European Perch Perca Fluviatilis Research Articles

New Annotated Records of Helminth Parasites with Light Microscopy IV Acanthocephala (Palaeacanthocephala)

We give an account of 6 species of acanthocephalans in one class Palaeacanthocephala and 3 families collected from hosts in different geographical locations in Canada, Ukraine, Italy, the Philippines, and the USA. Each species account is annotated and morphologically presented using light microscopy showing characteristic diagnostic features. None of these accounts has been completely previously published. Almost all geographical records and many host associations are new. In the family Echinorhynchidae, we include Echinorhynchus lateralis Leidy, 1851 from Salvelinus fontinalis (Mitchill), Canada. We added new descriptive information, especially of the cement glands, and compared its morphometrics with those of other collections by other observers. We also described two discrete sizes of specimens of Echinorhynchus salmonis Müller, 1784 from Coregonus artedii Lesueur in Lake Superior. In Paracanthocephalidae, we describe 3 species including Acanthocephalus lucii (Müller, 1776) Lühe, 1911 from the common European perch Perca fluviatilis Linn. in an unusual location in Ukraine at the Ubort River. We provide light microscopy documentation of that species for the first time. Acanthocephalus rhinensis Amin, Thielen, Mïnderie, Taraschewski, Sures, 2008 from Anguilla anguilla (Linn.) in Italy is described and compared with specimens that were described from Germany with corrections re the Italian notions of its color band at the anterior trunk. Acanthocephalus tahlequahensis Oetinger and Buckner, 1976 from Etheostoma punctulatum (Agassiz) in Oklahoma is documented with new morphological features for the first time and documented its distribution outside of Oklahoma. In Rhadinorhynchidae, we report Serrasentis sagittifer (Linton, 1889) Van Cleave, 1923 from Pterois volitans (Linn.). We describe these species in the context of comparative morphometrics with the original and other descriptions noted elsewhere when available.

Environmental abundances of the non-native round goby Neogobius melanostomus influence feeding of native fish predators.

The authors assessed the importance of the round goby Neogobius melanostomus as prey for three native predatory fish species, Atlantic cod Gadus morhua, European perch Perca fluviatilis and northern pike Esox lucius, in a northern and southern area of the Baltic Proper, using a combination of visual analysis and DNA metabarcoding of predator stomach contents. To explore the influence of environmental abundances of N. melanostomus on predation, they related the occurrence of N. melanostomus in predator diets to its abundance in survey fishing. Gadus morhua and E. lucius in the southern area showed the highest tendency to feed on N. melanostomus when it was abundant, as N. melanostomus occurred in up to 100% of stomachs and constituted up to 88% of the total diet volume proportion. The diet contribution of N. melanostomus was associated with N. melanostomus abundances for G. morhua and E. lucius, and when N. melanostomus was abundant, these predators exhibited lower prey richness and a higher degree of piscivory. G. morhua and P. fluviatilis also fed less on crustacean prey when N. melanostomus was abundant. The high importance of N. melanostomus in diets of native fish predators may modify indirect interactions between N. melanostomus and native prey species in invaded coastal communities.

Study of the diets of two coexisting species – invasive Chinese sleeper (Perccottus glenii Dybowski, 1877) and native European perch (Perca fluviatilis Linnaeus, 1758)

In Poland, the Chinese sleeper Perccottus glenii is one of the alien fish species which, by effectively competing with native species, may contribute to the weakening of their population and a reduction of the biodiversity. The aim of this paper is to study the diets of two coexisting species: the native European perch Perca fluviatilis and the invasive Chinese sleeper. The fish were collected from a watercourse used for draining water from a fishing farm, located in the Nida River water system (Poland), using the electrofishing method. The captured fish were killed, preserved in a 4% formaldehyde solution and the stomachs of the fish were dissected. Then, based on the materials collected from these stomachs, the abundance and taxonomic rankings of the individual diet components (quantity of individuals in the individual taxa) were determined. The overlap of the P. fluviatilis and P. glenii feeding spectra was studied using a principal component analysis (PCA). The analysis of the data collected demonstrated that the diets of these two species overlaps considerably. At the same time, the analysis of the major diet components showed that the niche used by P. fluviatilis is broader than that used by P. glenii. It seems that, due to its high level of plasticity, P. fluviatilis is able to withstand the pressures of P. glenii and is also able to limit its abundance. Both species frequently choose fish as their prey, including juvenile common carp Cyprinus carpio Linnaeus, 1758, which indicates that together with native predators, P. glenii may pose a considerable threat to farmed juvenile Cyprinidae.

