The larval and juvenile development was compared between Lefua echigonia and Lefua sp., both endemic and endangered species in Japan. L. echigonia larvae collected in sunny wetlands were planktonic and swam in the middle to upper layers in lentic waters, whereas L. sp. larvae swam with their abdomen facing toward the substrate along the river bottom in well shaded waters of mountain streams. Larvae and juveniles of both species have a distinct dark band on the lateral side of snout. L. echigonia larvae have melanophores on the dorsal body, gut region, and around the lateral midline, whereas melanophores distribute broadly on the body in L. sp. larvae. Eyes are located more dorsally in larvae of L. sp.: in the ventral view of the head, the eyes of L. echigonia larvae could be seen, but those of L. sp. larvae could not be seen. L. echigonia larvae and juveniles have relatively large eyes and eye diameters were larger than the snout lengths. Lefua sp. larvae and juveniles have relatively small eyes and eye diameters were smaller than the snout lengths. These characters of melanophore distribution, eye size, and eye location are concluded to show adaptation for each habitat.
Former studies demonstrated that the river loach species Lefua sp. and Lefua echigonia (Nemacheilidae) have thin white linear markings from the pectoral fin base to the ventral fin base on both right and left sides of the abdomen that can be used to identify individuals in laboratory and in the field. In the present study we demonstrate the existence of such markings and the uniqueness of their shape in reared individuals of a further six species of Nemacheilidae, but found them absent in three species of Balitoridae. Furthermore, the long-term stability of the shape of the markings was examined in reared individuals of the nemacheilid Barbatula toni over two years. The white line markings offer a non-invasive tool for the individual recognition of nemacheilid species, some of which are threatened with extinction.