Comparison of gonad development between wild and hatchery-bred silver therapon Leiopotherapon plumbeus (Teleostei: Teraponidae) during an annual reproductive cycle

Abstract

This study compared gonad development between wild-sourced and hatchery-bred silver therapon <i>Leiopotherapon plumbeus</i>. Wild fish from the east bay area of Laguna de Bay, Philippines, and hatchery-bred stocks grown to adult size in outdoor tanks were sampled, and somatic condition, gonad histology, gonadosomatic index (GSI), gut index (GI), and hepatosomatic index (HSI) were assessed during the annual reproductive cycle. Hatchery-bred fish condition was generally better than that of wild-sourced fish as a consequence of readily available food resources and environmental conditions. Hatchery-bred male GSIs were significantly higher than in wild male fish in November to February, coinciding with low water temperatures. However, female GSIs were significantly higher in July and November to December for the hatchery-bred fish, and in January to April for the wild-sourced fish. Together with spermatozoa and primary growth oocytes which were most abundant in the gonads, the presence of other gametogenic stages supports asynchronous gonad development. Hatchery-reared fish showed significantly higher GIs during the spawning season over their wild counterparts. Generally, mean HSI, regardless of sex, was also higher among hatchery-bred fish. These results suggest marked differences in the somatic and reproductive potential of wild and hatchery-bred silver therapon, although the presence of spermatozoa and vitellogenic oocytes in the gonads may allow this species to reproduce year-round.