Feeding effects of low-level fish meal replacement by algal meals of Schizochytrium limacinum and Nannochloropsis salina on largemouth bass (Micropterus salmoides)

Abstract

Microalgae exhibit diverse and high nutritional value, and therefore, have a huge potential application as a raw material for the preparation of aquafeeds. This study was conducted to evaluate the effects of low-level replacement of dietary fishmeals by algal meals comprised of Schizochytrium limacinum (SL) and Nannochloropsis salina (NS) individually and in combination in the diet of juvenile largemouth bass (LMB, Micropterus salmoides). Five isonitrogenous, isolipidic, and isoenergetic diets with fishmeal-based diets as control, and four experimental diets with replacement by individual 4% SL (4SL), individual 4% NS (4NS), 2% SL combined with 2% NS (2SL + 2NS) and 4% SL combined with 4% NS (4SL + 4NS) were formulated. Five hundred juvenile fish (average weight 8.72 ± 0.10 g) were evenly distributed to five groups with quadruplicate each, in twenty fiberglass tanks and fed for eight weeks. Our results showed that there were no significant difference in weight gain, special gain rate, hepatosomatic index, viscerasomatic index, conditioning factor, and the whole-body composition among the five groups (p > 0.05). However, feed intake and feed conversion ratio in the 4NS treatment were significantly higher (p < 0.05) compared with the control. Further, lipid content and intraperitoneal fat ratio in the liver of the 4NS and 4NS + 4SL groups were significantly decreased, suggesting that NS may reduce visceral fat accumulation in LMB. The serum superoxide dismutase (SOD) activity of LMB in the 4NS group was significantly increased compared with the control (p < 0.05). However, malondialdehyde (MDA) content in the liver of the 4NS group and intestine of the 4SL + 4NS group was significantly lower than that in the control (p < 0.05). Replacement with 4% SL significantly increased docosahexaenoic acid, polyunsaturated fatty acids (PUFAs), and n-3 PUFA proportions in the liver. Further, SL alone or in combination with NS increased the n-3 to n-6 ratio of PUFAs in the liver and muscle, creating more balanced unsaturated fatty acids. The fillet texture was significantly enhanced by taste and flavor. Nevertheless, the present study verified the successful addition of SL and NS algal meals to fish feed, which exhibited excellent potential to replace fishmeals and fishoil, respectively, as protein and lipid sources.