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Abstract

The article describes occurrence and distribution of Eustrongylides trematodes in fish in the waters of the Dnipro-Buh estuary and the delta of Dnipro River in Mykolaiv and Kherson Region. Study was conducted in 2015–2016. This parasite was found in natural water reservoirs in Mykolaiv and Kherson region in following fish species: Sander lucioperca (Linnaeus, 1758), Perca fluviatilis (Linnaeus, 1758) and Esox lucius (Linnaeus, 1758). Ichtyopathological investigation of 346 fishes was conducted. Parasites were observed in abdominal cavity, muscle tissue, wall of gastro-intestinal tract, gonads and hepatopancreas. P. fluviatilis was the most affected species, prevalence of infection was 85.1 %. Less infected were S. lucioperca and E. lucius, with the prevalence of infection 58.1 % and 58.9 % respectively. Mean prevalence of infection of predatory fish in studied reservoirs was 70.5 %. The intensity of infection was the highest in perch (1–14 nematodes per fish). The lowest intensity of infection was found in pike-perch (1–9 nematodes per fish).

The Composition of Fatty Acids in Muscles of Six Freshwater Fish Species from the Mazurian Great Lakes (Northeastern Poland)

Lipid content and fatty acids composition of non-predatory fish: roach, Rutilus rutilus (L.), bream, Abramis brama (L.), vendace, Coregonus albula (L.), and of predatory fish: Eurasian perch, Perca fluviatilis L., pike, Esox lucius L. and burbot, Lota lota (L.) were examined. These fish were caught from three lakes of Mazurian Great Lakes (Kisajno, Dargin, Niegocin). The content of total lipid and some fatty acids varied widely within and among species. Generally, the lipid content was low (0.56-2.78%). Among the saturated and monounsaturated fatty acids, the predominant fatty acids were palmitic C16:0 (19.24-33.44%), stearic C18:0 (4.37-6.87%), palmitoleic C16:1 (4.51-12.93%), and oleic C18:1 n-9 (6.85-14.49%). Arachidonic C20:4 n-6 (3.17-6.55%), eicosapentaenoic C20:5 n-3 (4.14-8.91%), and docosahexaenoic C22:6 n-3 (5.91-24.67%) acids were the most abundant polyunsaturated fatty acids. In the case of all the freshwater fish, with the exception of bream, higher contents of saturated fatty acids than monounsaturated fatty acids were noted. Among the fish studied, the highest value of total n-3 polyunsaturated fatty acids (43.86%) was noted in vendace, whereas bream contained the highest content of total n-6 polyunsaturated fatty acids (11.21%). The ratio of n-3/n-6 ranged between 1.50 (burbot) and 4.40 (vendace). Differences in the content of fatty acids in fish with different feeding strategies (non-predatory and predatory) were measured. Non-predatory fish were found to have lower values of saturated fatty acids than predatory fish (P ≤ 0.05). Non-predatory fish contained significantly more eicosapentaenoic acid (EPA) than predatory fish (P ≤ 0.01), whereas the amounts of monounsaturated and n-3 and n-6 polyunsaturated fatty acids in non-predatory and predatory fish were not statistically significant (P > 0.05). The total n-3 polyunsaturated fatty acids was higher in non-predatory fish, but not statistically significant (P > 0.05). Similarly, the differences in DHA and n-3/n-6 ratio in muscles of predatory and non-predatory fish were not statistically significant (P > 0.05).

Essential mineral components in the muscles of six freshwater fish from the Mazurian Great Lakes (northeastern Poland)

The concentrations of nine mineral elements in the muscles of roach, Rutilus rutilus (L.), bream, Abramis brama (L.), vendace, Coregonus albula (L.), pike, Esox lucius L., Eurasian perch, Perca fluviatilis L. and burbot, Lota lota (L.) were measured. The microelement content in the muscle tissues of the fish was identified to have the following decreasing sequence: Zn > Fe > Cu > Mn, and the concentrations of macroelements in fish were noted in the following order: K > P > Na > Mg > Ca. Roach and bream had more iron than perch and pike (P ≤ 0.01). There were no differences in the concentrations of copper between the species in the following groups: roach and bream; roach and perch; perch and pike (P > 0.01). The concentrations of the remaining elements did not differ among fish of different feeding types (P > 0.01). The only statistically significant differences were noted in the content of iron in the muscles of two fish groups: non-predatory (roach, bream and vendace) and predatory (perch, pike and burbot; P ≤ 0.01).

