The aetideid copepod Bradyidius angustus was originally described 67 years ago based on two males collected from the Pacific coast of central Japan. This species has been the only one with the female unknown in the genus. Based on specimens from the Seto Inland Sea, Japan, this study describes the female of B. angustus for the first time, together with a complementary description of the male and a brief description of the later copepodids. The female has no seta on the medial margin of the exopod terminal segment of the antenna, which is a unique character within the genus. The distinction of the female from the currently known 18 congeners is also possible by a combination of a body length less than 2.0 mm and ornamentation on the legs, the antenna exopod or the mandible basis. The male is distinct from all congeners with regards to leg 5, the ornamentation of the endopod of legs 3 and 4, or the rostrum. The male specimens have some minor differences from the figures of the original description. The later copepodids (CIV and CV) have a stockier prosome than the adult, but are similar to the adult in some easily observable morphologies, by which they could be possibly identified to the species. This species is considered to be an epipelagic form. Discussion is also made on a past description of B. armatus from Japan.
The spatial and temporal patterns of marine diversity are essential for the sustainable use of fishery resources and the effective management and conservation of marine ecosystems. We investigated the latitudinal diversity gradients of fish genera in Japanese waters using an environmental DNA (eDNA) data. A total of 1,765 environmental DNA surveys across Japan were obtained from the All Nippon eDNA Monitoring Network (ANEMONE) database. We found a negative correlation between fish genus richness and latitude, with a particularly pronounced gradient in summer. Seasonal change in the latitudinal gradient may reflect the increased occurrence of vagrant fish from tropical regions, rather than the commonly assumed pattern of seasonal migration (i.e., southwards in winter and northwards in summer). Furthermore, our results suggests that global warming may lead to a temporary increase in biodiversity by promoting the influx of tropical vagrant fish. However, such increases are unlikely sustainable, as these vagrant species may not establish long-term populations. We refer to this phenomenon as “pseudo biodiversity”, which may give the illusion of increase in biodiversity enhancement in short-term monitoring. This concept warrants attention as similar patterns of apparent biodiversity increase may occur under other circumstances as well.
We tested the use of a light trap to catch larval and juvenile non-native fish (largemouth bass, smallmouth bass, and bluegill) in lakes, reservoirs, and rivers at nine sites across four prefectures in Japan. A total of 18,409 individuals were captured in light traps lit with blue LEDs, with a trend towards capturing higher numbers of individuals in the early larval stages. The non-native fish were also captured in environments with a water clarity of <100 cm, confirming that light traps could be used to remove them even from muddy lakes. This method enabled the previously difficult capture of larval and juvenile non-native fish to be carried out effectively with little effort. However, it is necessary to consider the location and timing of installing traps to minimize bycatch.
