Bioacoustics of Rhinogobius taenigena

Remarks. The type locality of R. taenigena is Xe Pon (Se Pon), a tributary of the Banghiang River in the Mekong basin ( Chen et al. 1999 ). Though located in Laos , it is close to the border with Vietnam (a little downstream from the Xe Pon reaches shown in Fig. 1 ). This species was also reported from Quang Binh Province ( Fig. 1 ) in Vietnam from the Gianh River basin to Phong Nha River ( Serov et al. 2006 ). We found this species in two river systems in Thua Thien Hue Province of Vietnam ( Fig. 1 ). One of them, Xe Kong (Se Kong), is a tributary of the Mekong, originating in Thua Thien Hue Province and flowing through southern Laos and eastern Cambodia . It joins the Mekong near Stung Treng , Cambodia .Another site is in the upper reaches of the Song Bo (Bo River), a tributary of the Song Huong (Perfume River), which flows directly to the South China Sea near the city of Hue. These suggest that this species could be widely distributed in river systems near the Vietnam-Laos border in this region. Chen et al. (1999) described “four small blackish-brown spots on ventral edge of cheek” (on the ventral margin of the preopercle according to their fig. 16) of a male as a diagnostic character of R. taenigena . They described the coloration based on “observations from color slides taken of freshly preserved specimens.” Nagao Natural Environment Foundation (2021) noted that “the spots are not always evident” in specimens freshly collected near the type locality, and “if present, the number varies from one to four.” Photographs by the Nagao Natural Environment Foundation (2021: 441) show orange spots similar to spots on the opercular membrane, interopercle, and lower part of subopercle. Our material from Vietnam has neither blackish-brown spots nor spots of any other color on the preopercle, either in fresh or after preservation. This is the only point on which our observations do not agree with previous descriptions. No significant morphological differences were also found between the Xe Kong and Song Bo populations.