Makoto Nagoshi

Brood Defence and Parental Roles in a Biparental Cichlid Fish Lamprologus toae in Lake Tanganyika

Brood defence of a cichlid fish,Lamprologus toae, was investigated in its natural habitat in Lake Tanganyika. Both parents guarding a brood attacked both conspecific and heterospecific intruder fishes at different locations. The heterospecific intruder fishes could be classified into three groups on the basis of the locations at which the attacks against each species took place. The distinction of groups by the parents seemed to be primarily based on food habits and feeding behaviour of the intruder fishes. The piscivorous species which were more dangerous for the brood were attacked by both parents at more distant locations from the brood. Parental defence of breeding territory changed with the development of the young. The frequency of attacks against each group decreased after the young reached the size too large for the fishes of the group to prey on. Division of labour in the territorial defence was recognized between male and female. The male parent mainly defended the peripheral region of the territory and the female parent defended the inner region. Significance of the selective attack against intruders and the division of labour between the two sexes in brood defence is discussed.

Individual growth variation of red-spotted Masu Salmon, Oncorhynchus masou rhodurus, in a mountain stream

Individual growth patterns in red-spotted masu salmon,Oncorhynchus masou rhodurus, were examined by mark and recapture in a mountain stream, central Japan. The growth pattern varied substantially among individuals of the same age cohort in the stream. Mean absolute growth rates of the individuals were neither significantly different between years, study sections along the stream course, or sexes, but showed significant differences between seasons. No correlation was found between the individual growth rate of fish and the area of pools they inhabited. However, there was considerable growth variation among inhabitants of the same pool. Within a pool, larger individuals grew more rapidly than smaller ones, despite there being no significant relationship between individual growth rates and initial body weights in the stream overall. Individual growth differences probably resulted from growth depensation caused by intraspecific competition within individual pools.

Stomach contents of the landlocked dwarf ayu in Lake Biwa, Japan

Abstract The landlocked dwarf ayu (koayu) Plecoglossus altivelis in Lake Biwa was collected in June and July of 1995–1997, and its stomach contents were analyzed. On average, the standard length of koayu was 73 mm, its dry mass was 1.5 g, and the dry mass of the organisms in its stomach was 6.9 mg. Planktonic crustacea dominated the diet, and littoral benthic animals were minor prey. In particular, Daphnia galeata comprised a major fraction of the prey mass. Two copepods, Eodiaptomus japonicus and Mesocyclops dissimilis, were subdominant prey. About 80% of prey individuals had a dry mass of 2–10 μg, and individuals in this size range consisted mainly of D. galeata, with carapace lengths of 0.6 to 1.0 mm. Koayu occasionally ingested large organisms, such as D. galeata 1.5 mm in length, larval shrimps, aquatic insects, and even larval gobiid fishes. The stomachs of koayu were empty at night and were filled within 2 h after sunrise. The total prey mass then fluctuated until sunset, with a tendency toward reduction in the morning. The total prey mass and the size of ingested D. galeata tended to increase with predator size.

Hybridization, Isolation, and Low Genetic Diversity of Kirikuchi Char, the Southernmost Populations of the Genus Salvelinus

Abstract The Kirikuchi char Salvelinus leucomaenis japonicus, which is endemic to the Kii Peninsula, central Honshu, Japan, is a relict nonanadromous char adapted to the southernmost habitats of the genus Salvelinus. As a result of anthropogenic disturbance, the distribution of the Kirikuchi char is now limited to the two upper drainages of the Totsu River system in the Kii Peninsula and this subspecies is now threatened with extinction. The present study determined the genetic population structure of the Kirikuchi char by using partial sequences of the mitochondrial cytochrome b gene, seven microsatellites, and a major histocompatibility complex (MHC) gene (exon 2 of MHC class II beta). The results indicated that native Kirikuchi char populations in both drainages have hybridized extensively with stocked S. leucomaenis pluvius or S. leucomaenis leucomaenis that were originally distributed in eastern Honshu. Native populations were restricted to isolated headwaters above natural falls or sediment control ...

