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Survival and development of Atlantic salmon eggs and fry at three different temperatures
Aquaculture, 16 (1979) 211-218 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
211
SURVIVAL AND DEVELOPMENT OF ATLANTIC SALMON EGGS AND FRY AT THREE DIFFERENT TEMPERATURES
KNUT GUNNES Department (Norway) (Accepted
of Animal Genetics and Breeding, Agricultural
University of Norway, AS-NLH
7 December 1978)
ABSTRACT Gunnes, K., 1979. Survival and development of Atlantic salmon eggs and fry at three different temperatures. Aquaculture, 16: 211-218. Groups of Atlantic salmon (Salmo satar) eggs were incubated at 12, 10 and 8” C. At 12” C mortality was high and fry averaged little more than half the weight of those hatched at 10 or 8” C. Development of alevins to the ‘swim-up’ stage was also abnormal at 12” C. The results suggest that 10” C is optimal for incubating Atlantic salmon eggs. For the period between hatching and swim-up, the most favourable temperature varies according to the temperature used during incubation. Mortality rate during the first 6 weeks of feeding was correlated with mortality during earlier development. Total numbers of day-degrees required by the eggs and fry to reach the eyed, hatching, and swim-up stages of development were significantly less at 12” C than at 10 or 8” C. However, total day-degrees required to reach an average weight of 0.5 or 0.6 g were almost the same regardless of temperature during hatching.
INTRODUCTION
At the Research Station for Salmonids, Sunndals$ra Unit, Norway, Atlantic salmon (S&no s&r) eggs are normally incubated at 6-3” C. If a higher temperature were used the time required for eggs to hatch would be reduced. With a given period in fresh water, this would allow more days for growth and thereby produce a larger smolt and a higher percentage of l-year-old smolts. However, the effects of increased temperature on egg and fry mortality and on the subsequent growth rate of fry are not precisely known. The experiment reported here was designed to find the optimal temperature regime for egg incuba tion and early fry growth. MATERIALS
AND METHODS
Eggs of females from a single Norwegian Atlantic salmon strain were pooled and fertilized in bulk with pooled milt from a number of males. The fertilized eggs were divided into 27 groups, each containing about 1700 eggs (0.3 1).
212
Each group of eggs was placed in a separate hatching tray. Nine of the groups were incubated in water at 12” C, nine at 10” C, and nine at 8” C (Fig.1). After hatching, three of the groups incubated at each temperature were transferred to each of the three temperature levels and reared to the ‘swim-up’ stage. ‘Swim-up’ occurred when approximately two-thirds of the yolk sac had been absorbed. The periods ‘fertilization to hatch’ and ‘hatch to swim-up’ will be referred to in this paper as periods a and b (Fig.1). After swim-up, fry were transferred to 1-m’ fibreglass tanks for first feeding and subsequent culture, each group occupying a separate tank. The normal temperature of the hatchery water supply at Sunndals$ra is about 8” C. An electric heater made of aluminium was used to obtain water at 12” C. Water at 10” C was obtained by mixing the 8 and 12” C supplies. All water supplies were aerated before use, and regular measurements of dissolved oxygen and nitrogen were made. The range of dissolved nitrogen was 97-101% and for oxygen it was 98-103% air saturation. In practice, water temperatures fluctuated around the nominal levels of 8, 10 and 12” C. Actual temperatures were recorded automatically every hour, and averaged daily (Fig. 2). The nine hatching trays at each temperature received 12 1 water/min. To avoid the risk of fungal infection, troughs were treated with malachite green (1 : 200,000) every 3 days. After eyeing the eggs were shocked, and the number of dead in each group recorded. Subsequently the number of dead eggs and alevins in each group was recorded regularly. Ten alevins from each group were sampled at 50-day-degree intervals between hatching and swim-up and stored in 5% formalin. At the end of the experiment these alevins were blotted to remove surface fluid, then those in each sample were weighed both individually and in bulk. The yolk sacs were removed, and the body (alevin minus yolk sac) and the yolk sacs were weighed separately in bulk for each sample. Yolk sac constrictions, either complete or partial, were cut from the yolk sacs and also weighed in bulk for each sample. A constriction is a narrow pass in the yolk sac. The yolk sac mass behind this
12Y (9) -
/soc(3+ -IO”C
(3) -
’
(3) -
PC
Fig. 1. Flow diagram for the design of the experiment. given in parentheses.
