: Egg cases with early-middle staged embryos of the oval squid Aka-ika, Sepioteuthis sp. 1, that were spawned on an anemometer set in the deeper layers of the coastal waters of the Ryukyu Archipelago, were collected in 2013, 2016, and 2017. However, of these only the egg cases collected in 2016 were used in this study as they had been kept in stressful conditions; packed without seawater and kept in a refrigerator at 8 ° C for approximately 25 h immediately after collection and were then raised under normal captive conditions in the laboratory in order to examine the effects that exposure to low temperature and oxygen levels had on later embryonic development, hatching, and hatched juveniles. We also investigated the overall feasibility of aquaculture of this species. Embryonic development proceeded followed by hatching, and the hatched juveniles survived for over 4 months. These records were compared to the survival and growth of Aka-ika Sepioteuthis juveniles not exposed to stressful conditions during their embryonic development that hatched from egg cases spawned on an artificial spawning bed set in the coastal waters of the Ryukyu Archipelago in 2016. This comparison revealed that Aka-ika Sepioteuthis embryos can develop, hatch, survive, and grow normally, even under severe stress conditions during early-middle embryonic development. This suggests that the gelatinous coat of the egg case in cephalopods might function as barrier against changeable environments during the early life phase.
Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are synthesized in the pituitary gland and play important roles in reproduction in teleosts. In this study, the pituitary structure, the immune signals of FSHβ subunit (FSHβ) and LHβ subunit (LHβ), and the localization of these hormones in the pituitary were investigated using four species of grouper. The pituitary in each species consists of the neurohypophysis (NH) and adenohypophysis (AH). The AH is further divided into the rostral pars distalis (RPD), the proximal pars distalis (PPD), and the pars intermedia (PI). FSHβ and LHβ immune signals were detected in the PPD and PI areas in the areolate, red spotted, and honeycomb groupers. However, in the longtooth grouper, although FSHβ signals were detected in the PPD and PI areas, LHβ signals were only detected in the PPD area. These results indicate that FSHβ and LHβ expression in the pituitary differs among grouper species with the same pituitary structure, suggesting that the roles of both hormones may be different between species.
: Rearing experiments under controlled environmental conditions further our understanding of the population dynamics of walleye pollock Gadus chalcogrammus by supplementing the biological information collected in field surveys. However, walleye pollock rearing techniques, from eggs to juveniles, still require improvement. In the present study, we investigated the effects of taurine enrichment of early live food on the survival and growth of walleye pollock larvae. Larvae were fed with unenriched (control) and taurine-enriched rotifers (taurine supplementation: 400 mg/ml) from the first feeding until 22 or 23 days post hatching (DPH) in Experiment 1, and with unenriched (control) and taurine-enriched rotifers and Artemia nauplii (taurine supplementation: 800 mg/ml) until 55 DPH in Experiment 2. In both experiments, the survival and growth of the larvae reared on taurine-enriched food were improved, when compared with the control larvae. The growth rates and taurine content of the supplemented larvae were comparable to those of wild-caught larvae. Our findings suggested that taurine enrichment of early live food effectively improved the rearing performance of walleye pollock larvae. Such improvements may facilitate the supply of experimental fish for future laboratory studies on the biological characteristics of the larval and juvenile stages of this species.
