EMBRYO GENETIC CHRONOLOGY OF Heterobranchus bidorsalis (GEOFFROY ST. HILAIRE, 1809
Studies on the artificial breeding, eggs and larvae development of Heterobranchus biodorsalis were conducted in glass aquaria maintained in thermo-regulated laboratory at 260C. The duration between time of egg fertilization to the time of complete yolk absorption and embryological development were investigated. After 28 min of egg fertilization, the zygote divided into animal and vegetal poles. The first cleavage (2-cell stage) took place 44 min after fertilization. This was followed by 4-, 8-, 16-, 32– cell stages at 54, 65, 77 and 93min after activation respectively. Morula stage took place 169 min after activation and then gastrulation at 483 min. developing embryos hatched 1525min (25.4h) after fertilization having a mean length of 3.19mm; mean yolk length, 1.27mm and heart beat rate, 133 per min. hatched embryos were negatively phototaxic and remained in groups.