Reproduction, growth and vertical distribution of the meso- and bathypelagic fish Cyclothone atraria (Pisces: Gonostomatidae) in Sagami Bay, Central Japan

Abstract

The life history and vertical distribution of the meso- and bathypelagic fish Cyclothone atraria (family Gonostomatidae) are described on the basis of about 9800 specimens taken during a series of 20 cruises from December 1982 to November 1985 at a station near the center of Sagami Bay, Central Japan. C. atraria does not undertake overall diel vertical migrations, being concentrated in the lower mesopelagic and bathypelagic zones below 400 m, with peak abundance at about 600 m both day and night. Spawning occurs mainly during the summer and early autumn. C. atraria releases about 500–3000 eggs at once and may spawn several times during its life span. Duration of the egg and larval stages is estimated to be about 6–7 months. C. atraria is protandrous, attaining male maturation in 3 years at about 25 mm standard length (SL) and attaining female maturation in 5–6 years at about 40 mm SL. Length-frequency analysis demonstrated that modal progressions could be followed until about 55 mm SL; however, no length mode that increases with time was observed at 30–35 mm SL, which corresponds to the size of sex reversal. Such modal indistinctness results from rapid growth of individual fishes set free from male breeding activity during protracted spawning season.