Response of common carp (Cyprinus carpio) larvae to different dietary levels and forms of supply of medium-chain fatty acids

The effects of dietary medium-chain fatty acids (MCFA) on survival, growth and fatty acid composition of first-feeding carp larvae were investigated in two 21-day feeding trials. In trial 1, one diet CO was supplemented with 10% coconut oil, two diets, M1 and M2 with 1.7 or 4.2% interesterified medium-chain triacylglycerols (MCT), and two other diets T1 and T2 with 1% tricaprylin and 0.7% tricaprin, or 2.5% tricaprylin and 1.7% tricaprin. The five diets were made isolipidic (18% of dry diet) with triolein and compared to a control diet without MCFA. With a low dietary level (1% of dry diet) of caprylic acid (C8:0), final survival and mean weight of larvae fed CO, M1 and T1 were not significantly different from those of control (68 +/- 6% and 62 +/- 8 mg, respectively). In contrast, with a high dietary C8:0 level (2.5% of dry diet), final survival and mean weight of larvae fed M2 and T2 were markedly decreased (23 +/- 2% and 40 +/- 8 mg, respectively), without effect of the form of supply. In trial 2, larvae were fed six diets with graded tricaprylin contents (from 0 to 10% in diet). Survival was not significantly affected but growth was decreased by C8:0 levels higher than 2% of dry diet. Fatty acid composition of larval total lipids revealed high levels of lauric and myristic acids in larvae fed coconut oil. Deposition of C8:0 and capric acid (C10:0) was low after MCT feeding, but depended of the form of supply, being higher with pure than with interesterified MCT. Relatively high amounts of C8:0 and C10:0 were recorded in total lipids of larvae fed 10% tricaprylin. It is concluded that high levels of caprylic acid decrease growth but that low levels are well utilised by carp larvae, irrespective of the form of supply. (C) 2000 Ifremer/CNRS/INRA/IRD/Cemagref/Editions scientitiques et medicales Elsevier SAS.