Embryonic development of the rabbit fish Siganus rivulatus and allometric growth patterns during yolk sac larvae stage produced by hormone-induced broodstock

The embryonic development of the rabbitfish Siganus rivulatus produced from induced spawning broodstock is described under controlled laboratory conditions. The present workstudied the embryonic development of the laboratory reared Siganus rivulatus from eggs to yolk sac larval stage after high dose of hormonal induction with 100 μg kg^-1 of leuteinizing hormone releasing hormone (LHRHa) injection as the best dose for egg quality (baseline). This research was conducted to study the differences in the growth pattern during the yolk sac larval stage between two experiments 100, 50 μg kg^-1 as high and low dose of LHRHa injection that whereby recognize the appropriate dose for seed quality produced. Embryonic stages of Siganus rivulatus were observed. The morphometric parameters which were measured in larvae included: total length (TL), head length (HL), trunk length (TrL), head trunk length [pre-anal length (PreAl)] and tail length (TaL). Also, the Post-anal to Pre-anal ratio was calculated for each experiment. The allometric growth patterns were calculated by a power function of total length (TL) and describing the relation between every character (Y) by the growth coefficient (b), (Y = aTL^b). The seven embryonic developmental periods (stages) which were studied included: fertilized eggs, cleavage, morula, blastula, gastrula, segmentation and hatching stages. The mean total length of the newly hatched larvae was 1.975 mm and increased linearly until the end of the experiments with a high correlation and regression coefficient in both injected groups. Before the onset of exogenous feeding, there was a clear growth priority in the head region in relation to total length in larvae of the high dose treated group. Tail region had strong positive allometric growth in larvae of both injected groups; with faster larval growth rate in those of the high dose injected group. In conclusion the differences in the growth rate were directly proportional to the dose of injection.