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Janusz Golski, Jan Mazurkiewicz, Wojciech Andrzejewski, Antoni Przybył and Jerzy Kozak

Abstract

The aim of this study was to assess the efficiency of propagating juvenile trout, Salmo trutta L. in small lowland streams and to evaluate the impact of the environmental conditions in the streams on the juvenile fish. Brown trout (Salmo trutta fario) and sea trout (Salmo trutta trutta) early fry fed under controlled conditions were used to stock third-order lowland streams. During summer, fall, and spring catches, fry were counted, measured, and weighed. The following parameters were calculated using the data collected: fry stocking density (ind. m-2); survival; specific mortality rate (SMR); length range; mean specimen length; body weight; mean body weight; specific growth rate (SGR); body condition (Fulton’s index). The ichthyological studies were accompanied by simultaneous analyses of environmental conditions that were performed monthly, and benthic macroinvertebrates were sampled in spring and fall. No differences were observed in the biological parameters analyzed between sea trout and brown trout. Variability in environmental parameters such as temperature, oxygenation, conductivity, and stream width and depth were associated with differentiation in the biological parameters of the fry. The results clearly indicate that the considerable potential of small lowland streams for the propagation of salmonid juvenile stages is currently underexploited.

Open access

Jan Mazurkiewicz, Wojciech Andrzejewski, Katarzyna M. Żołnierowicz, Katarzyna Przybylska, Janusz Golski and Lilianna Graczyk

Abstract

Alternative proteins from vegetal sources are being studied, because of the high costs and limited resources of fish meal. The aim of this study was to determine the possibility of including cold-pressed rape cake (CPRC) as a partial protein substitute in diets for common carp, Cyprinus carpio L. Common carp fry were stocked into experimental ponds at a density of 30 fish per pond. The effects on growth, feeding efficiency, and fish body composition were studied for four amounts of CPRC (0, 70, 130, 200 g × kg-1). Statistically significant higher final weights (528-530 g) were obtained with fish fed diets with 130 and 200 g × kg-1 CPRC. The fish growth rate was nearly identical in all variants (SGR of 3.3-3.4 % d-1). Similar results were presented in FCR at 1.3, and in PER at 2.2. Our results suggest that it is possible to include up to 200 g × kg-1 of CPRC in diets for two-year old common carp without significant effects on growth, nutritive efficiency, or the proximate composition of the fish.