Preliminary report on early development of the Malagasy frog Dyscophus guineti (Grandidier, 1875) (Amphibia, Microhylidae, Dyscophinae

The genus Dyscophus, endemic to Madagascar, includes three species of large terrestrial frogs. Dyscophus guineti (Grandidier, 1875) is restricted to eastern rainforests, where it breeds in stagnant or very slow-moving water; its filter feeding tadpoles are of the characteristic microhylid type. Few information are reported in literature about early development. A colony of this species, collected in the area of Moramanga and subsequently transferred to the Aquarium of Genoa (Acquario di Genova) in the framework of a scientific cooperation beteween this institution and the University of Madagascar, bred in June 1998. This paper deals with the description of the external morphology of early development stages of D. guineti on the offspring obtained at the Aquarium of Genoa. For this purpose samples were collected every four hours between fertilization and hatching and daily during the following period. Embryos and larvae were formalin fixed (4% paraformaldehyde in phosphate buffer, o,2 M, pH 7,4), and transferred in 70% ethanol. The embryonic phase of development occurred quickly, only 48 hours after fertilization. After hatching, larval development became considerably slower (mean 40 days). After 1 day, the head-body became shorter and causes a strong winding of the intestinal tract, that indicates the vegetarian feeding habit. During further development, the head-body became big and transparent, so that it was possible to follow brain development, with two olfactory lobes, appearing before differentiation of the nostrils. The eyes were opened from the third day after hatching, with a spherical lens protruding outward. The mouth presented the shape of a frontal furrow, surrounded by transparent and thin epithelium. When opened by a forceps, it revealed a particular inner structure, suggesting a feeding behaviour based on suction, or filtration. Further histological investigation will clear up this question.