Growth and intestinal microbiota of Sabah giant grouper reared on food waste-based pellets supplemented with spirulina as a growth promoter and alternative protein source

Spirulina has been proven to be an effective growth promoter for many fish species. However, most related studies have focused on herbivorous and omnivorous fish, and limited research has been conducted on carnivorous fish. In this study, spirulina (Spirulina platensis) was administrated as a feed supplement (5%, 15 % and 30 % d.w.) in fish diets, for rearing Sabah giant grouper, a popular carnivorous fish farmed in South East Asia for its desirable taste and rapid growth. The results indicated that the total weight gain in fish fed with 5% spirulina-enriched diet almost tripled (163 ± 1.3 g) of that in the control group (67.7 ± 14.0 g). The intestinal microbial communities of the fish fed with diets supplemented with different levels of S. platensis were also investigated. The Tolumonas genus showed the highest relative abundance (44.5 %±15.0 %) in the control group, whereas the Vibrio genus showed the highest relative abundance (46.5 %–66.5 %) in all fish groups fed with spirulina-enriched diets. Simpson's diversity index showed high intestinal bacterial diversities in fish groups fed with spirulina-enriched diets. Our results demonstrated that spirulina supplementation in fish diets can modify the profile of dominant intestinal bacterial species and diversities in the fish, which affects nutrient uptake in the fish intestine.