Physiological and Metabolic Effects of Limnospira maxima Inclusion in Fish Feed on the Liver, Intestine, and Fillet of Juvenile Nile Tilapia (Oreochromis niloticus)

To reduce pressure on capture fisheries, sustainable aquaculture must decrease its dependency on fish meal and fish oil. Microalgae are a promising substitute due to their complete nutritional profile and low-footprint production process. This study examined the use of the cyanobacterium <i>Limnospira maxima</i> (commercially known as Spirulina) as a partial substitute for fish meal in feed for juvenile Nile tilapia (<i>Oreochromis niloticus</i>). We developed isoproteic (36%) and isoenergetic (3000 kcal kg^-1) fish feed formulations containing 0% (control), 10%, 20%, 30%, or 40% <i>L. maxima</i> dry biomass. The experimental diets were then fed to 360 juvenile <i>O. niloticus</i> (1.32 ± 0.35 g) for 85 days using a randomized experimental design. The hepatic, intestinal, and muscle (fillet) tissues of the fish were collected for morphophysiological, fatty acid, and proteomic analyses. The intestinal coefficient, number of intestinal villi, villus height, and hepatosomatic index were essentially the same for all treatments (<i>p</i> > 0.05). Treatments containing 20-30% <i>L. maxima</i> exhibited a higher degree of unsaturation and better dietary fat quality. A greater abundance of the enzymes SOD, GSR, PRX1, and PLD3 in the experimental groups indicated higher antioxidant activity, whereas a greater abundance of acyl-CoA dehydrogenases indicated better use of fatty acids as an energy source. These trends were more evident in the 20-30% inclusion range. Thus, adding <i>L. maxima</i> to fish feed improves farming performance, fish health, and product quality. The results encourage the use of microalgae to promote more sustainable aquaculture.