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 1 5-5 shows the fatty acids of unfertilized silverside eggs and 2 and 

 1 5-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 

 22:6oj3 comprised more than 35 percent of the total fatty acids. The coS 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 22:6oj3 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 to3/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 utiHzation was found by Hayes (19) and his associates in the 

 total lipids of developing steelhead trout, Salmo gairdneh. 



The brine shrimp diet was composed largely of 16:0, 16:1, 18:la;9, and 

 20:5co3 but contained no 22:6a;3 (Table 15-6). The analyses of silversides fed 

 this diet (Tables 15-5 and 15-6) showed that the fatty acids 16:1 and 18:1 u)9 

 increased from the 2-day-old yolk sac fry levels, while 16:0 and 22:6aj3 

 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, 24, 25). 



In silversides cultured for 137 days (30) the level of 20:5co3 and 22:6cj3 

 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 oj3 acids have been shown to 

 play a chief role in the metaboHsm of fish, it would seem that the amount of 

 lipid storage may be related to a certain minimal amount of cj3 PUFA, namely 

 22:6co3. A mechanism may exist which enhances the absorption and 

 deposition of lipids to ensure a minimal 22:6c<;3 tissue level. Therefore, the 



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