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Elevated ammonia levels in aquaculture systems could reduce fish growth and survival rates and produce a range of physiological problems. Ammonia toxicity in aquatic environments was regulated by various factors. Feeding was usually reported to help in the detoxification of fish, thereby increasing their capacity to tolerate ammonia nitrogen. However, the impact of different feeding amounts on fish in relation to ammonia exposure stress remains to be determined. To determine how feeding levels affected fish's responses to different ammonia nitrogen concentrations, two acute toxicity experiments were conducted with Carassius auratus gibelio, the major strain of gibel carp in aquaculture systems in China. In Test I, fed Carassius auratus gibelio (3 % body weight) showed a higher survival rate under a specific ammonia exposure stress. 96-h LC50 of NH3-N to 3 %F gibel carp was 1.1 times greater than that for NF (no feeding). In Test II, all fed groups (2 %F and 4 %F) under low and high ammonia stress exhibited improved ammonia detoxification, evidenced by higher liver GSase, GDH, and glutamine concentrations compared with the NF treatment. Muscle glycogen levels in feeding treatments were higher than those in NF, indicating that fed fish have more energy for ammonia detoxification. While compared with low ammonia treatment (2.70 mg L−1 TAN; NH3 0.06 mg L−1), fish exposed to high ammonia levels (26.03 mg L−1 TAN; NH3 0.57 mg L−1) demonstrated a decrease in food consumption, severe histopathological alterations in their liver, gill, and kidney, and decreased GSase, GDH, and glutamine production in the liver and brain. The results partly supported our hypothesis and suggested that increasing feeding enhances gibel carp's tolerance to ammonia nitrogen. The highest detoxification metabolism was observed under low ammonia stress. While excessive ammonia exposure could inhibit feeding and damage the detoxification organs of fish, and thus reduce the detoxification metabolism of gibel carp.

Lakes within river-floodplain ecosystems are key biodiversity refuges majorly threatened by eutrophication and hydrologic river-lake fragmentation. However, an integrative index, specifically designed to comprehensively assess the health of floodplain lakes, considering multiple biological taxa and major stressors, remains unavailable. Based on biological data collected from 68 isolated lakes in the eastern plain lake region of China, we constructed a reliable index for assessing floodplain lake ecosystem health: Integrated Bioassessment Index (L-IBAI). The L-IBAI consists of components of overall health and species diversity, eutrophication, and hydrological connectivity and water level regimes. To construct the L-IBAI, we firstly used the observed species (SO)-area (A) model to predict the expected species richness (SE), and then developed observed to expected indices by calculating the SO/SE ratio for fish (F-O/E-SA) and benthos (B-O/E-SA). The health level thresholds for the other four indices, namely the ratio of Secchi depth and water depth (ZSD/ZM), chlorophyll a in phytoplankton (Chl a), the percent of rheophile fish species, and emergent macrophytes coverage, were determined using cumulative frequency curves. The final L-IBAI score was obtained by summing the weighted values of the three components mentioned earlier. The L-IBAI can significantly discriminate rural from urban lakes, and is a reliable index for assessing lake ecosystem health. Moreover, we developed three simplified three-index integrated bioassessment indices, which consists of three indices belonging to the three elements are also effective. The developed L-IBAI is flexible to be extended and applied to other floodplain lakes, and outcomes of health assessments for the eastern plain lakes in China helped to identify conservation and restoration priorities.

Urbanization is one of the major drivers of biotic homogenization (i.e., decrease in beta diversity) in freshwater systems. However, only a few studies have simultaneously examined how urbanization affects multiple facets (i.e., taxonomic, functional and phylogenetic) of beta diversity and its underlying ecological drivers in urban river macroinvertebrates. Here, we distinguished the patterns and ecological mechanisms of multiple facets of macroinvertebrate beta diversity weighted by incidence and abundance data in a subtropical river system with a distinct urbanization gradient. We also investigated how total beta diversity patterns stem from replacement versus richness difference among sites. Our results showed that taxonomic and phylogenetic beta diversities weighted by incidence data were primarily driven by replacement of taxa, whereas the richness difference contributed more to multiple facets of beta diversity based on abundance data. Furthermore, multiple facets of beta diversity decreased with urbanization for both incidence-weighted and abundance-weighted data, but the former showed more substantial decreases. Both replacement and richness difference components contributed roughly equally to the decline of incidence-weighted beta diversity. In contrast, the losses of abundance-weighted beta diversity were mainly associated with replacement of taxa. Variation partitioning results revealed that all beta diversity measures based on incidence data were governed primarily by local and land-use variables, whereas spatial variables were more relevant in driving beta diversity weighted by abundance data. Overall, by comparing different facets and components of beta diversity weighted by incidence versus abundance data, we suggest that incidence-weighted data may be more sensitive in portraying the impacts of urbanization on macroinvertebrate diversity. This likely resulted from the fact that incidence-weighted data shows the importance of rare taxa in shaping homogenization induced by urbanization.

Identifying the biodiversity hotspots could enrich our understanding for biodiversity conservation. The Yangtze River Basin (YRB) is seriously threatened by multiple stressors leading to rapid biodiversity declines, thus urgently requires an integrated biodiversity conservation. Based on field samplings and the literatures, we described the macrozoobenthos compositions in different reaches and water bodies. We then predicted suitable habitat areas for the main groups, and linked those distributions with key environmental variables. Finally, we analyzed biodiversity hotspots (BHs) of macrozoobenthos and compared them with BHs of large aquatic animals (including fishes, Waterfowls, Yangtze finless porpoise, etc.), and discussed the applicability of selecting macrozoobenthos as biodiversity surrogate for biodiversity conservation. A total of 1033 taxa were recorded. From the upper to lower of YRB, genera number of Oligochaeta and Mollusca increased, of EPT (Ephemeroptera, Plecoptera, Trichoptera) decreased, and of Chironomidae barely changed. In different water bodies, genera number of Oligochaeta, Mollusca, Chironomidae are the highest in lakes of the mid-lower YRB, while that of EPT are the highest in tributaries. Key environmental variables were water body types, elevation and max temperature of the warmest month. The total BHs areas of macrozoobenthos and large aquatic animals in the upper, and mid­lower YRB were 3.54 × 105 km2 and 2.95 × 105 km2, 2.95 × 105 km2 and 1.70 × 105 km2, respectively. The overlapping BHs were 2.0 × 105 km2 and 1.1 × 105 km2, respectively. The BHs of macrozoobenthos had a wider range, and included most BHs of large aquatic animals. Meanwhile, BHs of macrozoobenthos could indicate some habitats those were difficult to cover by selecting large aquatic animals as conservation targets, e.g., seasonal streams and water bodies that suffered from human disturbances. Based on these results, we argue that macrozoobenthos is a good biodiversity surrogate for biodiversity conservation.