Effect of dietary methyl linoleate and linolenate on growth of carp - II.

A feeding trial was conducted to determine the essential fatty acid (EFA) requirement of carp fry weighing about 0.65g which had been kept on a fat-free diet for four months before the initiation of the feeding experiment. Fat-free and EFA-deficient diets resulted in retarded growth, and the addition of either methyl linoleate or linolenate to the diets improved growth conditions. Furthermore, carp seemed to require not only linoleic but also linolenic acids. The influence of EFA-deficiency on fatty acid composition of lipids in carp is essentially the same as that in rainbow trout. Feeding either the fat-free or EFA-deficient diets resulted in an increase of the 20:3ω9 acid level and this level was depressed by dietary methyl linoleate and linolenate. The former acid elevated levels of 20:4ω6 and 22:5ω6 acids and the latter that of 22: 6ω3 acid. In the case of rainbow trout which require linolenic acid as an EFA, we adopted the ratio of 20:3ω9/22:6ω3 for the index of EFA-deficiency. However, since carp appear to require fatty acids of both the linoleic and linolenic families for growth, it seems to be reasonable to consider the ratio of 20:3ω9/20:4ω6 as well as the ratio of 20:3ω9/22:6ω3 for the EFA index in carp. When both ratios were applied for carp at the index of EFA-deficiency, the fish fed diets containing fatty acids of both ω6 and ω3 types received a suf-ficient amount of EFA and therefore showed good growth conditions.