Interannual variability in the trophic niche of young‐of‐year fish belonging to four piscivorous species coexisting in a natural lake

Abstract Predatory fish species play a key role in aquatic ecosystems by exerting top‐down control on the food web. Also, their intra‐guild trophic interactions (i.e. competition) are crucial for the stability of the community. However, most studies focus on adult stages, while juveniles remain poorly studied, although their recruitment is the basis for the maintenance of predator populations. We analysed carbon and nitrogen stable isotopes ratios of the young‐of‐year of four coexisting widespread predatory fish species (northern pike Esox lucius, European perch Perca fluviatilis, pikeperch Sander lucioperca, and European catfish Silurus glanis), sampled over 3 years in a shallow natural lake. We found that the hierarchy in trophic position between species was consistent across years and similar to that known for adults, but with large variations around a general pattern: pike and pikeperch tended to occupy the highest trophic positions while perch occupied the lowest, and catfish had very varying positions. Species partitioned their niches to decrease interspecific competition, but with some occasional overlaps, contributing to preserving their body condition. Depending on density, which was particularly impacted by harsh environmental conditions, niche overlap fluctuated across years, leading to niche enlargement of densely populated species, except for catfish. These mechanisms enabled species coexistence, allowing the co‐occurrence of alien and native predators within the same ecosystem. This work advocates for time‐integrated studies of trophic webs because they capture the variability of their dynamics better than a static picture. This is particularly true for juveniles whose survival strongly depends on their capacity to cope with competition. Information from trophic mid‐term studies of juveniles provides valuable guidance for optimised management of species.

Evaluating 87Sr/86Sr and Sr/Ca ratios in otoliths of different European freshwater fish species as fishery management tool in an Alpine foreland with limited geological variability

The focus of this study was to assess the potential of otolith microchemistry as a fishery management tool for different European freshwater fish species in an Alpine foreland with a diverse range of different water bodies but low geological variation. 87Sr/86Sr isotope ratios and Sr/Ca ratios in water samples from 26 habitat sites in a pre-alpine catchment region around lake Chiemsee, Germany, an important region for recreational and economic fisheries, were analysed. 87Sr/86Sr isotope ratios and the Sr/Ca ratios in otoliths of 246 fish out of 16 species were determined using (laser ablation) inductively coupled plasma mass spectrometry ((LA)-ICP-MS). Habitats could be differentiated into seven clusters when using the 87Sr/86Sr isotope and Sr/Ca ratios in water in combination. When using the 87Sr/86Sr isotope ratio as individual parameter, the strontium isotope groups (SIGs) based on the 87Sr/86Sr isotope ratios including the measurement uncertainties justified a three-cluster solution. The direct comparison of 87Sr/86Sr isotope ratios in water and otolith samples allowed to identify fish that a) might have migrated, b) were transferred from other water bodies or c) stocked from fish farms. Sr/Ca ratios in water and otoliths were highly correlated, although significant differences between species from the same environment were documented. Sr/Ca ratios in sagittae of Perca fluviatilis were about 64–60% of those in sagittae of Coregonus spp and of lapilli of roach Rutilus rutilus from the same habitats, respectively. Partition coefficients for water to otolith Sr/Ca ratios were calculated and differed between species. Discrimination of fish otoliths according to habitat clusters by combining 87Sr/86Sr and Sr/Ca ratios was possible with success rates of up to 100% for whitefish Coregonus spp., 90% for European perch Perca fluviatilis, 87% for cyprinids, and 89% European grayling Thymallus thymallus, and 68% for salmonids. When using the 87Sr/86Sr isotope ratios as single parameter, assignment results were generally worse, except for salmonids, where an improved accuracy of 79% could be achieved, or for cyprinids when the number of clusters was reduced from five to three. The study indicates that otolith microchemistry has great potential to serve as a fishery management tool at smaller spatial scales such as in the studied Alpine foreland when combining the 87Sr/86Sr and Sr/Ca ratios, and considering the type and spatial distribution of habitats, the species and question under investigation.

