愛知県一宮市におけるドジョウ属魚類の分布

抄録

The weather loach Misgurnus anguillicaudatus, an important freshwater fish in rural areas of Japan, although comprising both native and non-native mitochondrial DNA lineages, exists in reduced populations in many prefectures and is listed as NT (Near Threatened) in the Red List (Ministry of the Environment of Japan, 2020). On the other hand, the pond loach M. dabryanus, introduced into Japan from continental Asia, is expanding its distribution in various parts of the country. A survey of the spatial distributions of M. anguillicaudatus (native and non-native lineages) and M. dabryanus in Ichinomiya (113.8 km²), Aichi Prefecture, Japan, examined 117 agricultural ditch sites for presence/absence of the loaches from May to August, 2020. Native and non-native M. anguillicaudatus were identified by mitochondrial cytb gene sequencing. Although loaches were collected from 52 of 117 sites, M. dabryanus was dominant (293 individuals from 41 sites) over M. anguillicaudatus (55 individuals from 14 sites), the species co-occurring at only three sites. The relationships between loach presence and several environmental factors were analyzed using the generalized linear model (GLM), which showed that the probability of loach presence (either species) was mainly explained by the presence of ditch vegetation (positive effect) and proportion of agricultural land use (but not paddy fields) (negative effect). The probability of M. anguillicaudatus presence (versus M. dabryanus) was mainly explained by water depth in winter. The results indicated that an increase in concrete ditch construction (no vegetation) and conversion of paddy fields to other agricultural usages, may result in habitat reduction for both species, whereas a decrease in water depth in winter may promote an increase in M. dabryanus. The mtDNA analysis showed that the native lineage of M. anguillicaudatus was found in only 7 sites, thus being critically endangered in the area.