Do the total mercury concentrations detected in fish from Czech ponds represent a risk for consumers?

Mercury is one of the important pollutants of the environment. Therefore, it’s necessary to monitor quantity of mercury especially in aquatic ecosystems. The main goal of the presented study was to compare the content of total mercury in tissues of fish coming from the Czech Republic, an important carp exporter, with focus on comparison of mercury content between 3 different ponds, its comparison between different fish species and between different tissues of the same species, and estimation whether the mercury content in tissues meets the limit given in the Commission Regulation (EC) No. 1881/2006 or not. Total mercury concentration was measured in 90 fish specimen sampled from three ponds (Velky Kocelovicky, Mysliv and Zehunsky) in autumn 2018. The values of total mercury in fish tissues was measured by atomic absorption spectrometry. The content of total mercury in the tissues decreased as follows: muscle > liver > gonads > scales. The highest average content of total mercury in muscle was 0.1517 ± 0.0176 mg/kg coming from pike caught in Velky Kocelovicky pond. In contrast, the lowest average content of total mercury in muscle 0.0036 ± 0.0003 mg/kg was found in carp tissue coming from the locality of Zehunsky pond. We confirmed that the predatory fish are more exposed to mercury than non-predatory fish. None of the monitored localities exceeded the set regulatory limit. Thus, our study shows that fish coming from these ponds are safe in terms of total mercury content.

Diet and isotopic niche dimensions of predatory fish in two estuaries with different degrees of anthropogenic disturbances: a case study of Wami and Pangani Tanzanian coastal estuaries

Diverse anthropogenic activities including alteration of hydrological regime and agricultural development in the upstream of the river catchments modify the structural components and ecological roles of the species in estuarine ecosystems. The present study compared the diet, carbon (δ13C) and nitrogen (δ15N) isotopic signals, trophic niches and metrics of trophic redundancy of predatory fish and their potential phytodetritivore prey-fish between two estuaries with different degrees of anthropogenic disturbances. The δ13C and δ15N signals, Bayesian mixing models and stomach content analyses were adopted. It was revealed that the diet among the predators Arius africanus, Epinephelus coioides, Sillago sihama and Pomadasys argenteus and their isotopic signals including their phytodetritivore-prey, Valamugil buchanani were significantly different between Wami and Pangani estuaries (PERMANOVA, Pseudo –F ≥ 3.1, p = 0.05). The total isotopic niche area between estuaries accounted by the comparable Bayesian standard ellipse area (SEAb) was significantly smaller in Wami than that of Pangani (t-test, t = 4.3, p < .001). The ANOVA test further confirmed significant variation in SEAb among fish populations in two estuaries (F = 27.84, p < 0.001). The Layman metric indices of trophic diversity and redundancy of Wami estuary were substantially smaller than those observed at Pangani estuary. These findings mean that despite Wami estuary being under conservation status, the extent of disturbances in the upstream is high enough to induce the ecological changes at the base of the food web, subsequently cascading its effect up to the higher-order consumers of the ecosystem. As a result, the ecological redundancy and ecosystem complexity of Wami is somewhat compromised relative to that of Pangani estuary. Therefore, the degree of anthropogenic disturbances in river catchments affect differently the trophic niches of predatory and phytodetritivore fish and hence overall food web structures, trophic redundancy and complexity of estuarine ecosystems.

A Food-Safety Risk Assessment of Mercury, Lead and Cadmium in Fish Recreationally Caught from Three Lakes in Poland

Heavy metals are introduced into water due to anthropogenic activities and can significantly affect an entire ecosystem. Due to their close integration with the water environment, fish are a sensitive indicator of contamination. In addition, fish is an important element in human diets, therefore, monitoring the concentrations of metallic contaminants in their meat is particularly important for food safety. This study aimed to assess the pollution of water ecosystems with selected toxic heavy metals in lakes Dratów, Czarne Sosnowickie, and Syczyńskie. The concentration of Pb, Cd, and Hg in water, sediment, and freshwater fish muscle tissue was determined, and a food safety assessment was performed. The analysis of water and sediments showed that the sediments were characterised by a significantly higher concentration of heavy metals. Presumably, this ecosystem element plays an important role in the uptake of heavy metal contaminants by fish whose levels were higher in planktonophagous and benthophagous fish species as compared to predatory fish. The food safety assessment showed that amounts of heavy metals in the muscle tissue posed no threat to the health of consumers ingesting that fish species, neither individually (THQ) nor collectively (TTHQ).

