During the evolutionary transition from land to water, cetaceans have undergone numerous critical challenges, with osmoregulation being the major one. Two subspecies of the narrow-ridged finless porpoise (Neophocaena asiaeorientalis), the freshwater Yangtze finless porpoise (N. a. asiaeorientalis, NAA) and the marine East Asian finless porpoise (N. a. sunameri, NAS), provide excellent subjects to understand the genetic basis of osmoregulatory divergence between freshwater and marine mammals. The kidney plays an important and well-established role in osmoregulation in marine mammals and thus, herein, we utilized RNA-seq to characterize the renal transcriptome and preliminarily analyze the divergence between the NAA and the NAS. Approximately 48.98 million clean reads from NAS and 49.40 million clean reads from NAA were obtained by RNA-Seq. And 73,449 (NAS) and 68,073 (NAA) unigenes were assembled. Among these annotations, 22,231 (NAS) and 21,849 (NAA) unigenes were annotated against the NCBI nr protein database. The ion channel complex GO term and four pathways were detected as relevant to osmoregulation by GO and KEGG pathway classification of these annotated unigenes. Although the endangered status of the study species prevented analysis of biological replicates, we identified nine differentially expressed genes (DEGs) that may be vital in the osmoregulation of the narrow-ridged finless porpoise and worthwhile for future studies. Of these DEGs, the differential expression and distribution of the aquaporin-2 (AQP2) in the collecting duct were verified using immunohistochemical experiments. Together, this work is the first report of renal transcriptome sequencing in cetaceans, and it will provide a valuable resource for future molecular genetics studies on cetacean osmoregulation.

Length–weight relationships (LWRs) of the three fish species, Pseudobagrus albomarginatus(Rendahl, 1928), Pseudobagrus crassilabris (Günther, 1864), and Rhinogobius davidi(Sauvage & Dabry de Thiersant, 1874), were determined respectively. Samples were collected from Qiantang River, China during March 2016–December 2017. The bvalues ranged from 2.525 to 2.917, the coefficient of determination (r²) ranged from 0.96 to 0.97. Prior to this study, the length–weight relationship for P. albomarginatus and R. davidi were unknown to FishBase and the new maximum total lengths for three species were not recorded in FishBase. These results are useful for the fishery research and management in Qiantang River.

Monitoring changes in fishery resources, such as the density and growth of fish, following large-scale fish stocking in a reservoir is important. In this study, BioSonics DT-X (201 kHz) was used to assess the seasonal changes in the density, size distribution, and biomass of fish in Duihekou Reservoir, Zhejiang province, China, in 2020. The fish density was significantly lower in spring (3.33 ind./1000 m³) than in summer (75.24 ind./1000 m³), autumn (56.22 ind./1000 m³), and winter (20.37 ind./1000 m³) (p < 0.01). No significant difference in fish density was apparent between summer and autumn. Additionally, the average target strength (TS) values in spring (−41.05 dB) were significantly higher than in summer (−44.66 dB) and autumn (−45.55 dB) (p < 0.01), but significantly higher in winter (−38.12 dB) than in the other seasons (p < 0.01); no significant difference was observed between the summer and autumn values (p > 0.01). The fish biomass in winter (14.3 g/m³) was 13 times that in spring (1.1 g/m³). These results indicate that large-scale fish stocking can effectively adapt to reservoir habitats to achieve growth. The catch composition revealed silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) to be dominant species, mostly comprising young individuals. Stock enhancement plays a critical role in reshaping the fishery population structure in a reservoir. These findings enhance our understanding of fishery resource changes in reservoirs after non-classical biomanipulation and demonstrate how hydroacoustic techniques can be successfully used to quantify the density and size distribution of fish for more effective fishery management.

The Oujiang River, the second‐largest river in Zhejiang Province, southern China, supports rich fishery resources. However, these resources have experienced significant decline due to multiple anthropogenic and environmental pressures. To assess the current status of fishery resources, this study investigated the length–weight relationships (LWRs) and length‐length relationships (LLRs) of 11 economically and ecologically important fish species. The results showed that the b values ranged from 2.534 to 3.469, with the coefficient of determination ( r ² ) ranging from 0.893 to 0.987. Notably, we provide the first LWR and LLR records for Acrossocheilus fasciatus and Microphysogobio oujiangensis in FishBase, along with a new maximum length record for Onychostoma barbatulum . These findings offer valuable baseline data to inform science‐based conservation and sustainable management of fisheries in the Oujiang River.