Early development of the endangered freshwater goby, Rhinogobius sp. BI (Gobiidae)

Abstract

The early development of the endangered freshwater goby, Rhinogobius sp. BI (ogasawara-yoshinobori in Japanese), was described in the course of a serial rearing experiment over generations as ex situ preservation. The eggs, measuring 2.0 mm in long diameter and 0.7 mm in short diameter, were elliptical with a colorless transparent chorion, a slightly yellowish yolk, and some oil globules. Hatching occurred naturally at 6 to 7 days after spawning at 24.0°C. Newly hatched larvae, measuring 3.2–3.4 mm in total length (TL), had opened mouth and a globular yolk sac. The yolk was completely absorbed at 3.5 mm TL (5 days after hatching). Notochord flexion initiated at 5.7 mm TL (18 days) and finished at <9.1 mm TL (30 days). First dorsal fin began to form in postflexion larvae at 10.0 mm TL (40 days), and a full complement was attained at 11.6 mm TL (45 days). Second dorsal fin emerged at 5.7 mm TL (18 days); full count was attained and segmentation initiated at 9.1 mm TL (30 days). Anal fin anlage appeared at 5.7 mm TL (18 days); its ray count was completed and segmentation initiated at 9.1 mm TL (30 days), and branching at 15.6 mm TL (60 days). Caudal fin support appeared at 4.5 mm TL (15 days); segmentation initiated at 6.0 mm TL (24 days) and branching at 10.0 mm TL (40 days). Fanlike pectoral fin present in newly hatched larvae. Pectoral fin rays appeared at 10.0 mm TL (40 days), and its ray count completed at 15.6 mm TL (60 days). Pelvic fin projected at 9.1 mm TL (30 days), and a sucking disc partially formed at 11.6 mm TL (45 days). Aggregate numbers of all fin rays were completed at 15.6 mm TL in 60 days after hatching. Pelagic period continued for about 40 days, and settlement was completed in postflexion larvae at 45 days.