The migration, diet, condition factor and maturation of skipjack tuna Katsuwonus pelamis associated with surface fish aggregating devices (FADs) were examined on the coast of Wakayama, Japan. 126 fish were tagged and released with dart tags around the FADs, and 39 fish (31.0%) were recaptured along the Pacific coast of Japan. Among the 39 fish recaptured, 25 fish (64.1%) were recaptured around the FADs where they had been released, and the elapsed number of days between release and recapture was 10.9±8.3 (mean±standard deviation). Stomach contents analyses indicated that the percentage of fish with prey items in the stomach (feeding incidence) was 0-28.6% for each daily sample. Ovarian histological observations indicated that a total of 76.9% fish were in the immature phase, although those in the post-ovulated phase were also observed (5.5%). Accordingly, the results of the present study suggest that the area around the FADs is not necessarily a feeding ground for skipjack tuna, and that spawning is limited around the FADs, although the FADs showed fish aggregating effects.

　The stock of the Isaza goby Gymnogobius isaza is known to fluctuate greatly. Because initial recruitment is considered to have a high impact on stock fluctuations, it is important to understand the spatial distribution patterns of Isaza larvae. We conducted towing net surveys at variable depths to clarify the vertical distribution of the larvae. Preflexion Isaza larvae were distributed in the lower water temperature range (10-15℃) regardless of depth, whereas flexion larvae thereafter were distributed under the thermocline. Polyarthra spp. were confirmed as the initial food source of the larvae, in addition to copepod nauplii (previously reported). Flexion (and thereafter) larvae preyed mainly on Eodiaptomus japonicus. The study suggested that Isaza larvae change their feeding preference, associated with habitat change and ontogenetic development in feeding functions.

　The effect of temperature and light on the photosynthesis of seedlings of Zostera marina from the annual population in Kagoshima, Japan was determined by field and laboratory measurements using a pulse amplitude modulation (PAM)-chlorophyll fluorometer. The response of oxygenic photosynthesis to temperature (8-40℃) was also examined with dissolved oxygen sensors to compare with effective quantum yields (ΔF/F_m′) of photosystem II. The temperature response of ΔF/F_m′ under 50 μmol photons m⁻² s⁻¹ (12L12D photoperiod) and during five days of cultivation revealed that ΔF/F_m′ gradually increased to the optimal temperature at 23.1℃ (T_opt^ΔF/F_m′; 19.0-27.4℃), then quickly declined at higher temperatures. The 12-hour chronic combined effects of temperature and light at 8 and 20℃, under 200 and 1,000 μmol photons m⁻² s⁻¹ showed that the depression of ΔF/F_m′ was more pronounced under the low temperature with high light, indicating the occurrence of chronic low temperature-light stress. The temperature response of the oxygenic gross-photosynthesis curve indicated an optimal temperature at 31.0℃ (T_opt^GP; 28.4-33.2℃), then declined at higher temperatures. The underwater measurements of natural communities of Z. marina in Kagoshima showed that ΔF/F_m′ declined with increasing incident light, with a minimum occurring during noon to early afternoon. Nevertheless, ΔF/F_m′ recovered by sunset.

　Sex reversal from female to male in the six-year-old longtooth grouper Epinephelus bruneus (mean body weight, 3.1 kg) was induced by the implantation of 17-alpha-methyltestosterone (MT) cholesterol pellets. We compared the efficacy of the cholesterol pellets at MT doses of 1 mg/kg BW (group A) and 2 mg/kg BW (group B) implanted in February, as well as 2 mg/kg BW implanted in April (group C). At 4 months after the treatment, 67% of the fish in groups A and B had been transformed into males. On the other hand, all fish in group C had been transformed into males at 2 months after the treatment, and all group C fish remained male even at 14 months after the implantation. These results indicate that the implantation of MT cholesterol pellets at a MT dose of 2 mg/kg BW in April is an effective and long-lasting treatment for inducing sex reversal in the longtooth grouper.

