Wild fish living downstream of wastewater treatment plants (WWTPs) often have increased body condition factors or body mass indices compared to upstream fish. This observation has been largely attributed to increased nutrient loading and food availability around wastewater effluent outflows. While a higher condition factor in fish is generally considered a predictor of healthy ecosystems, the metabolic status and capacity of the animals downstream of WWTPs may be a better predictor of fitness and potential population level effects. To address this, we sampled wild longnose dace (Rhinichthys cataractae), a native species in North American waterways, from sites upstream and downstream of WWTPs. Downstream fish had higher body mass indices, which corresponded with higher nutrient (lipid, protein, and glycogen) storage in somatic tissues compared to upstream fish. Liver transcriptome analysis revealed metabolic reprogramming favoring lipid synthesis, including higher hepatic triglyceride levels and transcript abundance of targeted lipogenic genes. This suggests that effluent exposure-mediated obesity in dace is a result of changes at the transcriptional level. To determine potential ecological consequences, we subjected these fish to an acute stressor in situ to determine their stress performance. Downstream fish failed to mobilize metabolites post-stress, and showed a reduction in liver aerobic and anaerobic metabolic capacity. Taken together, fish living downstream of WWTPs exhibit a greater lipid accumulation that results in metabolic disruption and may compromise the ability of these fish to cope with subsequent environmental and/or anthropogenic stressors.

It is a common method to analyse physiological mechanisms of organisms – commonly referred to as biomarkers – to indicate the presence of environmental pollutants. However, as biomarkers respond to a wide range of stressors we want to direct the attention on natural stressors, i.e. on parasites. After two years maintenance under controlled conditions, roach (Rutilus rutilus) revealed no influence on levels of metallothionein by the parasite Ligula intestinalis. The same was found for Gammarus fossarum infected with Polymorphus minutus. However, the heat shock protein (HSP70) response was affected in both host-parasite systems. While the infection of roach resulted in reduced levels of HSP70 compared to uninfected roach, the infection in G. fossarum led to higher levels of HSP70. We also analysed the effect of a 14 days Cd exposure (4 μg/L) on the uninfected and infected gammarids. The exposure resulted in induced levels for both, metallothionein and HSP70 whereas the combination of stressors, parasite and exposure, revealed a decrease for levels of HSP70 in comparison to the metal exposure only. Accordingly, parasites as natural parts of aquatic ecosystems have to be considered in ecotoxicological research.

Gala Lake is an internationally important lake due to its location on one of the world's most important bird migration routes. For this reason, water quality of the lake is of great concern. However, the lake surrounded by paddy fields may face eutrophication and toxic metal contamination due to excessive use of fertilizers and pesticides. In this study, impact of paddy fields on water quality of the Gala Lake was investigated. The concentrations of metal(loid)s and physico-chemical parameters in surface water samples taken from the lake were measured and compared with water quality guidelines. Also, human health risks and contamination status of metal(loid)s were assessed. The mean NO₂, SRP and BOD concentrations in the lake exceeded the permissible levels for both salmonid and cyprinid waters. The mean BOD value indicated contaminated water quality in the lake, while mean COD and SRP values indicated lightly contaminated water quality. The mean As, Cr and Pb values in the winter exceeded the drinking water limits set by WHO and EC, while the mean Cr and Zn values exceeded the limit values for the protection of freshwater aquatic organisms set by USEPA. Similarly, heavy metal pollution index and the degree of contamination values in the winter indicated that the lake water is moderately polluted. Health risk assessment results revealed that As and Cr in the lake water via ingestion exposure pathway may pose both non-carcinogenic and carcinogenic health risks to the residents. The results of this study indicated that paddy fields are a major source of nutrients, organic matter and toxic metal(loid)s to the Gala Lake. To improve the water quality of the lake, we suggest that excessive use of fertilizers and pesticides should be controlled to reduce metal(loid) and nutrient loads from the paddy fields.

We examined Hg biogeochemistry in Baihua Reservoir, a system affected by industrial wastewater containing mercury (Hg). As expected, we found high levels of total Hg (THg, 664–7421 ng g⁻¹) and monomethylmercury (MMHg, 3–21 ng g⁻¹) in the surface sediments (0–10 cm). In the water column, both THg and MMHg showed strong vertical variations with higher concentrations in the anoxic layer (>4m) than in the oxic layer (0–4 m), which was most pronounced for the dissolved MMHg (p < 0.001). However, mercury levels in biota samples (mostly cyprinid fish) were one order of magnitude lower than common regulatory values (i.e. 0.3–0.5 mg kg⁻¹) for human consumption. We identified three main reasons to explain the low fish Hg bioaccumulation: disconnection of the aquatic food web from the high MMHg zone, simple food web structures, and biodilution effect at the base of the food chain in this eutrophic reservoir.

