Osamu Katano

Species diversity and abundance of freshwater fishes in irrigation ditches around rice fields

The relationships between environmental variables, distribution of freshwater fishes and their diet were investigated at 40 sites on irrigation ditches for rice fields in central Japan. Multivariate analyses showed that fish species richness and diversity in ditches was high when fishes were able to easily invade the rice fields. Natural stream beds not covered by concrete had greater total number and biomass of fishes in irrigation ditches. The connection between ditches and rice fields was of secondary importance. Canonical correlation analysis indicated that the two principal fish community variables, abundance and diversity, were respectively represented by the presence of the minnow, Gnathopogon elongatus elongatus, and the absence of the loach, Misgurnus anguillicaudatus. Most fishes in the irrigation ditches predominantly preyed upon aquatic insects such as ephemeropteran nymphs, chironomid larvae and trichopteran larvae, but aerial insects and benthic algae were also fed upon by a few species. Small fishes (<4 cm SL) preyed more on chironomid and less on trichopteran larvae than large (≥4 cm SL) fishes. The diet overlap between species was extremely high for small fishes in ditches weakly connected with rice fields. The recent changes in rice fields and irrigation ditches to increase production efficiency has led to a decrease in fish diversity. For the coexistence of rice production and fish diversity in rice areas, a new irrigation system, where fishes can easily invade rice fields and where plenty of invertebrates are available for fishes, should be developed.

Origin and dispersal of bluegill sunfish, Lepomis macrochirus , in Japan and Korea

The bluegill sunfish, Lepomis macrochirus, is a notorious exotic species in many freshwater ecosystems, currently expanding its distribution worldwide. In 1960, a small group of bluegills captured in the Mississippi River at Guttenberg in Iowa were imported to Japan as a gift from the mayor of Chicago to the Japanese government. The offspring of these fish were released into the wild in Japan and also in Korea. Over 40 years after this first introduction, L. macrochirus now occupies all the freshwater ecosystems of both countries. We compared invading populations of L. macrochirus in Japan and Korea with native populations in the USA, using PCR–RFLP (polymerase chain reaction–restricted fragment length polymorphism) analyses of mitochondrial DNA, to estimate the origin and dispersal of L. macrochirus in Japan and Korea. Five haplotypes of mitochondrial DNA detected in Japanese and Korean populations completely coincided with the haplotypes of the Guttenberg population. Haplotype diversity of invading populations was shown to be highest in populations established in the 1960s, while genetic variability was lower in more recently established populations. Our results suggest that all L. macrochirus in Japan and Korea have originated from the 15 fish first introduced in 1960. Low haplotype diversity in newly established populations is probably due to genetic drift arising from repeated population bottlenecks, while the high similarity of haplotypes among neighbouring populations is considered to reflect the history of transplantation by humans.

Righty fish are hooked on the right side of their mouths :observations from an angling experiment with largemouth bass, Micropterus salmoides

Abstract The development of muscles and bones in fish is laterally asymmetric (laterality). A “lefty” individual has a “C”-shaped body, with its left-side muscles more developed and the left side of its head facing forward. The body of a “righty” is the mirror-image. This laterality causes asymmetric interactions between individuals of different fish species, in that a righty or lefty fish consumes more lefty or righty fish, respectively. To investigate the coupling mechanisms between body asymmetry and predatory behavior, we conducted angling experiments with largemouth bass (Micropterus salmoides). We used the position of the fishhook set in the mouth to indicate the movement direction of the fish when it took the bait. Righty fish had more hooks set on the right side, whereas lefty fish had more on the left side, indicating that righty fish moved more to the left, and lefty fish moved more to the right, in successful catches. The relationship between the hooked position and movement direction was confirmed by video-image analysis of the angling.

INDIRECT CONTRAMENSALISM THROUGH TROPHIC CASCADES BETWEEN TWO OMNIVOROUS FISHES

The impact of trophic cascades on the interspecific relationship between two omnivorous stream fish, ayu (Plecoglossus altivelis altivelis) and Japanese dace (Tribolodon hakonensis), were analyzed in experimental pools. Benthic algae grew on the pool beds, and macroinvertebrates colonized the pools. Ayu predominantly grazed the algae, occasionally forming territories. Japanese dace fed on both benthic algae and invertebrates when ayu were absent, and predominantly on invertebrates when ayu were present. The presence of Japanese dace reduced the number of invertebrates and increased algal biomass (chlorophyll a) through trophic cascades, but the effects of respiration and excretion of dace did not notably increase algal biomass probably because the water continuously pumped into the pools was already nutrient rich. The growth rate of ayu was enhanced in the presence of Japanese dace due to increased algal biomass. In contrast, as the number of ayu increased, the growth rate of Japanese dace was reduced bec...

Prey fish selection by Far Eastern catfish Silurus asotus and largemouth bass Micropterus salmoides

Prey fish selection by Far Eastern catfish and largemouth bass were examined using bluegill, Japanese dace and crucian carp as food fish. In both aquaria (1.2m × 0.45m) and ponds (2.8 m × 1.2 m), bluegill was not preyed on by catfish and bass more than dace and crucian carp. In aquaria, there was no significant difference in the consumption of dace and crucian carp between catfish and bass, but in ponds, catfish preyed on dace and crucian carp more and less than bass, respectively. In the case that only bluegill and catfish were introduced in ponds, catfish consumed 4–15 g of bluegill per day. The introduction of catfish into ponds and lakes for the purpose of eradicating bluegill is considered appropriate for areas with few native fish species.

