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The aim of the study was to determine the food preferences of the black cormorant and to assess fisheries losses in Włocławski Reservoir. Twenty fish species were identified in the cormorant diet. The dominant species were ruff and perch (29.4% and 24.4 % of the weight share, respectively). Roach (11.9%) and Prussian carp (10.9%) were also important components of the cormorant diet. The share of invasive species from Gobiidae family was negligible (0.2%). Among the fish species important to commercial and recreational fisheries management, the most numerous in the cormorant diet were: ide (10 t; 2.7% of the weight share), pikeperch (8.6 t; 2.3%), asp (6.3 t; 1.79%), and pike (4.9 t; 1.3%). The fish biomass consumed by cormorants was a mean of 372.8 t annually, which is 46.6 kg per ha (range of 44.6 to 49.6 kg per ha). The analysis of fisheries losses in 2009 was estimated at 980,000 PLN.
The aim of the present study was to verify the feasibility of using live Artemia salina nauplii embedded with fluorochromes for the mass marking of pike Esox lucius (L.) larvae. In the experiment, pike larvae 6 days post hatch were fed ad libitum with nauplii dyed with 600 ppm tetracycline hydrochloride (TC) or 200 ppm alizarin red S (ARS) for 3 or 6 days. The highest percentage of marked fish (100%) and the best quality of this marking was found in the groups fed A. salina stained with TC for either 3 or 6 days. In groups fed A. salina stained with ARS for 3 or 6 days exhibited a lower percentage of marked fish (ranging from 76.7–88.3%). No significant differences between experimental groups were noted regarding survival rate, final body weight and length of the reared pike larvae.
The aim of the study was to compare the share of hatchery-reared lake trout Salmo truttam.lacustrisin catches of fingerlings in the upper Wda and the Pilica Rivers in Autumn, following the stocking fish in spring 2005. Larvae in number of 40 thousand had been previously exposed to the thermal shock procedure (temperature decrease from 8.0 to 2.5oC for 2 hours, and back to initialvalue), then released to both the Wda and Pilica Rivers, connected with the Lake Wdzydze, when the source of the endemic lake trout population exist. The readability of the thermal mark on otoliths wasgood and was visible as an expanded dark band within the daily increments. Thermal marks were found in every otolith in sample of larvae dedicated for stocking. The percentage of marked otoliths infingerlings sampled from the Wda and Pilica rivers was, respectively, 79.3% and 85.0%. Results indicate the natural recruitment of lake trout in both tested rivers. Further research on necessity of supplemental stocking should be continued. Mass marking procedure presented here could be use fulin such investigations
The effectiveness of stocking brown trout summer fingerlings (0.5-1.3 g) into six moraine Pommeranian rivers was evaluated. Three groups of experimental fish were marked with alizarine red S to enable their identification during autumn and spring monitoring with electrofishing. The results indicated that stocking was more effective when done with summer fingerlings than one- year-old fish. In the three investigated rivers stocking resulted in 3.5 to 13.5 young-of-the-year trout increment. In two cases the share of stocked fish was lower than these from natural spawning.
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