Advantage was taken of 490 questionnaires completed by anglers to study the effectiveness of ground-baiting and its effect on nutrient (phosphorus and nitrogen) budgets in 37 water bodies. There was a strict relationship between daily amounts of baits used and daily catch of six cyprinid species. However, fish catch increased only to a bait rate of about 2 kg/day. Higher amounts resulted in lower catches.Calculations were also made of daily loads of phosphorus and nitrogen introduced by the 'average' angler inlo a water body, as well as of the amount of nutrients removed by this angler from the aquatic environment with the fish catch. It was shown that although ground-baiting represented an important source of nutrient input into the environment, using this method anglers removed 2 2 times more phosphorus and 1 7 times more nitrogen from the environment (with their catch) than they introduced into it. Turawa Reservoir was used as an example, showing that in Polish conditions, angling may have a beneficial effect on nutrient budgets of such water bodies.

Fisheries Institute in Olsztyn, Poland Citation: Teodorowicz M. 2013 -Surface water quality and intensive fish culture -Arch. Pol. Fish. 21: 65-111.Abstract. The aim of the study was to determine the impact fish farms have on water quality in rivers. An experimental system for estimating the amount of pollution produced by aquaculture and discharged into surface waters was tested through environmental research. The impact of clarifying ponds on the quality of post-production water was determined.

The influence of a constant magnetic field with an intensity ranging from 0.4 to 0.6 T (Tesla) was determined on physicochemical parameters of water and on rearing of larvae of the European sheatfish Silurus glanis L. larvae. In the experiment, feeding brood of European sheatfish was reared in two groups. One was kept in tanks supplied with magnetically treated water. The second group was kept in tanks supplied with water without treatment with a magnetic field (control). The fish tanks were supplied with circulating river water. Rearing was conducted for 15 days at an initial stocking density for both groups of 8 fish per litre. The mean fish mass obtained was 0.46 g, and in the control group – 0.78 g (P<0.05). Stocking mortality was 19.1% in the tanks with a constant magnetic field, and 13.5% in the control group. No changes were observed in water phosphate, ammonium, organic compounds or chloride concentrations.

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