Paternal egg guarding and mouthbrooding of larvae and juveniles were observed in the swamp-eel, Monopterus albus. In aquaria, the male guarded and cared for eggs in the bubble nest floating inside a plastic tube (5 cm in dia-meter, 50 cm in length). It was suggested that spawning and fertilization occurred outside the nest tube, and that the male carried the fertilized eggs (ca. 4 mm in diameter) in his mouth and inserted them into the bubble mass. Until the hatching of larvae (7-8 days after spawning), the male frequently added fresh bubbles into the bubble mass. As soon as the larvae (18-21 mm in TL) hatched and emerged from the bubble nest, the male sucked them into his mouth. Fifty juveniles (32-37 mm in TL) and two yolk-sac larvae (22 mm in TL) were released from the mouth of a male collected from a natural habitat. Those juveniles were retrieved by the male, some of them voluntarily returning to the male's mouth. The mouthbrooding male frequently performed pumping behavior (i.e., inflating and deflating the buccopharyngeal cavity), thereby acquiring to take fresh air. Eggs removed from the bubble nest successfully hatched only when directly exposed to aeration. In addition, only about 40% of the hatched larvae survived more than 10 days when they were kept in well-aerated water without the male parent. These suggest that both the bubble nest and mouthbrooding are indispensable for successful development and survival of eggs and larvae in this species, which inhabits swamps and paddy fields.
Hatatatenumeri dragonets (Repomucenus valenciennei) in Tokyo Bay, Japan, were collected by beam trawl (mesh size 1.6 mm-bar measure) from 15 stations every two months from September 1990 to September 1991, and similarly trawl (mesh size 3 cm-stretched measure) from 20 stations every season from June 1990 to February 1993. Settled juvenile and subadult fish were caught by the 1.6 mm mesh trawl, whereas subadult and adult fish were caught by the 3 cm mesh trawl. Dragonet distribution was estimated from abundance (indiv per tow) at each sampling station for each year class, the abundance data being divided into year classes from length frequency data. Settled juveniles appeared in autumn throughout the bay, with abundance being greater in the northern (innermost) part. The dragonet was restricted to the southern (close to the mouth) part in summer, but subsequently spread throughout the bay, with abundance being greater in the northern part from autumn to winter. Because of this seasonal change in distribution, the dragonet was believed to migrate seasonally between the northern and southern parts of Tokyo Bay, hypoxia in summer possibly causing the southward migration of immature fish from the northern part, in addition to restricting the distribution of mature fish at that time.
Thirty-six specimens of the Siberian lamprey, Lethenteron kessleri (Anikin, 1905), collected from the Kuji River, north-eastern Honshu Island, Japan, in 1965, represent the only record of this species from Honshu Island. Relative measurements of their snout length and eye diameter divided by branchial length, plus the number of trunk myomeres, showed lower values than those reported for specimens collected from Hokkaido Island, suggesting geographic variation. Lethenteron kessleri probably originated in the Siberian region, subsequently dispersing via freshwater into the northern part of Japan. The Kuji River population of L. kessleri is considered to represent the original distribution of the species in north-eastern Honshu Island, as already shown for Tribolodon ezoe and Cottus nozawae.
An endangered cyprinid, Pseudorasbora pumila subsp.sensu Nakamura (1969), was newly found in a small pond belonging to the Miya River System, Mie. The new locality is the most south-western site in the distribution of P. pumila complex. The population is distinguishable from the other local populations in the Nôbi Plain by such characters as a sharp snout and extremely swollen shoulder region. Once P. pumila subsp. was widely distributed in the Nôbi Plain, however, the local populations of this subspecies have drastically diminished, because of destruction of habitat and introduction of its related species, P. parva as well as predators. So, emergent conservation now is necessary for P.pumila subsp.with its habitat included.