Reciprocal Hybridization between Percocypris pingi and Schizothorax prenanti: Growth, Fin Development, and Morphological Divergence

Hybridization is increasingly recognized as an evolutionary force with potential applications in the study of aquatic organism evolution. However, the importance of morphological traits is often overlooked, as they are typically used only for taxonomic identification, and their potential relevance to growth and development in hybrids remains unclear. To evaluate reciprocal F1 hybrids between Percocypris pingi (PP) and Schizothorax prenanti (SS), we compared growth performance, fin development schedules, and morphological traits with parental self-cross progenies under common rearing conditions. Four cross types (PP, SS, PS, and SP) were produced and monitored from hatching to 360 days post-hatch. Growth analyses revealed significant differences among groups. SP exhibited significant heterosis, outperforming both parental groups in body length and weight. In contrast, PS showed intermediate performance and demonstrated partial superiority, exceeding only one parental group. Fin development followed a consistent sequence (caudal, pectoral, dorsal, anal, pelvic) across groups; however, SS completed fin formation earliest, while PP required the longest accumulated thermal time. Morphometric and truss analyses indicated that hybrids, particularly SP, displayed broader body forms and pronounced shifts in body–head proportions, whereas PS showed several moderate deviations. Cluster analysis further revealed that hybrids were morphologically closer to SS than PP. Collectively, these findings demonstrate that hybridization alters the relationship between developmental timing and body-shape expression, producing phenotypes with enhanced growth and morphological advantages. This study highlights the value of reciprocal hybrid evaluation for understanding heterosis mechanisms.