Inter-tissue variability in the stable isotope values of European perch (Perca fluviatilis) and pumpkinseed (Lepomis gibbosus)

Ecological studies on native and invasive populations of European perch Perca fluviatilis and pumpkinseed Lepomis gibbosus are often based on stable isotope (SI) analysis based on dorsal muscle, where samples are usually taken from sacrificed fishes. However, other tissues, such as scale and fin tissue, can be used as non-lethal alternatives, where their SI values can be standardised to dorsal muscle values for comparative purposes. In both perch and pumpkinseed, there was a pattern of δ13C enrichment and δ15N depletion from muscle to fin and scale. As comparative studies must account for these inter-tissue differences prior to analyses, conversion equations for SI data from scale and fin tissue to standardised muscle values are provided.

Does the feeding frequency influence the growth performance of European perch juveniles (Perca fluviatilis) during intensive rearing?

The European perch (Perca fluviatilis) is a predatory fish species. Its aquaculture production is increasing worldwide. Feeding and the frequency of feeding are important elements of intensive fish rearing. The aim of our experiment was to examine the optimal distribution of the amount of feed, at the same feed rations. The experiment lasted 42 days. Three treatments were applied in 4–4 replications. The first treatment was feeding twice per day (T2), the second treatment was feeding three times a day (T3), and the third group was fed four times a day (T4). 10 European perch juveniles were stocked per tank, with an individual mean body weight of 3.93 ± 0.06 g at the start of the experiment. The survival rate (S%) was above 90% for all treatments. The T2 treatments produced the most favourable harvest weight (13.96 ± 0.14 g) and specific growth rate (SGR = 3.08 ± 0.01% day-1), but no significant differences were observed between groups. In terms of feed conversion ratio, the best result was obtained by (T3) (FCR =1.06 ± 0.18 g g-1), but no significant difference was found for this indicator neither. The results of the trial indicate that the feeding frequency does not influence the production parameters.

The Effects of Contrast between Dark- and Light-Coloured Tanks on the Growth Performance and Antioxidant Parameters of Juvenile European Perch (Perca fluviatilis)

European perch (Perca fluviatilis) is a predatory fish species with a high degree of stress sensitivity during rearing in intensive systems. Our study was focused on the effects of contrast between two colours (black and light grey) in different parts of a tank (bottom and sidewall) on the production and antioxidant parameters of juvenile European perch during intensive rearing. The duration of the experiment was 8 weeks. In the first treatment, the bottoms of the tanks were black (DB); in the second treatment, the sides of the tank were black (DS); in the control treatment, the fish were kept in light-grey tanks (K). There were three replicates per treatment, and a total of 180 individuals were used; therefore, 60 individuals were used per treatment, with 20 individuals per tank. The mean body weight of the fish at the start of the experiment was 32.01 ± 0.79 g. At the end of the experiment, the antioxidant parameters (cortisol, glucose, MDA, catalase, vitamin C, GPx, GR, GSH, GSSG, and HSP70) of the fish were determined from blood samples. The results of our experiment show that different levels of contrast between the dark and light tank colours significantly influenced the production and antioxidant parameters of the juvenile European perch.

The comparison of the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of northern temperate lakes

The comparison of the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of northern temperate lakes

Effects of Garlic Allium sativum Powder on Nutrient Digestibility, Haematology, and Immune and Stress Responses in Eurasian Perch Perca fluviatilis Juveniles