This paper reports on the partitioning behaviour of 15 perfluorinated compounds (PFCs), including C₄–C₁₀ sulfonates and C₅–C₁₄ carboxylic acids, between water, sediment and fish (European chub, Leuciscus cephalus) in the Orge River (nearby Paris). Total PFC levels were 73.0±3.0ngL⁻¹ in water and 8.4±0.5ngg⁻¹ in sediment. They were in the range 43.1–4997.2ngg⁻¹ in fish, in which PFC tissue distribution followed the order plasma>liver>gills>gonads>muscle. Sediment–water distribution coefficients (logKd) and bioaccumulation factors (logBAF) were in the range 0.8–4.3 and 0.9–6.7, respectively. Both distribution coefficients positively correlated with perfluoroalkyl chain length. Field-based biota–sediment accumulation factors (BSAFs) are also reported, for the first time for PFCs other than perfluorooctane sulfonate. logBSAF ranged between −1.3 and 1.5 and was negatively correlated with the perfluoroalkyl chain length in the case of carboxylic acids.

The current work represents the study on morphology and reproductive biology of two indigenous torrential fishes, Balitora brucei and Psilorhynchus balitora, for the first time. The Gray’s stone loach Balitora brucei and balitora minnow Psilorhynchus balitora abound in the torrential water bodies of South East Asia. The current paper redescribes morphology based on the fresh collection. Specific parameters of reproductive biology on both the fishes have been studied for the first time. Both the species were adapted to the same ecological conditions of the river Ranganadi. Fish specimens were collected at a fortnightly interval from the river in the Lakhimpur district of Assam, India. The detailed study includes morphological data analyzed with Mann–Whitney U-test and specific reproductive parameters such as condition factor (K), gonado-somatic index (GSI), modified gonado-somatic index (MGSI), and Dobriyal index (DI). Progressive development of the gonads was confirmed with dissection and histological study. Both the species are multiple breeders with prolonged reproductive seasons ranging from 4 to 5 months. Both the fishes are found to be migrants from upstream, and a good number of individuals were recorded during the monsoon season, reflecting the sampling site as a breeding ground. During winter, the local people use various chemicals, piscicidal plants, and electric instruments for fishing resulting in a steep decline in the number of individuals for both the species. Moreover, the effect of the North Eastern Electric Power Corporation Limited (NEEPCO) dam is evident on the decline of the ichthyofaunal diversity of the river. The results of present study will provide the baseline information on these two species of fishes for planning conservation measures in future.

The present field study, conducted during the spawning period (April/May) of European chub (Squalius cephalus L.) from the Sava River in Croatia, indicates that seasonal changes of fish physiological state might cause variability in gastrointestinal metal (Cd, Cu, Fe, Mn and Zn), total cytosolic protein and metallothionein (MT) levels. During the period of fish spawning and increased metabolic activity, a significant relationship with chub hepatosomatic index was evident for Fe and Mn in gastrointestinal tissue (r = 0.35 and 0.26, respectively) and in cytosolic fraction (r = 0.32 and 0.41, respectively) and for Zn and Fe in the gut content (r = 0.36 and 0.31, respectively). Total cytosolic protein and MT concentrations followed the same spatial distribution as Fe and Mn in all gastrointestinal fractions and as Zn in the sub-cellular fractions, with higher levels at upstream locations. Due to the role of essential metals in metabolic processes and gonad development, increased feeding and spawning activity in April/May resulted in higher gastrointestinal essential metal (Fe, Mn and Zn) and MT concentrations, which probably follow an increase in Zn concentrations, known as the primary MT inducer. Therefore, biotic factors should be considered as important confounding factors in metal exposure assessment, while their influence on gastrointestinal metal and protein levels should be interpreted depending on the season studied.

