愛媛県今治周辺におけるシマウシノシタZebrias zebraの生活サイクル

瀬戸内海における沿岸性底棲魚シマウシノシタの成熟と産卵を中心とした生活サイクルについて, 愛媛県今治市沿岸周辺海域で1999年7月から2001年11月までの間に漁獲された296尾を用いて調べた。採集個体の体長(BL)は, それぞれ雄が101-236mm(128尾), 雌が102-301㎜(168尾)で, 雌に大型個体が多く出現しており, 雌が大型化する性的差異が示唆された。本種の生物学的最小形についても雄が125㎜, 雌が175㎜と雌が大きかった。成魚の生殖腺重量指数(GSI)・肝臓重量指数(HSI)・肥満度(CF)から, 産卵期が6-8月, 産卵期に伴う産卵準備期, 回復期がそれぞれ5-6月, 8-9月, 越冬準備期は10-12月, 越冬期が1-3月という生活サイクルを推定した。本種の産卵期における卵巣からは, 単峰の卵径組成が確認された。本種の産卵は, その単峰の卵団が卵径0.7㎜以上の大型卵団となり, 卵巣における大型卵団の占有率が90%ほどに達した後, 複数回に分けて放卵されるものと判断された。抱卵数は1個体あたり3-15万個であり, 体長と抱卵数(F)に正の相関関係が認められた:F=3.23×10-5BL3.94, r;0.884。

The annual life cycle of adult Z. zebra, a heterosomata fish in Seto Inland Sea, mainly focused on maturity and spawning was examined by 296 samples caught in the nearshore waters around Imabari from July 1999 to November 2001. Body lengths of samples were 101-236mm in males (128 fish) and 102-301mm in females (168 fish), which data suggested female has a tendency to grow bigger than male. The biological minimum size, 125mm of male and 175mm of female, also indicated the inclination. Judging from the gonadsomatic index (GSI), hepatosomatic index (HSI), and condition factor (CF) of adult fish, the annual life cycle of this species was calculated as follows: spawning season is from June to August, pre-spawning season and recovering season from spawning are from May to June and from August to September, respectively, pre-wintering season is from October to December and wintering season is from January to March. One modes in frequency distributions of egg diameter was found from the ovaries of samples during spawning season. It was estimated that the spawning of this species is performed by spawning their eggs some times after the mass of eggs indicated by one mode in frequency distribution of egg diameter becomes a mass of large-sized egg more than 0.7mm in egg diameter and the rate of the mass in the ovary reaches around 90%. The fecundity of this species was from thirty thousand to fifteen hundred thousand per individual, and there was a plus correlation of body length (BL) with fecundity (F) : F = 3.23 × 10-5 BL3.94, r; 0.884.