In this study, water from three urban wetlands of Gurugram – Sultanpur (WS), Damdama (WD), and Basai (WB), was studied for various physicochemical parameters to assess their suitability for the healthy survival of fishes and the results were compared with the limits of these parameters for fish farming. The parameters studied were colour, temperature, pH, alkalinity, hardness, Ca2+- Mg2+ ratio, NO3-, Cl-, SO42-, PO43-, and heavy metals (Fe, Mn, Cr, Cu, Zn, Ni and Pb). The results of the study indicate the majority of studied parameters are beyond the desirable limits in WB; thus, water is most unsuitable for fishes in WB. WB is unsuitable for parameters: colour, alkalinity, hardness, Ca -Mg ratio, NO3-, Cl-, SO42-, PO43-, Cr, Cu, Fe, Mn, Ni and Zn. WS needs consideration for temperature, NO3-, Cu, Ni and Zn, whereas WD needs improvement in temperature, TDS, NO3-, Cr, Cu, Fe, Mn, Ni and Zn concentration for better fish growth. Most of the parameters are high in summer as compared to winter, which is due to the dilution after rainfall. Hence, we recommend timely action for effective measures to improve the water quality of wetlands and their regular monitoring for improved fish habitat.

To assess the aquaculture-induced sediment conditions associated with sulfur cycles, shifts in bacterial communities across farming stages were investigated. The sulfate reduction rate (SRR), and concentrations of acid volatile sulfide (AVS) and H₂S were significantly higher at the mid- and post-farming stages than at the early stage, indicating that the aquaculture effects persist even after harvest. Incomplete organic carbon–oxidizing sulfate-reducing bacteria (IO-SRB) affiliated with Desulfobulbaceae, and gammaproteobacterial sulfur oxidizing bacteria (SOB) (Thiohalobacter, Thioprofundum, and Thiohalomonas) were dominant during the early stage, whereas fermenting bacteria (Bacteroidetes and Firmicutes) and complete oxidizing SRB (CO-SRB) belonging to Desulfobacteraceae, and epsilonproteobacterial SOB (Sulfurovum) dominated during the mid- and post-stages. The shift in SRB and SOB communities well reflected the anoxic and sulfidic conditions of farm sediment. Especially, the Sulfurovum-like SOB correlated highly and positively with H₂S, AVS, and SRR, suggesting that they could be relevant microbiological proxies to assess sulfidic conditions in farm sediment.

In the last decade, the salmon aquaculture industry has considerably increased the use of lumpfish juveniles as cleaner fish. Potential escape of reared lumpfish into the wild may spread diseases or genetically contaminate wild stocks. The guidelines for minimum sizes of cleaner fish to use in aquaculture cages are currently based on simple mesh penetration tests. However, these guidelines do not consider the potential compressibility of fish or changes in mesh state due to factors such as sea conditions and maintenance operations. This study shows that the industry-recommended minimum stocking sizes for a given mesh size may result in escape risk and that ignoring fish compressibility and mesh state can lead to underestimation of the lumpfish sizes that are able to escape. Our results can be used to develop new guidelines that will contribute to reduced escape of lumpfish from salmonid farms and lessen the potential environmental consequences.

Six cruises were conducted in a fish farm adjacent to the Ninghai Power Plant in Xiangshan Bay, East China Sea. Fish farming significantly increased NH4+, DIP, and TOC concentrations, while it significantly decreased the DO level. These increase/decrease trends were more pronounced in warmer seasons. Although culture practices did not significantly increase phytoplankton density, it drastically enhanced dinoflagellate abundance and domination. Significant differences in species diversity and community composition between the cages and the control area were also observed. Temperature elevation caused by thermal discharge associated with eutrophication resulted in a dominant species shift from diatoms alone to dinoflagellates and diatoms. This is the first report of stress-induced toxic dinoflagellate (Prorocentrum minimum) blooms in winter and the winter–spring transition in this bay. Therefore, the effects of aquaculture activity and power plant construction in such a eutrophic, semi-enclosed bay require further attention.

Eutrophication is a major threat to aquatic ecosystems, because excessive nutrient enrichment may result in the loss of ecosystem services. Fjord systems are specifically under pressure due to nutrient input from land (agriculture) and sea (aquaculture). In this bioassay study, we have analyzed the effect of different nutrient sources, as well as their combination, on growth, nutrient composition and recruitment of habitat-forming and ephemeral macrophytes. We found that agricultural fertilizer increased growth for all algae (except Fucus), while the fish farm effluents mainly increased growth of Ulva. The C:N ratio was hardly affected by the fish farm, but decreased significantly in all algae when agriculture fertilizer was added. Most interestingly, however, distance to the fish farm modulated the algal response to the fertilizer. Our results demonstrate the importance of studying effects of multiple stressors in aquatic ecosystems to sustainably manage the consequences of anthropogenic impacts.

Tidal flat is an important supplementary land resource. However, increasing tidal flat reclamation in China has resulted in severe environmental issues. Using single-metal pollution index and multi-metal Nemerow pollution index, this study aimed to evaluate the risks of heavy metal pollution among different tidal flat use types, including fish farm, farmland, pastoral land, industrial land, forest and unutilized land. The results indicated that, concentrations of all elements were higher than geochemical values; Cd posed the highest risk, followed by As and Ni. Fish farm created the highest risk, followed by farmland. Every one year increase in fish farming led to increases in sediment concentrations of Cu, Cr, Ni, Pb, Zn and As by 0.73, 1.25, 0.68, 0.41, 1.22 and 0.20 mg.kg⁻¹, respectively. Tidal flat reclamation in Jiangsu Province creates the risk of heavy metal pollution, and specific attention should be paid to the fodders and additives used in fish farming.