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A comparison of the growth performance of rainbow trout (Salmo gairdneri) in fresh and brackish water in Yugoslavia
Aquaculture,
77 (1989) l-10 Elsevier Science Publishers B.V., Amsterdam
-
Printed
in The Netherlands
A Comparison of the Growth Performance of Rainbow Trout (Salmo gairdneri) in Fresh and Brackish Water in Yugoslavia EMIN TESKEREDZIC, MODRUSAN
ZLATICA TESKEREDZIC,
“Ruder BoSkoviC” Institute,
Center for Marine
MARIJA TOMEC and ZVONKO
Research
Zagreb,
BijeniEka
54,410Ol
Zagreb
(Yugoslavia)
(Accepted
12 August 19881
ABSTRACT Teskerediic, E.. Teskerediid, Z., Tomec, M. and Modruian, Z., 1989. A comparison of the growth performance of rainbow trout (Salmo gairdneri) in fresh and brackish water in Yugoslavia. Aquaculture, 77: l-10. Rainbow trout of two year-classes (O+, 1+ ) and four different initial average weights (84, 118, 197 and 301 g) were grown-on in floating cages moored on the Adriatic coast of Yugoslavia, while two control groups (84 and 301 g) were kept in fresh water at a conventional fish farm. All fish were fed the same commercial diet at 2% of body weight per day and were reared for 8 months from October 1982 to June 1983. Physiochemical characteristics of water at the brackish and fresh-water sites were monitored, and all fish were weighed every month. Growth of fish in all groups held in brackish water was greatly superior (3 to 4 times) to that of their contemporaries at the fresh-water unit. The results point the way to a new type of trout farming in Yugoslavia, and possibly in other countries of the Adriatic and Mediterranean region, using conventional fresh-water farms to produce fingerlings which are then grown-on in sea water either using floating cages or pumped sea water. By comparison with the papers written so far, this work demonstrates the feasibility of rainbow trout culture in warm seas, opening up the possibility for developing a new technology of aquaculture.
INTRODUCTION
Rainbow trout (Salmo gairdneri) have been cultured in fresh water in Yugoslavia continuously since the first importation of eggs from the U.S.A. in 1890 (BojEid et al., 1982). Current annual production is around 4000 tonnes of portion-size fish from a total of almost 100 farms (Anon, 1987). However, despite the country’s favourable climatic and ecological conditions, production of rainbow trout on Yugoslavian fish farms averages 13.5 kg/m” (Anon., 1986). Fresh-water rearing of rainbow trout up to the portion-size of 200-300 g lasts for 18-26 months, while the rearing of big trout of over 1000 g lasts for 4-5 years and, therefore, is not practised (Teskerediid, 1985).
0044-8486/89/$03.50
0 1989 Elsevier Science Publishers
B.V.
2
The total recorded annual catch of fresh-water and sea fish in Yugoslavia of 75 057 tonnes (Anon., 1986) does not meet the demand from the local population and the large tourist market. Consequently the country imports about 30 000 tonnes of sea food per year. During the last 10 years this shortfall in local output has stimulated research aimed at increasing production from aquaculture (Filid, 1978; Teskerediit and Teskerediid, 1979; Teskerediib and Fijan, 1980 ). Building on overseas experience of cage culture of rainbow trout in cold seas (Gunstram, 1970; Tatum, 1973; Hahn, 1975; Edwards, 1978)) in 1979 the scientists of the Ruder Boskovid Institute, Center for Marine Research Zagreb, began investigations into the feasibility of culturing this species in the warm Adriatic Sea. Early experiments soon showed promise (Teskerediid, 1982 ) . In the present paper we compare growth of rainbow trout held in conventional Yugoslavian fresh-water farms with that of identical fish reared in floating cages on the Adriatic coast, and demonstrate the possibility of developing a new technology of rainbow trout farming in warm seas such as the Adriatic Sea. MATERIALSANDMETHODS The rainbow trout used in the experiment were obtained from Emona troutfarm, Dvor pri Zuienberku, an average-sized fresh-water commercial facility which produces about 200 tonnes of 200-300-g fish per year in concrete raceways. Experimental fish for on-growing in cages were selected from two yearclasses (aged 10 and 22 months) on 2 October 1982. From each year-class, individuals were taken from each end of the size distribution, as follows: Fish in group I were 10 months of age and averaged 84 g weight. Fish in group II were 10 months of age and averaged 118 g weight. Fish in group III were 22 months of age and averaged 197 g weight. Fish in group IV were 22 months of age and averaged 301 g weight. For comparison, two further groups (IA and IVA) comprising fish of the same size and age as those in groups I and IV were grown-on at the fresh-water farm. All fish were reared for 8 months until 2 June 1983. Eight experimental cages were moored in RakovaEa Bay near the town of Skradin in the River Krka Estuary (Fig. 1) , the experimental farm of the Ruder Boskovi& Institute. The 4 x 4 x 4 m cages were of timber + Styrofoam cylinder construction supporting 15 mm mesh knotted nylon nets. Fish from each of the experimental groups were divided between two replicate cages, each cage being stocked with 100 kg of trout. The control groups of fish were held in 20 x 4 x 1 m fresh-water raceways stocked at the same initial density. In the raceways, complete water exchange occurred between 40 and 60 times per day. The same dry, commercial, pelleted feed f40-42% crude protein, 6-8% fat, 12% ash, 10% water) was used at both fish farms. All fish were weighed and
3
Fig. 1. Location of the experimental farm near Skradin.
