The Effect of an Anthropogenic Magnetic Field on the Early Developmental Stages of Fishes—A Review

The number of sources of anthropogenic magnetic and electromagnetic fields generated by various underwater facilities, industrial equipment, and transferring devices in aquatic environment is increasing. These have an effect on an array of fish life processes, but especially the early developmental stages. The magnitude of these effects depends on field strength and time of exposure and is species-specific. We review studies on the effect of magnetic fields on the course of embryogenesis, with special reference to survival, the size of the embryos, embryonic motor function, changes in pigment cells, respiration hatching, and directional reactions. We also describe the effect of magnetic fields on sperm motility and egg activation. Magnetic fields can exert positive effects, as in the case of the considerable extension of sperm capability of activation, or have a negative influence in the form of a disturbance in heart rate or developmental instability in inner ear organs

Population structure and density of a new invasive species Rangia cuneata in the Szczecin Lagoon (Odra/Oder estuary, Poland)

The native North American bivalve species Rangia cuneata was unintentionally introduced into European waters during the first decade of the 21st century. In the Baltic Sea, it is mostly found along the southeastern coast, but in 2018 researchers also discovered the species in the Bay of Pomerania, which indicated that it could eventually inhabit the adjacent Szczecin Lagoon and Odra River. In 2021, the species was discovered for the first time in the Szczecin Lagoon during a sampling campaign, at 5 out of the 12 dispersed study sites with diverse bottom substrates. The goal of this study was to ascertain R. cuneata population density, morphometric parameters, individual growth, and the potential for further expansion in the southern Baltic Sea waters. For the study, 201 individuals of this species were collected. Compared to other sites in the southeast Baltic, the Szczecin Lagoon had a much lower average R. cuneata population density, at 13.2 ± 7.11 individuals m-2 of the bottom area. The highest population density was found at sites with more silt (4–63 µm) and less sand (>63 µm). R. cuneata shells had an average length of 30.9 ± 4.6 mm and an average weight of 6.6 ± 2.8 g. The collected specimens were greater in size than other populations of the species in the Baltic Sea and were comparable in size to populations from the nearby Bay of Pomerania. There were no specimens that were under 10 mm in length, and the population was dominated by specimens in the 25–30 mm and 30–35 mm ranges, as well as the 3+ and 4+ age groups. Given the R. cuneata's invasive potential and its fast rate of colonization of new areas, it would be prudent to monitor this population and the species migration patterns across the estuary waters of the western Baltic

The Effect of an Anthropogenic Magnetic Field on the Early Developmental Stages of Fishes—A Review

The number of sources of anthropogenic magnetic and electromagnetic fields generated by various underwater facilities, industrial equipment, and transferring devices in aquatic environment is increasing. These have an effect on an array of fish life processes, but especially the early developmental stages. The magnitude of these effects depends on field strength and time of exposure and is species-specific. We review studies on the effect of magnetic fields on the course of embryogenesis, with special reference to survival, the size of the embryos, embryonic motor function, changes in pigment cells, respiration hatching, and directional reactions. We also describe the effect of magnetic fields on sperm motility and egg activation. Magnetic fields can exert positive effects, as in the case of the considerable extension of sperm capability of activation, or have a negative influence in the form of a disturbance in heart rate or developmental instability in inner ear organs

Characterisation of Benthic Macroinvertebrate Communities in Small Watercourses of the European Central Plains Ecoregion and the Effect of Different Environmental Factors

Most publications on the influence of environmental factors on macroinvertebrate communities focus on large rivers, whereas relatively few examine small watercourses in agricultural areas, which, due to their size and pressure from intensive agricultural production, are much more susceptible to the effects of unfavourable environmental conditions or anthropopressure. The aim of our study was to compare the biodiversity of macrozoobenthos assemblages and to determine the effects of physicochemical and hydrological conditions on their abundance and density in 10 small rivers in agricultural areas located in northwest (53°23′ N 15°14′ E) and central (52°11′ N 20°48′ E) Poland. In total, 105 taxa were recorded, with the majority being euryoecious. Among the assessed physicochemical parameters, oxygenation was found to affect the density and number of taxa; another important factor was the content of nitrate nitrogen. Sensitivity to changes in water temperature was observed in some macrozoobenthos taxa (especially Decapoda). Of the examined hydrological parameters, the greatest effects were exerted by speed, flow, and depth

Fish Diversity and Abundance Patterns in Small Watercourses of the Central European Plain Ecoregion in Relation to Environmental Factors

Because of their size, small depth, periodic drying out, and often lack of buffer zone, small watercourses are especially sensitive to environmental changes, anthropopressure, and biodegradation which makes them extremely prone to decline in biodiversity. Small watercourses can harbor many species of fish, including alien and invasive species. The objectives of this study were the assessment of environmental conditions, the determination of the number of fish species, their density and diversity in 10 small water courses of the European ecoregion ‘Central Plains’, and to estimate the effect of individual habitat parameters on the ichthyofauna. The total number of fish caught during the study was 9339, representing 33 species. Statistical analyses showed that the density of rheophilous fish was under the effect of flow velocity, discharge, width, depth, oxygen content, and pH; for the limnophilous species, the decisive factors were: discharge, depth, width, and P-PO4. The density of the euryoecious species was affected by depth, pH, electric conductivity (EC), oxygen, as well as N-NO3. All the species were significantly influenced by sandy substratum and the development of aquatic vegetation. Each guild, and even individual species, had their preferred habitat conditions, which is important for water management, renaturisation, and restitution