Number of replicate groups is
Fig. 2. Temperature variation at the three experimental levels.
213
pass is not completely utilized by the fry. The cut was done at this pass. Dumas (1966) gives detailed drawings of the phenomenon of yolk sac constriction. After transfer to tanks for their first feeding, all fish received the same dry, pelleted food in excess from automatic feeders. All tanks received water at the same ambient temperature from the normal hatchery supply. Samples of 100 fish were weighed in bulk from each group every 2 weeks for a further 3-4 months. The significances of differences in mortality between egg and fry groups were tested by the least significant difference method of Hartley (Snedecor, 1956). Before statistical analysis, percentage figures were resealed using the arcsine % transformation. RESULTS
The mean sums of day-degrees required by eggs and fry to reach the eyed stage, to hatching, and to the swim-up stage at 8, 10 and 12” C are shown in Table I. Percentage mortality among eggs incubated at the three temperatures is given in Table II. Mortality was significantly greater at 12” C than at the other temperatures. Mortality of fry from hatching to ‘swim-up’ (Fig. 3) is expressed as percentage of alevins hatched. The lowest fry mortality occurred in fish from eggs TABLE
I
Sums of day-degrees to the eyed stage, to hatching and to the swim-up stage of salmon egg development at three temperatures Temperature (“Cl
Eyed stage
Hatching
Swim-up stage
12 10 8
208 223 228
453 492 504
742 788 791
TABLE
II
Salmon egg mortality in relation to incubation temperature. The percentages of dead eggs shown are based on the numbers of eggs alive at the start of the periods indicated. Mortality was significantly greater in each period at 12” C than at the other temperatures Temperature (“Cl
Dead eggs before eyed stage
Dead eggs from eyed stage to hatching
Dead eggs from fertilization to hatching
12 10 8
3&l* 7.6 11.3
47.2* 7.0 3.6
66.1* 14.0 14.5
*P < 0.05.
214
incubated at 8” C during period a, and for these there was no significant difference in mortahty between groups kept at different temperatures during period b. Fry from eggs incubated at 10” C during period a experienced higher mortality during period b, and for these the mortality was significantly (P < 0.05) higher in those groups held at 12” C during period b than in those held at 8” C. The highest fry mortality occurred in the groups with a history of incubation at 12” C during period a. Again mortality in period b was significantly greater in the groups held at higher temperature. The pattern of mortality of fry during the first 6 weeks of feeding was similar to that between hatching and swim-up (Fig.3). The highest mortality of fry occurred in the groups with a history of incubation at high temperature during periods a and b. The correlation between fry mortality of different groups during period b and the first feeding period was 0.62 (P < 0.01). The mean rate of development of fry, measured in day degrees, is shown in Fig.4. Development is expressed as body (alevin minus yolk sac) weight as a percentage of total alevin weight (body plus yolk sac). The development of total alevins, body and yolk sac components expressed as average weight in grams is shown in Fig.5. The rate of development of alevins kept at 8 and 10” C during period a was much the same in all temperature groups during period b (Fig.5). The standard deviation for body weight varied from 0.0012 to 0.0056 g, for yolk sac weight from 0.0013 to 0.031 g, and for total alevin weight from 0.0021 to 0.0055 g. Standard deviations were smallest at hatching. Development of fish incubated at 12” C during period a was abnormal compared with those incubated at 8” C and 10” C. Fish hatched at 12” C had average body weights little more than half as high as those incubated at 8” C or 10” C during period a. Yolk sac constrictions were formed at all three experimental temperatures. The mean percentage by weight of such constrictions in relation to total alevin weight is shown in Fig.6. The pattern of constriction formation and absorption
Fig. 3. Percentage mortality in relation to different temperatures in perioda andb. The mortality percentages are average figures of replicates and based on the numberaliveat the start of each period. o : Hatching-‘swim-up’; q : ‘swim-up’-6 weeks on feed. Fig.4. Developmentof body in percentage of total weight (body + yolk sac) for different temperature regimes. 12 (ak-12 (b):-; 12 (a)-10 (b): . . . . . ; 12 (a)-6 (b):---; the average values for the other temperature regimes in the experiment: *- e--:
215
In
Hatch
1
50
ma
l50
200 2.50 .?no Day-degrees
.
