Reproductive Cycle and Body Size and Age at Maturity of the Hexagrammid Fish Hexagrammos agrammus in Central Japan

Abstract

Reproductive cycle, maturation mode, and body size and age at maturity of the hexagrammid fish, Hexagrammos agrammus, at Aburatsubo in central Japan were examined by analyzing the seasonal trends in gonadosomatic index (GSI) and gonadal maturity as revealed by histological observations. Gonads were assigned to the following 5 phases of maturity: (0) immature phase, (I) maturing phase, (II) early spawning phase, (III) late spawning phase, and (IV) recovery phase, based on conditions of the most developed oocytes and the presence of empty follicles or atretic oocytes for females, and on the presence and the amount of spermatocytes or sperm for males. Females appeared to be multiple spawners, i.e., spawning more than once in a spawning season, judging from the coexistence of oocytes at the pre-mature stage and empty follicles in mature ovaries. Spawning, corresponding to maturity phases II and III, occurred from late November to late January. All females aged 1 + and older matured. Smaller 0 + females less than 105 mm in standard length (SL) did not spawn within the current spawning season, but larger fish (≥105mmSL) spawned in the season. Testes of all males were ripe at age 0+ (≥88mmSL), but the first egg-guarding age was 1 + (121 mmSL). © 1995, The Japanese Society of Fisheries Science. All rights reserved.