Simple SummaryHerbal medicine feed supplements are used as growth promoters, immune system stimulants, and to combat stress. We evaluated the effects of garlic powder in the diet of European perch. The inclusion of garlic powder was shown to improve whole body composition, feed digestibility, and biochemical and immunohematological effects, and increased resistance against overcrowding stress.The supplementation of fish diets with phytogenics can increase growth performance and can modulate immune system response. European perch Perca fluviatilis (initial weight 25.0 ± 0.4 g) were fed a diet including 0 (Control), 10 (G10), 20 (G20), and 30 (G30) g kg−1 garlic powder. No significant difference in the growth parameters and somatic indices were observed. Significantly higher fat digestibility was observed in G10 and G30 diets compared to in the control and G20 diets(p < 0.05). Significantly greater red blood cell and white blood cell counts were observed with the G10 diet (p < 0.05). Garlic significantly decreased serum cholesterol in all of the experimental groups. Serum albumin was significantly higher in the G10 and G20 diets (p < 0.05). Immediately after the overcrowding stress challenge, the garlic groups showed significantly higher cortisol levels than the control group, while no significant difference was observed in the glucose concentration among groups. At 1 h post-stress, all of the groups that had been fed a garlic-supplemented diet showed lower cortisol levels than the control group, and this trend was maintained at 6 and 24 h post stress (p < 0.05), and glucose level in all garlic groups was significantly lower than control (p < 0.05). Garlic at 10 g kg−1 in feed can improve apparent fat digestibility and selected blood parameters and can enhance resistance against high-density and net handling stress in Eurasian perch.

High Mercury Concentrations of European Perch (Perca fluviatilis) in Boreal Headwater Lakes with Variable History of Acidification and Recovery

High dissolved organic carbon and low pH are often associated with elevated mercury content of fish in boreal lakes, but less is known about the fish mercury dynamics in lakes recovering from acidification stress. We measured total mercury concentration (THg) in muscle of European perch (Perca fluviatilis) and evaluated the overall correlation with environmental and growth variables in 24 boreal headwater lakes in the 2010s. We found negative correlations of length-corrected perch THg with lake pH and perch growth, but no correlation with dissolved organic carbon. The main emphasis in the present study was focused to a subset of ten lakes in southern Finland with known perch THg during severe acidification in the 1980–1990s. The comparison of perch THg concentrations in the 2010s with values determined in the 1980–1990s showed a sharp increase in most acidic lakes where the perch populations suffered from severe acid stress in the 1980s. This increase was attributed to growth condensation caused by sharp decrease in perch growth during recovery of reproduction capacity and the consequent increases in population densities of perch. Our results highlight the importance of perch growth rate and population density for understanding the variability of fish Hg in boreal headwater lakes, where recovery from acidification can lead to higher mercury concentration of fish in certain cases.

Ecological aspects of the formation of the helminth fauna of Perca fluviatilis (Actinopterygii: Perciformes) of the Usinsky Bay (Kuibyshev Reservoir, Russia)

The fauna of the multicellular parasites of European perch Perca fluviatilis (Peciformes) of the Usinsky Bay of the Kuibyshev Reservoir was studied in 2019–2020; nine taxa of helminths were found. The parasite prevalence of most of the intestinal helminth species, associated with the zooplankton community, did not exceed 12–25%. In the fish with a body length of 117–200 mm, fish juveniles and benthos organisms played a significant role in the parasite transmission. The Usinsky Bay was a buffer zone at the margin of the “river-reservoir” system and had a specific hydrological regime. This promoted favorable conditions for the spreading of alien species of aquatic organisms in the ecosystem of the reservoir; in some cases this led to an increase in the invasion of indigenous fish (European perch) by invader parasites. As a result of this process, the invasive species of trematode Apophallus muehlingi became dominant in the helminth fauna of the European perch. High degree of infestation of European perch by this parasite indicated wide distribution of its first intermediate host, the alien mollusk Lithoglyphus naticoides, in the Usinsky Bay. Other species of parasites, associated with this invader, were not found in Perca fluviatilis. Helminths of the European perch can be used as biological markers to identify migratory activity, the vector of the invasion of some alien species, the range of their hosts, the population abundance, and indirect infection by alien hosts in different water bodies of the Volga River basin.

