Stanisław Sakowicz Inland Fisheries Institute

The purpose of this study is to enhance the performance of the mesohabitat model MesoHABSIM by lowering the necessary hydraulic modelling effort. This proof-of-concept study tests an application of the MesoHydraulics model to simulate the hydraulic characteristics of hydromorphological units (HMUs) occurring in a regulated river at different low discharges. In this quantitative approach, hydraulic patterns are transferred from a source site, where depth and velocity distributions were derived from field measurements and a 2D hydrodynamic model, to a target site, where only a single field hydrometric survey was conducted. Instead of modelling changes in individual hydraulic measurement values to estimate hydraulic responses to discharge, the model relies on statistical distributions of these values within HMUs. We were testing whether changes in the distribution of HMU’s and their hydraulics can be transferred between morphologically comparable river sections to serve as a sufficient hydraulic input for mesoscale habitat modelling. The hydrodynamic component of the River2D software (V.0.95a), routinely used in MesoHABSIM, served as a baseline for testing the MesoHydraulic model’s performance and for producing source data for deriving distribution functions. The test was conducted using data from two one-kilometre sites on the upper Oder River (Poland). The model transfers the HMU area distributions, along with corresponding depth and velocity frequency distributions, for a number of flows from one site (the source) to another (the target). The hydraulics at both sites were surveyed under single-discharge conditions. For the source site, the hydrodynamic model was applied to classify the HMU mosaic at three additional discharge stages. At the target reach, the HMU mapping was conducted based on survey data, and statistical frequency functions were used to model distributions of hydraulic patterns at discharges modelled for the source. The hydraulic model’s performance was evaluated at the target reach by comparing simulated hydraulics and HMU patterns with those modelled using River2D. Finally, both models were used to calculate habitat availability for the fish communities, and dissimilarities were observed. The resulting hydraulic distributions were similar, with an average affinity index of 90%. Higher affinity indices were reached at flows close to the measured value, with increasing model disagreement toward flow extremes, most notably for Run and Backwater units. Regardless, habitat models for the fish community were also highly correlated with R2 = 0.98 for amounts of suitable habitat and almost identical habitat distribution among the species. Yet, the MesoHydraulics-based model slightly, but consistently, overestimated habitat availability. While the model was tested in a large and regulated river system, its accuracy may vary depending on the natural river morphology. Further research should evaluate modelling uncertainties and their applicability in less-modified water bodies.

Abstract The European grayling ( Thymallus thymallus L.) is a vulnerable freshwater fish that plays an important role in the conservation of the biodiversity of European ichthyofauna and is a key species in recreational fishing. Multiplex PCR is a technique used to estimate genetic diversity that saves both time and money. This paper presents three multiplex PCR assays for amplifying 11 microsatellite markers from European grayling DNA. The steps necessary for constructing multiplex assays and verifying genotyping results are described. The compositions of the PCR mixture and the characteristics of the PCR thermal profile recommended for amplification in multiplex mode, and protocols used in genotyping them by using automatic DNA sequences are also described. Consequently, our method enables a near four-fold reduction in time and costs of the PCR stage of studies on genetic variation. Moreover, the next step of analysis (measuring the length of DNA fragments) can be done faster and easier without decreasing the precision or quality of genotyping results. This method was tested by assessing the genetic variation in a grayling stock kept under aquaculture conditions, and it has proved useful in the management of the genetic variation of this species.

Dystrophic lakes are unique ecosystems characterized by extreme conditions, including acidic waters, sharp thermal and oxygen gradients, and high dissolved organic carbon levels, which lead to specific dark coloration of water. While lacking submerged macrophytes, these lakes are bordered by Sphagnum mats, which create distinct ecological niches shaping plankton community structure and composition. We examined three key habitats (Sphagnum mats, shore zones, and open water) across seven temperate dystrophic lakes, analyzing a broad range of planktonic organisms (Crustacea, Rotifera, Ciliata, and phytoplankton). Our results revealed significant differences in plankton assemblages among these habitats, with distinct communities found in Sphagnum mats and open water, while the shore zone contained species typical of both habitats. Ciliata and phytoplankton in the shore zone showed greater similarity to open water communities. In contrast, microcrustacean assemblages in shore zones differed significantly from both Sphagnum mats and open water, supporting a high diversity of littoral and some planktonic species. These findings highlight the need to consider horizontal variability in plankton communities when interpreting paleolimnological records. Given the widespread use of Cladocera and diatoms remains in reconstructing past lake conditions, integrating habitat-specific data enhances the accuracy of environmental reconstructions and deepens our understanding of dystrophic lake evolution.

