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The proliferation of small-bodied fishes in lakes is often accompanied by deterioration of water quality and ecosystem function. However, the potential impacts of different types of small-bodied fish species (e.g., obligate zooplanktivores and omnivores) on subtropical lake ecosystems in particular have been overlooked mainly due to their small size, shorter life spans and lower economic value. Therefore, we conducted a mesocosm experiment to elucidate how plankton communities and water quality respond to different types of small-bodied fishes, including a common zooplanktivorous fish (thin sharpbelly Toxabramis swinhonis) and other small-bodied omnivorous fishes (bitterling Acheilognathus macropterus, crucian carp Carassius auratus and sharpbelly Hemiculter leucisculus). During the experiment, the mean weekly total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (CODMn), turbidity, chlorophyll-a (Chl.α) and trophic level index (TLI) values were generally higher in treatments where fish were present compared to treatments where fish were absent, but responses varied. At the end of the experiment, phytoplankton abundance and biomass and the relative abundance and biomass of cyanophyta were higher while the abundance and biomass of large-bodied zooplankton were lower in the fish-present treatments. Moreover, the mean weekly TP, CODMn, Chl.α and TLI values were generally higher in treatments with the obligate zooplanktivore, thin sharpbelly, when compared to treatments with omnivorous fishes. Also, the ratio of zooplankton to phytoplankton biomass was the lowest, and the ratio of Chl.α to TP was the highest in treatments with thin sharpbelly. Collectively, these general findings indicate that an overabundance of small-bodied fishes can have adverse effects on water quality and plankton communities and that small-bodied zooplanktivorous fishes likely induce stronger top-down effects on plankton and water quality than omnivorous fishes. Our results emphasise that small-bodied fishes should be monitored and controlled if overabundant when managing or restoring shallow subtropical lakes. From the perspective of environmental protection, the combined stocking of different piscivorous fish species that feed in different habitat types could be a way forward to control small-bodied fishes with different feeding habits, but more research is needed to assess the feasibility of this approach.

As aquaculture food production is expected to increase, introduced aquaculture species play an important role in meeting the rising demand for aquatic food products and contributing to great societal benefits. Species introduction forces sympatric species to coexist within the same ecosystem by niche segregation. Japanese smelt Hypomesus nipponensis and sharpbelly Hemiculter leucisculus are ecologically similar species and were introduced to Lake Bosten, the largest inland lake in Northwest China, accounting for more than 60% of the total production. We predicted that the coexistence of the two invasive species is mediated by habitat segregation. We analyzed spatiotemporal patterns of Japanese smelt and sharpbelly abundance in Lake Bosten to determine the patterns of spatial segregation between the two dominant fish species. Our results showed that, in Lake Bosten, sharpbelly are typically littoral dwellers when the surface temperature increases in spring and summer, while Japanese smelt often prefer pelagic waters, especially during summer and autumn when the surface temperature rises. Japanese smelt showed an affinity for deeper waters, using median depths 1.7 m deeper than those of sharpbelly, irrespective of the sampling season. Water temperature was the main underlying driver of such spatial segregation and coexistence of these two closely related species in Lake Bosten. Spawning, food resources, and fishing were also important possible factors affecting spatial segregation between the two species. Our results provide new information on niche partitioning patterns as strategies for the coexistence of the two dominant non-native fish in Lake Bosten, supporting the idea that ecologically similar species can avoid resource competition through spatial habitat segregation.

Exopalaemon modestus (Heller, 1862) and Macrobrachium nipponensis (De Haan, 1840) (Palaemonidae) are ecologically and commercially important fishery resources in the Three Gorges Reservoir (TGR), China, and co-occur in demersal habitats. Little information is available on their biology. We compared the reproductive traits of both species on the upper, middle, and lower sections of the TGR. Both species differed in mean size at maturity, which increased from upper to middle and lower sections. Sex ratios were significantly biased toward females, but no significant differences were observed among the three sites for either species. Both species displayed an obvious trade-off between embryo size and fecundity, with the size of embryos being the smallest but with the highest fecundity at the upper section, followed by the middle and lower sections. Exopalaemon modestus spawned from early April to late September, with a peak in May and June, whereas M. nipponensis spawned from late April to early October with a peak in June and July. The spatially distinct reproductive traits, which were concordant across species, are likely related to differences in habitat characteristics such as water flow. We suggest that management strategies should account for the reproductive biology of the two species in order to maintain a sustainable fishery in the reservoir.

