Abstract.-Largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu have been introduced into freshwater habitats in Japan, with potentially serious consequences for native fish populations. In this paper we apply the technique of ecological niche modeling using the genetic algorithm for rule-set prediction (GARP) to predict the potential distributions of these two species in Japan. This algorithm constructs a niche model based on point occurrence records and ecological coverages. The model can be visualized in geographic space, yielding a prediction of potential geographic range. The model can then be tested by determining how well independent point occurrence data are predicted according to the criteria of sensitivity and specificity provided by receiver-operator curve analysis. We ground-truthed GARP's ability to forecast the geographic occurrence of each species in its native range. The predictions were statistically significant for both species (P Ͻ 0.001). We projected the niche models onto the Japanese landscape to visualize the potential geographic ranges of both species in Japan. We tested these predictions using known occurrences from introduced populations of largemouth bass, both in the aggregate and by habitat type. All analyses robustly predicted known Japanese occurrences (P Ͻ 0.001). The number of smallmouth bass in Japan was too small for statistical tests, but the 10 known occurrences were predicted by the majority of models.Assessing the threat of species invasions and the possible spread of such species is a global challenge that requires a global perspective (Carlton * Corresponding author: ewiley@ku.edu.1 Order of authorship is alphabetical, reflecting the collaborative nature of this paper.2 Present address: Biodiversity Research Center, University of Kansas, Lawrence, Kansas 66045, USA.3 Present address: Department of Life Science, Faculty of Bioresources, Mie University, 1515 Kamihama, Tsu, Mie 514-8507, Japan. Received October 9, 2003; accepted December 3, 2003 1996; Enserink 1999). To achieve this perspective, we can apply analytical tools and use information on ecological landscapes that can be gathered on a global scale as well as specimen records to seek the sets of factors that are useful in forecasting places where the establishment of species is possible. The point is not necessarily to learn more about the ecology of the species-this would require detailed study of local landscapes. Rather, the aim is to build models of the ecological niche requirements of a particular species within its native range with respect to factors that are available globally, to test whether these models can predict

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.

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Densities of two sympatric amphidromous grazing fishes, Plecoglossus altivelis and Sicyopterus japonicus, and gross primary production of benthic algae were investigated at the second, third and fourth-order sites located, respectively, 7.0, 6.7 and 3.6 km from the mouth of the Choshi River, Japan. Gross primary production estimated by multiplying gross photosynthetic rates by hours of insolation on the streambed increased downstream with decreasing canopy cover by valley walls and trees standing along the river. Density of P. altivelis was greatest at the fourth-order site with the higher primary production, while the distribution pattern of S. japonicus differed between adult (> ca. 7 cm in total length) and young individuals. Density of adult of S. japonicus was greater at the third-order site, although the young were more abundant at the fourth-order site. Aggressive acts against conspecifics and different species were observed only by adults of S. japonicus and most frequently observed at the third-order site. The upstream shift in the distribution of the adults of S. japonicus would mitigate interference competition with P. altivelis and contribute to their coexistence in the river.

Age and growth of the largemouth bass Micropterus salmoides (Pisces: Centrarchidae) were esti mated from otoliths taken from samples collected in Lakes Shorenji (Mie Prefecture) and Nishinoko (Shiga Prefecture), water bodies having different physical and biological environments, from October 1991 to March 1993. The otoliths of the fish had narrow opaque and wide transparent zones, with opaque foci. Ring marks (outer margin of opaque zones) were formed on the otoliths once a year from June to August and May to July in Lake Shorenji and Lake Nishinoko specimens, respectively. The number of ring marks indicated approximately the full age of the fish because the marks formed one or two months after the spawning period. The fish from Lake Nishinoko were significantly heavier than those from Lake Shorenji for the same length. The growth curves for length were calculated to be SL" =341(1-exp (-0 .4977(n+0.0697))) (Lake Shorenji) and SL"=362(1-exp(-0.4576(n+0.0892))) (Lake Nishinoko). Lake Nishinoko largemouth bass grew somewhat more rapidly than those in Lake Shorenji.