The brown bullhead is a fish native to North America that became an invasive species after being introduced into the waters of Europe and other regions. Studies on its sexual cycle and fecundity were conducted on a population from an oxbow lake of the central Vistula River in Poland. The fish ranged in age from 1 + to 9+. The average body length (SL) was 14.4 ± 3.4 cm. Individuals as young as 1 + were already mature. Females lay eggs multiple times from mid-April to mid-June, with absolute fecundity averaging 3227 oocytes and relative fecundity at 46 oocytes g−1. The highest mean GSI of 1.9 during spawning was recorded in June. The reproductive tract of males takes the shape of lobes and consists of a paired cranial region formed by testes and a caudal region of undefined function. In males, semi-cystic spermatogenesis occurs, with secondary spermatocytes leaving cysts. Males overwinter with tubules filled with spermatids and initiate spermatozoa formation. The highest average GSI of 0.49 was recorded in early April. The brown bullhead observed in the new habitat was characterized by multiple egg laying, earlier maturation of individuals, and spawning in the earlier part of the calendar year, i.e. mid-April to mid-June, compared to its native habitat.

Fish eggs activated with UV-irradiated spermatozoa and exposed to the High Hydrostatic Pressure (HHP) shock to inhibit first cell cleavage develop as gynogenetic Doubled Haploids (DHs) that are fully homozygous individuals. Due to the expression of the recessive genes and side effects of the gamete treatment, survival of fish DHs is rather low, and most of the mitotic gynogenotes die before hatching. Nevertheless, as maternal gene products provided during oogenesis control the initial steps of embryonic development in fish, a maternal effect on the survival of gynogenotes needs to be also considered to affect efficiency of gynogenesis. Thus, the objective of this research was to apply an RNA-seq approach to discriminate transcriptional differences between rainbow trout (Oncorhynchus mykiss) eggs with varied abilities to develop after gynogenetic activation. Gynogenetic development of rainbow trout was induced in eggs originated from eight females. Maternal RNA was isolated and sequenced using RNA-Seq approach. Survival rates of gynogenotes and transcriptome profiles of eggs from different females were compared. RNA-seq analysis revealed substantial transcriptional differences between eggs originated from different females, and a significant correlation between the ability of the eggs for gynogenesis and their transcriptomic profiles was observed. Genes whose expression was altered in eggs with the increased survival of DHs were mostly associated (GO BP) with the following biological processes: development, cell differentiation, cell migration and protein transport. Some of the genes are involved in the oocyte maturation (RASL11b), apoptosis (CASPASE 6, PGAM5) and early embryogenesis, including maternal to zygotic transition (GATA2). Inter-individual variation of the transcription of maternal genes correlated with the competence of eggs for gynogenesis suggest that at least part of the mortality of the rainbow trout DHs appear before activation of zygotic genome and expression of the lethal recessive traits.

Aloe barbadensis (L.) Mill. ( A. vera ) is a well-recognized herbal supplement in aquaculture feeds, known for its ability to promote overall health. This research demonstrates the beneficial effects of dietary A. vera supplementation on growth, carcass composition, digestibility, hematology, antioxidant status, and immune parameters in Catla catla . A total of 270 C. catla fish (average weight: 6.50 ± 0.03 g) were uniformly assigned into six treatment groups, each replicated in triplicate. The groups fed diets containing equal amounts of canola meal and varying levels of A. vera supplementation (0 %, 1 %, 2 %, 3 %, 4 %, and 5 %). The fish were fed at a rate equivalent to 5 % of their live wet body weight. The findings determined that fish fed an A. vera supplemented diet exhibited significant improvements in all parameters. Supplementation with 3 % A. vera resulted in a significant (p < 0.05) increase in weight gain (%) and an improved feed conversion ratio. Moreover, highest digestibility coefficients for crude protein, gross energy, and crude fat, as well as optimal carcass values for fat and crude protein content, were observed at 3 % A. vera supplementation level. Hematological analysis revealed significant differences (p < 0.05) in white blood cells, red blood cells, platelets, and hemoglobin levels in fish fed at 3 % A. vera diet. Notably, antioxidant activities and immune parameters also showed maximum output at the 3 % A. vera supplementation level. • Aloe vera is a well-recognized herbal supplement that promotes overall health in aquatic animals. • Inclusion of A. vera in the diet of Catla catla enhances growth, carcass, digestibility and hematology. • 3 % A. vera supplementation is appropriate and can be utilized in the diet of C. catla .

This study compared the quality of northern pike eggs collected using traditional methods (hand stripping) and pneumatic methods (air stripping). The effects of different activation solutions (0.4% NaCl, 0.8% NaCl, and hatchery water) on egg fertilization under controlled conditions were also investigated. After egg collection, the Pseudo-Gonado-Somatic Index (PGSI) was measured; the PGSI values in the samples obtained using the pneumatic method (13.8 ± 3.9%) were lower, but did not differ statistically from those obtained by hand stripping (16.5 ± 5.4%). The 0.4% NaCl solution proved to be the most effective for sperm activation, as assessed by the Computer-Assisted Sperm Analysis (CASA) system, compared to the 0.8% NaCl solution. The pneumatic method achieved a higher egg collection efficiency (93.7% occlusion) than the traditional method, with significant differences observed in groups activated with water. The average hatching percentage of larvae was 89.5% in groups using the pneumatic method, compared to 71.2% in the traditional groups, highlighting the advantages of this modern approach. The application of the pneumatic method and 0.4% NaCl for the artificial fertilization of northern pike resulted in higher fertilization and hatching rates compared to other techniques, making this method a promising option for the artificial reproduction of other fish species.

