2012 Volume 6 Pages 1-16
Largemouth bass, Micropterus salmoides, is a piscivorous fish species native to North America. This species has been introduced into many regions outside its native range for sport fishing and food. Due to predation, introduced largemouth bass have altered native fish communities, lowering both the species richness and abundance of native fish species. The diet of largemouth bass changes as they grow. Largemouth bass either move directly from zooplanktivory to piscivory, or they may include a period of insectivory. In this review, we first examined studies discussing the timing of the switch to piscivory in native and introduced areas with the minimum size of individuals being used as an indicator of timing. Then we discuss the significance of ontogenetic shift to piscivory of largemouth bass, the dietary switch at the population level during the first year and the factors affecting the shift to piscivory. The minimum body size at the onset of the shift to piscivory is variable among regions and water systems. After the switch to piscivory, the growth rates of bass increase significantly due to the higher energy content of prey fish, resulting in large body size in autumn. Since over winter mortality is size-dependent, an early shift to piscivory increases the recruitment of 0+ largemouth bass to the future adult population. In their native range, 0+ bass often fail to shift to piscivory during their first year. Such a phenomenon could divide the 0+ population into large piscivorous and small zooplanktivorous individuals, resulting in bimodal body size distribution. In introduced areas, to our knowledge, there has been no investigation on the ontogenetic shift to piscivory at the population level except for 2 studies in Japan. One of these studies shows that all 0+ individuals can become piscivorous during their first year; another shows that some individuals can become piscivorous, but others cannot. Based mainly on investigations in their native range, the success of 0+ bass to switch to piscivory is considered to be influenced by the following factors; 1) growth rate before the shift to piscivory, 2) hatching date, and 3) the relative timing of spawning season in reference to those of prey fishes. However, few studies have examined the effects of the above 3 factors on the diet shift to piscivory in introduced areas. Further studies are required to enhance a more complete understanding of the factors affecting the shift of 0+ bass to piscivory especially in introduced areas.
