Brown trout in Oder estuary tributaries: genetic structure, stocking, and admixture.

Several rivers that are tributaries of the Oder estuary are inhabited by Salmo trutta L, the most important of which are Ina, Gowienica, and Wolczenica. Both forms of the species, sea trout and resident brown trout, are present. All rivers are traditionally stocked with either sea trout from the neighboring Pomeranian river Rega basin or resident brown trout from various locations. To examine populations in these rivers in terms of genetic structure, genetic diversity, and origin, they were analyzed using 13 microsatellite loci. Relatedness was also assessed for fish stocked in the same year. The obtained genotypes were compared with breeding stocks used for stocking in Poland. The analyses revealed a significant genetic distance between adult individuals from Ina and Rega Rivers and fish caught during electrofishing. Strong kinship relationships were identified in the sampled areas, with high proportions of fish originating from stocking and their dominance in numbers over wild juveniles, primarily in smaller tributaries. Additionally, clear separation in the origin of stocked individuals was observed. Adult trout from Ina and Rega are genetically closer to northern brown trout lineages, providing crucial information for the management and biodiversity conservation of Polish Salmo trutta populations.

The impact of electromagnetic fields generated by high-voltage power lines on the spatial arrangement of pike (Esox Lucius Linnaeus 1758) embryos.

Urbanization and technological advancements result in the dispersion of antropogenic electromagnetic fields (EMF) that can affect on ecosystems. Therefore, it is important to understand their impact on the environment. Aquatic ecosystems are subject to EMF as part of various electricity sources, e.g., high-voltage transmission lines (HVTL). We examined the impact of EMF generated by HVTL on the spatial arrangement and survival of pike (Esox lucius) embryos. Fertilized eggs were incubated under two HVTL configurations 110 kV and 220 kV compared with a control group devoid of anthropogenic EMF. Embryo orientation and survival were monitored until blastopore closure. The control group showed dominance in the arrangement of embryos along the N-S, NNW-SSE, and NNE-SSW axes, with a slight prevalence of northern directions. EMF originating from HVTL did not exert a significant influence on the spatial arrangement of pike embryos, although some deviations from the arrangement noticed in the control group were observed. Increased embryo mortality was observed only at 110 kV site, but probably due to factors unrelated to EMF. In conclusion, EMF generated by HVTL did not significantly change pike embryo orientation or chances of survival. However, longer exposure or higher EMF levels could provoke notable reactions, requiring ongoing evaluation as power networks continue to spread more widely.

Early Ontogeny of Cichlids Using Selected Species as Examples.

The purpose of this study was to characterize in detail the reproductive strategy, course of embryogenesis, and development of larvae in three species of fishes of the genus Cichlasoma: the green terror (Andinoacara rivulatus), the red discus (Symphysodon discus), and the jaguar cichlid (Parachromis managuensis). Eggs for the study were obtained from five pairs of each species (300 eggs from each female) and incubated at 26 °C. The developing eggs were observed under a microscope (Carl Zeiss Stereo Discovery. V12 and Nikon 2000SE software (NIS-Elements F 4.30.01 64-bit) from fertilization to larval hatching until complete yolk-sac resorption. The largest average number of eggs per female was found in the jaguar cichlid (x¯ = 2991 eggs), a smaller average number of eggs was shown in the green terror (x¯ = 922 eggs), and the red discus showed the smallest average number of eggs (x¯ = 300 eggs). There were significant differences in the sizes of the eggs of the studied species: jaguar cichlid eggs were the smallest (1.060 ± 0.05 mm3), red discus eggs were larger (1.070 ± 0.07 mm3), and green terror eggs were the largest (1.365 ± 0.16 mm3). The embryogenesis time in the red discus was 2132 °H (82 Hpf), in the green terror it was 2158 °H (83 Hpf), and the longest in the jaguar cichlid was 2470 °H (87 Hpf). At the end of embryogenesis, the average size of the larvae after hatching was measured (red discus x¯ = 4.346 mm, green terror x¯ = 5.203 mm, and jaguar cichlid x¯ = 5.301 mm) and the time of yolk-sac resorption from the moment of hatching to the transition from endogenous to exogenous feeding was determined (jaguar cichlid 5 days, green terror 6 days, and red discus 3 days). The results of this study may contribute to the development of reproductive biotechnology for the studied fishes that could be used in aquaculture and, thus, help protect them in their natural habitats.

Habitat Conditions of the Microbiota in Ballast Water of Ships Entering the Oder Estuary.

