Influences of Size-Selective Harvesting on Growth Characteristics and Associated Gene Expression Patterns in Marine Medaka (Oryzias melastigma).

Fisheries-induced evolution (FIE) poses a critical threat to global fisheries sustainability, but the molecular mechanisms that translate harvesting pressure into rapid, heritable trait changes remain largely unknown. Here, using a multi-generational experimental evolution approach with the marine medaka (Oryzias melastigma), we investigated divergence under different size-selective harvesting regimes. We observed phenotypic divergence under different size-selective harvesting regimes. This divergence correlated strongly with the heritable shifts in the expression of key components of the growth hormone/insulin-like growth factor (GH/IGF) axis. Strikingly, lines selected for large body size exhibited an upregulation of gh gene expression by several orders of magnitude compared to other lines, implicating the regulation of this axis as a key molecular driver underlying the observed divergence. Conversely, intense selection against large size prompted a complex adaptive response involving a shift in body allometry rather than a simple reduction in size, suggesting the influence of underlying physiological constraints. Our findings highlight heritable regulatory divergence as a plausible and rapid candidate mechanism contributing to FIE. They provide a crucial mechanistic hypothesis and a foundation for developing evolution-aware strategies for sustainable fisheries management, though further studies isolating selection from other potential drivers, such as adaptation to captivity, are warranted.