IF,
hbtch
50
I
fO0
I
150
200
250 .?Qo * Day-dqmes
Fig. 5. Development of (a) total alevin, (b) body, and (c) yolk sac, expressed as average weight in grams for different temperature regimes: 12(a)-12(b): - ; 12(a)-10(b): --e--; 12(a)-8(b): ---; the average values for the other temperature regimes in the experiment: Fig.6. Constriction of yolk sac in grams as a percentage of total alevin weight for different temperatures after hatching.
Fig.?. Growth of Atlantic salmon fry at the ambient water temperature regime shown, following rearing at 8, 10 and 12” C during experimental periods a and b.
was very similar in groups of fish kept at 8 or 10” C but rather different at 12” C, although the significance of this finding is not clear. The growth of fry held at a common temperature during the feeding period was compared for groups of fish held at each temperature level (8,10, 12” C) during both periods a and b (Fig.7). Fish reared at 12” C were ready to begin feeding earlier, and were fed for a longer period. They achieved a mean weight more than twice that of the 8” C fish by the end of the experiment. The 10” C fish were intermediate between the other two groups. Fish reared at 12” C during period a and then transferred to 8” or 10” C for period b showed no difference in growth during the feeding period from those held at 12” C during
216
both periods a and b. Similar results were obtained for fish held at 8” C or 10°C during period a and subsequently transferred to other temperatures. The number of day-degrees required from fertilization until’a mean fry weight of 0.5 and 0.6 g was reached was calculated for fish held at each of the three experimental temperatures during periods a and b (Table III). In spite of the different sums of day-degrees required for the eggs to hatch, sums of daydegrees to a fry weight of 0.5 or 0.6 g were remarkably constant regardless of temperature history (Fig.7). TABLE
III
Sums of day-degrees from fertilization to 0.5 and 0.6 g average salmon fry weights at the three temperatures used before the swim-up stage of development Temperature ’ (” C)
Average weight 0.5 g
0.6 g
12 10 8
1616 1606 1610
1716 1708 1710
DISCUSSION
Mean sums of day-degrees from fertilization to hatching were in good agreement with the results of Peterson et al. (1977). These authors experienced difficulties with fungal infections at 1.2” C, a problem not encountered in the present study. In spite of this, their mortalities were considerably lower at 12” C than those reported here. It is possible that the Norwegian fish strain used here is adapted to a lower temperature, and that 12” C is too high for the strain during the egg incubation period. On the basis of these results, the highest temperature that could be recommended for incubation of Norwegian Atlantic salmon eggs is 10” C. Combs and Burrows (1957) recommended 57.5 to 60” F (14.2-15.5” C) as the upper temperature limit for incubating chinook salmon eggs. For rainbow trout, Kawajiri (1927) considered 9” C to be optimal. Vernidub (1963, reported by Timoshina, 1972) showed that discrete stages of embyonic development in Atlantic and Baltic salmon had different temperature requirements, the optimal temperature tending to increase as embryonic development advanced. However, his recommended temperatures for all developmental stages were less than lO”C, whereas Marr (1966) found that the gross efficiency of growth of the Atlantic salmon embryo is highest at about 10” C. The present results indicate that the optimum temperature from hatching to swim-up varies’according to the temperature experienced during egg incubation (Fig.3). If 10” C is used for incubation, it appears advantageous to reduce the temperature to 8” C during the following period. During the first 6 weeks of feeding, all fry were held in water at much the
