The Danjiangkou Reservoir (DJKR) serves as the water source for the world’s biggest water diversion project, the Middle Route of the South-to-North Water Diversion Project (MR-SNWDP) in China, and this project concerns the water security of tens of millions of people in northern China. Hence, the maintenance of ecosystem health and optimization of management necessitate studies to assess the composition and dynamics of key aquatic living resources. Zooplankton represent a critical component of the reservoir ecosystem and are sensitive to environmental changes and anthropogenic disturbances. In this study, the zooplankton compositions in DJKR were quantified and compared in May, August, and November 2017. Simultaneously, the effects of water trophic states on the zooplankton community structure were analyzed at three levels (overall, taxonomic, and functional groups). A total of 65 zooplankton taxa were recorded, with the taxonomic richness of Rotifera (28 taxa) being the highest among taxonomic groups, which were further classified into 10 functional groups. The community was characterized by low diversity and high evenness. Compared with historical studies, the biomass had increased remarkably, while the abundance showed a decreasing trend in DJKR, and there were more large-bodied zooplankton in this study. The multivariate analysis revealed that zooplankton compositions changed significantly among the three sampling months without distinguishable spatial variations. Moreover, the zooplankton compositions at all three levels correlated significantly with total nitrogen, water transparency, and permanganate index in most situations, as verified by db-RDA and Mantel’s test. However, the contributions of chlorophyll a and total phosphorus were only significant for the LCF group, implying that the bottom-up effects of phytoplankton on zooplankton were weak in DJKR. Therefore, analysis based on functional groups may reflect a more accurate snapshot of the relationships. Our findings will contribute to enriching the long-term fundamental ecological knowledge of the DJKR and the MR-SNWDP, as well as provide key taxonomic information for ecosystem assessment and management.

Cultivation of the redtail culter Culter mongolicus has been increasing substantially over the last decade along the Yangtze River basin; such increases in production lead to increased juvenile transportation. However, redtail culter juveniles have high transport mortality rates due to a strong stress response that is exacerbated by the accumulation of toxic metabolic waste. Through a 24‐h simulated transport experiment (sampling every 6 h), we assessed effects of tricaine methanesulfonate (MS‐222) at 10 mg/L of water, 20 mg/L, and 40 mg/L on redtail culter survival and water quality parameters, and similarly we assessed clove oil at 2 mg/L of water, 5 mg/L, and 10 mg/L. None of the anesthetics significantly improved water quality during the initial 6–12 h of the experiment. However, MS‐222 treatments at the first 12–24 h of the experiment had significantly higher dissolved oxygen (DO), ammonia, and pH than the control but failed to decrease un‐ionized ammonia content. In contrast, the clove oil treatment significantly reduced the un‐ionized ammonia but failed to improve DO and pH at 12–24 h. The improvements in water quality were reflected in cumulative mortality, MS‐222 and clove oil anesthetic treatments having significantly lower cumulative mortality than the control at 12–24 h. The MS‐222 and clove oil slowed water quality deterioration, ensured a better transport environment, and improved juvenile survival during transportation. We recommend 5 mg/L clove oil be used when transporting juvenile redtail culters because that concentration improves fish survival while keeping cost low.

Redtail culter Culter mongolicus, a threatened piscivorous fish species in China's inland waters, has exhibited serious population decline. As part of a stock enhancement research project in shallow lakes of the Yangtze River basin, China, we evaluated the performance of coded wire tags (CWTs) for marking juvenile redtail culter. Through a short‐term indoor experiment, we marked hatchery‐reared juveniles from three size groups (mean ± SE, small: 46.85 ± 0.67 mm, intermediate: 53.76 ± 0.62 mm, large: 63.42 ± 1.05 mm) in the dorsal muscle with CWTs and tested whether marking effects on tag retention and mortality were size‐specific. Tag retention was more than 98% in all the three size groups and appeared to be unaffected by fish size. Tag losses were found only within 3 d of marking. Tagging‐induced mortality of small marked juveniles (58%) was significantly higher than those of intermediate (5%) and large (1%) marked juveniles and was also significantly higher than small unmarked ones (17%). The relationship of marked mortality and total length was quantitatively described by an exponential decay model. Mortality in small marked juveniles occurred mainly within 24 h after marking, which accounted for 71% of the mortality in this marked size. In order to avoid high posttagging mortality and biases in stocking assessment programs, we suggest it is worth the extra fish‐culture costs to use juveniles of at least 57 mm (which displayed 90% survival in our experiment) for stocking assessment programs that utilize CWTs for a handling‐sensitive species like redtail culter. Received December 1, 2011; accepted June 28, 2012