Partial fish meal replacement by soy protein concentrate, squid and algal meals in low fish-oil diets containing Schizochytrium limacinum for longfin yellowtail Seriola rivoliana

Fish meal (FM) was partially replaced by soy protein concentrate (SPC), squid meal and a defatted algal meal from Haematococcus pluvialis in low-fish oil (FO) diets for longfin yellowtail (Seriola rivoliana). A 50% protein/15% lipid, FM-based diet (FM100) was used as a Control, and four experimental diets were formulated replacing FM with SPC, squid and H. pluvialis meals at levels of 25% (FM75), 40% (FM60), 60% (FM40) and 80% (FM20). Dietary lipid was supplied by blends of FO, a docosahexaenoic acid (DHA)-rich algal meal from Schizochytrium limacinum, and canola oil. With exception of FM100, all diets were supplemented with methionine and lysine. Taurine was supplemented in all diets to achieve a dietary concentration of 1.5%. Diets were fed twice daily for nine weeks to triplicate groups of 20 fish (initial mean weight 2.5 +/- 0.1 g) kept in 1000-L circular tanks in a flow-through seawater system. The effects of diet treatment on fish growth, feed utilization, body proximate composition, nutrient retention, fillet fatty composition, and intestinal integrity were evaluated. Growth rate and feed conversion ratio of longfin yellowtail fed the SPC-algal diets were largely comparable to that of fish fed the FM100 diet. Small, but significant differences in nitrogen retention were observed, with fish fed the FM100 diet outperforming those fed the FM40 and FM 20 diets. Lipid retention was highest in fish fed the FM20 diet and the lowest in the FM75 diet treatment. Fillet fatty acid profile reflected dietary composition and was altered by the level of FM replacement. Lower n-3 and long-chain polyunsaturated fatty acid (LC-PUFA) levels, higher n-6 fatty acid levels, and reduced n-3:n-6 ratios were associated with increasing FM replacement. Incorporation of the S. limacinum meal partially attenuated dietary and tissue loss of DHA, however, EPA levels declined with increasing FM sparing. No major histological differences or signs of enteritis were observed in any dietary treatments. Results indicate that up to 80% of FM can be replaced by SPC and algal meal, even in low-FO diets, without significantly affecting performance or intestinal integrity of longfin yellowtail. Statement of relevance It is shown that FM can be substantially reduced using blends of SPC, squid and algal meals in diets for longfin yellowtail with no significant effect on fish growth and intestinal tissue integrity. The results contribute to the knowledge to improve the sustainability of aquafeeds by using blends of terrestrial and aquatic plant ingredients. (C) 2015 Elsevier B.V. All rights reserved.