217
same temperature, and the substantial differences in mortality that occurred in different fish groups (Fig.3) must have been associated with the temperature differences they experienced during periods a and b. Fry hatched at 12” C were small compared with fish from other temperature groups (Fig.5). The development at 12” C was probably too rapid, and this resulted in inefficiency in terms of conversion of yolk to fish tissue. Many authors have reported reduced size in embryos hatched at high temperature (Gray, 1929; Wood, 1932; Hamdorf, 1961; Alderdice and Forrester, 1971; Alderdice and Velsen, 1971; Peterson et al., 1977). Yolk sac constrictions were produced under all the temperature regimes used (Fig.6). Dumas (1966) reported the occurrence of similar constrictions at both 47” F (8.3” C) and 53” F (11.7” C) in fry of landlocked Atlantic salmon. The difference in the pattern of constriction formation and absorption between 12” C and the other two temperatures did not seem to influence the subsequent growth in the feeding period (Fig.7). First feeding and subsequent growth began earlier for fish reared at 12” C during periods a and b compared with the other groups. The 12” C fish maintained their size advantage until the end of the experiment, by which time they averaged twice the weight of fish reared at 8” C during periods a and b. If the water temperature during the feeding period had been higher, and closer to the optimum for salmon growth of 13-15” C, it is highly probable that the difference in size between the 12” C fish and the other groups would have been even greater. In commercial smolt production it is economically important to produce a high percentage of l-year-old smolts. To do this it is essential that feeding and growth start as early as possible. It is therefore important to use the highest recommended temperature whenever possible.
REFERENCES Alderdice, D.F. and Forrester, C.R., 1971. Effects of salinity, temperature and dissolved oxygen on early development of the Pacific cod (Gadus macrocephalus). J. Fish. Res. Board Can., 28: 883-902. 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. Combs, B.D. and Burrows, R.E., 1957. Threshold temperatures for the normal development of chinook salmon eggs. Prog. Fish Cult., 19: 3-6. Dumas, R.F., 1966. Observations on yolk sac constriction in landlocked Atlantic salmon fry. Prog. Fish Cult., 2: 73-75. Gray, J., 1929. The growth of fish. III. The effect of temperature on the development of the eggs of Salmo fario. Br. J. Exp. Biol., 6: 125-130. Hamdorf, K., 1961. Die Beeinflussung der embryonal und larvalentwicklung der Regenbogenforelle (Salmo irideus Gibb) durch die Umweltfaktoren 0,, Partialdruck und Temperatur. Z. Verg. Physiol., 44: 523-549. Kawajiri, M., 1927. The influence of variation in temperature of water on growth of salmonid embryos. Nature, London, 212 (5065): 957-959. Marr, D-H-A., 1966. Influence of temperature of the efficiency of growth of salmonid embryos. Nature, London, 212 (5065): 957-959.
218 Peterson, R.H., Spinney, H.C.E. and Sreedharan, A., 1977. Development of Atlantic salmon (S&no s&r) eggs and alevins under varied temperature regimes. J. Fish. Res. Board Can., 34: 31-43. Snedecor, G-W., 1956. Statistical Methods Applied to Experiments in Agriculture and Biology. Fifth Edition. The Iowa State College Press, Ames, Iowa, 534 pp. Timoshina, L.A, 1972. Embryonic development of the rainbow trout (S&no guirdneri, irideus Gibb) at different temperatures. J. Ichthyol., 12(3): 425-432. Wood, A.H., 1932. The effect of temperature on the growth and respiration of fish embryos (Sulmo fario). J! Exp. Biol., 9 (3): 271-276.
