Diurnal maturation rhythm, spawning frequency and fecundity of Diaphus fulgens (Teleostei: Myctophidae) in the Kuroshio waters of the East China Sea

Abstract

Diaphus fulgens is a diel vertical migrating myctophid, and it is the dominant Diaphus species in the Kuroshio waters of the East China Sea. The diurnal maturation rhythm, spawning frequency, and fecundity of this species were examined based on individuals (24.3–43.1 mm standard length) collected in different periods of the day during the primary spawning season of late winter. Based on ovarian histological analysis, the nucleus migration occurred during the nighttime to the following early morning, and hydration occurred during the daytime in the mesopelagic layer. The appearance of late stage hydrated oocytes and early stage post-ovulatory follicles showed that D. fulgens actively spawned shortly after sunset during 2000–2100 h. This species is concluded to migrate vertically with the eggs to the epipelagic layer during twilight, although the possibility of spawning in the mesopelagic layer before reaching the epipelagic layer can not be ruled out. Darkening after sunset would potentially work as the triggering mechanism for spawning behavior. Based on the diurnal maturation rhythm, estimation methods of the spawning frequency and batch fecundity were confirmed for myctophids. Diaphus fulgens is a multiple batch spawner with a short interspawn period of 2.2–4.0 days. Mean batch fecundity (± standard deviation) was 399 ± 102 eggs, and the lifetime egg production per female was estimated to be 3000–5400 eggs. The high potential of egg production would contribute to the recruitment of sufficient numbers to maintain populations.