counted each month, and at the same time fish health was monitored. The daily food ration of 2% of total fish weight was corrected after each sampling in line with weight gain. Physiochemical measurements of the water at the two farms were made monthly. At the cage site, temperature, pH, oxygen concentration and salinity were determined at depths of 0.5, 2, 4 and 6 m. In the fresh-water raceways, temperature, pH and oxygen concentration were determined at 0.5 m. Growth rates were calculated in %/day using the formula (Tesseyre, 1979; Spannhof, 1983)
4 RESULTS
In Figs. 2 and 3, broken lines show the growth rates of rainbow trout at the experimental brackish-water cage farm, while the solid lines show the growth rate at the fresh-water farm. The growth rate of the control fish held in freshwater raceways fell within the normal range of performance for such fish, i.e. 0.233 to 0.411 %/day. However, the growth rates of fish in the four groups transferred to cages in sea water rapidly surpassed that of their counterparts in fresh water, i.e. 0.705 to 0.993 %/day (Table 1). The initial and final weights of fish in the experimental and control groups over the 8 months trial period are shown in Table 1.
1200 Gmup 1100
I A
-
fresh
water
O---O GKlUfl II
- brackish
water
/
/
/
d /
//
/ 600
/
w-’
/
P’
/I
1. d /
/I p/’ ,* / ,’
IA
AGE
T
OL
OF
12
10 I
I
X
XII 1982
Fig. 2. The growth of lo-month-old
RAINBOW
(months) 16
II
IV 1983
I
’ I
TROUT
‘4
I
18 I
VI
month year
rainbow trout in fresh water and in brackish water.
J
1700 0
N
/
lb@4
/ /
-o---o
1500
A
Group N s&Y N
14110
m
-
-
/
frest, water
brad&h
d
water
/
/
l3OO
d
12w
I loo
loo0
?” 9oo
3 i
.F
Boo
I
d
5 P -
mo
?’ / /
/
Y
/ /
.:I_:.//> /
6OO
500
bal
300
d’
200
T I
AGE
OF
RAINBOW
TROUT
(months
NA
)
22
24
26
28
50
I
I
X
XII
I II
I N
I VI month
t
1983
1982
;
year
Fig. 3. The growth of 22-month-old rainbow trout in fresh water and in brackish water.
The growth performance of the zero-age trout in sea water was superior to the growth of the 1+ trout in this medium (Table 1). During the period from December to February, the average growth of the fish stocked at 22 months
6 TABLE I Initial weights, final weights and growth rates of rainbow trout reared in sea-water cages and freshwater raceways. Data show the mean of two replicates Group
I II III IV IA IVA
Site
SW SW SW SW FW FW
Initial wt.
Final wt.
