Lipid body composition of black catfish, Rhamdia quelen (Siluriformes, Heptapteridae), of two populations adapted to different environmental conditions

Abstract

The muscle lipid composition in fishes is affected by intrinsic (metabolic characteristics, migratory habits, age) and/or extrinsic factors (habitat, temperature, salinity). In particular, the fatty acids composition and the n-3:n-6 ratio in the different tissues are affected by salinity. In the present study, wild individuals of black catfish, Rhamdia quelen, were captured in two places exhibiting different environmental characteristics: a freshwater river (SG) and a shallow coastal lagoon (LR) with significant variations in salinity. Muscle lipid composition of individuals of the two populations was determined and compared. The highest values of total lipid were recorded in SG, reflecting, probably, the high food availability in the summer, period in which the fishes were captured. In the present study, the value of the n-3:n-6 ratio was approximately 2, characterizing a freshwater fish. However, when the two populations were analyzed, the value of the n-3:n-6 ratio in SG was significant lower than that registered in LR. This may be associated to ambient conditions and/or differences in the diets. While the specimens were collected from two different sites, during different seasons and under different environmental conditions, the ratios of the muscle essential fatty acids remained constant. Further studies should be held focusing these ratios under extreme environmental conditions in order to confirm these findings and, above all, to contribute to optimal diet formulation.