Ovarian Developmental Characteristics and Hypothalamic Transcriptomic Analysis of P. leopardus Under Different Aquaculture Modes

Two rearing systems are used for Plectropomus leopardus: sea-cage culture and the land-based flow-through aquaculture system. Cages approximate natural conditions and yield many high-quality eggs but offer limited control over ovarian development; the land-based system is highly controllable yet ovaries develop slowly and seldom reach full maturity. We compared these systems by analyzing growth–gonad relationships, monthly hormone profiles (GnRH, E2, GnIH), and hypothalamic transcriptomes in 14- and 18-month-old females. Within each system, body weight did not predict gonadal stage and energy allocation was size-independent. In cages, ovaries reached full maturity with normal histology; in tanks, gonads of all sizes remained at stage III, indicating arrested development. Serum GnRH and E2 displayed parallel increases from 12 to 14 months, declined at 16 months and surged at 18 months in both systems, while GnIH fluctuated inversely, suggesting antagonistic control. Transcriptome analysis identified fshr, cyp11a1 and sox17 as key down-regulated genes in tank-reared fish. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment implicated GnRH, oxidative phosphorylation, ribosome and Wnt pathways in ovarian progression. These findings elucidate reproductive constraints under artificial conditions and provide molecular targets for controllable breeding of P. leopardus.