To advance breeding techniques for freshwater pufferfishes, Pao abei, P. baileyi and P. suvattii reproduction in captivity was undertaken, and compared with published reproductive characteristics of P. cochinchinensis, P. palembangensis and P. turgidus. All six species breed in freshwater under stable water temperature (25-27°C) and lighting (L12D12) conditions, with an acceptable spawning bed, such as an earthenware pipe or sunken driftwood with a flat surface suitable for establishing and guarding eggs in a single layer. A pair of individuals of each species spawned a number of times over two to seven month periods, a single egg batch containing hundreds of 2 or 3 mm diameter eggs. Hatching occurred in 7-10 days, larvae initially being fed with Artemia larvae. The data collected should contribute to successful breeding of the genus in captivity.

The blacktip grouper Epinephelus fasciatus is a commercially important food fish in several Asian countries, including Japan. In this study, we investigated the reproductive cycle and changes in 17β-estradiol (E₂) in blacktip grouper reared under photothermal conditions during a one-year period from July 2018. In addition, the effects of water temperature and photoperiod on induction of gonadal development and maturation were investigated using artificial photothermal manipulation (an increase in water temperature from 18°C to 26°C and a 14 h light/day photoperiod treatment). In the reproductive cycle experiment, primary yolk (Py) and tertiary yolk (Ty) stage fish were observed in May at approximately 20°C, followed by the appearance of ripe (R) stage fish in July at approximately 25°C, with a photoperiod of approximately 14 h light/day. Plasma E₂ levels were high in Ty stage fish during these periods. In the artificial photothermal manipulation experiment, Py, secondary yolk (Sy) stage fish were first observed after 2.5 months, and Ty stage fish appeared 4.5 months after the photothermal manipulation was initiated. Plasma E₂ levels were high in Sy and Ty stage fish at 26°C. These results suggested that gonadal development is affected by environmental factors.

In this study, we examined changes in the specific gravity of Pacific bluefin tuna (PBT) eggs inferred from neutral buoyancy salinity during embryo development. The specific gravity of PBT eggs was approximately constant at 27.0-28.5 PSU from the four-cell stage to the beginning of the heartbeat at 24.0 °C. However, the specific gravity sharply increased to the maximum level (35.8 PSU) just before hatching, exceeding that of rearing seawater (34.8 PSU). These results suggest that providing adequate levels of aeration and water circulation is necessary to prevent egg death caused by sinking. To determine suitable aeration rates for egg incubation, we further examined the effects of different aeration rates (0.0-2.0 l/min) on hatching and survival of 0.1 million eggs incubated in nylon net (volume: 200 l). The optimal aeration rates required to be adjusted to 0.3-0.9 l/min to maximize larval hatching and reduce abnormalities. Aeration rates > 1.2 l/min decreased the percentage of hatching eggs and increased the percentage of hatched larvae with skin injuries, suggesting that high aeration rates would cause the death of hatched larvae by physical contact with each other or the net walls.

A multiplex PCR for genetic sexing of salmonid fishes was developed. With newly designed universal primers for the master sex-determining sdY gene and 18S rRNA as a positive control, the genetic sex of three major farmed salmonid species in Japan, Oncorhynchus mykiss, O. masou ishikawae, and Salvelinus leucomaenis, were successfully identified using the same procedure. In addition, the developed method was applied for the genetic sexing of pseudomales of O. mykiss and O. masou ishikawae, as well as for triploids of O. mykiss. The results demonstrated that the PCR reliably discriminated the genetic sex of these species irrespective of the used target tissues, their functional sex, and ploidy. Further, incorporating crude extraction of DNA from fin, blood, and semen, the developed method enabled a quick and low-cost sex assessment compared to the previously reported methods. These results indicated that the newly developed sex identification PCR has high applicability and versatility in the aquaculture field targeting various salmonid species farmed in Japan, including their triploid hybrids.

The age and growth of hatsume Sebastes owstoni in the Sea of Japan off the Tango Peninsula, Kyoto Prefecture, were examined using cross-sectioned otoliths. An examination of the otolith margins showed that ring marks were formed once a year. Ages were determined based on the number of ring marks, and the maximum ages were inferred to be 10.50 and 7.83 years for females and males, respectively. The von Bertalanffy growth curves for standard length (SL) (L_t) at full age (t) were as follows: L_t = 223 {1 - exp [-0.26 (t + 0.23)]} for females and L_t = 166 {1 - exp [-0.40 (t + 0.09)]} for males. The difference in the SL between the sexes was small (≤ 5 mm) until 2 years of age; however, the SL in females was 9 mm greater than that in males at 3 years of age, and the difference in the SL between the sexes increased gradually with age. Our results provide, for the first time, biological traits such as age and growth for both resource evaluation and stock management of S. owstoni.