Growth rate
(9)
(gf
(%/daY)
84 118 197 301 84 301
900 1136 1134 1625 225 526
0.993 0.948 0.732 0.705 0.411 0.233
(groups III, IV, IVA) slowed down (Fig. 3). This was due to maturation of some of the male fish in these groups. No disease or parasite problems occurred during the experiment, and fish mortality in all groups was low (0.8-2.1% ). Table 2 shows the physiochemical characteristics of water at the brackishwater site throughout the experiment, and those of the fresh-water farm. Salinity was low in surface waters at the brackish-water site in all months except November and December. At 6 m, salinity was over 30%0 in all months, with the exception of February. At the brackish-water site the pH range was 8.08.2 while at the fresh-water site the pH range was 7.5-7.8. DISCUSSION
The results clearly show that growth of rainbow trout held in cages in sea/ brackish water on the Adriatic coast is greatly superior to that of similar fish kept in conventional fresh-water trout farms in Yugoslavia during the coldest 8 months of the year. The precise reasons for such a vast difference in performance are less clear. Higher water temperature at the sea site is obviously a contributing factor. Average temperature in the vicinity of the cages at 2 m depth was 12.6” C (the total number of day-degrees being 3033) and at the fresh-water farm 9.3”C (2236 day-degrees). However, it seems unlikely that this alone can explain the results. Salinity at the sea farm varied with time and water depth, but there was always a wide range available for use by the fish. It is possible that the fish expended less energy counteracting osmotic forces at this site than in fresh water, although some authors (McKay and Gjerde, 1985) have denied that salinity itself is a significant growth-promoting factor. However, it was established that the food intake was significantly greater at salinities of 15.0-28.0%0 than in fresh water (MacLeod, 1977) and that the daily specific growth rate was si~i~c~tly higher when the fish were fed ad libitum in sea water (0.789% )
15.3 11.4 10.0
9.3 8.9 9.8 12.5 17.3 20.3
1983 1 2 3 4 5 6
T (“C)
0.5m
1982 10 11 12
Depth Year/ month
12.4 12.0 10.0 11.9 11.5 9.6
9.4 10.5 11.4
0, tmg/l)
108.0 103.2 87.5 111.2 118.6 105.6
93.4 95.7 101.0
2.4 1.0 2.0 2.0 1.8 2.4
7.0 14.0 20.0
0, sat. Sal. (%I (so)
Brackish-water cage farm
9.7 9.9 10.2 12.8 17.4 21.1
17.5 14.8 11.9
T (“C)
2m
12.5 11.9 11.0 12.5 11.1 10.4
8.3 9.9 8.6
O2 tmg/l)
109.4 105.1 97.2 117.3 115.0 115.8
86.2 97.0 79.0
02sat. (%)
2.6 1.1 2.0 2.0 2.0 11.6
21.0 19.0 34.0
Sal. (%0)
13.4 11.3 13.0 13.4 18.3 21.1
21.2 17.2 12.2
T (“C)
4m
8.0 10.0 8.8 12.0 11.0 10.4
7.5 7.3 7.5
0, (mg/l)
75.7 90.8 82.7 113.8 115.6 116.3
83.2 75.4 69.5
0, sat. (%)
26.3 11.0 22.4 11.9 31.3 29.8
33.0 35.0 38.0
Sal. GO)
15.0 12.6 13.6 14.3 17.8
20.8 17.0 13.0
T (“C)
6m
6.4 7.7 7.3 10.2 11.4 9.9
6.2 3.2 8.3
O2 (mg/l)
62.6 71.9 69.6 99.4 119.0 108.5
68.6 32.8 78.7
33.0 22.3 32.2 30.8 35.3 33.6
35.0 39.0 38.0
O2 sat. Sal. (%) &I
7.4 8.2 a.4 11.8 13.4 12.4
9.4 9.2 7.0
T (“C)
12.4 14.4 15.5 11.6 11.6 11.0
11.8 11.6 11.9
02 (mg/l)
102.0 121.0 132.0 106.0 110.0 102.0
102.0 100.0 97.0
O2 sat. (W)
Fresh-water farm
Physiochemical characteristics of the water at the experimental brackish-water cage farm in the estuary of the Krka River, and at the fresh-water farm
TABLE 2
8
than in fresh water (0.587% ) in July and August (Smith and Thorpe, 1976). These results are in accord with those presented in this paper, in which specific growth rates ranged from 0.705% to 0.993% in sea water, and from 0.233% to 0.411% in fresh water (Table 1). Also, at the relatively low density utilized in this experiment, it is possible that the trout in the marine pens were able to supplement their diet with small quantities of natural feed. Future research may reveal a more complex explanation, involving synergistic effects of salinity, temperature and oxygen concentration (Rao, 1968). The potential exists to further improve sea-water growth performance through genetic selection. The results point the way towards a new industry for trout culture on the Adriatic coast of Yugoslavia. An FAO expert who has visited Yugoslavia on several occasions described in his report the application of these results to commercial culture and the transfer of new