Evaluation of Post-Larval Diets for Indoor Weaned Largemouth Bass (Micropterus salmoides)

SIMPLE SUMMARY: This study aimed to evaluate the efficacy of complete commercially available feeds with varying nutritive profiles in the diet of juvenile largemouth bass (LMB) reared in a closed tank system. LMB is a lean fish rich in health-promoting ω3 fats. It is a promising new species for aquaculture worldwide, given its lack of intramuscular bones and delicious taste. Conditions for rearing LMB in tank systems as well as its nutritive demands from the early life stage have not yet been defined. The results of this study revealed monounsaturated (MUFA) and polyunsaturated (PUFA) ω3 fatty acids to be important nutrients for juvenile LMB, with MUFA possibly outbalancing the potential negative effects of oxidative stress caused by membrane-stabilizing ω3 fats. In addition, this study suggested an interesting feature of juvenile LMB: to sacrifice the development of some parts of the skeleton (possibly scales) for rapid growth. Among the tested feeds, one was selected as optimal for tank-reared juvenile LMB. ABSTRACT: This study aimed to evaluate different commercial diets (Otohime C1, Aller Futura (AF), Biomar Inicio Plus (BIP)) and one experimental feed (EF) in terms of their effectiveness as post-larval diets for indoor weaned largemouth bass, LMB (Micropterus salmoides). Key variations in the content of nutritive values were monounsaturated fatty acid (MUFA) and highly unsaturated FA (HUFA) ω3. Fish were fed with one of four tested diets from the 33rd to the 40th day post-hatch (DPH). Biometric indices, digestive enzyme-specific activities, thyroid hormone status, and mRNA expression of genes coding for skeleton, neuron, and muscle growth were analyzed. The lowest skeletal deformity rate and highest survival among the treatments were seen in BIP-fed fish. Dietary lipids, with an appropriate balance between MUFA and polyunsaturated FA (PUFA), alongside amino acid balance, were shown to be the main contributors to the growth of the skeleton and/or fish survival. On the other hand, fish growth is correlated with fish digestive capacity and feed moisture percent rather than feed quality. Unexpectedly, BIP-fed fish were attributed with the lowest expression of skeleton differentiation markers, which may reflect the sacrifice of scale and/or cranium growth at the expense of somatic growth. This study highlights the role of non-marine ingredients in the nutrition of post-larval LMB.