The study described was aimed at determining levels of selected macro– (Mg) and microelements (Ni, Fe, Cu, Zn) as well as those of heavy metals (Cd) in tissues and organs of the carp farmed in Western Pomerania, with a particular reference to fish-rearing facilities in River Odra. The study involved 5-month-old carp acquired from the research station of the Agricultural University of Szczecin. The levels of the metals were determined and compared with the data available in the literature, a particular attention being paid to values reported from the fish reared in the Odra. The results showed the contents of the elements studied to be within physiological reference ranges of cyprinids.

The perch, a species present in most Polish freshwater reservoirs, is not protected. A continuous decline of the perch population abundance in Poland, reflected in catches of fishermen and anglers over the second half of the last century and in the first years of the 21st century, is mainly a result of increased intensity of fishing. At present, the perch abundance is much lower than that required by sustainable functioning of aquatic communities in which the species diversity and abundance of fish is kept at a stable level corresponding to the trophic status of an area. The aim of the analysis presented was to asses the size and fecundity of perch females at age of maturity and to use the results to propose a protective size which, when deemed legally binding, would contribute to a faster recovery of overfished perch populations without drastic restrictions to fisheries. Materials for the study were collected from the Polish coastal lakes on the southern Baltic coast, from the Vistula Lagoon, from Mazurian lakes in the vicinity of Olsztyn, and from the power station-heated lakes near Konin. Samples were collected in 2000–2005 from catches effected with trap and drag nets; sampling was conducted in late autumn, when the perch growth is arrested, as well as in winter and spring, prior to and during spawning. The smallest females which were ready to spawn had survived three growth seasons (age group 2+) and measured 14.1–16.0 cm total length (L.t.). They contributed 25%to all the females of that age group caught by fishermen. The largest 3-year-old females (22.1–24.0 cm L.t.) occurred sporadically in the catches. The most frequent females at age of first maturity measured about 17.5 cm L.t.Absolute fecundity of the smallest females that spawned for the first time was 5–10 thou. eggs per fish.Afemale measuring 17.5 cm L.t. at age of first maturity carried about 13 thou. eggs. A protective size of 18.0 cm L.t. is sufficient for spawning of 70% of the perch females that have reached maturity for the first time.

Column, thin-layer, and high-performance liquid chromatographic techniques were used to study carotenoids in the herbivorous and carnivorous piranhas cultured in aquarium. Assays were run on tissue samples from skin, muscles, liver and intestines dissected from individuals of both sexes. A total of 16 carotenoids were identified, lutein and astaxanthin (herbivorous piranha), astaxanthin and zeaxanthin (carnivorous piranha) being the dominant pigments. Εpsilon-carotene and diadinoxanthin were identified only in the herbivorous piranha while cynthiaxanthin in the carnivorous fish. The total carotenoid content ranged from 1.889 (muscles) to 12.215 µg·g^–1 wet weight (intestines) in the herbivorous piranha and from 0.907 (muscles) to 5.235 µg·g^–1 wet weight (liver) in the carnivorous piranha.

Benthic fauna was collected in 1976–1979, with a small bottom sampler and a dredge, from areas of up to 12 nautical miles off the Pomeranian Bay coast of theWolin Island and off Ustka in the central part of the Polish Baltic coast. Because the sampling devices used scooped the surficial sediment layer only, adult infaunal forms were not retrieved. The animals washed out from the sediment were separated on an 0.3 mm mesh size gauze. The small mesh size of the screening material resulted in a high proportion of juvenile representatives of most macrofaunal taxa in the samples and allowed to reveal the presence of small-bodied species not reported by other studies conducted with the use of a 1 mm mesh size sieves. The sieve mesh size was one of the reasons why the number of macrofaunal taxa found in this study was higher than reported by other authors. The dredge made it possible to collect representatives of taxa capable of evading grabs, which contributed to a longer list of species as well. The macrobenthic taxa found were much more abundant in the Pomeranian Bay than off Ustka (central Polish coast). It was only Streptosyllis websteri, fairly abundant off Ustka, that was recorded sporadically in the Pomeranian Bay.

The effectiveness of fish catching using three different methods, in six shallow lakes of Łęczyńsko-Włodawskie Lakeland was compared. The lakes concerned were: Kleszczów, Rotcze, Długie, Sumin, Głębokie Uścimowskie and Syczyńskie and the methods were as follows: electrical fishing, gill net and fyke net. The most fish species and their biggest biomass were reported while using electrofishing.When fishing on the open waters the best effects were obtained using nets of gill net Norden S type, while fyke nets, which were put in littoral, were found to be the least effective method and of greatest selectiveness of species. For fish sampling in shallow lakes, it is best to use several methods, for example, electrofishing in the littoral zone but net fishing on the open waters.

Alimentary tracts of 692 Prussian carp were examined. Diet components were identified using the keys published by Rybak [1971] and Pennak [1953]. The Prussian carp food was found to consist of 19 items identified to species, genus, or family/order. The food composition was also characterised by calculating contributions of individual food items to the total number of food items (UL), frequency of occurrence of each item (CZW), and each item’s contribution to the gut content weight. The fish feeding intensity was presented using a per cent general consumption index. The fish were found to have fed at the highest intensity in July, the lowest feeding intensity being recorded in November and December. The length-weight relationship of the Prussian carp examined was analysed as well and described as W = 0.0355L^3.017. Fish condition in various periods of time was assessed using the Fulton and Le Cren coefficients for whole fish and Clark’s method for gutted fish. The lowest values of the Fulton and Le Cren coefficients were typical of the Prussian carp caught in the Szczecin Lagoon (April 2000) and Lake Zbęchy (November 2000); the lowest condition coefficients calculated using Clark’s method were those found in the fish from Lake Wonieść (September 2002). The highest Fulton and Le Cren coefficientswere recorded in the Lake Zbęchy Prussian carp (November 2000); similarly, the Lake Zbęchy fish, when gutted, showed the highest Clark coefficients.

The ratio values of the concentrations of the elements which exist in a given water body are important indicators that define the restraining role of nitrogen or phosphorus in the productivity of surface waters. In the years 1986–1996 the relationship between this ratio and thermal conditions, primary production (chlorophyll “a”) and the rate of water mineralisation (conductivity, chloride and sulphate concentrations), and also on their optical properties (visibility of the Secchi disk) were examined in the shallow coastal lakes: Koprowo, Liwia Łuża and Resko Przymorskie. In the waters of the analysed lakes phosphate phosphorus content ranged from 0.028 to 0.365; mineral nitrogen content ranged from 0.289 do 1.897 mg·dm^–3; and the N:P ratio changed from 5.4 to 34.3; the concentrations of chlorides and sulphates amounted from 87.0 to 1079.2 and from 53.0 to 266.4 mg·dm^–3 respectively. The visibility of the Secchi disk equalled to 0.75m, whereas, chlorophyll „a” concentrations changed from33.5 do 73.2mg·m^–3. The values of these indexes prove that the discussed lakes were highly eutrophic. The investigations showed significant changeability of the concentrations of chlorides and sulphates which linked inversely proportionally to the values of the N:P ratio. This relationship was not observed with respect to conductivity. Moreover, the authors stated that the content of chlorophyll “a” in the lake waters of Koprowo, Liwia Łuża and Resko Przymorskie was mostly influenced by phosphorus concentrations (dissolved reactive phosphorus) and light conditions (the visibility of the Secchi disk). Thus, they were the factors restraining the primary production of these water bodies.