To study how fish assemblages changed at different fillings stages, we compared the present fish assemblages (2015–2017; after the third filling in 2009) with those from periods prior to impoundment (1975), after the first closure (1997–2000), after the first filling (2005–2006), and after the second filling (2006–2009) in the upper, middle and lower sections of the Three Gorges Reservoir, the largest in the world. Our results demonstrated that species richness was higher in the upper section than in the lower and middle sections, whereas the overall richness was lower than that prior to damming. The present assemblages were different among sections associated with their specific habitats; i.e., the proportion of rheophilic fishes decreased, whereas those of limnophilic and eurytopic fishes increased from the upper to the lower sections. Temporal comparisons suggested significant declines in proportions of rheophilic and migratory fishes, whereas small‐bodied and eurytopic fishes increased after the impoundment. Fish biomass (CPUE) was greater in the upper section than in the lower and middle sections, and significantly increased after the third filling in the upper section. Overall, our results indicated that the Three Gorges Dam significantly impacted fish assemblages, and the effects of impoundment were magnified by the increased filling scales. The fish assemblages in the upper section were less impacted, demonstrating the high conservation value offered by the upper section to the fish species inhabiting the upper reaches of the Yangtze River.

Summary The paper reports the length–weight relationships of 55 species from the Three Gorges Reservoir (TGR) of the Yangtze River, China, and the largest reservoir in the world. A total of 24,176 specimens were collected from July 2012 to January 2015. Length–weight relationships for 33 fish species not recorded previously in FishBase, and the maximum total lengths computed for eight species are presented. The a values varied between 0.00054 and 0.01923, and the b values ranged from 2.729 to 3.583. The results will be useful for the application of sustainable management and conservation of these fishes in the TGR of the Yangtze River.

The construction of the Three Gorges Reservoir (TGR), the largest dam in the world, created novel spatial and seasonal fluctuations in food availability along the Yangtze River. We studied changes in diet and niche overlap of three co-occurring catfish species between the upper and lower sections of the TGR and across four hydrological seasons to investigate whether the diets of native catfish species reflect the fluctuations in food availability. Zoobenthos dominated the diets of the three species in the upper section, but shrimp made the bulk of the diet in the lower section. This was the case in every season except during the rising-water season when all three species increased the consumption of allochthonous foods. Diet breadth was significantly broader in the upper section relative to the lower section, and expanded during the rising-water season in the lower section. Niche overlap was significantly lower in the upper section than in the lower section. A non-significant trend of reduced niche overlap during the rising-water season was observed in both sections. Our results suggest that, in less than a decade, dietary plasticity facilitated the adaptation of these species to novel habitats and a shifted food-resource base formed by the impoundment.

The reproductive biology of three yellow catfish congeners was studied in the Three Gorges Reservoir of the Yangtze River, China. We compared reproductive traits among the lentic, transitional, and lotic zones. A total of 4502 individuals of the three species was collected, and the sex ratio, size at 50% maturity, spawning season, fecundity, and egg size were determined. Results showed that populations inhabiting the lotic zone spawned earlier than those inhabiting the lentic zone. For the three species, fecundities were significantly higher for populations in the lotic zone than for those in the lentic and transitional zones (P < 0.05). Pelteobagrus vachelli (Richardson) and P. fulvidraco (Richardson) displayed an obvious trade-off between egg size and fecundity, whereas P. nitidus (Sauvage et Dabry) produced the largest eggs in the lotic zone. Sex ratios were significantly different among zones (P < 0.05, for each species), but the bias patterns were different. Sizes at 50% maturity of female P. nitidus and P. vachelli were the largest in the lotic zone and the smallest in the transitional zone, but was similar among zones for P. fulvidraco. Overall results suggest that the three yellow catfish species developed different reproductive traits among the three habitats in the TGR, whereas the variations reflected further interspecific differences. Our study indicates the importance of riverine habitats for the conservation of species of fish, even for species such as these eurytopic catfish inhabiting the upper reach of the Yangtze River. This study further suggests that species-specific responses should be considered when evaluating the influences of new hydropower projects, even for such closely related species of fish. Earmarked Fund for China Agriculture Research System [CARS-45]; National Science and Technology Supporting Program of China [2012BAD25B08]; China Three Gorges Corporation Project [CT-12-08-01]; State Key Laboratory of Freshwater Ecology and Biotechnology [2014FBZ04]; USDA National Institute of Food and Agriculture (Hatch Project) [230537]; Acorn Alcinda Foundation, Lewes, Delaware, USA This work was funded by (1) The Earmarked Fund for China Agriculture Research System (CARS-45), http://www.moa.gov.cn/zwllm/tzgg/tz/201703/t20170320_5530342.htm, Jiashou Liu; (2) The National Science and Technology Supporting Program of China (2012BAD25B08), http://program.most.gov.cn/, Jiashou Liu; (3) The China Three Gorges Corporation Project (CT-12-08-01), http://www.ctg.com.cn/sxjt/kjcx/_301965/index.html, Zhongjie Li and Jiashou Liu; (4) The State Key Laboratory of Freshwater Ecology and Biotechnology (2014FBZ04), http://febl.ihb.cas.cn/, Jiashou Liu and Zhongjie Li; (5) USDA National Institute of Food and Agriculture (Hatch Project 230537), Brian R. Murphy; and (6) The Acorn Alcinda Foundation, Lewes, Delaware, USA, Brian R Murphy. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.