noun
Biwa trout; Biwa salmon
A subspecies of masu salmon endemic to Lake Biwa in Shiga Prefecture, Japan. Often treated as a regional delicacy.
ビワマスは琵琶湖だけに生息する固有種です。
The Biwa trout is an endemic species found only in Lake Biwa.
春になるとビワマス漁が解禁されます。
Fishing for Biwa trout opens in spring.
From 琵琶 (Biwa, referring to Lake Biwa) + 鱒 (masu, trout/salmon). The exact derivation is straightforward; the name reflects its habitat.