Embryonic Morphogenesis of the Boesemani Rainbowfish (Melanotaenia boesemani): Developmental and Aquaculture Perspectives

Embryogenesis is a crucial stage of teleost development, influencing embryonic viability and later larval function. This study offers the inaugural full chronological assessment of embryonic development in the Boesemani rainbowfish (Melanotaenia boesemani), a valuable ornamental species for whom species-specific developmental staging is currently insufficient. Fertilized eggs acquired via natural spawning were incubated under regulated laboratory settings, with temperature and dissolved oxygen levels continuously monitored during the incubation period. Embryos were analyzed via light microscopy at defined intervals to record the progressive morphogenetic development from fertilization to hatching. Development progressed through specific phases of meroblastic discoidal cleavage, morula, blastula, gastrulation, organogenesis, and hatching. Initial cleavage was observed around 30 minutes after fertilization, succeeded by morula development at 5 hours post-fertilization. The transition to the blastula stage, characterized by blastoderm growth and the initiation of epiboly, transpired between 11.5 and 14.5 hours post-fertilization. Gastrulation became apparent at around 16 hours post-fertilization, marked by vigorous epibolic movement and the establishment of the embryonic axis. Organogenesis began about 21.5 hours post-fertilization, featuring gradual axial elongation, differentiation of optic structures, notable ocular pigmentation by 72 hours post-fertilization, and heightened embryonic motility before hatching. Larval emergence transpired at 144 hours post-fertilization, yielding completely elongated larvae with pigmented eyes, discernible pectoral fin structures, active locomotion, and residual yolk reserves. These findings create a temporally organized embryonic stage framework for M. boesemani, enhancing comparative teleost developmental biology and offering a scientific reference for refining incubation procedures in sustainable ornamental aquaculture. This study contributes to Sustainable Development Goal (SDG 14: Life Below Water) by providing a scientific basis for improving hatchery practices and supporting sustainable ornamental aquaculture through a better understanding of fish embryonic development.