Habitat partitioning among three predatory fish in a temperate reservoir

AbstractThe diversity of predatory species plays a key role in ecosystem functioning but our understanding of the mechanisms underlying their coexistence is limited, particularly in freshwater ecosystems. Northern pike Esox lucius, European perch Perca fluviatilis and pikeperch Sander lucioperca are three widespread predatory species in European lakes, where they often coexist. As potential competitors, we hypothesised that partitioning habitat is a determinant of species coexistence. This was tested by quantifying the variability of their habitat use in tracking adult individuals in the Bariousses reservoir (France, 86.6 ha, mean depth 7.1 m). Specifically, we investigated their distribution along the littoral–pelagic and depth axes along the daily cycle and across seasons. From littoral to pelagic waters were first found pike, then perch and finally pikeperch. Pike was the closest to the surface while pikeperch was the deepest. This general pattern was, however, variable across seasons with the three species located in the upper layer in summer during reservoir stratification. Individuals were more evenly distributed along the littoral–pelagic axis and closer to the bottom when water was mixing (autumn, winter). In summer, perch used more intensively in the pelagic zone during the daytime. Other species did not show any diel change of habitats. Our results highlighted that species coexistence is associated with habitat partitioning among these three predators, with perch showing a more variable behaviour regarding habitat characteristics. Now more than ever, in the context of global change which modifies habitats, it is of crucial importance to understand the coexistence mechanisms of species that shape ecosystems.

Examining the production parameters of European perch (Perca fluviatilis) juveniles under different lighting conditions

European perch (Perca fluviatilis) is a native predatory fish in Hungary, and a promising new species of fresh water aquaculture nowadays. The European perch can be characterized by a high stress sensitivity during the intensive rearing, thus the optimization of environmental conditions has significant importance in the early life stages of fish. The aim of our study was to determine whether the light intensity and darkening of the water by humic acid affect the survival and growth performance of European perch juveniles. The experiment lasted for 28 days. Rectangular aquariums were arranged in 3 lines, the test environment consisted of 24 units. The experiment was set up with 10–10 fish per aquarium, total of 240 individuals. The average wet body weight of the fish at the start of the experiment was 1.69 grams. During the experiment, 6 treatments in 4 replicates were set up. In the first row, we set up 305.6±66.0 LUX (L), in the second row 118.0±24.4 LUX (C), and in the third row (D) 17.0±8.6 LUX illumination was set up. In each row the water of four aquariums were darkened by the addition of humic acid (H) (L, LH, C, CH, D, and DH). At the end of the experiment high survival rate was observed in all treatments. Examining the survival rate, the best results were found in the strongly illuminated treatments (L; LH- SR%=100±0.00). The observed mortality was caused by cannibalism. Regarding the individual body weight, the best results were shown by the treatments where the aquariums were illuminated with lower light intensity (C: 4.66±0.33 grams) and the aquarium water was darkened by humic acid (CH: 4.93±0.15 grams). The results of the C and CH groups were significantly better compared to the other treatments, however, they did not differ statistically from each other. The darkening of the water had a positive effect on the individual body weight of fish reared under full light (L: 3.73±0.28 grams; LH: 4.33±0.28 grams), whereas in the case of fish reared in the lowest illumination, the addition of humic acid did not affect the results (D: 3.78±0.15 grams; DH: 3.80±0.26 grams). In case of SGR (C: 3.64%/day and CH: 3.74%/day) and FCR (C: 0.84 g/g and CH: 0.78g/g) the best results were obtained by the C and CH treatments, also.

ГЕМАТОЛОГИЧЕСКИЕ ПОКАЗАТЕЛИ ЕВРОПЕЙСКОГО ОКУНЯ (Perca fluviatilis Linnaeus, 1758) ПРИ ПАРАЗИТАРНОЙ ИНВАЗИИ