Effects of individual differences in foraging of pale chub on algal biomass through trophic cascades

The foraging behavior of pale chub, Zacco platypus in experimental ponds was observed and the fish were classified according to whether they predominantly employed near-bed cruising and bottom feeding (type B) or whether they exhibited sit-and-wait and near-surface cruising, with occasional drift and surface feeding (type S). Fish that exhibited both behaviors were classified as type I. The effects of pale chub on trophic cascades were examined in pools into which river water was pumped. Twenty pools were assigned to four treatments and contained either no fish, or six pale chub of type B, or of type I, or of type S. Fish behavior was consistent throughout the experiments, and was not related to body length or sex. All types of pale chub predominantly preyed on invertebrates, but type B consumed more benthic algae than did type S. The algal biomass in pools with types S and I was greater than that in pools without pale chub as a result of trophic cascades. In pools with type B fish, the number of algal-grazing invertebrates on the upper surface of tiles was reduced as in pools with types S and I, but algal biomass did not increase because of direct grazing by type B fish. The mechanisms of reduction of algal-grazing invertebrates were different between types B and S; type S predominantly preyed on invertebrates in the water current, whereas type B preyed on and threatened invertebrates on the upper surface of tiles and removed them. Individual differences in foraging mode had significant effects on the mechanism of trophic cascades.

The role of propagule pressure in the invasion success of bluegill sunfish, Lepomis macrochirus, in Japan

The bluegill sunfish, Lepomis macrochirus, is a widespread exotic species in Japan that is considered to have originated from 15 fish introduced from Guttenberg, Iowa, in 1960. Here, the genetic and phenotypic traits of Japanese populations were examined, together with 11 native populations of the USA using 10 microsatellite markers and six meristic traits. Phylogenetic analysis reconfirmed a single origin of Japanese populations, among which populations established in the 1960s were genetically close to Guttenberg population, keeping high genetic diversity comparable to the ancestral population. In contrast, genetic diversity of later‐established populations significantly declined with genetic divergence from the ancestral population. Among the 1960s established populations, that from Lake Biwa showed a significant isolation‐by‐distance pattern with surrounding populations in which genetic bottlenecks increased with geographical distance from Lake Biwa. Although phenotypic divergence among populations was recognized in both neutral and adaptive traits, PST–FST comparisons showed that it is independent of neutral genetic divergence. Divergent selection was suggested in some populations from reservoirs with unstable habitats, while stabilizing selection was dominant. Accordingly, many Japanese populations of L. macrochirus appear to have derived from Lake Biwa population, expanding their distribution with population bottlenecks. Despite low propagule pressure, the invasion success of L. macrochirus is probably because of its drastic population growth in Lake Biwa shortly after its introduction, together with artificial transplantations. It not only enabled the avoidance of a loss in genetic diversity but also formed a major gene pool that supported local adaptation with high phenotypic plasticity.

Experimental analysis of the territorial establishment of ayu, Plecoglossus altivelis

Ayu mainly grazes benthic algae on river beds. To clarify the effects of individual behavioral differences on the territory establishment of ayu, we first recorded the number of active movements, aggression towards a wooden ayu model, and scraping feeding activities for 40 ayu, each in an aquarium with a ceramic plate with benthic algae. We then released 10 randomly chosen ayu and other cyprinids, 10 Tribolodon hakonensis and 10 Zacco platypus, into each of the four ponds with recirculating water. Four to six ayu established a territory for 1–20 of the 21 days observed in each pond. Territories were unstable in the first half period but became stable in the latter period. Territorial period was positively correlated with the number of active movements in aquaria and negatively with the number of conspecific invasions. The percentage of attacks against other species was positively correlated with the number of scraping behavior in aquaria and negatively with standard length of ayu. The growth rate of non-territorial ayu was large in case the ayu scraped more than half of ceramic plates in aquaria. In contrast, the growth rate of territorial ayu was correlated negatively with the standard length of ayu, and the percentage of attacks against other species, indicating that individual behavioral differences and the defending cost were both important in territory establishment and growth.

Summer daytime habitat and population density of the torrent catfish, Liobagrus reini, in the Urano River

The population density and summer daytime habitat characteristics of the endangered torrent catfish, Liobagrus reini, in the Urano River, a tributary of the Chikuma River in Nagano, central Japan, were investigated. A total of 105 individuals were captured in 2001–2003, and the estimated population density 100 m−2 in the whole study area ranged from 0.20 to 2.96. Liobagrus reini were captured from under cobbles and boulders, interstices in bedrock, and in clumps of roots of terrestrial vegetation along banks. Compared with the distribution of physical factors in the study area, the fish selected shallow habitats with the riverbed covered by cobbles and boulders. Boulders and larger cobbles were chosen by larger individuals as a habitat. Habitat selection was not correlated with current velocity, and some individuals were sampled near (<1 m) the riverbank with no current. For the conservation of L. reini, the preservation of natural riverbanks and areas with boulders and large cobbles in the riverbed is concluded to be important.

Population density, growth and migration via the sea to different streams of Japanese dace Tribolodon hakonensis in lower reaches of small streams

Ecological characteristics of Japanese dace Tribolodon hakonensis were investigated in three small streams in Niigata Prefecture from 2001 to 2005 with special reference to the effect of Ayu Plecoglossus altivelis altivelis on the dace. Japanese dace were distributed in short sections below dams near the mouth of the streams flowing into the Sea of Japan. In this section, Ayu were numerically dominant from June to August, and the growth rate of dace in this period was negatively correlated with the density of Ayu. The population density of dace was high in October, but some adults stayed in the streams in June and August. When data for the five years were combined, the density of dace was negatively correlated with that of Ayu in two of the three streams. The increase in density of dace in October is considered to be due to the migration of dace from the sea. Eight dace were confirmed to migrate to different streams via the sea. Therefore, the life history of Japanese dace in the study region contained considerable individual variation.