Effect of Filter Medium on Water Quality during Passive Biofilter Activation in a Recirculating Aquaculture System for Oncorhynchus mykiss

High-performance biofilters for water purification in recirculating aquaculture systems (RAS) ensure the safety of cultures of highly nutritious fish. As the most critical step in the functioning of biofilters is their activation, the objective of this study was to evaluate the suitability of commercial artificial media, namely RK Plast (BR-1), Mutag-BioChip30 (BR-2), and LevaPor (BR-3), for the passive activation of biofilters used in rainbow trout farming. Changes in NH4+-N, NO2−-N, NO3− -N, phosphorus, and carbon concentrations were analyzed. In the first period, an increase in NH4+-N concentration was recorded, before an increase in NO2−-N concentration (maximum concentrations ranged 0.728–1.290 and 0.982–5.198 mg N dm−3, respectively), followed by a reduction and stabilization to a level safe for the fish (both below 0.100 mg N dm−3). Concurrently, a steady increase in NO3−-N concentration was noted, with a maximum concentration between 6.521 and 7.326 mg N dm−3. Total phosphorus and total carbon ranged from 0.423 to 0.548 mg P dm−3, and from 43.8 to 45.2 mg C dm−3. The study confirmed the feasibility of using the tested artificial biofilter media for rainbow trout farming in RAS with passive biofilter activation. Biofilter activation efficiency was highest for the media with the highest specific surface area (BR-2 and BR-3). The removal of ammonium nitrogen and nitrite nitrogen was above 90%. Nitrogen biotransformation was not limited by phosphorus or carbon concentrations

Fish Diversity and Abundance Patterns in Small Watercourses of the Central European Plain Ecoregion in Relation to Environmental Factors

Because of their size, small depth, periodic drying out, and often lack of buffer zone, small watercourses are especially sensitive to environmental changes, anthropopressure, and biodegradation which makes them extremely prone to decline in biodiversity. Small watercourses can harbor many species of fish, including alien and invasive species. The objectives of this study were the assessment of environmental conditions, the determination of the number of fish species, their density and diversity in 10 small water courses of the European ecoregion ‘Central Plains’, and to estimate the effect of individual habitat parameters on the ichthyofauna. The total number of fish caught during the study was 9339, representing 33 species. Statistical analyses showed that the density of rheophilous fish was under the effect of flow velocity, discharge, width, depth, oxygen content, and pH; for the limnophilous species, the decisive factors were: discharge, depth, width, and P-PO4. The density of the euryoecious species was affected by depth, pH, electric conductivity (EC), oxygen, as well as N-NO3. All the species were significantly influenced by sandy substratum and the development of aquatic vegetation. Each guild, and even individual species, had their preferred habitat conditions, which is important for water management, renaturisation, and restitution

A Visual Feedback for Water-Flow Monitoring in Recirculating Aquaculture Systems

The optimal water flow in fish breeding tanks is one of the crucial elements necessary for the well-being and proper growth of fish, such as salmon or trout. Considering the round tanks and the uneven distribution of water-flow velocity, ensuring a nearly optimal flow is an important task that may be performed using various sensors installed to monitor the water flow. Nevertheless, observing the rapid development of video analysis methods and considering the increasing availability of relatively cheap cameras, the use of video feedback has become an interesting alternative that limits the number of sensors inside the water tanks in accordance with the requirements of fish breeders. In this paper, an analysis of the use of optical flow algorithms for this purpose is performed and an estimation method based on their features is proposed. The results of the flow estimation using the proposed method are verified experimentally and compared with the measurement results obtained using the professional water-flow meter, demonstrating a high correlation, exceeding 0.9, confirming the proposed solution as a good alternative in comparison to the use of expensive sensors and meters

Effect of Filter Medium on Water Quality during Passive Biofilter Activation in a Recirculating Aquaculture System for <i>Oncorhynchus mykiss</i>

High-performance biofilters for water purification in recirculating aquaculture systems (RAS) ensure the safety of cultures of highly nutritious fish. As the most critical step in the functioning of biofilters is their activation, the objective of this study was to evaluate the suitability of commercial artificial media, namely RK Plast (BR-1), Mutag-BioChip30 (BR-2), and LevaPor (BR-3), for the passive activation of biofilters used in rainbow trout farming. Changes in NH4+-N, NO2−-N, NO3− -N, phosphorus, and carbon concentrations were analyzed. In the first period, an increase in NH4+-N concentration was recorded, before an increase in NO2−-N concentration (maximum concentrations ranged 0.728–1.290 and 0.982–5.198 mg N dm−3, respectively), followed by a reduction and stabilization to a level safe for the fish (both below 0.100 mg N dm−3). Concurrently, a steady increase in NO3−-N concentration was noted, with a maximum concentration between 6.521 and 7.326 mg N dm−3. Total phosphorus and total carbon ranged from 0.423 to 0.548 mg P dm−3, and from 43.8 to 45.2 mg C dm−3. The study confirmed the feasibility of using the tested artificial biofilter media for rainbow trout farming in RAS with passive biofilter activation. Biofilter activation efficiency was highest for the media with the highest specific surface area (BR-2 and BR-3). The removal of ammonium nitrogen and nitrite nitrogen was above 90%. Nitrogen biotransformation was not limited by phosphorus or carbon concentrations