In a commercial fishery, some fish are classified as low-value, but their classification varies in different countries. The aim of this study was to determine the abundance, contribution, and dominance of low-value fish species, such as Abramis brama &lt; 1000 g, Alburnus alburnus, Blicca bjoerkna, Gymnocephalus cernua, Perca fluviatilis &lt; 100 g, Rutilus rutilus &lt; 200 g, and Scardinius erythrophthalmus &lt; 200 g, in 145 Polish lakes of different areas, depths, and trophic statuses situated in the northern and central parts of Poland in 2021. Perca fluviatilis and R. rutilus were the most frequent low-value species (100% and 99%, respectively). The contribution of all low-value fish to the total biomass of caught fish was relatively high, ranging from 37% in the mesotrophic lake to 100% in the eutrophic lake (mean of 77 ± 14%). Lakes in which the contribution of low-value species exceeded 90% were relatively numerous (24 lakes, 17% of the studied lakes). Among a total of about 437.5 thousand low-value fish, 261 thousand specimens (60%) had a body weight of below 10 g. All low-value fish species, except for P. fluviatilis and S. erythrophthalmus, were related to the studied environmental variables. The relative biomass of these species increased with increasing lake productivity, while it decreased with the increasing maximum and mean depth of the studied lakes. The high contribution of low-value fish to the total biomass in many lakes indicates the need for the constant monitoring of the abundance and structure of fish communities and the use of appropriate actions (biomanipulation and stocking with piscivorous fish species) to improve the ecological condition of lakes.

The aim of this study was to evaluate the one-month effect of oral vaccination against Yersinia ruckeri based on oxidative stress biomarkers in the hepatic tissue of rainbow trout (Oncorhynchus mykiss Walbaum). The vaccine consisted of three strains of Y. ruckeri (serotype O1) obtained from rainbow trout from different farms where fish showed clinical signs of enteric redmouth disease. The vaccine was produced at the Department of Fish Diseases, National Veterinary Research Institute in Pulawy (Poland) according to the process covered by patent no. P.428259. The concentrated vaccine was added to the fish feed. Treatment was administered three times at one-day intervals. Livers were sampled one month after immunisation. Our results show that immunisation with the anti-Yersinia vaccine did not alter the liver tissue of rainbow trout. aldehydic and ketonic derivatives of oxidatively modified proteins (OMP) were not significantly altered in the hepatic tissue of vaccinated fish prior to immunisation. One month after immunisation, the levels of ketonic derivatives of OMP in the hepatic tissue of untreated trout were reduced compared to the untreated group before immunisation. Similar to the untreated groups, the levels of ketonic derivatives of OMP in the hepatic tissue of the vaccinated group one month after immunisation were reduced compared to the vaccinated group before immunisation. A statistically non-significant decrease in the total antioxidant capacity (TAC) levels was observed between the values obtained in the untreated and vaccinated groups before vaccination and one month after vaccination. Understanding the role of oxidative stress in the tissues of vaccinated trout has important implications for understanding the complex physiological changes that occur during vaccination, and also for improving aquaculture practices to maximise tissue growth and health of vaccinated trout.

Abstract The aim of the study was to determine the influence of diets (factor D) and the time period (factor T) during which they were applied on the growth performance and physiological condition (blood plasma hematological and biochemical indicators of stress and immunity) in juvenile sea trout ( Salmo trutta ; initial body weight approximately 73 g). The diet of the fish that was used prior to the experiment (formulated feed; initial fish sample) was modified as follows: a different formulated feed (group B), mixed feed (feed B + prey fish; group B/N), prey fish exclusively (group N). The fish from group A were given the feed that was used prior to the beginning of the experiment. During the 28-day trial neither factors D nor T influenced absolute or relative fish growth rates. Factor D significantly influenced hematological indicators and leukograms, while the phagocytic index and cidal ability were determined by the time test (factor T). Myeloperoxidase (A MPO ) was related significantly with the influence of factors D and T and also with the interaction of D×T. A significant decrease in A MPO was noted after two weeks of the test in groups B, N, and B/N, but after four weeks this indicator did not differ from that confirmed in the initial fish sample. The factors tested influenced stress indicators, i.e., cortisol (D and T) and glucose (D). Significant increases in cortisol (group B) and glucose (groups A, B, and B/N) concentrations were noted after two weeks of the test. After the subsequent two weeks (four weeks of the test) these indicators also stabilized. Sea trout from aquaculture readily accept prey fish; however, changes in diet cause stress reactions such as temporarily reduced immunity. Thus, the procedure for preparing sea trout stocking material for release, which is to change the feed from formulated to natural (live fish), should last approximately four weeks.