211
SURVIVAL AND DEVELOPMENT OF ATLANTIC SALMON EGGS AND FRY AT THREE DIFFERENT TEMPERATURES
KNUT GUNNES Department (Norway) (Accepted
of Animal Genetics and Breeding, Agricultural
University of Norway, AS-NLH
7 December 1978)
ABSTRACT Gunnes, K., 1979. Survival and development of Atlantic salmon eggs and fry at three different temperatures. Aquaculture, 16: 211-218. Groups of Atlantic salmon (Salmo satar) eggs were incubated at 12, 10 and 8” C. At 12” C mortality was high and fry averaged little more than half the weight of those hatched at 10 or 8” C. Development of alevins to the ‘swim-up’ stage was also abnormal at 12” C. The results suggest that 10” C is optimal for incubating Atlantic salmon eggs. For the period between hatching and swim-up, the most favourable temperature varies according to the temperature used during incubation. Mortality rate during the first 6 weeks of feeding was correlated with mortality during earlier development. Total numbers of day-degrees required by the eggs and fry to reach the eyed, hatching, and swim-up stages of development were significantly less at 12” C than at 10 or 8” C. However, total day-degrees required to reach an average weight of 0.5 or 0.6 g were almost the same regardless of temperature during hatching.
INTRODUCTION
At the Research Station for Salmonids, Sunndals$ra Unit, Norway, Atlantic salmon (S&no s&r) eggs are normally incubated at 6-3” C. If a higher temperature were used the time required for eggs to hatch would be reduced. With a given period in fresh water, this would allow more days for growth and thereby produce a larger smolt and a higher percentage of l-year-old smolts. However, the effects of increased temperature on egg and fry mortality and on the subsequent growth rate of fry are not precisely known. The experiment reported here was designed to find the optimal temperature regime for egg incuba tion and early fry growth. MATERIALS
AND METHODS
Eggs of females from a single Norwegian Atlantic salmon strain were pooled and fertilized in bulk with pooled milt from a number of males. The fertilized eggs were divided into 27 groups, each containing about 1700 eggs (0.3 1).
212
Each group of eggs was placed in a separate hatching tray. Nine of the groups were incubated in water at 12” C, nine at 10” C, and nine at 8” C (Fig.1). After hatching, three of the groups incubated at each temperature were transferred to each of the three temperature levels and reared to the ‘swim-up’ stage. ‘Swim-up’ occurred when approximately two-thirds of the yolk sac had been absorbed. The periods ‘fertilization to hatch’ and ‘hatch to swim-up’ will be referred to in this paper as periods a and b (Fig.1). After swim-up, fry were transferred to 1-m’ fibreglass tanks for first feeding and subsequent culture, each group occupying a separate tank. The normal temperature of the hatchery water supply at Sunndals$ra is about 8” C. An electric heater made of aluminium was used to obtain water at 12” C. Water at 10” C was obtained by mixing the 8 and 12” C supplies. All water supplies were aerated before use, and regular measurements of dissolved oxygen and nitrogen were made. The range of dissolved nitrogen was 97-101% and for oxygen it was 98-103% air saturation. In practice, water temperatures fluctuated around the nominal levels of 8, 10 and 12” C. Actual temperatures were recorded automatically every hour, and averaged daily (Fig. 2). The nine hatching trays at each temperature received 12 1 water/min. To avoid the risk of fungal infection, troughs were treated with malachite green (1 : 200,000) every 3 days. After eyeing the eggs were shocked, and the number of dead in each group recorded. Subsequently the number of dead eggs and alevins in each group was recorded regularly. Ten alevins from each group were sampled at 50-day-degree intervals between hatching and swim-up and stored in 5% formalin. At the end of the experiment these alevins were blotted to remove surface fluid, then those in each sample were weighed both individually and in bulk. The yolk sacs were removed, and the body (alevin minus yolk sac) and the yolk sacs were weighed separately in bulk for each sample. Yolk sac constrictions, either complete or partial, were cut from the yolk sacs and also weighed in bulk for each sample. A constriction is a narrow pass in the yolk sac. The yolk sac mass behind this
12Y (9) -
/soc(3+ -IO”C
(3) -
’
(3) -
PC
Fig. 1. Flow diagram for the design of the experiment. given in parentheses.
