Lake Biwa rock catfish
(Silurus lithophilus)

Silurus lithophilus is a small catfish species endemic to Lake Biwa, central Japan, inhabiting rocky and gravel slopes of the lake. It is consumed locally, but it is classed as a near-threatened species in the Japanese Red Data Book.

Common length is 20-25 cm, and the max. size is 58 cm and 1,5 kg.

Some aspects of the reproductive ecology were investigated from April to July in 1989–1994. Field observations were conducted at a rocky shoal, which was also a spawning ground of S. biwaensis, along the shore of the Seta River, the lake’s outlet.

Spawning of S. lithophilus occurred around midnight at shallow, rocky places on the shoal (5–70 cm in water depth) from early May to mid-July, starting earlier than S. biwaensis (mid-May to mid-July). Spawning tended to occur at low water temperatures irrespective of high-water events, unlike S. biwaensis, and in low densities (fewer than 8 fish per night) compared to S. biwaensis (1–45 fish per night). Although the rock catfish tended to appear and spawn at higher frequencies on nights when S. biwaensis spawned or appeared, it always avoided conflict with the latter species by spawning at sites far from those used by S. biwaensis or after S. biwaensis had left the vicinity. The survival of eggs of S. lithophilus might be favored by a strategy of diverting predator attention from them by synchronizing spawning nights with S. biwaensis.