Triggering compensatory growth by completely replacing fishmeal with novel protein sources in the diets of juvenile largemouth bass (Micropterus salmoides): Effects on growth performance and liver health

To trigger compensatory growth (CG) with novel protein sources in juvenile largemouth bass ( Micropterus salmoides ) (initial weight: 4.73 ± 0.04 g), Chlorella ( Chlorella vulgaris , ChM), cottonseed protein concentrate (CSM), Clostridium autoethanogenum (CAP) and yellow mealworm ( Tenebrio molitor , TM) were applied to completely substitute fishmeal in the diet during a four-week dietary restriction phase (the first phase). After being refed with fishmeal (FM) diet for the next four weeks (the second phase), the growth performance, proximate composition, biochemical parameters and liver condition of treatment groups (denoted as ChM, CSM, CAP, TM group, respectively) were assessed and compared with the control group (denoted as FM group), which was consistently fed with fishmeal diets. All groups exhibited different responses during restriction and refeeding phases. The CSM, CAP, and TM groups experienced initial growth reduction followed by accelerated growth, whereas the ChM group maintained steady growth. Compensation coefficient results indicated that only ChM and CSM groups achieved compensatory growth, although there was still a gap in final weight compared with FM group. Regarding the liver condition, histopathological analysis and biochemical parameters revealed a gradual increase in lipid accumulation in the FM group during the second phase, accompanied by slowing growth. The CSM, CAP, TM groups showed varying degrees of liver injury, with the CAP group exhibiting elevated serum transaminase (ALT and AST) activity and a dramatically higher content of malondialdehyde (MDA) in liver. Conversely, the ChM group possessed healthier livers, characterized by active antioxidative capacity and low content of total triglyceride (TG). Meanwhile, abnormal lipid deposition and different amino acid content were observed throughout the FM group, potentially affecting the fish quality compared with the ChM group. Overall, the results demonstrated the feasibility and potential of triggering compensatory growth by completely replacing fishmeal with Chlorella, which exhibited the showed superior performance among novel protein sources. • Chlorella replacement triggered compensatory growth in largemouth bass with improved liver health. • Eight weeks of fishmeal diets feeding caused significant liver lipid accumulation. • Prolonged refeeding duration is recommended for full recovery of fish weight.