scientific knowledge into production (Edwards, 1986 ). Fingerlings cultured in conventional fresh-water trout farms are grown-on in floating cages during that period of the year when temperatures are low enough. By stocking rainbow trout of 50-100 g it is possible to obtain three production cycles of 200-300 g fish during the winter. The number of farming cycles possible may be even greater, since it has been established that rainbow trout of only 15 g grew normally when transferred directly from fresh water into the sea (Landless, 1976). One production cycle of big trout is obtained if fish of 200-300 g are stocked. In this way fish of over 1 kg average weight can be produced in a little more than 2 years, instead of the 4-5 years required in fresh-water farms in this country. Existing hatcheries have sufficient capacity to supply a large salmonid aquaculture industry. The water in many parts of the Yugoslavian coastline has physiochemical characteristics suitable for growth of rainbow trout, e.g. the Podvelebit Channel, the estuaries of the rivers Cetina, Krka, Raga, Zrmanja, Neretva and DubrovaEka, as well as Maloston and Bokokotor Bays (Fig. 4). It has been estimated that production of about 10 000 tonnes of salmonids per year is possible in floating cages using only 0.1% of the available area (Teskerediid, 1984). FAO experts who have visited Yugoslavian cage culture sites in brackish/sea water are of the opinion that this new technology of salmonid culture in warm seas will be applicable also to other northern Mediterranean countries (Edwards, 1986; Donaldson, 1987 ). Further, in the entire Me~terranean and Adriatic Sea basins, water below the thermocline (at c. 20 m depth) has a constant temperature of about 13” C throughout the year. By pumping this water into on-shore ponds, salmonids could be cultured at any site in the region where a supply of fresh water is also available. One of the conclusions of the FAO Report was that an FAO workshop should
9
TRIESTE
,RWEKA
43’N
I 1°E
14%
‘E
Fig. 4. Localities along the Adriatic coast suitable for rainbow trout culture.
be held in order to discuss the transfer of knowledge about the new salmonid aquaculture technology, acquired by the scientists of the Ruder Boi?kovic Institute, Center for Marine Research Zagreb, to other Mediterranean countries sea (Donaldson, 1987 1, with a view to use the relatively warm Mediterranean for culture of salmonids and consequently to increase the production of quality high-protein food of animal origin. ACKNOWLEDGEMENTS
The authors express their gratitude to the Self-Management Community of Interest for Scientific Research of Croatia for financial support, and to Dr. David Edwards and Dr. Edward Donaldson for suggestions concerning the presentation of the paper and for language correction.
REFERENCES Anon., 19%. Statistizki statistiku, Beograd.
bilten, “StoEarstvo i ribarstvo” (Statistical
Bulletin).
Savenzi zavod
za
10 Anon., 1987. StatistiEki bilten, “StoEarstvo i ribartsvo” (Statistical Bulletin). Savezni zavod za statistiku, Beograd. BojEiE, C., Debeljak, Lj., VukoviC, T., Jovanovid-Krglanin, B., Apostolski, K., Rianitanin, B., Turk, M., Volk, S., Drecun, D., Habekovii, D., HristiE, S., Fijan, N., Paiur, K., Bunjevac, I. and MarogeviC, S.. 1982. Slatkovodno ribarstvo (Freshwater Fishery), Jumena, Zagreb, 605 PP. Donaldson, E.M., 1987. Managing the biological resources of the Adriatic Sea - aquaculture of salmonids. Report on visit to Yugoslavia and Rome, Project YUG/83/011,11 pp. Edwards, D.-J., 1978. Salmon and Trout Farming in Norway. Fishing News Books, Farnham, Surrey, 178 pp. Edwards, D.J., 1986. Progress in brackish/seawater cage culture of salmonids in Yugoslavia. FAO Report, Project YUG/83/011,26 pp. FiliC, Z., 1978. Marikultura - realnost i perspektiva uzgoja lubina u Jugoslaviji (Mariculture reality and prospects of sea-bass culture in Yugoslavia). Morsko Ribarstvo, 2: 145-151. Gunstram, G.K., 1970. Canadian mariculture facility begins operation. Am. Fish Farmer World Aquacult. News, 2: 8-11. Hahn D.R., 1975. The biological and economical aspects of cage rearing rainbow trout (S&no gairdneri) in North Dakota. Ph.D. Thesis, Univ. N. Dakota, 192 pp. Landless, P.J., 1976. Acclimation of rainbow trout to sea water. Aquaculture, 7: 173-179. MacLeod, H.G., 