Life history and reproductive ecology of the endangered Itasenpara bitterling Acheilognathus longipinnis (Cyprinidae) in the Himi region, central Japan

Reproductive ecology and adaptive host choice correlated with body size in an autumn-spawning bitterling Acheilognathus typus

The life history and reproductive ecology of an autumn-spawning bitterling Acheilognathus typus were studied under natural and experimental conditions. In the study pond, the embryos of A. typus emerged from mussels in May and grew rapidly until August, whereas overwintered age-1 fish grew slowly. Adult A. typus in the pond was smaller (32-47 mm in standard length) than they were in other habitats and mainly spawned in smaller mussels. The number of A. typus embryos in mussels was negatively correlated with the shell length of the mussel, and a lower number of embryos were observed in larger mussels (over 110 mm in shell length). In the mussel size-choice experiment conducted in an enclosure, smaller A. typus selected smaller mussels, and larger A. typus selected larger mussels for spawning. In some cases, smaller A. typus spawned in larger mussels and the number of spawned eggs ejected increased by over four times compared with other cases. These results of the enclosure experiment explained the lower number of embryos in larger mussels in the study pond. In addition, reproductive traits such as ovipositor length and the number of ovulated eggs of female A. typus, which are considered to contribute to their size-dependent host utilization, were positively correlated with their standard length. Because A. typus is geologically or seasonally isolated from other bitterling species, this size-dependent host utilization contributes to a reduction in intraspecies rather than interspecies competition.

Life history of the endangered Japanese striped loach, Cobitis kaibarai (Cypriniformes: Cobitidae), with special reference to its reproductive ecology and the influence of creek reshapings on its population density

In recent years, the biodiversity of freshwater fishes has been markedly decreasing worldwide because of anthropogenic activities. The Japanese striped loach, Cobitis kaibarai (Cypriniformes: Cobitidae), is a primary freshwater fish endemic to northern Kyushu, Japan. This species is designated as endangered IB class in the Red List by the Japan Ministry of the Environment. Its population is decreasing, possibly because of habitat loss and degradation. To conserve C. kaibarai populations, information on its basic ecology is necessary; nonetheless, its detailed life history and reproductive ecology have yet to be clarified. In this study, the authors conducted monthly capture-mark-recapture surveys and periodical observations to investigate the life history, spawning sites and season of C. kaibarai. They also evaluated the influence of creek reshaping (concrete revetment) on the C. kaibarai population in Saga Plain, northern Kyushu. Between 2015 and 2018, more individuals were captured during winter than summer. The average body width of females peaked in early June and small immatures were confirmed from July. Some individuals were captured across 15 or more months after their initial marking. In the survey of reproductive sites, eggs and larvae of C. kaibarai were found in shallow areas in mid-June; these were temporarily submerged following the increase in water level from early June. Therefore, C. kaibarai spawns in shallow areas during this season. Based on the capture-mark-recapture surveys, the estimated population density of C. kaibarai significantly decreased in a census site that had undergone creek reshaping, which contrasted with the results in a control site, where no significant difference was detected. The standard length of C. kaibarai increased following creek reshaping, suggesting that the proportion of C. kaibarai postponing spawning had increased, possibly because of degradation of spawning environments. The results of this study provide important ecological knowledge for the conservation of C. kaibarai and emphasize the importance of shallow waters for floodplain spawners.

Fine-scale genetic structure of the endangered bitterling in the middle river basin of the Kiso River, Japan

Recently, anthropogenic alterations have had severe and negative impacts on the terrestrial and aquatic species and environments. To conserve species that have a small and limited habitat, it is necessary to focus on fine-scale population structure and its effects on persistence. The deepbodied bitterling Acheilognathus longipinnis is an endangered freshwater fish that occupies ponds scattered in lateral bars in the Kiso River. In this study, we conducted multi-locus microsatellite DNA analysis to evaluate both fine-scale population structure and genetic diversity, in order to conserve A. longipinnis. The smaller number of loci deviating from the Hardy-Weinberg equilibrium in ponds scattered in individual lateral bars compared to the whole river system suggests that A. longipinnis forms a local breeding population in units of ponds. The population was roughly split between the river banks and the local population located in ponds in the mid-channel bar showed intermediate relationships with the river bank populations. Gene flow between local populations was not always homogeneous and was not influenced by geographical distances between local populations or the direction of river flow. The dispersal of A. longipinnis across both river bank sides may be constrained and is probably affected by the ecological characteristics of A. longipinnis and the hydrological regimes. Consequently, A. longipinnis in the Kiso River is maintained as a complex of multiple local populations with appropriate gene flow among them. To conserve A. longipinnis, both the persistence of the unstable ponds and moderate genetic exchanges by individual migration are required.

Mitochondrial genotyping of an endangered bitterling Acheilognathus typus (Cyprinidae)

Genotyping of endangered species is helpful for establishing and evaluating conservation strategies. Mitochondrial sequence data was analyzed from 541 individuals of a critically endangered fish, Acheilognathustypus from present-day range-wide localities to re-evaluate an in-progress restoration program around Lake Izunuma-Uchinuma, Miyagi, Japan. Acheilognathustypus showed low sequence diversity with only eight haplotypes and π and ĥ values of 0.59129 and 0.00118 respectively. Genetic data suggests Acheilognathustypus is adapted to pulsed environments and prone to population flush and crash. Genotyping of populations in introduced localities revealed that their source is not from nearby localities.