First record of exotic alligator gar, Atractosteus spatula (Actinopterygii: Lepisosteiformes: Lepisosteidae), from Ganga River system, India: A possible threat to indigenous riverine fish diversity

A new record of an exotic alligator gar, Atractosteus spatula (Lacepède, 1803), from an open wetland of the Ganga River was presented in this paper and discussed along with the environmental parameters. Entry of the exotic fish into the natural system was probably a result of uncontrolled ornamental fish trading. Considering threats of this predatory fish to become invasive and disturb riverine fish diversity, possible ways to avoid such risk have been discussed.

Environmental Preferences and Fish Handling Practice among European Freshwater Anglers with Different Fishing Specialization Profiles

Recreational specialization is characteristic of many activities, including recreational fishing, which is a popular and important form of recreation throughout the world. The pressure on the environmental resources used by anglers is increasing. It is becoming crucial to understand the preferences and behaviors of anglers, which can accumulate and multiply the risk of damage to fish stocks and aquatic habitats. The main objective of the study was to comprehensively analyze the differences between anglers with diverse specialization profiles. By investigating the fishing preferences within the context of the socioeconomic, demographic and engagement factors, three groups of anglers were identified: anglers who specialize in predatory fish, anglers who specialize in non-predatory fish and unspecialized anglers. Specialized anglers, regardless of type, were found to be more supportive of releasing caught fish (71% on average) and were less likely to keep them (16%) than unspecialized anglers (55% and 27%, respectively). Unspecialized anglers (26.5% of the surveyed population) show less commitment to ethical values. The potential negative environmental impact of the least specialized anglers is an accumulation of the preferences for the use of ground bait, artificial lures, and live fish as bait. Anglers specializing in predatory fish are the most critical in their evaluation of fish resources and water quality and are least attached to specific fisheries. This work provides insight into angler experience and it may help to better identify anglers who are disrespectful towards the fishing laws in place. The results of this work may be incorporated into fishery management strategies, including strategies to reduce naïve anglers and deter disrespectful anglers, which are lucrative in the fishing process.

Restored Coastal Habitat Can “Reel In” Juvenile Sportfish: Population and Community Responses in the Indian River Lagoon, Florida, USA

Coastal habitats are declining worldwide, which has impacted economically important fisheries, especially in the Indian River Lagoon, Florida. As a result, extensive intertidal oyster reef and living shoreline restoration projects have been implemented. Restoration can also theoretically benefit predator populations, but this relationship is understudied. Here, the impact of habitat restoration on juvenile predatory fish (i.e., sportfish) populations (abundance) and communities (species richness, diversity, and assemblage) was assessed prior to and following oyster reef restoration and living shoreline stabilization for up to three years, and incorporated the influence of 17 environmental predictor variables. Juvenile sportfish abundance and richness (n = 11) were variable over time but collectively higher on restored oyster reefs compared to controls, and similar between control and stabilized shorelines. Sportfish abundance was best described by a combination of biotic features of the site (e.g., reef height and benthic substrate cover), prey abundance, decreasing distance to the nearest ocean inlet and dissolved oxygen. Results suggest future restoration site selection should emphasize adequate dissolved oxygen (~6 mg/L), oyster densities above 50/m2 and reef height above 55 mm, and minimum shoreline vegetation coverage of 50% to support macrofaunal prey and subsequently attract sportfish. These findings can help natural resource managers better use habitat restoration as a tool for enhancing fish populations in the future.

Effects of chlorpyrifos on early development and anti-predator behavior of agile frogs

The widespread application of pesticides makes it important to understand the impacts of these chemicals on wildlife populations. Chlorpyrifos is an organophosphate insecticide which can affect the development and behavior of aquatic organisms and may thereby alter predator-prey interactions. To investigate how environmentally relevant, sublethal concentrations of chlorpyrifos affect anti-predator behavior and larval development of the agile frog (Rana dalmatina), we exposed tadpoles to one of three concentrations (0, 0.5 and 5 μg chlorpyrifos / L) either for a brief period of three days (acute exposure) or throughout larval development (chronic exposure). We observed tadpole activity and space use in the presence or absence of chemical cues of predatory fish. We also assessed mortality, time to metamorphosis, mass at metamorphosis, brain morphology and sex ratio. We found that tadpoles chronically exposed to 5 μg/L chlorpyrifos swam distances that were longer by more than 20 % and exhibited body masses at metamorphosis that were lower by ca. 7 % than in control individuals, but the other fitness-related traits remained unaffected. The lower concentration of chlorpyrifos applied chronically, and either one of the acute chlorpyrifos treatments did not influence any measured trait. Our results demonstrate that exposure to chlorpyrifos can induce changes in locomotor activity and may result in lowered body mass of agile frog tadpoles, but only if the insecticide is present chronically at concentrations which are rarely reached in natural waterbodies. Thus, agile frog tadpoles appear to be relatively tolerant to chlorpyrifos, but may nonetheless suffer from its presence in situations of repeated high-dose application.