With the decrease in fish diversity, the monitoring of fish has become a current research hotspot. Here, the fish diversity and spatial distribution along a salinity gradient (0.28‰–3.32‰) in Xinglinwan Reservoir, China, were investigated using eDNA and the TSM. With the combination of both methods, 12 species from 6 orders, 9 families, and 11 genera were observed. The invasive species Oreochromis niloticus had the highest relative abundance, accounting for 56.91% in the TSM and 89.80% in eDNA, respectively. eDNA detected 83.33% of the species detected using the TSM, and an additional six species (50.0% of the total species) were detected via only eDNA. Moreover, eDNA supplemented the unavailable abundance data from the TSM. The TSM revealed that the diversity and relative abundance of fish inhabiting seawater and brackish water increased with an increase in salinity, but this was not found using eDNA. Thus, our study highlights that Xinglinwan Reservoir has a low species richness and is suffering from the great harm of ecological invasion. Our findings also show that eDNA could be reliable for providing a comprehensive picture of fish, but discriminating the spatial heterogeneity of fish communities is a challenge for its widespread adoption in lentic brackish systems.

Organic matter in the productive mangrove–estuary ecosystem plays an important role in global climate changes. In recent years, the eutrophication in such areas caused by anthropogenic inputs of sewage has been revealed, highlighting the need to understand its influence on organic matter. In this study, δ¹³C and δ¹⁵N were used to reveal the effects of sewage on organic matters in the Zhangjiang mangrove–estuary ecosystem. Our results indicate that sewage contributed the most of the total particulate organic matter (41%) in the Zhangjiang estuary, while mangrove plants contributed most of the soil organic matter (45%) in the neighboring Yunxiao mangrove. Phytoplankton was another important source of organic matter, accounting for about 21.8% and 49.8% of the particulate and soil organic matter, respectively. Sewage was also a major source of dissolved inorganic nitrogen, providing 28.9%, 12.2%, and 100% of the total NO₃⁻, NO₂⁻, and NH₄⁺ in the Zhangjiang estuary, respectively. This may be the major reason for the productive phytoplankton here, which contributed 21.8% and 49.8% of the total particulate and soil organic matter in the study area. Our results reveal the direct contribution and the potential effects of sewage on the contents and bioavailability of organic matter in mangrove–estuary ecosystems, providing new insights into understanding the response of coastal areas to the influence of human activities.

The quantitative evaluation of restocking and stock replenishment is essential for providing operational feedback and implementing adaptive management for future restoration projects. Since 2010, approximately 700 million juvenile shrimp (Penaeus penicillatus) have been released into Xiamen Bay, Fujian Province, China, each year, through stock replenishment programs. The recruited shrimp were sampled through three-year bottom trawl surveys from 2014 to 2017. The biological characteristics and catch equation were used to evaluate the effect of restocking and stock replenishment. The analysis uses the FAO-ICLARM Stock Assessment Tool (FISAT II) program. In general, there are two sources of recruitments—one from spawning brood stock and the other from released juvenile shrimp. We constructed an evaluation model for an effect evaluation based on Baranov’s catch equation to separate the initial recruitment volume using survey data. The relationship between body weight and total length was W = 1.638 TL^2.9307. There is no statistically significant difference between males and females. The von Bertalanffy growth parameters derived for prawns, using FiSAT II, were L_∞ = 209.6 mm and K = 0.51 per year. In spring 2014, the initial resource amount was 49,200, while the ratio of effective recruitment and parent amount was 3.92. The survival rate of the released shrimp larvae, 1.88‱, seems to be very unsatisfactory. The resource amount in summer and autumn is higher than in winter and spring. Obviously, the restocking effect is lower and the programs need to be improved. To improve the restocking effect, the replenishment performance should be adjusted to reduce the mortality rate and increase its release effectiveness. Therefore, corresponding implementations are recommended, including standard extensive culture, reduction in stress during transportation, and temporary culture.

Controversies surrounding the phylogenetic relationships within the family Apogonidae have persisted due to the limited molecular data, obscuring the evolution of these diverse tropical marine fishes. This study presents the first complete mitochondrial genome of Fowleria variegata, a previously unrepresented genus, using high-throughput Illumina sequencing. Through a comparative mitogenomic analysis, F. variegate was shown to exhibit a typical genome architecture and composition, including 13 protein-coding, 22 tRNA and 2 rRNA genes and a control region, consistent with studies of other Apogonidae species. Nearly all protein-coding genes started with ATG, while stop codons TAA/TAG/T were observed, along with evidence of strong functional constraints imposed via purifying selection. Phylogenetic reconstruction based on maximum likelihood and Bayesian approaches provided robust evidence that F. variegata forms a basal lineage closely related to P. trimaculatus within Apogonidae, offering novel perspectives into the molecular evolution of this family. By generating new mitogenomic resources and evolutionary insights, this study makes important headway in elucidating the phylogenetic relationships and mitogenomic characteristics of Apogonidae fishes. The findings provide critical groundwork for future investigations into the drivers of diversification, speciation patterns, and adaptive radiation underlying the extensive ecological diversity and biological success of these marine fishes using phylogenomics and population genomics approaches.

The rapid development of China’s economy has brought tremendous pressure to the marine ecosystem, and about 57% of marine fish populations have been overexploited or collapsed. A series of fisheries policies have been implemented successively to improve the decline of resources. Over the past decade, the fisheries sector has particularly increased focus on resource and ecosystem sustainability, which has led to the wider use of stock management policies in China. Therefore, fishery resource assessment is crucial, such as assessing the long-term changes in biological information. This study is based on biological characteristics of Johnius belengerii captured by bottom trawls in Xiamen Bay during two periods, beginning in 2006 and 2016. Length composition, length–weight relationship, growth, mortality, sexual maturation, and feeding intensity were analyzed. The changes in biological characteristics show that there is a phenomenon of improvement in the later period, of which the changes are closely related to a series of fisheries management strategies, such as setting closed fishing periods and non-fishing areas, and establishing fishery restoration marine protected areas. This result seems to reveal the effectiveness of a long-term series of fisheries policies. It can provide an important basis and visibility for management effectiveness.