Diet composition, diel feeding periodicity and daily ration of mature adult Diaphus fulgens (Teleostei: Myctophidae) in the Kuroshio waters

Abstract Diaphus fulgens is a diel vertical migrant myctophid, occurring abundantly in the Kuroshio waters of the East China Sea. They are multiple batch spawners with a short interspawn period, resulting in high egg productivity. Multiple spawning would be supported by feeding during their spawning season; however, there is no information on the feeding habits of this species. The present study examined the diet composition, diel feeding periodicity and daily ration of mature adult D. fulgens collected at different periods of the day during February to March. The most prevalent item was appendicularians and their mucus houses, which dominated the stomach contents in both number and weight. Additionally, various species of copepods were predated, with a prevalence, by weight, of the large-sized Pleuromamma piseki. Diaphus fulgens feeds actively in the epipelagic layer at night and moves down to the mesopelagic layer in the early morning, and digests most of the consumed food by the late afternoon, showing a typical nocturnal feeding pattern. Based on diel changes in the stomach content index and instantaneous gastric evacuation rate estimated in this study (0.118–0.129 h−1), the daily ration was calculated to be 4.0–4.2% of body weight, equivalent to a daily caloric intake of 21.2–22.3 cal day−1. Since the caloric value to produce a batch of oocytes was estimated to be 8.2–11.5 cal day−1, on an energetic basis, D. fulgens can maintain the multiple spawning at a cost of approximately 37–54% of its daily caloric intake.