Analysis of relationship between growth traits and feed conversion ratio provides insights into aquaculture and breeding of largemouth bass Micropterus salmoides

Feed costs constitute the largest expense in aquaculture production. Therefore, studies on feed efficiency (FE), measured by feed conversion ratio (FCR), have attracted much attention from both breeders and researchers. In this study, the differences of growth traits and feed utilization traits between largemouth bass (LMB) with LowFCR and High-FCR were compared, and the relationships and correlations between different traits were analyzed. The results showed that the Low-FCR group exhibited better growth performance expressed as higher weight gain (WG) and specific growth rate (SGR), and higher FE namely lower FCR and higher protein efficiency ratio (PER), than the High-FCR group. Thirteen of fourteen measured growth traits in the Low-FCR group were significantly higher than those in the High-FCR group. Seven normalized growth traits presented significant differences between the two groups, with the Low-FCR group observed to have a relatively larger body size. Additionally, in all individuals, the feeding rate (FR) showed significant correlations with the weight growth traits (WG and SGR) but not with the feed utilization traits (FCR and PER), suggesting the increase of FR can promote growth but have little effect on FE. Further, six equations were established to quantitatively estimate the effects of various morphological growth traits on growth and feed utilization. Finally, two discriminant equations were successfully constructed to distinguish Low-FCR and High-FCR LMB based on growth indexes. These results will enhance our understanding of the relationships between FE and growth traits and provide valuable reference information for selective breeding in FE for LMB.