Rhinogobius biwaensis, a new gobiid fish of the "yoshinobori" species complex, Rhinogobius spp., endemic to Lake Biwa, Japan

The endemic lentic goby of Lake Biwa in Japan, which has hitherto been designated informally as Rhinogobius sp. BW, is formally described as Rhinogobius biwaensis sp. nov. It is distinguished from other members of the genus by the following combination of characters: vertebral count 26 (rarely 27); pectoral fin rays 18-22 (mostly 20-21); longitudinal scales 31-36 (mostly 31-34, mode 32); predorsal scales absent or few; D1 low with non-filamentous spines, all of almost same length except for shorter 1st and 6th (last) spines in both sexes; pelvic fin disk composed of thin membranes, its frenum undeveloped with a low, thin lamella; cheek unmarked; back and sides of body with 5-6 unclear dark saddles and 6-9 dark blotches; D1 lacking blotches but melanized to greater or lesser degree along rays; dorsal edge of pectoral base with one small, dark spot tinged with blue metallic luster; in breeding males, yellow on suboperculum and branchiostegal region and on basal part of anal fin, blue on medial part of under jaw.