1977. Effects of salinity on food intake, absorption and conversion in the rainbow trout Salno guirdneri. Mar. Biol., 43: 93-102. McKay, L.R. and Gjerde, B., 1985. The effect of salinity on growth of rainbow trout. Aquaculture, 49: 325-331. Rao, G.M.M., 1968. Oxygen consumption of rainbow trout (Salmogairdneri) in relation to activity and salinity. Can. J. Zool., 46: 781-786. Smith, M.A.K. and Thorpe, A., 1976. Nitrogen metabolism and trophic input in relation to growth in freshwater and saltwater Salmo gairdneri. Biol. Bull., 150: 139-151. Spannhof. L.. 1983. Untersuchungen zur Optimierung der Futterration fur Forellen unter Produktionsbedingungen im Kiistenbereich der DDR. Fischereiforschung, 21: 16-18. TeskerediiC, E., 1982. Uzgoj kalifornijske pastrve (Salmo gairdneri) u plutajuCim kavezima u mijeganoj vodi (Culture of rainbow trout (Sulmo gaidneri) in floating cages in mixed water). Disertacija, SveuEiliite u Zagrebu, Zagreb, 113 pp. Teskerediii, E., 1984. Mogubnost akvakulturne proizvodnje ribe u boEatoj i morskoj vodi Jadrana (Feasibility of aquacultural fish production in brackish and sea water of the Adriatic Sea). Morsko Ribarstvo, 2: 67-71. TeskerediiC, E., 1985. Uzgoj riba u plutajuEim kavezima (Fish culture in floating cages). Rib. Jugoslavije, 40: 42-48. TeskerediiC, E. and Fijan, N., 1980. Pripreme za tov morskih riba u kavezima u nas (Preparations for sea fish fattening in cages in Yugoslavia). Ichthyologia, 12: 77-82. TeskerediiC, E. and TeskerediiC, Z., 1979. Kontrolirano mrije%enje garga (Diplodus surgus) (Controlled spawning of white sea bream). Ichthyologia, 11: 51-55. Tesseyre, C., 1979. Etude des conditions d’elevage intensif du loup (Dicentrurchus lubrux L.). These Doctorat de 3eme cycle, Universite Scientifique et Technique Languedoc, Montpellier, 115 pp.
77 (1989) l-10 Elsevier Science Publishers B.V., Amsterdam
-
Printed
in The Netherlands
A Comparison of the Growth Performance of Rainbow Trout (Salmo gairdneri) in Fresh and Brackish Water in Yugoslavia EMIN TESKEREDZIC, MODRUSAN
ZLATICA TESKEREDZIC,
“Ruder BoSkoviC” Institute,
Center for Marine
MARIJA TOMEC and ZVONKO
Research
Zagreb,
BijeniEka
54,410Ol
Zagreb
(Yugoslavia)
(Accepted
12 August 19881
ABSTRACT Teskerediic, E.. Teskerediid, Z., Tomec, M. and Modruian, Z., 1989. A comparison of the growth performance of rainbow trout (Salmo gairdneri) in fresh and brackish water in Yugoslavia. Aquaculture, 77: l-10. Rainbow trout of two year-classes (O+, 1+ ) and four different initial average weights (84, 118, 197 and 301 g) were grown-on in floating cages moored on the Adriatic coast of Yugoslavia, while two control groups (84 and 301 g) were kept in fresh water at a conventional fish farm. All fish were fed the same commercial diet at 2% of body weight per day and were reared for 8 months from October 1982 to June 1983. Physiochemical characteristics of water at the brackish and fresh-water sites were monitored, and all fish were weighed every month. Growth of fish in all groups held in brackish water was greatly superior (3 to 4 times) to that of their contemporaries at the fresh-water unit. The results point the way to a new type of trout farming in Yugoslavia, and possibly in other countries of the Adriatic and Mediterranean region, using conventional fresh-water farms to produce fingerlings which are then grown-on in sea water either using floating cages or pumped sea water. By comparison with the papers written so far, this work demonstrates the feasibility of rainbow trout culture in warm seas, opening up the possibility for developing a new technology of aquaculture.
INTRODUCTION
Rainbow trout (Salmo gairdneri) have been cultured in fresh water in Yugoslavia continuously since the first importation of eggs from the U.S.A. in 1890 (BojEid et al., 1982). Current annual production is around 4000 tonnes of portion-size fish from a total of almost 100 farms (Anon, 1987). However, despite the country’s favourable climatic and ecological conditions, production of rainbow trout on Yugoslavian fish farms averages 13.5 kg/m” (Anon., 1986). Fresh-water rearing of rainbow trout up to the portion-size of 200-300 g lasts for 18-26 months, while the rearing of big trout of over 1000 g lasts for 4-5 years and, therefore, is not practised (Teskerediid, 1985).