European perch (Perca fluviatilis Linnaeus, 1758) is widespread in water basins and has a commercial value. However, in the natural environment, fish are often infected with invasive diseases, which exclude its processing for food purposes. Being in the body of fish, parasites produce toxic substances that affect various organs of fish. Widespread in the Volga Delta pathogenic species, Eustrongylides excisus, in large quantities occurs in perch in larval state in the abdominal cavity of the body, in the walls of the intestine, in the liver, in the calf and in the spinal muscle tissue, reaching up to 30 or more parasites per fish. Sexual maturity of the parasite occurs in the stomach of the birds. This disease is peculiar to perch species; larvae of this nematode cause granulomatous inflammatory reaction. In addition, these worms, penetrating deep into the muscles of the perch, spoil the commercial quality of fish, which leads to the culling of fish raw materials and rejection of foodstuff. This work, for the first time, compares the hematological status of infected and healthy perch of natural populations. The work aimed to assess biological and physiological effects of various parasitic invasions on European perch Perca fluviatilis(Linnaeus, 1758). Fish of both sexes at the age from 0 to 4 years were caught in natural reservoirs of the Lower Volga (Bolshaya Bolda and Bely Ilmen rivers, Astrakhan region) in September 2016 to June 2019. The total body length, the length to the end of the scale cover, body weight and age were determined, and the Fulton’s fatness coefficient was calculated. The skin, fins, mouth, gills, eyes, heart, abdominal cavity, muscles, brain, and spinal cord of fish were examined for parasitological contamination. Blood for analysis was taken from the tail vein in vivo. Nematodes were found in more than 55 % of the caught perch. Nematodes were found in the liver (30 %), abdominal cavity (45 %), intestines (10 %), muscles (15 %), and gills (5 %). Parasites were found free within the body cavity, or encapsulated, with Eustrongylides excisus being the most abundant. In the infected fish, the average body weight and body condition coefficient decreased as compared to the healthy fish of the same age. However, the revealed growth retardation in the infected perch was statistically insignificant (p > 0.05), while the body condition coefficient was significantly lower than in uninfected fish (p < 0.01 for 3-year-old perch). The parasitic infestation of P. fluviatilis with Eustrongylides nematode caused symptoms of anemia, suppression of erythropoiesis (i.e., a decrease in the proportion of blast forms of the erythrocytic cell series), an increase in the proportion of neutrophils, monocytes, and lymphoblasts in the leucocyte count. In infected perch, the number of red blood cells significantly decreased (83.01×104±4.17×104 vs. 137.22×104±5,26×104/mm3), as well as the concentration of total protein (40.81±1.19 vs. 48.97±2.07 g/l) and blood cholesterol (5.17±0.28 vs. 6.81±0.30 mmol/l). MCH (mean corpuscular hemoglobin), erythrocyte sedimentation rate, the total number of leukocytes and platelets also increased compared to uninfected fish. The level of pathological red blood cells increased in the infected perch (9,17±0,23 % vs. 4,87±0,11 %). Changes in cell cytoplasm and nucleus, degenerative changes in the cell, changes associated with cell division were the main types of the discovered cell pathology of the infected perch.

HEMATOLOGICAL PARAMETERS OF EUROPEAN PERCH (Perca fluviatilis Linnaeus, 1758) ASSOCIATED WITH PARASITIC INVASIONS

European perch (Perca fluviatilis Linnaeus, 1758) is widespread in water basins and has a commercial value. However, in the natural environment, fish are often infected with invasive diseases, which exclude its processing for food purposes. Being in the body of fish, parasites produce toxic substances that affect various organs of fish. Widespread in the Volga Delta pathogenic species, Eustrongylides excisus, in large quantities occurs in perch in larval state in the abdominal cavity of the body, in the walls of the intestine, in the liver, in the calf and in the spinal muscle tissue, reaching up to 30 or more parasites per fish. Sexual maturity of the parasite occurs in the stomach of the birds. This disease is peculiar to perch species; larvae of this nematode cause granulomatous inflammatory reaction. In addition, these worms, penetrating deep into the muscles of the perch, spoil the commercial quality of fish, which leads to the culling of fish raw materials and rejection of foodstuff. This work, for the first time, compares the hematological status of infected and healthy perch of natural populations. The work aimed to assess biological and physiological effects of various parasitic invasions on European perch Perca fluviatilis(Linnaeus, 1758). Fish of both sexes at the age from 0 to 4 years were caught in natural reservoirs of the Lower Volga (Bolshaya Bolda and Bely Ilmen rivers, Astrakhan region) in September 2016 to June 2019. The total body length, the length to the end of the scale cover, body weight and age were determined, and the Fulton’s fatness coefficient was calculated. The skin, fins, mouth, gills, eyes, heart, abdominal cavity, muscles, brain, and spinal cord of fish were examined for parasitological contamination. Blood for analysis was taken from the tail vein in vivo. Nematodes were found in more than 55 % of the caught perch. Nematodes were found in the liver (30 %), abdominal cavity (45 %), intestines (10 %), muscles (15 %), and gills (5 %). Parasites were found free within the body cavity, or encapsulated, with Eustrongylides excisus being the most abundant. In the infected fish, the average body weight and body condition coefficient decreased as compared to the healthy fish of the same age. However, the revealed growth retardation in the infected perch was statistically insignificant (p > 0.05), while the body condition coefficient was significantly lower than in uninfected fish (p < 0.01 for 3-year-old perch). The parasitic infestation of P. fluviatilis with Eustrongylides nematode caused symptoms of anemia, suppression of erythropoiesis (i.e., a decrease in the proportion of blast forms of the erythrocytic cell series), an increase in the proportion of neutrophils, monocytes, and lymphoblasts in the leucocyte count. In infected perch, the number of red blood cells significantly decreased (83.01×104±4.17×104 vs. 137.22×104±5,26×104/mm3), as well as the concentration of total protein (40.81±1.19 vs. 48.97±2.07 g/l) and blood cholesterol (5.17±0.28 vs. 6.81±0.30 mmol/l). MCH (mean corpuscular hemoglobin), erythrocyte sedimentation rate, the total number of leukocytes and platelets also increased compared to uninfected fish. The level of pathological red blood cells increased in the infected perch (9,17±0,23 % vs. 4,87±0,11 %). Changes in cell cytoplasm and nucleus, degenerative changes in the cell, changes associated with cell division were the main types of the discovered cell pathology of the infected perch.

