Substituição do óleo de peixe por óleo de soja em dietas para o beijupirá (Rachycentron canadum)

Abstract

Among the various marine fish native to the Brazilian coast, cobia, Rachycentron canadum, is considered to have a great potential for intensive culture. Feeding is a main concern in the production of cobia, especially due to the reliance on fish oil from wild caught fisheries as a source of essential fatty acids. In this study, we assessed the possibility of replacing fish oil by soybean oil in practical diets for cobia juveniles. Groups of 10 fish (mean weight of 12 g) were randomly distributed in 20 fiberglass tanks each containing 480L.Fish were fed to apparent satiety twice daily. Dietary lipid levels were 12%. Experimental diets contained different proportions of fish and soybean oils and were therefore named Op0, Op25, Op50, Op75 and Op100 according to the level of fish oil inclusion (0, 25, 50, 75 and 100%, respectively). Water quality variables (temperature, salinity, pH, dissolved oxygen, total ammonia, nitrite and nitrate) were not significantly different between treatments. Specific growth rates were somehow lower in comparison to previous studies. Increasing dietary fish oil levels resulted in higher survival. Fish fed diets Op75 and Op100 presented higher weight gain than those fed diets Op0 and Op25, whereas fish fed diet Op50 had intermediate weight gain. Feed intake also increased as dietary fish oil levels increased - from 216.67g in fish fed diet Op0 to 314.25g for those fed diet Op100. Overall, performance parameters were enhanced at higher levels of dietary fish oil. At the end of the experiment, no significant differences (P<0.05) in terms of protein and lipid contents of fish carcass were observed between treatments. On the other hand, water and ash content differed significantly between treatments. The use of relatively high levels of plant ingredients probably affected feed intake, which resulted in lower fish growth. The present results suggest the possibility of replacing at least 50% of fish oil by soybean oil in diets for cobia juveniles.