0044-8486/89/$03.50
0 1989 Elsevier Science Publishers
B.V.
2
The total recorded annual catch of fresh-water and sea fish in Yugoslavia of 75 057 tonnes (Anon., 1986) does not meet the demand from the local population and the large tourist market. Consequently the country imports about 30 000 tonnes of sea food per year. During the last 10 years this shortfall in local output has stimulated research aimed at increasing production from aquaculture (Filid, 1978; Teskerediit and Teskerediid, 1979; Teskerediib and Fijan, 1980 ). Building on overseas experience of cage culture of rainbow trout in cold seas (Gunstram, 1970; Tatum, 1973; Hahn, 1975; Edwards, 1978)) in 1979 the scientists of the Ruder Boskovid Institute, Center for Marine Research Zagreb, began investigations into the feasibility of culturing this species in the warm Adriatic Sea. Early experiments soon showed promise (Teskerediid, 1982 ) . In the present paper we compare growth of rainbow trout held in conventional Yugoslavian fresh-water farms with that of identical fish reared in floating cages on the Adriatic coast, and demonstrate the possibility of developing a new technology of rainbow trout farming in warm seas such as the Adriatic Sea. MATERIALSANDMETHODS The rainbow trout used in the experiment were obtained from Emona troutfarm, Dvor pri Zuienberku, an average-sized fresh-water commercial facility which produces about 200 tonnes of 200-300-g fish per year in concrete raceways. Experimental fish for on-growing in cages were selected from two yearclasses (aged 10 and 22 months) on 2 October 1982. From each year-class, individuals were taken from each end of the size distribution, as follows: Fish in group I were 10 months of age and averaged 84 g weight. Fish in group II were 10 months of age and averaged 118 g weight. Fish in group III were 22 months of age and averaged 197 g weight. Fish in group IV were 22 months of age and averaged 301 g weight. For comparison, two further groups (IA and IVA) comprising fish of the same size and age as those in groups I and IV were grown-on at the fresh-water farm. All fish were reared for 8 months until 2 June 1983. Eight experimental cages were moored in RakovaEa Bay near the town of Skradin in the River Krka Estuary (Fig. 1) , the experimental farm of the Ruder Boskovi& Institute. The 4 x 4 x 4 m cages were of timber + Styrofoam cylinder construction supporting 15 mm mesh knotted nylon nets. Fish from each of the experimental groups were divided between two replicate cages, each cage being stocked with 100 kg of trout. The control groups of fish were held in 20 x 4 x 1 m fresh-water raceways stocked at the same initial density. In the raceways, complete water exchange occurred between 40 and 60 times per day. The same dry, commercial, pelleted feed f40-42% crude protein, 6-8% fat, 12% ash, 10% water) was used at both fish farms. All fish were weighed and
3
Fig. 1. Location of the experimental farm near Skradin.
counted each month, and at the same time fish health was monitored. The daily food ration of 2% of total fish weight was corrected after each sampling in line with weight gain. Physiochemical measurements of the water at the two farms were made monthly. At the cage site, temperature, pH, oxygen concentration and salinity were determined at depths of 0.5, 2, 4 and 6 m. In the fresh-water raceways, temperature, pH and oxygen concentration were determined at 0.5 m. Growth rates were calculated in %/day using the formula (Tesseyre, 1979; Spannhof, 1983)
4 RESULTS
In Figs. 2 and 3, broken lines show the growth rates of rainbow trout at the experimental brackish-water cage farm, while the solid lines show the growth rate at the fresh-water farm. The growth rate of the control fish held in freshwater raceways fell within the normal range of performance for such fish, i.e. 0.233 to 0.411 %/day. However, the growth rates of fish in the four groups transferred to cages in sea water rapidly surpassed that of their counterparts in fresh water, i.e. 0.705 to 0.993 %/day (Table 1). The initial and final weights of fish in the experimental and control groups over the 8 months trial period are shown in Table 1.
