaying initial feeding until the second, third or fifth day after mouth opening was initiated. Although growth during the first week after feeding was initiated was best at the lowest salinities tested (13’/00 and 16’/00), after an additional week growth was consistently best at 26O/oo. Larval sea bass survival can be increased and their growth enhanced by culturing them in dilute sea water. Initial feeding of sea bass larvae can be delayed as long as 5 days without affecting growth or survival if they are held in dilute sea water. ACKNOWLEDGEMENTS The production of larvae and their maintenance resulted from the conscientious work of A. Majic (phytoplankton culture), M. Karljevic and M. Kozuh (tank maintenance and zooplankton production), and M. Tonkovic (chemical analyses). Partial support was provided by Natural Resource Consultants, as well as U.S. International Communication Agency and the Commission for Educational Exchange Between the U.S.A. and Yugoslavia through a Fulbright Scholar award to D.W. Johnson.
REFERENCES Alderdice, D.F. and Velsen, F.P.J., 1971. Some effects of salinity and temperature on early development of Pacific herring (Clupea pallasi). J. Fish. Res. Board Can., 28: 1545-1562. Alliot, E., Pastoureaud, A. and Thebault, H., 1983. Influence de la temperature et de la saliniti! sur la croissance et la composition corporelle d’alevins de Dicentrarchus labrax. Aquaculture, 31: 181-194. Barahona-Fernandes, M.H. and Girin, M., 1977. Effect of different food levels on the growth and survival of laboratory-reared sea bass larvae (Dicentrarchus Zabrax (L.)). Actes Colloq. CNEXO, 4: 69-84. Bardach, J.E., Ryther, J.J. and McLarney, W.O., 1972. Aquaculture - The Farming and Husbandry of Freshwater and Marine Organisms. Wiley-Inter Science, New York, NY, 868 pp. Blaxter, J.H.S. and Hempel, G., 1963. The influence of egg size on herring larvae. J. Cons., Cons. Int. Explor. Mer, 28: 211-240. Hazel, C.R., Thompsen, W. and Meith, S.J., 1971. Sensitivity of striped bass and stickleback to ammonia in relation to temperature and salinity. Calif. Fish Game, 57: 138153. Holliday, F.G.T., 1965. Osmoregulation in marine teleost eggs and larvae. Calif. Coop. Oceanic Fish. Invest. Rep., 10: 89-95. Holliday, F.G.T., 1969. The effects of salinity on the eggs and larvae of teleosts. In: W.S. Hoar and D.J. Randall (Editors), Fish physiology, Vol. I. Excretion, Ionic Regulation, and Metabolism. Academic Press, New York, NY, pp. 293-311. Houde, E.D., 1973. Some recent advances and unsolved problems in the culture of marine fish larvae. Proc. World Maricult. Sot., 3: 83-112. Houde, E.D., 1974. Effects of temperature and delayed feeding on growth and survival of larvae of three species of sub-tropical marine fishes. Mar. Biol., 26: 271-285.
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Hunter, J.R., 1980. The feeding behavior and ecology of marine fish larvae. In: J.E. Bardach, J.J. Magnuson, R.C. May and J.M. Reinhart (Editors), Fish Behavior and Its Use In Capture and Culture of Fishes. ICLARM Conference Proceedings 5. International Center for Living Aquatic Resources Management, Manila, Philippines, pp. 287-330. Iwai, T., 1980. Sensory anatomy and feeding of larvae. In: J.E. Bardach, J.J. Magnuson, R.C. May and J.M. Reinhart (Editors), Fish Behavior and Its Use In Capture and Culture of Fishes. ICLARM Conference Proceedings 5. International Center for Living Aquatic Resources Management, Manila, Philippines, pp. 124-145. Johnson, D.W. and Katavic, I., 1984. Mortality, growth and swim bladder stress syndrome of sea bass (Dicentrarchus Zabrux) larvae under varied environmental conditions. Aquaculture, 38: 67-78. Lasker, R., Feder, H.M., Theilacker, G.H. and May, R.C., 1970. Feeding, growth, and survival of Engraulis mordox larvae reared in the laboratory. Mar. Biol., 5: 345-353. May, R.C., 1971. Effects of delayed initial feeding on larvae of the grunion, Leuresfhes tenuis (Ayres). Fish. Bull., U.S., 69: 411-425. May, R.C., 1975. Effects of temperature and salinity in fertilization, embryonic development, and hatching in Bairdiella icistia (Pisces:Sciaenidae), and the effect of parental salinity acclimation on embryonic and larval salinity tolerance. Fish. Bull., U.S., 73: l-22. Paffenhofer, C.A., 1967. Caloric content of larvae of the brine shrimp Artemia salina. Helgol. Wiss. Meeresunters., 16: 130-135. Qasim, S.Z., 1959. Laboratory experiments on some factors affecting the survival of marine teleost larvae. J. Mar. Biol. Assoc. India, 1: 13-25. Rao, B.M.M., 1968. Oxygen consumption of rainbow trout (Salmo guirdneri) in relation to activity and salinity. Can. J. Zool., 46: 781-786. Sokal, R.R. and Rohlf, F.J., 1969. Biometry. W.H. Freeman and Company, London, 776 pp. Theilacker, G. and Dorsey, K., 1980. Larval fish diversity, a summary of laboratory and field research. In: Workshop On The Effects Of Environmental Variation On The Survival Of Larval Pelagic Fishes. IOC Workshop Report No. 28, pp. 105-142.