Number of replicate groups is
Fig. 2. Temperature variation at the three experimental levels.
213
pass is not completely utilized by the fry. The cut was done at this pass. Dumas (1966) gives detailed drawings of the phenomenon of yolk sac constriction. After transfer to tanks for their first feeding, all fish received the same dry, pelleted food in excess from automatic feeders. All tanks received water at the same ambient temperature from the normal hatchery supply. Samples of 100 fish were weighed in bulk from each group every 2 weeks for a further 3-4 months. The significances of differences in mortality between egg and fry groups were tested by the least significant difference method of Hartley (Snedecor, 1956). Before statistical analysis, percentage figures were resealed using the arcsine % transformation. RESULTS
The mean sums of day-degrees required by eggs and fry to reach the eyed stage, to hatching, and to the swim-up stage at 8, 10 and 12” C are shown in Table I. Percentage mortality among eggs incubated at the three temperatures is given in Table II. Mortality was significantly greater at 12” C than at the other temperatures. Mortality of fry from hatching to ‘swim-up’ (Fig. 3) is expressed as percentage of alevins hatched. The lowest fry mortality occurred in fish from eggs TABLE
I
Sums of day-degrees to the eyed stage, to hatching and to the swim-up stage of salmon egg development at three temperatures Temperature (“Cl
Eyed stage
Hatching
Swim-up stage
12 10 8
208 223 228
453 492 504
742 788 791
TABLE
II
Salmon egg mortality in relation to incubation temperature. The percentages of dead eggs shown are based on the numbers of eggs alive at the start of the periods indicated. Mortality was significantly greater in each period at 12” C than at the other temperatures Temperature (“Cl
Dead eggs before eyed stage
Dead eggs from eyed stage to hatching
Dead eggs from fertilization to hatching
12 10 8
3&l* 7.6 11.3
47.2* 7.0 3.6
66.1* 14.0 14.5
*P < 0.05.
214
incubated at 8” C during period a, and for these there was no significant difference in mortahty between groups kept at different temperatures during period b. Fry from eggs incubated at 10” C during period a experienced higher mortality during period b, and for these the mortality was significantly (P < 0.05) higher in those groups held at 12” C during period b than in those held at 8” C. The highest fry mortality occurred in the groups with a history of incubation at 12” C during period a. Again mortality in period b was significantly greater in the groups held at higher temperature. The pattern of mortality of fry during the first 6 weeks of feeding was similar to that between hatching and swim-up (Fig.3). The highest mortality of fry occurred in the groups with a history of incubation at high temperature during periods a and b. The correlation between fry mortality of different groups during period b and the first feeding period was 0.62 (P < 0.01). The mean rate of development of fry, measured in day degrees, is shown in Fig.4. Development is expressed as body (alevin minus yolk sac) weight as a percentage of total alevin weight (body plus yolk sac). The development of total alevins, body and yolk sac components expressed as average weight in grams is shown in Fig.5. The rate of development of alevins kept at 8 and 10” C during period a was much the same in all temperature groups during period b (Fig.5). The standard deviation for body weight varied from 0.0012 to 0.0056 g, for yolk sac weight from 0.0013 to 0.031 g, and for total alevin weight from 0.0021 to 0.0055 g. Standard deviations were smallest at hatching. Development of fish incubated at 12” C during period a was abnormal compared with those incubated at 8” C and 10” C. Fish hatched at 12” C had average body weights little more than half as high as those incubated at 8” C or 10” C during period a. Yolk sac constrictions were formed at all three experimental temperatures. The mean percentage by weight of such constrictions in relation to total alevin weight is shown in Fig.6. The pattern of constriction formation and absorption
Fig. 3. Percentage mortality in relation to different temperatures in perioda andb. The mortality percentages are average figures of replicates and based on the numberaliveat the start of each period. o : Hatching-‘swim-up’; q : ‘swim-up’-6 weeks on feed. Fig.4. Developmentof body in percentage of total weight (body + yolk sac) for different temperature regimes. 12 (ak-12 (b):-; 12 (a)-10 (b): . . . . . ; 12 (a)-6 (b):---; the average values for the other temperature regimes in the experiment: *- e--:
215
In
Hatch
1
50
ma
l50
200 2.50 .?no Day-degrees
.
