Effect of the Human Utilization of Northern Snakehead (Channa argus Cantor, 1842) on the Settlement of Exotic Fish and Cladoceran Community Structure

Abstract

Empirical studies suggest that changes in the density of top predators, such as carnivorous fish, in freshwater food webs, strongly affect not only fish communities but also various primary and secondary consumers. Based on these findings, we explored how differences in the utilization of carnivorous fish (i.e., Northern Snakehead, Channa argus) by humans affected the fish and cladoceran community structure as well as the settlement of exotic fish species (i.e., Lepomis macrochirus and Micropterus salmoides) in 30 wetlands located in the upper and lower reaches of the Nakdong River. Our results show that in the mid–lower reaches of the Nakdong River, the density of C. argus was low, while high densities of L. macrochirus and M. salmoides were observed. Exotic fish species are frequently consumed by C. argus, leading to a low density of L. macrochirus and M. salmoides in the upper reaches, which supported a high density of C. argus. However, in the mid–lower reaches, the density of L. macrochirus was high because of the frequent collection of C. argus by fishing activities. The dominance of L. macrochirus significantly changed the structure of cladoceran communities. L. macrochirus mainly feeds on pelagic species, increasing the density of epiphytic species in the mid–lower reaches. The continued utilization of C. argus by humans induced a stable settlement of exotic fish species and strongly affected the community structures of primary consumers in the 30 wetlands. The frequency of C. argus collection has to be reduced to secure biodiversity in the mid–lower reaches of the Nakdong River, which will reduce the proportion of exotic fish species and increase the conservation of native fish.

The Use of Winter Water Temperature and Food Composition by the Copepod Cyclops vicinus (Uljanin, 1875) to Provide a Temporal Refuge from Fish Predation

“…In this study, L. macrochirus consumed more cladocerans every spring than copepods; however, their choice changed to concentrated consumption of copepods in summer and autumn. Choi et al [63] suggested that the dominance of L. macrochirus in wetlands in this area may lead to the near extinction of pelagic cladocerans. Pelagic cladocerans have a relatively large body size and frequent movements, making them relatively easy for fish such as L. macrochirus to locate and capture.…”

“…In this study, L. macrochirus, a dominant fish species in the Upo Wetlands, consumed more copepods and cladocerans than any other food source. Previous studies have also suggested that L. macrochirus is a representative planktivorous fish, which mainly consumes zooplankton [62,63]. Cladocerans, which have relatively poor swimming capabilities, are preferred by fish predators over copepods, which leads to rapid depletion of cladoceran populations in the field [62].…”

“…The use of this temporal refuge by C. vicinus is an evolutionary defense strategy to resist the predatory activities of L. macrochirus, which has developed to enable efficient food acquisition in areas with a high aquatic macrophyte cover. L. macrochirus has also evolved to use aquatic macrophytes as refuge to avoid predation by M. salmoides [29,63]. Currently, C. vicinus is positioned at a higher trophic level than its main predator through an evolved defense strategy-winter distribution.…”

Changes in Antibiotic-Resistance Genes Induced by the Grazing Effect in Three Cladoceran Species

“…We investigated the cladoceran community and tet (A) gene in 20 riverine wetlands located in the mid-lower reaches of the Nakdong River from May to June 2019. Among the 40 wetlands studied by Choi and Kim [ 19 ], wetlands 1–20, where cladocerans were abundant, were selected as the survey site. Among the 11 L water samples collected from each wetland, 10 L were used for the quantification of cladoceran individuals, and the remaining 1 L was used to analyze the ARG.…”

“…In this study, we focused on the gene transfer of ARGs between bacteria and cladocerans. Cladoceran communities are primary consumers commonly distributed in various freshwater ecosystems that mainly consume bacteria and phytoplankton [ 18 , 19 ]. Furthermore, considering that cladocerans are frequently used as food sources for top predators such as fish and macroinvertebrates, the continuous accumulation of ARGs induced by cladocerans can be an important mediator of ARG proliferation and vertical transmission in freshwater environments.…”