Impact of feed ration on growth, feed conversion, and variation in body weights of juvenile pike, Esox lucius L., reared in a recirculating aquaculture system

The aim of the study was to determine the impact of different feed rations on growth rate, feed conversion, and variation in body weights in juvenile pike, Esox lucius (L.), cultured in a recirculating system. Three different feed rations were used in the experiment: 0.5% (group L), 0.8% (group O), and 1.1% (group H) of fish biomass. The fish in each group were fitted with Carlin tags and classified according to size as individuals that were small (class S) with a mean body weight of 63.0 g, medium (class M) at 90.7 g, and large (class L) at 137.2 g. After eight weeks of culture, the fish from group O had the highest mean body weight. The final body weight in this group was 7% higher than that in group H and 22.5% higher than that in group L. Differences were also noted among groups with regard to daily (DGR) and specific (SGR) growth rates in body weight and in the protein efficiency ratio (PER). The results indicate that the best culture effects of pike weighing a mean of 100 g and held at a water temperature of 22.5°C were obtained with a daily feed ration of 0.8% of the fish biomass. This ration did not result in increased pike size variation, and it permitted obtaining the greatest increases in body mass in each size group.

Abstract

Introduction: The study examined the concentration of total mercury and correlation coefficients between fish size or FCF (condition factor) and the content of Hg in muscle tissue of six freshwater fish: bream (Abramis brama L.), roach (Rutilus rutilus L.), whitefish (Coregonus lavaretus L.), vendace (Coregonus albula L.), perch (Perca fluviatilis L.), and pike (Esox lucius L.). Material and Methods: The fish were caught from the Lake Pluszne located in the Olsztyn Lake District (Poland). Mercury was analysed by atomic absorption spectrometry using Milestone DMA-80 (with dual-cell). Results: The content of the element in the muscles of the examined fish was as follows: pike (0.197 mg/kg) ≈ perch (0.173 mg/kg) > vendace (0.114 mg/kg) ≈ roach (0.095 mg/kg) and roach ≈ whitefish (0.065 mg/kg), and whitefish ≈ bream (0.042 mg/kg) (p ≤ 0.05). In all cases, the content of mercury correlated positively with the body weight and total length of the fish. Only the correlation coefficients between mercury concentration and weight or length of bream were slightly higher (0.979 and 0.977 respectively, p ≤ 0.001). The length and weight relationship of the fish was also determined. Conclusion: The results showed that the levels of mercury were lower than the maximum acceptable limit established by the Commission Regulation (EC) No 629/2008 of 2 July 2008. Thus, they are safe from consumer health point of view.

, 10: 129-155 (in Polish). Prejs A. 1973 – Experimentally increased fish stock in the pond type lake Warniak. IV. Feeding of introduced and autochthonous non-predatory fish – Ekol. Pol. 21: 465-504. Pulina S., Brutemark A., Suikkanen S., Padedda B.M., Grubisic L.M., Satta C.T., Caddeo T., Farina P., Sechi N., Luglé A. 2016 – Effects of warming on a Mediterranean phytoplankton community – Web Ecol. 16: 89-92. Radke R.J., Kahl U. 2002 – Effects of a filter-feeding fish [silver carp, Hypophthalmichthys molitrix (Val.)] on phyto- and zooplankton in a mesotrophic

Changes occurring over time in commercially exploited fish assemblages in lowland dam reservoirs

Changes in the ichthyofauna assemblages of three shallow dam reservoirs located in central and eastern Poland are presented based on long-term records of commercial fish catches. As the reservoirs age the evolution in the sizes of the shares of exploited fish species is depicted by temporal trend lines described with regression functions. The species targeted by commercial fishing are assigned to one of four ecological groups - predatory, eutrophying cyprinid, rheophilic, and others, depending on the role they play in the reservoir. Catches of cyprinid fishes from the eutrophying group increased in each of the reservoirs studied as the years passed. This was most notable in the Siemianówka Reservoir since in the period immediately following inundation the slope factor b trend line was 7.25 at r2 = 0.9. The population of predatory fish was also noted to increase continually in this reservoir, and this was linked to intense stocking with pike, Esox lucius L. The shares of predatory fish in the other reservoirs decreased from inundation onwards, only to stabilize in recent years at minimal levels with slight increasing trends. As time passed from the inundation of the reservoirs the general dependency between the average shares of fish groups in catches was highly significant for all of fish groups identified.

