Sexual size dimorphism, growth, and maturity of the fluvial eight-barbel loach in the Kako River, Japan

Abstract

The maturation and growth pattern of the fl uvial eight-barbel loach Lefua sp. (Japanese name: nagare-hotoke-dojo), an endangered species, was investigated using an individual identifi cation-recapture method from 1995 to 1998 in an upper reach of a headwater tributary of the Kako River, Hyogo Prefecture, Japan. Based on observations of the gonads through the abdominal skin, the loach was estimated to breed mostly from May to July. All the males matured by age 1 + , and all the females matured by age 2 + . Gamete release in all individuals of both males and females was predicted from recaptured loaches during each breeding season. The standard length of mature females was signifi cantly larger than that of males, showing sexual size dimorphism (SSD). The maximum sizes recorded were 75.4 mm SL for females and 61.2 mm SL for males. Both males and females of immature specimens grew mainly from May to November, including the breeding season, with no signifi cant differences in growth rates between them. After sexual maturity, both males and females grew mainly from July to October (or November), after the breeding season, and the females exhibited higher growth rates than males. Therefore, SSD of the species seems to be attributable to the different growth rates after maturity. The longevity of the loach was estimated to exceed ten years based on individual growth patterns of various sizes during the survey period. It is likely that the loach has an iteroparous life history, breeding every year, and moderate growth rates after maturity.

Seasonal and inter‐stream variations in the population dynamics, growth and secondary production of an algivorous fish (Pseudogastromyzon myersi: Balitoridae) in monsoonal Hong Kong

“…Data on balitorid reproduction are scarce: in temperate Asia, the Japanese balitorid Lefua sp. spawns once a year in the summer (May to July; Aoyama, 2007; Aoyama & Doi, 2006), which is similar to P. myersi . Seasonal changes in gonad development of the Indian balitorid Bhavania australis suggest that it might reproduce twice each year at the beginning and the end of monsoon season (Jacob & Suryanarayanan, 1990), although trends in the Gonado‐Somatic Index for this species indicate a single extended period of breeding throughout the monsoon (fig.…”

“…By contrast, Lefua sp. in Palaearctic Japan attains a similar size to P. myersi but may live for as long as 10 years, although breeding is possible at 1‐year old (Aoyama, 2007). We suspect that P. myersi is also capable of breeding after 1 year, and probably breeds twice during its life span, but this has yet to be confirmed.…”

Morphological comparison of early stages of two Japanese species of eight-barbel loaches: Lefua echigonia and Lefua sp. (Nemacheilidae)

“…Meanwhile the breeding season of L. sp. is mostly from May to July (Aoyama & Doi 2006, Aoyama 2007 and it is just before or during the rainy season. Moving along substrate without floating in early stages of L. sp.…”