Influence of high contents of dietary soybean oil on growth, feed utilization, tissue fatty acid composition, heart histology and standard oxygen consumption of Atlantic salmon raised at two temperatures

Summary

The uncertain supply and variable price of fish oil warrants the investigation of other sources of energy in salmon diets. A study was done to test the effects on growth, feed utilization, tissue fatty acid composition, heart histology and standard oxygen consumption of replacing 50% or 100% of the supplementary fish oil (FO) with soybean oil (SO) in high energy, fish meal-based diets for Atlantic salmon smolts. Triplicate groups of fish were tested for approximately 950 day-degrees (DD) at both 5 (initial weight, 108 g) and 12 degreesC (initial weight, 118 g). The salmon tripled their weight during the trial. Total feed intake and growth were significantly greater in the groups fed the 100% FO diet compared with those fed the 50% SO diet, with the 100% SO-fed groups in the middle. Feed efficiency ratios were not affected by dietary treatment or water temperature. No histological pathologies were found in heart tissue of salmon sampled at the end of the trial. Neither diet nor temperature affected whole body composition or lipid content in the heart of fish sampled at the end of the trial. Standard oxygen consumption was significantly lower in salmon fed the 50% SO diet (83 +/- 2 mg O-2 kg(-1) h(-1)) compared with fish fed the 100% FO and 100% SO diets (90 +/- 2 and 92 +/- 2 mg O-2 kg(-1) h(-1), respectively). In general, the levels of the individual fatty acids in the triacylglyerol fraction of the heart and fillet lipids showed either no response or a linear response to the corresponding fatty acids in the diets. Thus, no relationship was evident between the tissue fatty acid levels and oxygen consumption. This study showed that Atlantic salmon grow well and with high efficiency on high energy, fish meal-based diets containing up to 100% supplementary soybean oil. No evidence of detrimental effects of the soybean oil on the health of the fish was found.