Ballast water is a vector for the transfer of microorganisms between ecospheres that can subsequently have a negative impact on native species of aquatic fauna. In this study, we determined the microbiota and selected physicochemical properties of ballast water from long- and short-range ships entering a southern Baltic port within a large estuary in autumn and winter (Police, Poland). Microbiological tests of the ballast water samples were carried out according to ISO 6887-1, and physicochemical tests were performed according to standard methods. Low amounts of oxygen (1.6-3.10 mg/dm3 in autumn and 0.60-2.10 mg/dm3 in winter) were recorded in all ship ballast water samples, with pH (above 7.90) and PSU (above 1.20) were higher than in the port waters. Yeast, mold, Pseudomonas bacteria (including Pseudomonas fluorescens), and halophilic bacteria as well as lipolytic, amylolytic, and proteolytic bacteria were found in the ballast water samples. Heterotrophic bacteria and mold fungi (log. 2.45-3.26) dominated in the autumn period, while Pseudomonas bacteria (log. 3.32-4.40) dominated in the winter period. In addition, the ballast water samples taken during the autumn period were characterized by a statistically significantly higher (p < 0.1) abundance of microorganisms (log 1.97-2.55) than in the winter period (log 1.39-2.27).

Heavy Metals and the Occurrence of Ulcerative Dermal Necrosis (UDN) in Sea Trout from the RIVER REGA, Poland-Consumer Health Assessment.

Various factors, including heavy metals, can make fish more susceptible to disease. This study investigated, inter alia, the relationship between Pb, Cd, and Hg contamination of the organs and muscles of sea trout from the river Rega (Poland) and the occurrence of UDN (ulcerative skin necrosis) symptoms. Moreover, the dietary risk of Pb, Cd, and Hg uptake from the muscles of healthy sea trout was assessed based on estimated daily intake (EDI), target hazard quotient (THQ), benchmark dose lower confidence limits (BMDL01 and BMDL10), and tolerable weekly intake (TWI). The metal concentrations varied, depending on the fish organs and the fish condition. A significantly higher amount of Pb was found in the gonads, gills, and muscles, Cd in the kidneys, and Hg in the muscles of sea trout with UDN symptoms. The lowest concentrations of Pb and Cd were detected in the muscles, and of Hg in the gonads. Dietary exposure to Pb, Cd, and Hg accounted for: 0.4% of BMDL01 and 1.0% of BMDL10, 0.56% of TWI, and 16.5% of TWI, respectively. THQs for each metal and the HI value for combined metals were below 1. The weakening of fish due to UDN-like disease probably increased the accumulation of Pb in the gonads, gills, and muscles, and of Cd in the kidneys, of the sea trout. As regards the maximum levels (MRLs), the muscles of healthy sea trout are safe for consumption. The risk assessment suggests no concern for the health of consumers.

Quest for breathing: proliferation of alveolar type 1 cells.

There is much evidence that the vertebrate lung originated from a progenitor structure which was present in bony fish. However, critical basic elements for the evolution of breathing in tetrapods, such as the central rhythm generator sensitive to CO2/pH and the pulmonary surfactant, were present in the lungless primitive vertebrate. This suggests that the evolution of air breathing in all vertebrates may have evolved through exaptations. It appears that the capability for proliferation of alveolar type 1 (AT1) cells is the "critical factor" which rendered possible the most radical subsequent innovation-the possibility of air breathing. "Epithelial remodeling," which consists in proliferation of alveolar cells-the structural basis for gas diffusion-observed in the alimentary tract of the gut-breathing fishes (GBF) has great potential for application in biomedical research. Such a process probably led to the gradual evolutionary development of lungs in terrestrial vertebrates. Research on the cellular and molecular mechanisms controlling proliferation of squamous epithelial cells in the GBF should contribute to explaining the regeneration-associated phenomena that occur in mammal lungs, and especially to the understanding of signal pathways which govern the process.

Influence of selected precipitating agents used for restoration of water reservoirs on the embryogenesis of pike (Esox lucius L.).

The aim of the study was to investigate the effect of iron coagulant (IC), aluminum coagulant (AC) and lanthanum modified bentonite (LMB) on the embryogenesis of pike. Physicochemical indicators of the water were determined according to the methods recommended by APHA (1999). The applied precipitating agents (IC, AC, LMB) at appropriate concentrations were sprayed on the surface of water in aquariums with the pike eggs placed on nets. The eggs were observed under a microscope, documenting their development using digital photography NIS Elements Br software. The number of fertilized eggs, embryo survival, and the percentage of malformed larvae were determined. The pike eggs and hatched larvae were recorded and measured. The percentage of fertilized eggs was found to be the highest in the control sample (LW) and in the IC sample (94% and 93.3%, respectively), 85.9% in the AC sample and 81.8% in the LMB sample. The pace of pike embryogenesis in the samples was identical - the embryos in both the control and other samples reached individual stages of embryonic development with an equal number of degree days (DD). The IC group hatched the earliest, and the control sample was the last to hatch (LW). In the control sample, the hatched larvae were the longest and had the lowest percentage of malformed individuals. The control sample also had the highest rate of embryo survival (85.9%), while the lowest was in the LMB sample (68.6%). These results indicate that the application of precipitating measures to improve water quality should not coincide with the periods of fish reproduction.

