Gonadal maturation of largemouth Bass Micropterus salmoides in Lakes Shorenji and Nishinoko, Central Japan

Abstract

Gonadal maturations of the largemouth bass collected from Lakes Shorenji (typical reservoir) and Nishinoko (typical swamp) were histologically analyzed. The age and the minimum size at first maturation in both lakes and both sexes were estimated as 2-year-old and about 230 mm SL, respectively. Although their spawning periods were estimated as being from late April to late June in Lake Shorenji and from mid-April to mid-May in Lake Nishinoko, well-developed yolked oocytes were found in the ovaries of the fish from both lakes from late fall to early summer. The peaks of spermatogenesis occurred in spring and fall, male gonadosomatic indices indicating high values in winter. These reproductive cycles of largemouth bass, which started to develop from fall, extended their spawning period and May have been an important factor of naturalization of the species into various environments in Japanese inland waters.