Morphological variation in largemouth bassMicropterus salmoidesin Lake Biwa, Japan

Abstract

-Largemouth bass, Micropterus salmoides, have inhabited Lake Biwa in central Japan for over three decades as top predators. Lake Biwa consists of two basins -a large, deep north basin and a small, shallow south basin. Since the mid 1990s, vegetation and bluegill sunfish, Lepomis macrochirus, have thrived in the lake -especially in the south basin. Because dense vegetation can mediate the predator-prey relationship between largemouth bass and bluegill, the largemouth bass in the south basin are assumed to be under less favorable conditions than those in the north basin. The length-weight relationship of the largemouth bass in the two basins differed; the body weights of largemouth bass in the north basin significantly exceeded those in the south basin. Moreover, largemouth bass in the south basin appeared to have significantly larger gapes than those in the north basin. Such fish in the south basin were likely selected during and after the ontogenetic diet shift stage, probably because they are capable of handling bluegill more efficiently than those with normal-sized gapes.

Adaptation to water level variation: Responses of a floating-leaved macrophyteNymphoides peltatato terrestrial habitats

“…Adaptive plasticity to temporal environmental variations is common and may be important for adaptation to varying environments (Schlichting and Pigliucci, 1995;Bazzaz, 1996;Yamamoto and Tsukada, 2010). In many wetland and floodplain ecosystems, periodic flooding and drought occurrences play an important role in the composition, and productivity of species (Li et al, 2004;Leira and Cantonati, 2008).…”

Indirect impact of bluegillLepomis macrochiruson the development of cyanobacterial blooms in Lake Biwa, Japan

“…Macrophytes favor the dominance of bluegill by providing a habitat for large-bodied cladocerans, which are their prey (Lauridsen and Buenk 1996;Tu¨zu¨n and Mason 1996;Oberholster et al 2007), and providing refuge from their predators such as largemouth bass (Savino and Stein 1982;Hayse and Wissing 1996). Although largemouth bass also propagate in Lake Biwa, their population density in the south basin is assumed to be low (Yamamoto and Tsukada 2010). Given that the propagation of bluegill in the south basin of Lake Biwa became evident around 1995 (Nakai and Hamabata 2002), the bluegill population may have increased in response to the propagation of macrophytes.…”