The distribution and habitat of the endangered 'ezo' eight-barbell loach, Lefua nikkonis (Jordan and Fowler), on Hokkaido Island, Japan

The 'ezo' eight-barbell loach, Lefua nikkonis, is endemic to Hokkaido, Japan. Although it is categorized as a vulnerable species in the Japanese edition of the Red Data Book, little is known about its distribution or habitat. Therefore, we examined (1) their habitat in Hokkaido and (2) their distribution within and around Nopporo Forest Park, Ebetsu-City, Japan. In the first experiment, we sampled ten points within five water systems where L. nikkonis had previously been collected. Fish were collected in traps and then released. We also documented the physiological conditions and water quality at each sampling point. L. nikkonis were found at five sampling points and dominated the fish fauna at these sites. The following environmental conditions characterized sites where loaches were collected: (1) gentle running water or pools in ditches, or ponds, (2) water with high chemical oxygen demand and with hypoxia in the bottom layer. In the second experiment, we collected loaches from 18 sites in Nopporo Forest Park. More individuals were collected in reservoirs than elsewhere ; we also collected loaches in the downstream reaches of these reservoirs. The reservoirs were swamp-like ; therefore, we collected other swamp-dependent fish species, including near threatened species, at these sites. Swamp conditions are generally deteriorating due to human activity, but the endangered species we came across may be found in other unregulated swampy reservoirs. To conserve L. nikkonis and other swamp-dependent species in Hokkaido, the surviving species should be studied, and reservoirs and ponds should be conserved.