T. C. Yu

Effect of dietary linolenic acid and docosahexaenoic acid on growth and fatty acid composition of rainbow trout (Salmo gairdneri).

Methyl linolenate 18∶3ω3 and docosahexaenoate 22∶6ω3 were incorporated in semipurified diets at several levels and fed to trout previously maintained on a fat-free diet. After 14 weeks, the weight gain and feed conversion of the fish on each diet were determined. The fatty acid composition of the lipid from each group of fish was analyzed by gas liquid chromatography. Both 18∶3ω3 and 22∶6ω3 fed at the 1% level supported maximum growth of the fish. The control group, which were fed no ω3 fatty acids, exhibited a shock syndrome, poor appetite and a very slow growth rate. Tissue fatty acid analysis revealed eicosatrienoic acid 20∶3ω9 accumulated in the phospholipid fraction of this group. The 20∶3ω9 level was lowered when either 18∶3ω3 or 22∶6ω3 was included in the diet. Analysis showed that the dietary 18∶3ω3 was rapidly converted by the fish into 22∶6ω3 with a high concentration in the phospholipid. However 22∶6ω3 fed to the fish remained unchanged and little or no retroconversion of this fatty acid was observed.

Effect of dietary lipids on fatty acid composition of body lipid in rainbow trout (Salmo gairdneri)

Three isocaloric diets were prepared. Diet 1 (Control) contained 22% herring oil. In diets 2 and 3, a third and a half of the herring oil was replaced, respectively, by an animal fat (lard) which contained a high percentage of saturated fatty acids. Each diet was fed to duplicate groups of rainbow trout for 14 wk. The results of the feeding trial indicated that the concentration of the saturated fatty acids in trout body lipid did not increase despite the high concentration of these fatty acids in Diets 2 and 3. Fish growth, feed efficiency, mortality and the level of fatty acid deposited in fish body lipid and phospholipids are discussed.

Effect of dietary linolenic and linoleic acids upon growth and lipid metabolism of rainbow trout (Salmo gairdneri)

Nine diets, each containing different levels of linoleic acid (18∶2ω6) and linolenic (18∶3ω3) were fed to duplicate groups of rainbow trout for 14 weeks. The growth rate, feed efficiency, accumulated mortality, and fatty acid composition of neutral fat and phospholipids of these groups of fish were determined. The growth was slow in the groups of fish receiving diets containing (A) low concentration of 18∶3ω3 and (B) high concentration (5%) of 18∶2ω6. The accumulated mortality was high in these groups of fish. The diet containing 1% 18∶3ω3 alone supported rapid fish growth with low mortality. The feed efficiency of this diet was also high. The metabolism of 18∶2ω6 and 18∶3ω3 in fish and their conversion to more unsaturated fatty acids typical of fish lipids was investigated.