The assessment of general condition of fish in the moderately contaminated aquatic environment was performed on the European chub (Squalius cephalus) caught in September 2009 in the Sutla River in Croatia. Although increases of the contaminants in this river (trace and macro elements, bacteria), as well as physico-chemical changes (decreased oxygen saturation, increased conductivity), were still within the environmentally acceptable limits, their concurrent presence in the river water possibly could have induced stress in aquatic organisms. Several biometric parameters, metallothionein (MT), and total cytosolic protein concentrations in chub liver and gills were determined as indicators of chub condition. Microbiological and parasitological analyses were performed with the aim to evaluate chub predisposition for bacterial bioconcentration and parasitic infections. At upstream river sections with decreased oxygen saturation (∼50 %), decreased Fulton condition indices were observed (FCI: 0.94 g cm(-3)), whereas gonadosomatic (GSI: 2.4 %), hepatosomatic (HSI: 1.31 %), and gill indices (1.3 %) were increased compared to oxygen rich downstream river sections (dissolved oxygen ∼90 %; FCI: 1.02 g cm(-3); GSI: 0.6 %; HIS: ∼1.08 %; gill index: 1.0 %). Slight increase of MT concentrations in both organs at upstream (gills: 1.67 mg g(-1); liver: 1.63 mg g(-1)) compared to downstream sites (gills: 1.56 mg g(-1); liver: 1.23 mg g(-1)), could not be explained by induction caused by increased metal levels in the river water, but presumably by physiological changes caused by general stress due to low oxygen saturation. In addition, at the sampling site characterized by inorganic and fecal contamination, increased incidence of bacterial bioconcentration in internal organs (liver, spleen, kidney) was observed, as well as decrease of intestinal parasitic infections, which is a common finding for metal-contaminated waters. Based on our results, it could be concluded that even moderate contamination of river water by multiple contaminants could result in unfavourable living conditions and cause detectable stress for aquatic organisms.

Long-term cyanobacterial blooms and hypereutrophic state have been typical for the shallow, urban Swarzędzkie Lake for many years. Diversion of sewage did not change its trophic status, so restoration began in autumn 2011 using the sustainable approach based on three methods. The aim of the study was to analyse how sustainable restoration affects zooplankton. We hypothesised that bottom-up and top-down methods reconstructed zooplankton composition. Thus, the abundance of large-size cladocerans increased and controlled phytoplankton effectively. The elimination of cyanobacteria bloom, the decrease of rotifer abundance and the twofold increase of filter-feeder effectiveness were observed in summer 2012. However, high phosphorus concentration, lack of regular cyprinid removal and insufficient fish stocking together with high temperature prevented zooplankton from controlling cyanobacteria bloom in summer 2013. Rotifer domination with high trophy species was noted, as before restoration. The number of rotifers decreased in 2014, while crustaceans increased due to the significant decrease of nutrient concentrations and an intensification of biomanipulation treatments. Therefore, summer phytoplankton growth was low, without cyanobacteria dominance. The rebuilding of zooplankton in Swarzędzkie Lake was observed during sustainable restoration. However, the treatments should be intensified when adverse changes were observed to obtain better results for the improvement of water quality.

Treatment performance, fish production, crop plant biomass production, water consumption, and water use efficiency of a pilot aquaponic system for small-scale land-based cyprinid fish farms were evaluated. The system consisted of a 36 m³Pond A with an initial carp load of 0.6 kg/m³; of a treatment chain with a lamellar settler, a roughing filter, a vertical constructed wetland filled with expanded clay and planted with tomatoes; and of a low power ultrasound unit installed in the corner of the pond. The average circulation of the water in the system was 1.2 times per day. Pond A was compared with Pond B of the same dimensions and fish load but with no treatment chain or ultrasound. The treatment chain was efficient in mass removal of total suspended solids , biochemical oxygen demand, chemical oxygen demand, NH₄-N, total nitrogen, and total phosphorous (57, 49, 35, 42, 31, and 25 %, respectively). Negative removal of NO₃-N, NO₂-N, and PO₄-P indicated the need for the introduction of additional hydroponic beds in the system. Pond A had markedly lower nutrient concentrations compared with Pond B. Fish body weight increase and specific growth rate in Pond A were higher than in Pond B (102.6 %, 72.1 %; 0.19 %/day, 0.14 %/day, respectively) indicating better rearing conditions in Pond A. Tomato biomass production was high. Water use efficiency was higher in Pond A compared with Pond B (0.31 kg of produced fish/m³inflow water and 0.22 kg of produced fish/m³inflow water, respectively). The presented aquaponic system could be useful for semi-natural fish farming with fish loads up to 2 kg/m³.