IF,
hbtch
50
I
fO0
I
150
200
250 .?Qo * Day-dqmes
Fig. 5. Development of (a) total alevin, (b) body, and (c) yolk sac, expressed as average weight in grams for different temperature regimes: 12(a)-12(b): - ; 12(a)-10(b): --e--; 12(a)-8(b): ---; the average values for the other temperature regimes in the experiment: Fig.6. Constriction of yolk sac in grams as a percentage of total alevin weight for different temperatures after hatching.
Fig.?. Growth of Atlantic salmon fry at the ambient water temperature regime shown, following rearing at 8, 10 and 12” C during experimental periods a and b.
was very similar in groups of fish kept at 8 or 10” C but rather different at 12” C, although the significance of this finding is not clear. The growth of fry held at a common temperature during the feeding period was compared for groups of fish held at each temperature level (8,10, 12” C) during both periods a and b (Fig.7). Fish reared at 12” C were ready to begin feeding earlier, and were fed for a longer period. They achieved a mean weight more than twice that of the 8” C fish by the end of the experiment. The 10” C fish were intermediate between the other two groups. Fish reared at 12” C during period a and then transferred to 8” or 10” C for period b showed no difference in growth during the feeding period from those held at 12” C during
216
both periods a and b. Similar results were obtained for fish held at 8” C or 10°C during period a and subsequently transferred to other temperatures. The number of day-degrees required from fertilization until’a mean fry weight of 0.5 and 0.6 g was reached was calculated for fish held at each of the three experimental temperatures during periods a and b (Table III). In spite of the different sums of day-degrees required for the eggs to hatch, sums of daydegrees to a fry weight of 0.5 or 0.6 g were remarkably constant regardless of temperature history (Fig.7). TABLE
III
Sums of day-degrees from fertilization to 0.5 and 0.6 g average salmon fry weights at the three temperatures used before the swim-up stage of development Temperature ’ (” C)
Average weight 0.5 g
0.6 g
12 10 8
1616 1606 1610
1716 1708 1710
DISCUSSION
Mean sums of day-degrees from fertilization to hatching were in good agreement with the results of Peterson et al. (1977). These authors experienced difficulties with fungal infections at 1.2” C, a problem not encountered in the present study. In spite of this, their mortalities were considerably lower at 12” C than those reported here. It is possible that the Norwegian fish strain used here is adapted to a lower temperature, and that 12” C is too high for the strain during the egg incubation period. On the basis of these results, the highest temperature that could be recommended for incubation of Norwegian Atlantic salmon eggs is 10” C. Combs and Burrows (1957) recommended 57.5 to 60” F (14.2-15.5” C) as the upper temperature limit for incubating chinook salmon eggs. For rainbow trout, Kawajiri (1927) considered 9” C to be optimal. Vernidub (1963, reported by Timoshina, 1972) showed that discrete stages of embyonic development in Atlantic and Baltic salmon had different temperature requirements, the optimal temperature tending to increase as embryonic development advanced. However, his recommended temperatures for all developmental stages were less than lO”C, whereas Marr (1966) found that the gross efficiency of growth of the Atlantic salmon embryo is highest at about 10” C. The present results indicate that the optimum temperature from hatching to swim-up varies’according to the temperature experienced during egg incubation (Fig.3). If 10” C is used for incubation, it appears advantageous to reduce the temperature to 8” C during the following period. During the first 6 weeks of feeding, all fry were held in water at much the