Does dietary Tenebrio molitor affect swimming capacity, energy use, and physiological responses of European perch Perca fluviatilis?

We assessed swimming capacity, energy expenditure, and physiological responses of European perch (Perca fluviatilis) fed four isonitrogenous and isoenergetic diets containing yellow mealworm (Tenebrio molitor) larvae meal at 0, 25, 50, and 75% substitution for fishmeal (abbreviated diets, TM0, TM25, TM50, and TM75). Each diet was fed to quadruplicate group of perch (initial biometrics, body weight 20.81 ± 3.36 g, total length 11.77 ± 0.72 cm) for 119 days. At the terminal of feeding trial following 24 h starvation, eighty fish (20 fish/diet group) were individually selected for swimming performance tests, which were conducted in a 10 L enclosed swimming tunnel with velocity increased from 5 cm/s in 2 cm/s increments every 60 s. Exercised fish, fish experienced swimming tests, and non-exercised fish, fish not involved in swimming tests were, at the same time, sampled for serum biochemistry, muscle traits. Whole-body of non-exercised fish were also analyzed for proximate composition and fatty acid profile.Critical swimming speed (Ucrit, cm/s and body length/s), oxygen consumption (MO2, mg/kg/h), and energy cost of transport (COT, J/kg/m) of perch did not differ among diet treatments. Exercised perch significantly increased serum glucose and cortisol compared to non-exercised fish. Substitution of fishmeal by T. molitor larvae meal induced significant changes in aspartate aminotransferase across treatment groups, lactate dehydrogenase in TM0 and TM75, K+ concentration in fish fed TM75, and muscle water content in TM50 of exercised compared to non-exercised perch. Oleic acid of whole-body fish had a significant linear correlation with the critical swimming speed of European perch. Since fish swimming behavior is an indicator of animal welfare, our findings suggest that dietary insect meals could ensure the welfare of farmed fish.

Environmental DNA monitoring of noble crayfish Astacus astacus: Comparison and refining of methodology

