Growth Patterns, and Age and Size at Maturity in Female Cottus hangiongensis, with Special Reference to Their Life-History Variation

Abstract

Growth patterns of the 1982 year-class, individual growth patterns, age and size at sexual maturity and longevity in females of the river-sculpin,Cottus hangiongensis (Cottidae), were examined along the course of the Daitobetsu River of southern Hokkaido, Japan. Growth of females slightly varied both along the river course and among individual fishes: slow growth occurs in females from the lower reaches, while more rapid growth occurs in females from upstream areas. Body size and age at the first sexual maturity of females slightly increased towards the upstream, from 52 mm SL and 2 years in the most downstream area to 72 mm SL and 2–3 years in the uppermost site. Longevity was estimated to be 7 years in the downstream areas and 8–9 years in the upstream sites. These results suggest that female life history varies along the course of the river and thus allow us to consider the following alternative reproductive tactics: when females stay in the lower reaches, they attain sexual maturity at a smaller body size and younger age, and have a small clutch size, but when females migrate into the upper reaches, their maturity is delayed until they reach a larger body size and older age, and have a greater clutch size.