From the Fifth to the 58th day of culture, the amino acid profiles did not 
change markedly. The only changes which occurred were a decrease in glutamic 
acid and an increase in alanine and histidine. Compared to the 3-day-old brine 
shrimp diet, the 58-day-old fish differed only in the levels of histidine and 
arginine. Therefore, it seems that the dietary amino acids were absorbed and 
deposited as early as the fifth day of life. 
Table 15-5 shows the fatty acids of unfertilized silverside eggs and 2 and 
15-day-old fry fed on 3-day-old brine shrimp nauplii. The unfertilized eggs had 
a whole body lipid level of 13.9 percent and the fatty acids 20:5co3 and 
22:6co3 comprised more than 35 percent of the total fatty acids. The co3 acids 
exceeded the co6 component by greater than eight times. It would appear that 
the high energy level coupled with the large co3 polyunsaturated fatty acid 
(PUFA) component are indicative of their metabolic and physiological 
importance in the early life stages of silversides. 
In the 2-day-old yolk sac fry the acids 16:0, 18:0 and 22:6co3 were 
preferentially retained from the energy rich egg, while 16:1, 18: lco9, 20:5co3 
and those acids which comprise individual contributions of less than 4 percent 
each showed reduced levels. The co3/co6 ratio of the 2-day-old yolk sack fry 
increased to 12.6, from the egg level of 8.5. A similar pattern of fatty acid 
retention and utilization was found by Hayes (19) and his associates in the 
total lipids of developing steelhead trout, Salmo gairdneri. 
The brine shrimp diet was composed largely of 16:0, 16:1, 18:lou9, and 
20:5oo3 but contained no 22:6co3 (Table 15-6). The analyses of silversides fed 
this diet (Tables 15-5 and 15-6) showed that the fatty acids 16:1 and 18:lco9 
increased from the 2-day-old yolk sac fry levels, while 16:0 and 22:6co3 
decreased. It is evident that the fish change their concentration of fatty acids 
to reflect the general composition of their diets. Other researchers have made 
the same correlation between the diet and tissue fatty acids of cultured fish (1, 
9,14, 23,24). 
In silversides cultured for 137 days (30) the level of 20:5co3 and 22:6co3 
represented as little as three percent of the total fatty acid composition. The 
level of these two fatty acids in the wild fish represent an amount about ten 
times this level. Additionally, the wild fish had an oil content of only about 
eight percent, whereas 137-day-old cultured fish had a lipid level of 21.4 
percent (30). Thus, brine shrimp fed fish did not closely resemble the lipid 
content of their natural counterparts. Since the co3 acids have been shown to 
play a chief role in the metabolism of fish, it would seem that the amount of 
lipid storage may be related to a certain minimal amount of to3 PUFA, namely 
22:6 gj 3. A mechanism may exist which enhances the absorption and 
deposition of lipids to ensure a minimal 22:6co3 tissue level. Therefore, the 
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