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 demonstrate that size-selective harvesting drives profound phenotypic divergence within just two generations. This evolutionary response is directly underpinned by the heritable reprogramming of the core growth hormone/insulin-like growth factor (GH/IGF) axis. Strikingly, selection for large body size led to an upregulation of gh gene expression by several orders of magnitude, cementing this pathway as a primary target of selection. 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 establish heritable gene expression reprogramming as a key rapid mechanism for FIE, providing a crucial mechanistic foundation for developing evolution-aware strategies for sustainable fisheries management.