Stages of lesser spiny eel, Macrognathus aculeatus in captive condition embryonic development

摘要

The lesser spiny eel, Macrognathus aculeatus is one of the popular indigenous fish in Bangladesh but the biological information of the fish is rare. It is necessary to understand the embryonic development process to establish artificial propagation in captive condition. The embryonic development stages were examined in the aquarium condition and the embryogenesis is divided into seven major phases: Zygote phase, Cleavage phase, Morula phase, Blastula phase, Gastrula phase, Organogenesis phase and Hatching phase. The major phases also separated into different sub stages whenever possible according to their development characteristics. Fertilized eggs were adhesive, greenish and demersal with equal perivitelline space. The diameter of the fertilized eggs ranged between 0.85-1.00 mm. The perivitelline space and blastodisc formation occurred at 0.35 h after fertilization (AF). The first cleavage furrow noticed at the animal pole at 0.50 h AF. The further cell division like, four cells, eight cells, sixteen cells, thirty-two cells and multi cells stages were found at 1.05, 1.50, 2.30, 3.20 and 4.30 h of AF respectively. The morula, blastula, gastrula and organogenesis were visualized at 6.45, 10.5, 15 to 21, 24.5 to 32 h AF. The blastoderm covered almost 3/4SUPth/SUP of the egg during 21.05 h AF. The first heartbeat noticed within about 31-32 h AF. At the same hours, the notochord in cellular structure was also visible. The head and tail ends of the embryo were clearly distinguished at 35.0 h AF. The hatching started 35 h AF and completed within 40 h at 29.11 ± 0.29 °C.