Effects of instream structures on Kirikuchi charr, southernmost population of genus Salvelinus, in a small mountain stream of Japan

The changes in physical habitats and responses of fish, e.g. the Kirikuchi charr Salvelinus leucomaenis japonicus, were examined by placing instream structures in a stream on the upper drainage of the Totsu River system of the Kii Peninsula, Japan, over a two-year period. Instream structures created pools below the structures, and these pools have maintained their functions as fish habitats over two years. In two treatment sections, sections A and B (some red-spotted masu salmon were removed in advance in section B), mean water depth increased soon after placing the structures, but decreased over two years. Mean water velocity slowed after placing the structures in both sections. Total fish abundance has been relatively high at the two treatment sections compared with a control section after placing the structures. Age 1 Kirikuchi charr, however, increased only in section B. These results indicate that instream structures can serve as habitat enhancement for fish, including Kirikuchi charr, in the study area if other appropriate habitat factors for respective species are taken into consideration.

Intergeneric Hybridization between Sympatric Kirikuchi Char and Red-Spotted Masu Salmon in a Small Japanese Mountain Stream

Abstract Hybridization occurs widely across salmonid species. Intergeneric hybridization of salmonid species in nature, however, has been rarely reported. Using microsatellite and mitochondrial DNA (mtDNA) markers, we obtained evidence of intergeneric hybridization between threatened, naturally sympatric Kirikuchi char Salvelinus leucomaenis japonicus and red-spotted masu salmon Oncorhynchus masou ishikawae in an upper drainage of the Totsu River system, which is located on Kii Peninsula, central Honshu, Japan. Fifteen suspected hybrid juveniles were captured in August 2005 in a tributary within a surveyed drainage, where an intergeneric pair consisting of a female Kirikuchi char and a male red-spotted masu salmon was observed during the preceding spawning season. The suspected hybrids all appeared to be F1 on the basis of microsatellite genotypes at five loci, which is consistent with the previously reported infertility of such hybrids. The maternal parent species was presumed to be the Kirikuchi char, s...

Relationships between trematode infection and habitat depth in a freshwater snail, Semisulcospira libertina (Gould)

We found that in natural conditions, the freshwater snail Semisulcospira libertina was distributed in deeper sites when infected with trematode larvae than when uninfected, and examined whether water-depth selection was different between infected and uninfected snails in the laboratory. We compared the mean size of infected and uninfected snails, and the correlation between mean water depth and shell size in uninfected snails. Small uninfected snails (up to 11 mm in shell width) showed a correlation between shell width and water depth, while large snails (larger than 11 mm) did not, but used deeper sites on average than smaller snails. In the small-size class, snails infected with mature cercariae used significantly deeper sites than uninfected snails. On the other hand, in the large-size class, snails infected with immature cercariae used significantly shallower sites than uninfected snails. In each size class, snails infected with mature cercariae used deeper sites than snails infected with immature cercariae or parthenitae. Thus, the influence of trematode infection to host behavior varies according to the development stage of trematodes. In the field, snails infected with mature and immature cercariae had a tendency to occur in deeper sites than uninfected snails of both small and large size classes. These results suggest that some factor other than active selection of water depth by snails determined the distribution pattern of infected snails in natural conditions.

Drumming behavior of two stonefly species, Microperla brevicauda Kawai (Peltoperlidae) and Kamimuria tibialis (Pictet) (Perlidae), in relation to other behaviors

Drumming and other behaviors of two stonefly species, Microperla brevicauda Kawai and Kamimuria tibialis (Pictet) were observed in the field. M. brevicauda exhibited both contact drumming and non‐contact drumming. Contact drumming was performed by a male or female mounted by other individuals, and the temporal and spatial patterns of contact drumming correlated with copulative behaviors. Non‐contact drumming was produced only by males, especially dark‐colored males, in the field. But in the laboratory, females responded with non‐contact drumming to males drummings. The frequency of non‐contact drumming in M. brevicauda correlated with that of walking, but not with that of copulation in time and space. In K. tibialis only non‐contact drumming by males was observed in the field, and it showed temporal and spatial correlation with walking and flight, and also with copulative behaviors. Male‐female exchanges of non‐contact drumming were observed in the laboratory, indicating that they function during mate se...