1200 Gmup 1100
I A
-
fresh
water
O---O GKlUfl II
- brackish
water
/
/
/
d /
//
/ 600
/
w-’
/
P’
/I
1. d /
/I p/’ ,* / ,’
IA
AGE
T
OL
OF
12
10 I
I
X
XII 1982
Fig. 2. The growth of lo-month-old
RAINBOW
(months) 16
II
IV 1983
I
’ I
TROUT
‘4
I
18 I
VI
month year
rainbow trout in fresh water and in brackish water.
J
1700 0
N
/
lb@4
/ /
-o---o
1500
A
Group N s&Y N
14110
m
-
-
/
frest, water
brad&h
d
water
/
/
l3OO
d
12w
I loo
loo0
?” 9oo
3 i
.F
Boo
I
d
5 P -
mo
?’ / /
/
Y
/ /
.:I_:.//> /
6OO
500
bal
300
d’
200
T I
AGE
OF
RAINBOW
TROUT
(months
NA
)
22
24
26
28
50
I
I
X
XII
I II
I N
I VI month
t
1983
1982
;
year
Fig. 3. The growth of 22-month-old rainbow trout in fresh water and in brackish water.
The growth performance of the zero-age trout in sea water was superior to the growth of the 1+ trout in this medium (Table 1). During the period from December to February, the average growth of the fish stocked at 22 months
6 TABLE I Initial weights, final weights and growth rates of rainbow trout reared in sea-water cages and freshwater raceways. Data show the mean of two replicates Group
I II III IV IA IVA
Site
SW SW SW SW FW FW
Initial wt.
Final wt.
Growth rate
(9)
(gf
(%/daY)
84 118 197 301 84 301
900 1136 1134 1625 225 526
0.993 0.948 0.732 0.705 0.411 0.233
(groups III, IV, IVA) slowed down (Fig. 3). This was due to maturation of some of the male fish in these groups. No disease or parasite problems occurred during the experiment, and fish mortality in all groups was low (0.8-2.1% ). Table 2 shows the physiochemical characteristics of water at the brackishwater site throughout the experiment, and those of the fresh-water farm. Salinity was low in surface waters at the brackish-water site in all months except November and December. At 6 m, salinity was over 30%0 in all months, with the exception of February. At the brackish-water site the pH range was 8.08.2 while at the fresh-water site the pH range was 7.5-7.8. DISCUSSION
The results clearly show that growth of rainbow trout held in cages in sea/ brackish water on the Adriatic coast is greatly superior to that of similar fish kept in conventional fresh-water trout farms in Yugoslavia during the coldest 8 months of the year. The precise reasons for such a vast difference in performance are less clear. Higher water temperature at the sea site is obviously a contributing factor. Average temperature in the vicinity of the cages at 2 m depth was 12.6” C (the total number of day-degrees being 3033) and at the fresh-water farm 9.3”C (2236 day-degrees). However, it seems unlikely that this alone can explain the results. Salinity at the sea farm varied with time and water depth, but there was always a wide range available for use by the fish. It is possible that the fish expended less energy counteracting osmotic forces at this site than in fresh water, although some authors (McKay and Gjerde, 1985) have denied that salinity itself is a significant growth-promoting factor. However, it was established that the food intake was significantly greater at salinities of 15.0-28.0%0 than in fresh water (MacLeod, 1977) and that the daily specific growth rate was si~i~c~tly higher when the fish were fed ad libitum in sea water (0.789% )
15.3 11.4 10.0
9.3 8.9 9.8 12.5 17.3 20.3
1983 1 2 3 4 5 6
T (“C)
0.5m
1982 10 11 12
Depth Year/ month
12.4 12.0 10.0 11.9 11.5 9.6
9.4 10.5 11.4
0, tmg/l)
108.0 103.2 87.5 111.2 118.6 105.6
93.4 95.7 101.0
2.4 1.0 2.0 2.0 1.8 2.4
7.0 14.0 20.0
0, sat. Sal. (%I (so)
Brackish-water cage farm
9.7 9.9 10.2 12.8 17.4 21.1
17.5 14.8 11.9
T (“C)
2m
12.5 11.9 11.0 12.5 11.1 10.4
8.3 9.9 8.6
O2 tmg/l)
109.4 105.1 97.2 117.3 115.0 115.8
86.2 97.0 79.0
02sat. (%)
2.6 1.1 2.0 2.0 2.0 11.6
21.0 19.0 34.0
Sal. (%0)
13.4 11.3 13.0 13.4 18.3 21.1
21.2 17.2 12.2
T (“C)
4m
8.0 10.0 8.8 12.0 11.0 10.4
7.5 7.3 7.5
0, (mg/l)
75.7 90.8 82.7 113.8 115.6 116.3
83.2 75.4 69.5
0, sat. (%)
26.3 11.0 22.4 11.9 31.3 29.8
33.0 35.0 38.0
Sal. GO)
15.0 12.6 13.6 14.3 17.8
20.8 17.0 13.0
T (“C)
6m
6.4 7.7 7.3 10.2 11.4 9.9
6.2 3.2 8.3
O2 (mg/l)
62.6 71.9 69.6 99.4 119.0 108.5
68.6 32.8 78.7
33.0 22.3 32.2 30.8 35.3 33.6
35.0 39.0 38.0
O2 sat. Sal. (%) &I