We examined the ability of a feeding of sugarcane bagasse extract (SBE) diet to accelerate the somatic growth of rainbow trout Oncorhynchus mykiss and char Salvelinus leucomaenis. Feeding with diets containing 100 mg, 500 mg, and 1,000 mg/kg SBE to rainbow trout resulted in a significant increase of both fork length and body weight in comparison to the control. Similar growth promoting effects of the SBE diet were also observed in char. Higher growth hormone (GH) levels in the pituitary and insulin-like growth factor-I (IGF-I) mRNA levels in the liver were observed in fish fed the SBE diet. These results suggest that a feeding with SBE diet may enhance the expression of GH and IGF-I mRNA, and subsequently improved the somatic growth of rainbow trout and char.

The diurnal change in photochemical efficiency of a seagrass, Enhalus acoroides was determined in Okinawa, Japan. The measurements under incident sunlight were conducted from sunrise through sunset using a submersible pulse amplitude modulation (PAM)-chlorophyll fluorometer (Diving-PAM). The effective quantum yield (ΔF/F_m’) declined with increasing incident sunlight in the morning, with a ΔF/F_m’ minima occurring during noon-time. Thereafter, the ΔF/F_m’ gradually recovered during the afternoon incident sunlight decreased, indicating a dynamic negative response to the excess sunlight. The decline of ΔF/F_m’ in the habitat is likely a photoprotective response to protect the photosynthetic reaction center from damage by excess light energy.

The present study aimed to provide accurate information on maturation and spawning season of green tiger prawn Penaeus semisulcatus in the Kii Channel based on ovarian histological observations. The observation showed that vitellogenesis began in April and ended in August. Based on the occurrence of cortical crypts (ripe oocyte), the spawning season of green tiger prawn lasted from June to August with the peak spawning of July in the Kii Channel.

This study aimed to evaluate the impact of the presence of probiotic Lactococcus lactis subsp. lactis strain K-C2 on the release of free amino acids from aquafeeds and gut microbiota in amberjack, Seriola dumerili and common carp, Cyprinus carpio. The addition of strain K-C2 to feeds significantly promoted the release of free amino acids within 3 h. The single feeding of feeds containing strain K-C2 changed predominant bacterial flora in the amberjack gut. This study showed that strain K-C2 promoted the release of free amino acids in a short time, and the microbiota in the amberjack gut was changed by a single feeding with strain K-C2.

The small benthic octopus Amphioctopus fangsiao is one of important cephalopod within coastal fisheries in Japan. To examine the growth and reproductive season of this cephalopod in the Seto Inland Sea, we reared thirteen wild-caught octopuses in individual tanks from September 2019 to July 2020, with individuals ranging from 15.0 to 57.0 g in body weight (BW). Except for one non-growing individual, the BW of the octopuses gradually increased from the start of the experiment until February, after which BW decreased greatly until the death. The growth rate gradually decreased with age and became negative after late March. Females laid eggs from February to April, with eggs hatching after 2-4 months. The males died mainly between May and June, whereas the females died in late July, after 2-4 weeks from the end of hatching period. The mean maximum BW (range) for females and males was 60.8 (46.0-70.0) g and 57.2 (28.0-77.0) g, respectively, and the mean final BW for females and males was 25.0 (12.0-36.0) g and 35.7 (17.0-49.0) g, respectively; these results indicate that the BW for females was greatly decreased compared to males.

The present study investigated the effect of various concentrations of ammonia and the number of additions on the acquisition of nitrification of new filter materials. Experiments were performed using ceramic filter materials 1,000 g in artificial seawater at 25°C. In the first experiment, ammonium chloride additions (total ammonia-nitrogen concentrations of 10, 40, 70, 100 and 130 mg-N/l) were conducted only once. In the second experiment, ammonia additions (total ammonia-nitrogen concentrations of 10, 20, 30 and 40 mg-N/l) were conducted once and then again when the total ammonia-nitrogen concentration reached 0 mg-N/l. After the additions, total ammonia- and nitrite-nitrogen were measured every seven days. We judged the success of acquisition of nitrification as when both ammonia- and nitrite-nitrogen were not detected within a 12 weeks period. Experiments in which ammonia was added only once under 20 mg-N/l succeeded in acquisition of nitrification. Other addition conditions might fail. Therefore, we propose ammonia addition only once 10 mg-N/l for acquisition of nitrification of new filter materials.