Abstract

Samples for analysis were collected from 10 areas, including the major Polish rivers and lakes, with different sources of environmental pollution (industrial, municipal, and farming). The materials was taken from the lakes of Mazury, located in a non-industrialised region, from the Brda River, an area impacted by pig farms, from the lakes of Lipczyno Wielkie/Pomerania, from the Wkra River, an area impacted by poultry farms, from the Dunajec River at the Roznowski Reservoir, from the Vistula River at Cracow and Warsaw, from the Odra River at Wroclaw and the Warta River estuary, and also from Rybnik Power Station Reservoir. Concentrations of Pb, Cd, Hg, and As were analysed in 397 fish muscle and 128 sediment samples using an atomic absorption spectrometry technique. The analytical procedures were covered by a quality assurance programme. It was demonstrated that the average concentrations of lead, cadmium, and arsenic in fish were in the low hundredths and thousandths of a mg/kg and never exceeded permitted limits established for food. Higher values of these elements were found in fish from bodies of water located in the zone of influence of large urban agglomerations, especially the Cracow region. High concentrations of lead and cadmium were also found in Vistula River sediments near Cracow, where the maximum values were 134.10 mg/kg and 21.24 mg/kg dry weight for lead and cadmium respectively. The average concentration of mercury in a predatory fish muscle (0.179 mg/kg) was almost twice as high as in the omnivorous fish (0.103 mg/kg). Only a single fish sample exceeded the maximum limit for this metal (0.50 mg/kg) and did not present a risk to consumers’ health.

Contaminants in Fish: Risk-Benefit Considerations

Fish provide a healthful source of dietary protein and are high in nutrients such as omega-3 fatty acids. There is evidence of beneficial effects of fish consumption in coronary heart disease, stroke, age-related macular degeneration, and growth and development. Yet, benefits may be offset by the presence of contaminants, such as methylmercury (MeHg), dioxins, polychlorinated biphenyls (PCBs) and several other halogenated persistent organic pollutants. MeHg is a known developmental neurotoxicant, as evidenced by several animal studies and episodes of human intoxication in Japan and Iraq. Fish represent the main source of exposure to MeHg for the general population, and large predatory fish (swordfish, tuna) have the highest levels of MeHg contamination. Provisional tolerable weekly intakes of 0.7 μg kg-1 to 1.6 μg kg-1 have been set by regulatory agencies. Concern for contamination of fish with dioxins and dioxin-like PCBs stems from their reported carcinogenicity, immunotoxicity, and reproductive and developmental toxicities. Farmed and wild-caught fish appear to have similar levels of contaminants. Advisories are in place that recommend limited consumption of certain fish in children, pregnant women and women of childbearing age. Careful risk-benefit considerations should foster fish consumption while minimizing exposure to toxic contaminants.

Assessing angling catches in dam reservoirs on the example of Zegrze Dam Reservoir

Three methods were used to estimate the size and structure of angling catches in Zegrze Dam Reservoir in the 1999-2001 period. The material analyzed comprised data collected from direct monitoring (798 times), 153 questionnaires, and 687 reports. The catch structure according to the questionnaires and direct monitoring was similar. Recreational anglers who completed the questionnaires reported catches of 14 fish species; three of these (bream, Abramis brama (L.), roach, Rutilus rutilus (L.), and white bream, Abramis bjoerkna (L.)), comprised 51.6% of the total catch weight. The share of predatory fish comprising pike, Esox lucius L., pikeperch, Stizostedion lucioperca (L.), and wels, Silurus glanis L., was 31.1% of the total catch weight. The anglers who were monitored directly caught 12 species of fish, and bream dominated the catch weight at 55.0%. The share of predatory species was 33.4%. The anglers using the fishing camps demonstrated the greatest interest in predatory species, which comprised a total of 35.4% of the overall biomass of their catch. The estimated size of the catch according to questionnaires was 42842 kg or 13.0 kg ha-1, while the fishing intensity was 0.20 kg fisher-1 hour.-1. According to direct monitoring, the size of the annual catch was 33544 kg, which corresponds to an effectiveness of 10.2 kg ha-1. The results indicate that the questionnaire and direct monitoring methods are compatible, and that it is generally necessary to choose uniform study methods. When using the questionnaire method, it is essential to verify the results obtained through direct monitoring at the fishing grounds. The method of catch reporting by the fishers using the fishing camp is only of auxiliary significance.