Four new species of freshwater goby from the Rhinogobius genus have been described from northern Vietnam.
The new gobies, which have been named Rhinogobius boa, R. sulcatus, R. variolatus and R. virgigena by Kottelat and Chen were all collected from freshwater coastal streams between the Sino-Vietnamese border and the Song Hong or Red River drainage.
Rhinogobius boa was found in a series of boulder and leaf-litter strewn forest streams in the Ka Longo drainage.
This small goby has six or seven dark brown blotches on its body, two round dark spots on the base of the pectoral fin and a grey branchiostegal membrane (that's the flap of skin on the underside of the opercula).
Male R. boa have a browny-black mark on the front of the fourth dorsal spine which is absent in females. Males also have 8-10 dark grey marks on their branchiostegal membrane which are not seen in the female.
R. sulcatus, which was collected along with the related R. variolatus (another new species) from a small coastal stream in Cam Pha, on the north east coast of Vietnam, has three or four obliquie browny-black bands and one or two stripes on its cheek and gill cover.
Males of R. sulcatus have 14-17 red or orange spots on the branchiostegal membrane and a brown-black spot on the third spine of the first dorsal fin.
Males of Rhinogobius variolatus, which lives alongside R. sulcatus in the wild, are much more striking than females, which are relatively plain in comparison.
Male variolatus have two rows of brown spots which form longitudinal stripes, two black spots on the base of the pectoral fin and a plain branchiostegal membrane.
The fourth of the new gobies, Rhinogobius virgigena, which was collected with specimens of variolatus from the Ba Che drainage in northern Vietnam, is said to be very similar to Rhinogobius duospilus, a species commonly sold as R. wui in the UK aquatic trade.
Kottelat and Chen provide an excellent artificial key for identifying the Rhinogobius species if you are trying to determine what species you have in your aquarium. Most of the characters used in the key are easy enough to identify from living fishes, too.
For more details on the new gobies see the paper: Chen, IS and Kottelat, M. (2005) - Four new freshwater gobies of the genus Rhinogobius (Teleostei: Gobiidae) from northern Vietnam. Journal of Natural History. Vol. 39. No. 17. pp. 1407-1429.