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

## TL;DR

This study shows that adding the microalga Spirulina to fish feed improves fish health and sustainability in aquaculture.

## Contribution

The study demonstrates that Limnospira maxima improves antioxidant activity and lipid metabolism in Nile tilapia, supporting sustainable aquaculture.

## Key findings

- Fish fed with 20–30% L. maxima had better fatty acid profiles and dietary fat quality.
- Proteomic analysis showed increased antioxidant enzymes and improved lipid metabolism in Spirulina-fed fish.
- The study supports using microalgae as a sustainable alternative to fishmeal in aquaculture feed.

## Abstract

Aquaculture is a fundamentally important sector of the global food supply, but it is also environmentally intensive. Conventionally used feed ingredients stand out among the factors that contribute to its high environmental footprint. For instance, fishmeal and fish oil rely on overexploited wild fisheries, while soybeans compete with human food resources. This study investigated how partially replacing fishmeal with the microalga Spirulina affects the morphophysiology and metabolism of Nile tilapia, one of the most widely farmed fish. In a previous study, we demonstrated that Spirulina improved the zootechnical performance of Nile tilapia. Here, we expand on those results by showing improvements in the fatty acid profiles and dietary fat quality of Spirulina-fed fish. Furthermore, proteomic analysis indicates a higher antioxidant capacity and more efficient lipid metabolism. Taken together, these results support the use of Spirulina as a fish feed ingredient to promote more sustainable aquaculture practices. Finally, this study provides a policy-based foundation for overcoming obstacles to implementing microalgae as an aquaculture feed ingredient.

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 Limnospira maxima (commercially known as Spirulina) as a partial substitute for fish meal in feed for juvenile Nile tilapia (Oreochromis niloticus). We developed isoproteic (36%) and isoenergetic (3000 kcal kg−1) fish feed formulations containing 0% (control), 10%, 20%, 30%, or 40% L. maxima dry biomass. The experimental diets were then fed to 360 juvenile O. niloticus (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 (p > 0.05). Treatments containing 20–30% L. maxima 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 L. maxima to fish feed improves farming performance, fish health, and product quality. The results encourage the use of microalgae to promote more sustainable aquaculture.