During the past decade, environmental DNA (eDNA) methodology has become an important non-invasive tool to monitor aquatic micro- and macro-organisms, including freshwater crayfish. In Europe, noble crayfish Astacus astacus is the most widespread native freshwater crayfish. However, the species is threatened in its entire distribution range. It is therefore included on the International Union for Conservation Nature (IUCN) red list, and on several national red lists. Reliable monitoring is essential for implementation of conservation measures. For crayfish, traditional population trends have been obtained from catch per unit effort (CPUE) data. In order to successfully apply and use eDNA monitoring for noble crayfish, or any species, it is a prerequisite to know the strengths and weaknesses of the applied methods and how they perform compared to traditional methodology. Sampling strategy and analysis methodology also depends on choice of species to be monitored, and which questions to be answered. Further, refinement of the employed methods may improve the detection probability for eDNA monitoring. Here we report the results from 1) a recently published study on noble crayfish eDNA monitoring (Johnsen et al. 2020) and 2) an ongoing study comparing and optimising the methods used for monitoring noble crayfish. 1) We compared eDNA monitoring (transects with ten 5L samples) with traditional trapping (transects with 50 traps) for noble crayfish in lentic habitats, in order to evaluate detection probability and if eDNA concentration correlates with relative density of crayfish. We also compared two commonly used analytical methods [quantitative real-time PCR (qPCR) and droplet digital PCR (ddPCR)] for eDNA monitoring. We found that qPCR outperformed ddPCR in detection frequency (Fig. 1), most likely due to some inhibition in the ddPCR analysis. eDNA monitoring provided reliable presence/absence data for noble crayfish, even in lakes with very low crayfish densities. Detection frequency increased with increasing CPUE (Fig. 1). However, we did not observe any correlation between relative crayfish densities and eDNA concentrations of crayfish. eDNA concentrations were consistently very low, even in lakes with very high crayfish densities. For lakes with very low crayfish densities, we estimated that ~5 samples (5L samples) are needed for 95 % detection likelihood, while for lakes with high densities 2 samples were needed. 2) We compared two eDNA sampling strategies (sampling from bottom or the surface), commonly used for crayfish or fish in Norway to investigate how both strategies perform. The sampled filters were divided and two DNA extraction protocols were evaluated (CTAB based vs Column based). We found that the DNA yield was higher from the column based DNA extraction protocol, and that eDNA concentrations from fish (brown trout Salmon trutta, northern pike Esox lucius and European perch Perca fluviatilis) were significantly higher than for crayfish. For crayfish and brown trout, there was little difference between detection probability for bottom and surface samples, while for northern pike and European perch the detection probability was higher for the bottom samples. Currently, we are analysing eDNA samples collected with glass fibre filters and NatureMetrix filters for noble crayfish in both lentic and lotic habitats and the preliminary results will be presented. We conclude that eDNA monitoring cannot substitute CPUE monitoring for freshwater crayfish, but it offers reliable presence-absence data, provided sufficient sampling efforts. Thus, it is suitable for large scale monitoring of threatened crayfish and combined with eDNA analysis of alien crayfish and diseases such as crayfish plague, this is a cost-efficient supplement offering a more holistic approach for aquatic environments and native crayfish conservation. Furthermore, the synergy effect of using collected eDNA samples from different projects to monitor additional species is substantial.

Fluctuating Asymmetry of the Traits of the Seismosensory System of the Roach Rutilus rutilus (L.) (Cyprinidae, Pisces) and the European Perch Perca fluviatilis L. (Percidae, Pisces) in Small Ponds with Various Water Mineralization

Fluctuating Asymmetry of the Traits of the Seismosensory System of the Roach Rutilus rutilus (L.) (Cyprinidae, Pisces) and the European Perch Perca fluviatilis L. (Percidae, Pisces) in Small Ponds with Various Water Mineralization

Population ecology, growth, and physico-chemical habitat of anadromous European perch Perca fluviatilis

Anadromous sub-populations of stenohaline freshwater fish are vastly understudied in the estuarine environment. The purpose of the present study was therefore to study the population ecology, growth rate, and physico-chemical environment of an anadromous sub-population of European perch (Perca fluviatilis) from the western Baltic Sea. Fish (301) were marked with external identification tags, and anglers and fishermen reported recaptures in a citizen science set-up over three years. In addition, scale samples were collected for population growth rate determination. Furthermore, water temperature, salinity, and oxygen concentration were monitored in the area. The fish showed a consistent annual migration pattern over the three years residing in a bay during summer while being in a delta during autumn, winter, and spring. The population had a high growth rate, but a meta-analysis showed that growth of European perch is not distinctly different between estuarine and freshwater populations. The average salinity measured in the area was around 10, but increased on multiple occasions to salinity levels known for being physiologically challenging for European perch. We argue that high growth rates of estuarine European perch is more likely due to high food availability and low interspecific competition in this environment, rather than due to physiologically optimal salinities. Furthermore, the European perch in the present study lived on the edge of the species salinity tolerance, and the migration into the delta during winter is likely a combination of avoiding high salinities at low temperatures and a spawning migration. These results are important knowledge for the management of estuaries and coastal areas, especially as climate change is locally altering these environments drastically, and calls for further studies on other anadromous sub-populations of stenohaline freshwater fish.