　The effects of dietary yuzu peel powder (YP) on growth and lipid oxidation of Epinephelus akaara were examined. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) scavenging activity of methanol-dimethyl sulfoxide extract from YP was measured and the antioxidant compounds in the extract were identified by mass spectrometry. E. akaara was reared for 4 weeks and fed diets with and without 3% YP (test and control). Thereafter, the plasma biochemical markers and thiobarbituric acid reactive substance (TBARS) levels in the liver and meat homogenates were measured. The antioxidant compounds identified in YP included narirutin, naringin, hesperidin, and neohesperidin; hesperidin contributed the most to YP antioxidant activity. The diet containing YP had no effect on the diet amount and fish weight; however, TBARS levels in the plasma and liver homogenates were lower than those in the control group. No significant difference was observed in the TBARS levels of fresh meat between the test and control groups, whereas the TBARS level in the meat of the test group stored at 4℃ for 24 h was substantially lower than that in the control group. These results indicate that a diet containing YP does not affect the growth of E. akaara but suppresses lipid oxidation of fish meat during storage.

　The effects of sodium chloride treatment for 15 min, dehydration using food dehydration sheets, and aging period on pH, drip loss, and the amount of taste-related compounds in meat of the red sea bream Pagrus major were examined during aging at 0℃ for 14 days. Changes in the extraction rate were investigated by the proportion of the total amount of adenosine 5′-triphosphate (ATP)-related compounds extracted using a paddle blender, which was used as an alternative to chewing, and a tapered tissue grinder. The use of a dehydration sheet decreased the extractability of ATP-related compounds from the meat. In addition, sodium chloride treatment increased the drip loss and decreased the extractability of ATP-related compounds in the meat. The inosine 5′-monophosphate (IMP) content increased until the first day of aging and decreased from the third day of aging. However, the glutamic acid (Glu) content increased until the 14th day of aging. The umami intensity, which is obtained from IMP and Glu, did not reach its peak on the first day of aging; however, it achieved a high value at least by the fifth day of aging.

　The validity of an immunochromatographic test kit for tetrodotoxin (TTX) was examined. In the tests using the TTX certified standard, a strong negative correlation (r=−0.9658) was observed between the logarithm of TTX concentration and the intensity ratio of C- and T-lines (T/C) formed on the test plate in the final TTX concentration range of 0.0125-0.2 mouse unit (MU)/mL. When the intensity of the T-line was visually determined on a 5-level scale (++ > + > w+ > vw+ > −), with ++ and +(T/C > 0.4) as TTX negative and w+, vw+, and −(T/C < 0.4) as TTX positive, the presence/absence of TTX could be judged with a final concentration of ～0.06 MU/mL as the detection limit. Matrix effects were examined using non-toxic cultured pufferfish tissues, indicating that ultrafiltration and/or 5-fold dilution can reduce the matrix-induced decrease in T/C to a low level. A comparison of liquid chromatography-tandem mass spectrometry and TTX detection kit results using the toxic wild pufferfish livers showed that the kit produced false positives by about 20％, but no false negatives were observed at all. In conclusion, this TTX test kit is useful as a primary screening method for TTX.

　In Japan, the utilization of advanced technologies such as information and communication technology (ICT) and the Internet of Things (IoT) in fisheries has been promoted since the 2010s. However, the dissemination of these innovative technologies to the fishery industry has not progressed smoothly. In this study, we used the example of “Ubiquitous Navi,” a pilot technology introduced in Rebun, Hokkaido, to examine the actual situation and promote its dissemination. From a questionnaire survey and interviews with fishermen, we found that dissemination of this technology has stagnated mainly due to low awareness and low perception of its benefits. This study suggests that it is important to make fishermen aware of the existence and advantages of innovative technology to promote its dissemination. Technical development and improvement are important for achieving “smart fisheries” but it is also crucial to inform the existence of new technology and its advantages for fishermen.