Search

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. • Effects of fishmeal replacement by algal meals on largemouth bass were evaluated. • Low-level substitution had no negative effect on growth or whole-body composition. • Fishmeal replacement (4%) with Nannochloropsis salina decreased lipid deposition. • Fishmeal replacement (4%) with Schizochytrium limacinum increased docosahexaenoic acid. [ABSTRACT FROM AUTHOR]

Fish is currently considered a primary protein in the human diet, and the high demand for fish will stimulate the growth of aquaculture. However, a lack of high-quality fish feed (fishmeal) has led to a decline in the quality and yield of aquatic products. Therefore, an alternative high-quality protein source for fish meal is required to sustain the industry. This study assessed the effects of incorporating Spirulina platensis (SP) dried powder as a partial replacement for fishmeal and supplementing with S. platensis purified polysaccharides (PSP) on the growth, nutritional value, and health status of the largemouth bass, Micropterus salmoides, to address the challenges of fishmeal scarcity and promote sustainable development in fish aquaculture. Juveniles were fed four isonitrogenous and isolipidic diets containing SP at 0% (SP0), 3% (SP3) and 6% (SP6) and PSP at 0.3% for 56 days. The results showed that both the SP3 and SP6 groups displayed significantly (P < 0.05) improved growth performance and lower hepatosomatic indices than the control diet (SP0). Whole-body crude protein and protein efficiency significantly increased in both the SP3 and SP6 groups compared with SP0 (P < 0.05). Conversely, crude lipid content notably (P < 0.05) decreased in SP3 (5.96%) and SP6 (5.41%) in contrast to SP0 (6.59%). The muscle amino acid composition of the PSP, SP3, and SP6 groups also improved significantly (P < 0.05) compared to that of the SP0. Liver SOD activity was significantly increased from 1.11 U/mg in SP0 to 1.22–1.24 U/mg in SP3 and SP6 (P < 0.05), while MDA levels declined accordingly. Serum triglyceride levels were significantly lower in SP3 than in SP0 (P < 0.05) but remained stable in the SP6 and PSP groups. Low-density lipoprotein cholesterol decreased significantly in the SP3 and SP6 groups, but no significant effect was observed in the PSP group. Alanine aminotransferase activity was significantly (P < 0.05) lower in the PSP, SP3, and SP6 groups than in SP0. Aspartate aminotransferase activity in PSP and SP3 was significantly lower than in SP0 (P < 0.05), but showed no significant difference with SP6 (P > 0.05). Intestinal trypsin and amylase activities significantly improved in the PSP, SP3, and SP6 groups (P < 0.05), and lipase activities in PSP and SP3 increased significantly compared to those in SP0 (P < 0.05). The intestinal microbiome displayed significantly higher Shannon index scores for SP3 (0.83) and SP6 (0.93) than for SP0 (0.61). The relative abundances of the phylum Fusobacteria and genus Cetobacterium were significantly increased, whereas Proteobacteria and Plesiomonas were significantly decreased in the PSP and SP3 groups compared with that in SP0 (P < 0.05). The present study indicated that the replacement of fishmeal with 3–6% SP and 0.3% PSP addition could improve the growth performance, protein efficiency, muscle nutritional value, liver health, antioxidant capacity, intestinal digestive enzyme activity, and intestinal microbiota diversity of the largemouth bass. Therefore, the partial replacement of SP or the addition of PSP has great potential in promoting healthy aquaculture of largemouth bass. • Effects of adding Spirulina dried powder (SP) and polysaccharide (PSP) to the diet of Micropterus salmoides were assessed. • Including 3% and 6% SP in the diet led to enhanced growth performance and improved protein efficiency. • Both SP and PSP resulted in reduced lipid deposition, enhanced liver health, and increased antioxidant capacity. • Both SP and PSP led to improvements in gut digestive enzymes and enhanced the nutritional value of fish muscle. • Both SP and PSP promoted greater biodiversity in gut microbiota and an increase in beneficial species. [ABSTRACT FROM AUTHOR]