This study presents concentrations of iron, manganese, zinc, and copper in selected tissues of two fish species: pike (Esox lucius L.) and bream (Abramis brama L.) living in lakes Ińsko and Wisola, Northwestern Poland. The lakes differ in their trophic status. The effect of gender and environmental conditions on metals accumulation was also investigated. Metal analyses were performed using inductively coupled plasma atomic emission spectroscopy. Considering all studied fish species and tissues, the average metal concentrations (micrograms per gram wet weight) in both lakes occurred in the following ranges: Fe 0.8–240.6, Mn 0.2–8.4, Zn 3.0–185.9, and Cu 0.14–7.76. The lowest levels of the studied metals were always detected in the muscles. The spleen, kidneys, and liver were found to accumulate the highest amounts of Fe. In the case of the other metals, the highest levels were found, as follows: Mn in skin, gills, and gonads, Zn in digestive tract and gills, Cu in liver. Heavy metal content in fish gonads was observed to be sex dependent.

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Crayfish accumulate trace metals, which is why they often serve as environmental indicators. Among heavy metals, Hg, Cd and Pb are considered toxic substances, while Fe, Zn, Cu, Cr, Ni, Mn, V, Al and Li are involved in vital functions, which makes them essential elements in animal organisms. The study objective was to determine concentrations of the above metals in the abdominal muscles, hepatopancreas and exoskeleton of spinycheek crayfish (Orconectes limosus Raff.) and signal crayfish (Pacifastacus leniusculus Dana) from Dga³ Wielki Lake and Pob³êdzie Lake in the Mazurian Lake District, Poland. The analyses were carried out with the use of the following methods: CV AAS (Hg), GF AAS (Cd, Pb) and ICP-AES (Al, Cr, Cu, Fe, Li, Mn, Ni, V, Zn) after wet digestion in HNO 3 and HClO 4 concentrated acid mixture. Regarding mean concentrations (mg kg-1 wet weight) in crayfish, metals formed the following order:

The aim of the study was to estimate the effect of culture conditions and culture site on magnesium (Mg) and zinc (Zn) concentrations in freshwater fish. The study encompassed dorsal muscles in five fish species: common carp (Cyprinus carpio L.), rainbow trout (Oncorhynchus mykiss Walbaum) and Siberian sturgeon (Acipenser baeri Brandt), northern pike (Esox lucius L.) and grass carp (Ctenopharyngodon idella Valenciennes). A total of 125 fish comprised 25 individuals of each species, aged from 6, 9, and 12 months. The fish were cultured in privately owned fish breeding ponds (Western Pomerania, Poland). For chemical and biochemical assays, samples of dorsal muscles were taken from each fish. Tissue samples were wet mineralised in concentrated HNO 3 in a CEM MDS 2000 microwave oven. Magnesium and zinc concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-MS) in a Jobin Yvon type JY-24 apparatus. The pursuit of the research we had an approval of the Polish Local Ethics Committee nr 9/05. The magnesium concentration in the dorsal muscles ranged from 95.3÷347.6 mg kg-1 w.w. The highest Mg concentration was found in rainbow trout 240 (347.6±32.2 mg kg-1 w.w.), and the lowest in grass carp (95.3±11.3 mg kg-1 w.w.). Zinc concentration varied from 6.7÷98.8 mg kg-1 w.w. The highest was found in the muscles of Siberian sturgeon (98.8±0.4 mg kg-1 w.w.), and the lowest in rainbow trout (6.7±0.7 mg kg-1 w.w.). It was found that the breeding place significantly affected the Zn and Mg concentrations in the muscle tissue among individual freshwater fish species. The magnesium and zinc concentrations were also significantly affected by the type of feed.