The Role of Algae Extract (Ulva lactuca and Solieria chordalis) in Fishmeal Substitution in Gibel Carp (Carrassius auratus gibeilo)

SIMPLE SUMMARY: The issue of fishmeal substitution has become increasingly important as the price of fishmeal has soared in recent years, driving up the cost of aquaculture feed and farming. However, fishmeal is one of the best protein sources, and problems such as growth inhibition and immune regulation disorders often occur after fishmeal substitution, which restricts a further reduction in the use of fishmeal. This study investigated the role of algal extract in fishmeal substitution and found that supplementation of algal extract when fishmeal reduction was effective in alleviating problems such as growth inhibition and reduced immunity. These results confirm that this algal extract can play an important role in fishmeal substitution, reduce feed costs, and provide a theoretical data basis for fishmeal substitution. ABSTRACT: The function of algae extract (AE) in fishmeal (FM) substitution with plant proteins in the diets of Gibel carp (Carrassius auratus gibeilo) was investigated during a 56-day trial. Diets 1 and 2 contained 10% FM, Diets 3 and 4 contained 5% FM, and Diet 5 and 6 contained 0% FM. In contrast, Diets 2, 4, and 6 were supplemented with 0.2% AE. The results showed that FM reduction inhibited growth performance, while AE supplementation alleviated growth inhibition. FM reduction significantly decreased the crude protein levels of the whole body, while the contents of whole-body lipids were significantly decreased with AE supplementation. There were no significant changes in ALB, ALP, ALT, AST, TP, GLU, GLU, and TC in plasma. FM reduction with AE supplementation mitigated the decrease in antioxidant capacity by heightening the activity of antioxidant enzymes and related gene expressions, which mitigated the decrease in immune capacity by affecting the expression of inflammatory factors. In summary, AE supplementation could alleviate the negative effects of FM reduction in Gibel carp.