Thrissina belvedere, a new thryssa from Ha Long Bay, northern Vietnam and redescription of Thrissina chefuensis (Günther 1874) (Clupeiformes: Engraulidae)

Thrissina belvedere sp. nov. is described from 14 specimens collected in Ha Long Bay, northern Vietnam. The new species is closely related to Thrissina chefuensis (Günther 1874) (redescribed herein), both species having a short upper jaw with the posterior tip slightly shortened to the posterior margin of the preopercle, an indistinct black blotch on the nape (but not on the dorsum just before the dorsal-fin origin), and similar numbers of scutes on the ventral edge of the body. However, the former is characterized by higher total gill-raker counts on the first, second, third, and fourth gill arches, and the third gill arch posterior face (59–66, 53–59, 33–37, 25–29, 7–10 respectively vs. 50–57, 44–52, 29–35, 23–27, and 5–8 in T. chefuensis ), fewer branched anal-fin rays [24–27 vs. 24–30 (usually 27–29)], a deeper body (body depth 25.6–27.9% SL vs. 21.9–26.0%, the distance between the dorsal and anal fin origins 29.6–31.7% SL vs. 26.1–30.2%, and the caudal-peduncle depth 10.5–11.7% SL vs. 8.8–10.6%).