217
same temperature, and the substantial differences in mortality that occurred in different fish groups (Fig.3) must have been associated with the temperature differences they experienced during periods a and b. Fry hatched at 12” C were small compared with fish from other temperature groups (Fig.5). The development at 12” C was probably too rapid, and this resulted in inefficiency in terms of conversion of yolk to fish tissue. Many authors have reported reduced size in embryos hatched at high temperature (Gray, 1929; Wood, 1932; Hamdorf, 1961; Alderdice and Forrester, 1971; Alderdice and Velsen, 1971; Peterson et al., 1977). Yolk sac constrictions were produced under all the temperature regimes used (Fig.6). Dumas (1966) reported the occurrence of similar constrictions at both 47” F (8.3” C) and 53” F (11.7” C) in fry of landlocked Atlantic salmon. The difference in the pattern of constriction formation and absorption between 12” C and the other two temperatures did not seem to influence the subsequent growth in the feeding period (Fig.7). First feeding and subsequent growth began earlier for fish reared at 12” C during periods a and b compared with the other groups. The 12” C fish maintained their size advantage until the end of the experiment, by which time they averaged twice the weight of fish reared at 8” C during periods a and b. If the water temperature during the feeding period had been higher, and closer to the optimum for salmon growth of 13-15” C, it is highly probable that the difference in size between the 12” C fish and the other groups would have been even greater. In commercial smolt production it is economically important to produce a high percentage of l-year-old smolts. To do this it is essential that feeding and growth start as early as possible. It is therefore important to use the highest recommended temperature whenever possible.
REFERENCES Alderdice, D.F. and Forrester, C.R., 1971. Effects of salinity, temperature and dissolved oxygen on early development of the Pacific cod (Gadus macrocephalus). J. Fish. Res. Board Can., 28: 883-902. 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. Combs, B.D. and Burrows, R.E., 1957. Threshold temperatures for the normal development of chinook salmon eggs. Prog. Fish Cult., 19: 3-6. Dumas, R.F., 1966. Observations on yolk sac constriction in landlocked Atlantic salmon fry. Prog. Fish Cult., 2: 73-75. Gray, J., 1929. The growth of fish. III. The effect of temperature on the development of the eggs of Salmo fario. Br. J. Exp. Biol., 6: 125-130. Hamdorf, K., 1961. Die Beeinflussung der embryonal und larvalentwicklung der Regenbogenforelle (Salmo irideus Gibb) durch die Umweltfaktoren 0,, Partialdruck und Temperatur. Z. Verg. Physiol., 44: 523-549. Kawajiri, M., 1927. The influence of variation in temperature of water on growth of salmonid embryos. Nature, London, 212 (5065): 957-959. Marr, D-H-A., 1966. Influence of temperature of the efficiency of growth of salmonid embryos. Nature, London, 212 (5065): 957-959.
218 Peterson, R.H., Spinney, H.C.E. and Sreedharan, A., 1977. Development of Atlantic salmon (S&no s&r) eggs and alevins under varied temperature regimes. J. Fish. Res. Board Can., 34: 31-43. Snedecor, G-W., 1956. Statistical Methods Applied to Experiments in Agriculture and Biology. Fifth Edition. The Iowa State College Press, Ames, Iowa, 534 pp. Timoshina, L.A, 1972. Embryonic development of the rainbow trout (S&no guirdneri, irideus Gibb) at different temperatures. J. Ichthyol., 12(3): 425-432. Wood, A.H., 1932. The effect of temperature on the growth and respiration of fish embryos (Sulmo fario). J! Exp. Biol., 9 (3): 271-276.