Planktonic larvae of Luciogobius sp. (Gobiidae) in a tropical estuary

Abstract

Species of Luciogobius genus (Gobiidae) are distributed along the east coast of the West Pacific, and their early life stages occur in coastal waters and bays and estuaries. Little is known about their planktonic larval dispersal and morphology. To obtain baseline information on early larval stages of Luciogobius sp., we performed monthly ichthyoplankton net collections from September 2014 to August 2015 within the Kalong estuary in northern Vietnam. Successful collections of Luciogobius denote a new southern range extension of the genus, and northern Vietnam may be the southernmost distributional range of the Luciogobius. A total of 146 larvae [preflexion to postflexion stages, 1.8–13.3 mm body length (BL)] of Luciogobius sp. were collected from the center channels of the estuary in December to February and April. The larvae collected in Kalong were similar in general morphology to congeners. Still, they were distinguished from other descriptions of Luciogobius species by their melanophores being heavier along the mid-tail vertebrae, and shorter at the dorsal midline. The abundance of Luciogobius sp. was highest in January, and at the mid-outer stations of the estuary, where smaller and earlier preflexion larvae were collected, suggesting that these larvae are likely not be from the middle or upper reaches of the Kalong River. Based on the spatial and temporal occurrence of newly hatched larvae, it suggests that the Luciogobius sp. spawning season is from December to February when the water temperatures are lowest, and the spawning grounds being within the estuary or very close to coastal area. These findings further indicate the importance of this tropical estuary as a nursery for temperate and subtropical fish. The differentiation in its morphology and geographical distributions with higher latitudinal Luciogobius species was also discussed to reveal this genus’ diversity, and suggests further investigations into examining to possibility of new species.