Níveis de ácido linoleico e ácido linolênico em dietas para tambaqui (Colossoma macropomum)

Abstract

Fish, like other vertebrates, are not able to synthesize fatty acids of the n-6 and n-3 series again, and require supplementation in their diet. Unlike marine fish, freshwater tropical fish demand linoleic (LA, C18:2n-6) and linolenic (ALA, C18:3n-3) fatty acids, since they are capable of elongate and desaturate these precursors to compounds with higher biological value. The LA is the precursor of ARA (C20:4n-6) and ALA precursor of EPA (C20:5n-3) and DHA (C22: 6n-3), and these precursors of 18 carbons compete for the same elongases and desaturates. Therefore, besides providing each separate precursor, the relation between them is of great importance. Furthermore, fish is among the main sources of EPA and DHA in human nutrition, which are metabolically essential compounds and of great importance in health maintenance. Thus, the objective was to evaluate the effect of the ratio of n-6/n-3 fatty acids dietary on performance, morphometric parameters, bromatological composition, plasma lipoproteins, energetic metabolism and fatty acid profile in liver and fillet of tambaqui (Colossoma macropomum). An experimental trial was conducted with iso-protein and iso-lipidic diets, in which six diets were with different ratios of LA/ALA (3.1; 3.8; 5.0; 7.2; 12.0; and 26.9) and a control diet with fish oil. There were no differences observed in performance, morphometric parameters and plasma lipoproteins of animals fed with the LA/ALA or control ratios, except HDL-C, which was lower in 3.8 ratio than in 3.1 or 5.0 (P<0.05). Blood glucose was higher in the fish fed with the 7.2 ratio (P<0.05). Furthermore, it was observed an effect on the glucose content in the muscle of tambaqui, being lower in fish fed with the 26.9 ratio (P<0.05). The measurements of composition showed that the protein in carcass was lower in fish fed with the control diet and 3.1 ratio (P<0.05). In general, the liver fatty acids reflected the composition of fatty acids of the diet. The LA/ALA ratio affected the fatty acid profile and the nutritional quality of tambaqui fillet. The EPA content decreased with the increase of LA/ALA ratio of the dietary. The higher concentration of ARA, DHA and EPA+DHA in the fillet was observed in animals fed with the LA/ALA ratio of 5.0, among the fish fed with vegetable oil. In conclusion, the 5.0 LA/ALA ratio is the best for young tambaqui, which besides not affecting performance or metabolism, this ratio improves the nutritional quality of fish for human consumption.