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Sexual reproduction data are important to understand how organisms can replenish their populations and proliferate on coral reefs. Despite the importance of such data, the reproductive characteristics of most soft coral species are still unknown. Here, we examined the reproductive strategies of a species from the often‐dominant genus Sclerophytum in a coral reef on subtropical Okinawa Island, Japan. DNA barcoding and histological examinations of the tissues were conducted to confirm colony conspecificity and identify reproductive characteristics, respectively, between March 2020 and March 2021. Results indicated that the studied species, identified as Sclerophytum cf. heterospiculatum, exhibits gonochorism with longer oogenesis and shorter spermatogenesis. Female colonies produced immature oocytes throughout the year, with mature oocytes observed from late July to early September, and thus, extended spawning is likely characteristic of this species. In male colonies, spermatogenesis took place over ~5 months, with spermaries present from April through August. Mature spermaries were noted beginning in July and the inferred peak of sperm release was between late August and early September, which suggests that spermatogenesis duration was ~5 months. The largest mean oocyte and spermary sizes (628.45 ± 61.36 and 240.04 ± 49.49 μm, respectively) were both recorded in August. Gamete spawning presumably occurred during the summer season, which suggests seasonality in reproduction as influenced by changes in seawater temperature. However, the proximate cue for exact dates of spawning could be the lunar period because the inferred release of spawning materials seemed to occur between full moon and last‐quarter moon phases in both the months of August and September. The results of this study represent the first detailed report of reproductive characteristics of the genus Sclerophytum in Japan. [ABSTRACT FROM AUTHOR]

The reproduction and early growth of fish are essential elements that affect recruitment and provide breakthrough points for understanding population fluctuations. In this study, larval and juvenile Japanese anchovy (Engraulis japonicus) were collected from five coastal waters off the Pacific coast of Japan in 2020 and 2021 to gain more insight into life history traits such as reproduction and early growth of this species on the basis of otolith microstructure analysis. The spawning period appeared to be related to temperature and chlorophyll-a concentrations, showing latitudinal gradient variation among fishing areas. We detected a significant positive allometric growth pattern between standard length and body weight. The Gompertz model best fits the growth of standard length, showing an initial stage of growth that was quick and accelerating. The mean daily growth rate for standard length was 0.64 ± 0.09 mm per day. A series of mixed-effect models was constructed to investigate the sources of differences in the mean growth rates among individuals. The results revealed regional variability in fish growth, with individuals in the central Pacific stock growing faster. Individuals that grew slower were heavier than those of the same length, indicating a trade-off between length growth and weight growth. The mean growth of individual fish was positively influenced by environmental factors (surface water temperature and chlorophyll-a concentration), and individuals within the same school of fish displayed a striking homogeneity of growth. Our research demonstrates the significance of including both physiological characteristics and environmental influences in early growth studies on fish. [ABSTRACT FROM AUTHOR]

Changes in the proportions of river‐ and lake‐produced eggs of a landlocked amphidromous fish, ayu (Plecoglossus altivelis altivelis) in the Lake Biwa water system, Japan, were monitored by stable isotope analysis, based on different δ15N and δ13C values of prey organisms between the lake and its tributaries. During the 3 month reproduction season, the δ15N values of spawned eggs decreased with time. This result implies that there was a shift from lake‐produced eggs to river‐produced eggs within a reproductive season, based on the observation that adult fish in the lake had previously been shown to have eggs with distinctly higher δ15N values in their ovaries than those in the tributaries. This explanation was also supported by the change in δ13C values of the spawned eggs. Furthermore, eggs with lower δ15N and higher δ13C values tended to be spawned at less variable depths, suggesting that females spawning river‐produced eggs selected the spawning sites from a narrower range. We conclude that stable isotope ratios of spawned eggs can be indicators of the relative contributions of different food chains and can enable comparisons of reproductive characteristics between types of egg. [ABSTRACT FROM AUTHOR]

The humpback red snapper Lutjanus gibbus (Lutjanidae) is an important species for fisheries in the Kagoshima and Okinawan region of Japan. The present study estimated the age, growth and reproduction of this lutjanid species in the waters around Ishigaki Island, southern part of Okinawa. An opaque zone was formed on the otolith every year, and this formation correlated with their spawning season; these zones were identified as annual rings. Maximum ages of 21 and 24 years were observed for males and females, respectively. The von Bertalanffy growth parameters clarifying the age–fork length relationship were as follows: L∞ = 390.5 mm, K = 0.210 year−1 and t0 = −1.88 year for males, and L∞ = 303.4, K = 0.256 year−1 and t0 = −3.05 year for females. The main spawning season was estimated as between May and October, since greater values of gonadosomatic index for females as well as maturation oocytes and/or postovulatory follicles were observed during those six months. [ABSTRACT FROM AUTHOR]

The checkered snapper, Lutjanus decussatus, is an important species for fisheries in the Okinawan region. This study estimated the reproduction of this lutjanid species in the waters around Ishigaki Island. The main spawning season was estimated to be between June and October, since oocytes at the maturation stage and/or postovulatory follicles were found during the study period. In the main spawning season, high gonadosomatic index values were found around the time of the last quarter moon for each month from June to September. It is suggested that L. decussatus is a lunar-synchronized spawner off Ishigaki Island. [ABSTRACT FROM AUTHOR]