7.4 8.2 a.4 11.8 13.4 12.4
9.4 9.2 7.0
T (“C)
12.4 14.4 15.5 11.6 11.6 11.0
11.8 11.6 11.9
02 (mg/l)
102.0 121.0 132.0 106.0 110.0 102.0
102.0 100.0 97.0
O2 sat. (W)
Fresh-water farm
Physiochemical characteristics of the water at the experimental brackish-water cage farm in the estuary of the Krka River, and at the fresh-water farm
TABLE 2
8
than in fresh water (0.587% ) in July and August (Smith and Thorpe, 1976). These results are in accord with those presented in this paper, in which specific growth rates ranged from 0.705% to 0.993% in sea water, and from 0.233% to 0.411% in fresh water (Table 1). Also, at the relatively low density utilized in this experiment, it is possible that the trout in the marine pens were able to supplement their diet with small quantities of natural feed. Future research may reveal a more complex explanation, involving synergistic effects of salinity, temperature and oxygen concentration (Rao, 1968). The potential exists to further improve sea-water growth performance through genetic selection. The results point the way towards a new industry for trout culture on the Adriatic coast of Yugoslavia. An FAO expert who has visited Yugoslavia on several occasions described in his report the application of these results to commercial culture and the transfer of new scientific knowledge into production (Edwards, 1986 ). Fingerlings cultured in conventional fresh-water trout farms are grown-on in floating cages during that period of the year when temperatures are low enough. By stocking rainbow trout of 50-100 g it is possible to obtain three production cycles of 200-300 g fish during the winter. The number of farming cycles possible may be even greater, since it has been established that rainbow trout of only 15 g grew normally when transferred directly from fresh water into the sea (Landless, 1976). One production cycle of big trout is obtained if fish of 200-300 g are stocked. In this way fish of over 1 kg average weight can be produced in a little more than 2 years, instead of the 4-5 years required in fresh-water farms in this country. Existing hatcheries have sufficient capacity to supply a large salmonid aquaculture industry. The water in many parts of the Yugoslavian coastline has physiochemical characteristics suitable for growth of rainbow trout, e.g. the Podvelebit Channel, the estuaries of the rivers Cetina, Krka, Raga, Zrmanja, Neretva and DubrovaEka, as well as Maloston and Bokokotor Bays (Fig. 4). It has been estimated that production of about 10 000 tonnes of salmonids per year is possible in floating cages using only 0.1% of the available area (Teskerediid, 1984). FAO experts who have visited Yugoslavian cage culture sites in brackish/sea water are of the opinion that this new technology of salmonid culture in warm seas will be applicable also to other northern Mediterranean countries (Edwards, 1986; Donaldson, 1987 ). Further, in the entire Me~terranean and Adriatic Sea basins, water below the thermocline (at c. 20 m depth) has a constant temperature of about 13” C throughout the year. By pumping this water into on-shore ponds, salmonids could be cultured at any site in the region where a supply of fresh water is also available. One of the conclusions of the FAO Report was that an FAO workshop should
9
TRIESTE
,RWEKA
43’N
I 1°E
14%
‘E
Fig. 4. Localities along the Adriatic coast suitable for rainbow trout culture.
be held in order to discuss the transfer of knowledge about the new salmonid aquaculture technology, acquired by the scientists of the Ruder Boi?kovic Institute, Center for Marine Research Zagreb, to other Mediterranean countries sea (Donaldson, 1987 1, with a view to use the relatively warm Mediterranean for culture of salmonids and consequently to increase the production of quality high-protein food of animal origin. ACKNOWLEDGEMENTS
The authors express their gratitude to the Self-Management Community of Interest for Scientific Research of Croatia for financial support, and to Dr. David Edwards and Dr. Edward Donaldson for suggestions concerning the presentation of the paper and for language correction.
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