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.

Magnetoreception in fish.

Magnetoreception is the ability of organisms to perceive magnetic fields in the surrounding environment and changes in its properties such as field direction, intensity and gradient, where the effect on organisms can manifest as an array of reactions. As the magnetic sense is found in many taxa, both evolutionarily young and old, it can be assumed that magnetoreception came into existence as one of the first sensory systems. Many studies on the effect of magnetic fields on fishes have considered both fishes that migrate for long distances and those that are more or less sedentary. Research has focused on tracing the perception of the geomagnetic field by fishes and understanding magnetic fields that are smaller and larger than the ambient Earth's geomagnetic field. The question of the effect of magnetic fields of values higher than the Earth's is gaining importance with the increasing effect of anthropogenic magnetic and electromagnetic fields in aquatic ecosystems. This review draws together the results of studies on the effect and reception of natural and human-generated magnetic fields on fishes at various stages of ontogeny, chronologically arranged from gametes, through embryonic development, embryonic and larval motor function, directional reactions of embryos and larvae, orientation of fishes, to the mechanisms of magnetic field reception. The present state of knowledge indicates a common nature of effect on various ontogenetic stages of fishes. However, understanding of the mechanisms of magnetic sense in fishes and its relevance for ecological outcomes highlights that further progress requires more detailed research.

Early ontogenesis of the angelfish, Pterophyllum scalare Schultze, 1823 (Cichlidae)

This study describes the egg membrane structures of angelfish (Pterophyllum scalare), morpho-physiological changes during angelfish embryogenesis from activation to hatching under optimal conditions (28°C; pH 6.8), the developing larvae and fry, the effect of alkaline pH on the early developmental stages of the species, the relationship between food item size and fry survival. Egg membranes (thin, transparent, 1.67-2.18 µm thick) are covered by a sticky substance. The amber-coloured angelfish eggs were oval in shape, with average diameters of 1.436 and 1.171 mm, i.e., a mean volume of 1.033 ± 0.095 mm³. The survival rate of embryos and larvae kept in water with an elevated, slightly alkaline pH was very low: as few as 2% of the embryos survived, while in the batch kept in optimal water conditions very few eggs died. The first larvae hatched after 1288 h of embryonic development. The newly hatched larvae measured on average 2.60 ± 0.093 mm and had large (0.64 ± 0.077 mm³) yolk sacs. They attached themselves to the substrate with a secretion of thin, viscous threads, which was released from glands situated on the top of the head. The glands vanished on day 5. The 1-day-old larvae showed the first pigment cells on the body and the eyes of the 2-day-olds were already fully pigmented. Between day 4 and 5 of larval life, the larvae began feeding on live food. The 23-day-old fry looked like a miniature versions of the adults. Mortality of the angelfish larvae during their first days after hatching was higher in those fed brine shrimp (Artemia salina) nauplii than those fed protozoans and rotifers.

En este trabajo se ha descrito la estructura de las túnicas ovulares del escalar o pez ángel (Pterophyllum scalare), las modificaciones morfo-fisiológicas que transcurren durante la embriogénesis del escalar desde el momento de activización para el desove en condiciones ambientales óptimas (28ºC y pH 6,8) y, se han caracterizado las larvas y los alevines desarrollándose. Adicionalmente, se ha estudiado el efecto del pH básico del agua sobre los primeros estadios de desarrollo y la dependencia entre la cantidad de alimento y la supervivencia de los alevines. Las túnicas ovulares del escalar son finas (1,67-2,18 mm), transparentes, cubiertas de una sustancia viscosa. Los huevos de color ámbar tienen forma ovalada de diámetros medios 1,436 y 1,171 mm y de un volumen medio de 1,033 ± 0,095mm³. El porcentaje de supervivencia de embriones y de larvas en agua con pH aumentado, ligeramente básico, fue muy bajo, ya que sólo el 2% de los embriones sobrevivió, mientras que en agua de parámetros óptimos sólo algunos huevos palidecieron. Las larvas recién salidas del huevo medían 2,60 ± 0,093 mm por término medio y poseían grandes (0,64 ± 0,077 mm³) sacos vitelinos. Se han adherido al substrato mediante una secreción en forma de filamentos finos y viscosos. Esta secreción se ha desprendido de las glándulas ubicadas en la cumbre de la cabeza. Las glándulas desaparecieron al 5º día de vida de las larvas. Las larvas de un día poseían ya las primeras células pigmentarias en el cuerpo, los ojos de las larvas de dos días estaban pigmentadas plenamente. Entre el 4º y 5º día de vida las larvas empezaron a tomar alimento. Las larvas de 23 días se parecían a una versión miniaturizada de los adultos. La mortalidad de las larvas del escalar alimentadas durante los primeros días a partir del desove con larvas de artemia salina (Artemia salina) fue mayor que la de las alimentadas con protozoarios y rotíferos.