Hatchability and growth performance of F1, F2, and backcross progenies of Epinephelus bruneus and Epinephelus lanceolatus

In recent years, the aquaculture of hybrid groupers has gained popularity due to their favourable traits, such as superior growth and enhanced disease resistance compared to purebred species. In Japan, the hybrid grouper Kue-Tama (KT), a crossbreed of Epinephelus bruneus (LG) eggs and Epinephelus lanceolatus (GG) sperm, has emerged as a promising target for aquaculture. However, the sustainable production of KT seedlings is hindered by low egg hatching rates. In this study, we obtained eggs from KT reared in a subtropical region of Japan and conducted breeding experiments involving KT and GG to produce KT × KT (F2) and KT × GG (BC1) backcross hybrids. Direct comparison experiments revealed that the viable hatching rate of BC1 was ten times higher than that of KT, at 7.5 ± 4.3% and 0.7 ± 1.3%, respectively. During 7 months of juvenile rearing, both BC1 and KT exhibited comparable growth performance, significantly outperforming F2, with markedly better feed efficiency and specific growth rates. The weight gain ratio of BC1 (227.8 ± 70.0%) was 1.9 times greater than that of F2 (119.3 ± 20.4%) and similar to that of KT (214.8 ± 15.5%). These findings suggest that the BC1 hybrid could be a valuable species for aquaculture, offering greater hatching success and growth performance than KT.