Józef Domagała, Robert Czerniawski and Tomasz Krepski
This study examined the availability of food and its selection by sea trout Salmo trutta L. fry in the first four weeks of life after yolk sac resorption. The food base and stomach contents of sea trout fry after release in the wild were determined. The study was performed in two small forest streams from April 25 to May 23, 2014. Macro-zoobenthos that comprised the food base for the fry were collected from the streams weekly using a bottom scraper. On the same day, the fry were captured with electrofishing gear. Analysis of the width of the benthic organisms in the food base and in the fish stomachs indicated the prey size range that the fish were feeding on. Further, the study showed that all food items found in both streams during the study weeks were also represented in the intensity of the fish: Cyclopoida, the larvae of Baetidae, Simuliidae and Nemouridae.
Józef Domagała, Robert Czerniawski and Małgorzata Pilecka-Rapacz
The aim of this study was to determine the best moment to stock trout, Salmo trutta L., larvae into the wild. This goal was accomplished by determining weekly changes in the growth parameters of larvae that were fed in seven variants: on the day of 2/3 yolk sac resorption; from the first week after the day of 2/3 yolk sac resorption; from the second week after the day of 2/3 yolk sac resorption; from the third week after the day of 2/3 yolk sac resorption; from the fourth week after the day of 2/3 yolk sac resorption; from the fifth week after the day of 2/3 yolk sac resorption; from the sixth week after the day of 2/3 yolk sac resorption. Based on our results, we concluded the following: 1) trout larvae are ready to start eating at the time of the resorption of 2/3 of the yolk sac; 2) trout larvae can live without food for three weeks following the resorption 2/3 of the yolk sac without any notable losses; 3) the best moment to stock trout larvae into the wild is in the period from the resorption of 2/3 of the yolk sac to the third week after this resorption, so one week after full resorption. This is the optimal period to stock any waters with trout larvae.
Józef Domagała, Katarzyna Dziewulska and Robert Czerniawski
The aim of the study was to assess the growth and development of sea trout, Salmo trutta L., fry obtained from frozen, thawed semen after the fish had been released into the wild and were feeding there. The semen was cryopreserved with either methanol (MeOH) or dimethyl sulfoxide (DMSO). Fresh eggs were collected and fertilized with the thawed semen. The control was eggs fertilized with fresh semen that had been kept on ice. The eggs were incubated and reared in a closed recirculating system. The fertilized eggs were counted for visible eye pigment. After rearing, three groups of fish were tagged and stocked into a stream. The fish aged 6 months were caught from the stream. The fish were measured, weighed, identified to which experimental variant they belonged, and their survival rate was estimated. No significant differences in survival rate, length, weight, or condition factor among the control, DMSO, and MeOH groups were noted during larval development in a closed recirculating system. These parameters were also similar in the control and experimental groups after the fish had grow in a natural stream. The use of frozen semen to fertilize fresh sea trout eggs resulted in a normal incubation process, larval stage, and regular fry growth and survival, both under laboratory conditions, and, most importantly, in the wild. The results indicate it is possible to use frozen semen for fry production and the restoration of wild fish populations.
Józef Domagała, Słukasz Ługocki, Robert Czerniawski and Małgorzata Pilecka-Rapacz
The aim of this study was to determine the prevalence peak of the smallest plankters that are an adequate food resource for vendace (Coregonus albula L.) larvae. This goal was accomplished by determining weekly changes in zooplankton biomass, especially rotifers and nauplii, against changes in basic physicochemical parameters of lake waters. As the results of this paper show, the highest abundance of the smallest plankters, rotifers and nauplii, occurs at a particular temperature for a period of two weeks. The most important variable that determined the peak of small plankter biomass is temperature. Thus, the period of stocking lakes with vendace larvae should be synchronized with this temperature and the coinciding biomass peak of rotifers and nauplii, which are the basic food of vendace larvae.
Michał Łopata, Przemysław Czerniejewski, Grzegorz Wiśniewski, Robert Czerniawski and Jakub Drozdowski
The paper presents a proposal for the treatment of river water based on expanded clay (ceramsite). It is a lightweight mineral aggregate containing components relative to phosphorus adsorption (calcium, iron, manganese, aluminum). A pilot plant on a fractional technical scale was built on a nutrient rich (phosphorus up to 0.4 mg dm−3, nitrogen up to 10.0 mg dm−3), small (mean annual flow about 0.04 m3 s−1), natural watercourse (Młynówka River, a tributary of the Otok Channel, Noteć basin, the municipality of Strzelce Krajeńskie). The monitoring included quantitative and qualitative measurements of the water stream in 2014-2015. On the basis of the examinations, the calculated effectiveness of ceramsite filters in removing major contaminants from water was: for total nitrogen 5-6%, phosphorus 12-16%, and for suspensions 17-29%. The effectiveness of the treatment is highly influenced by hydraulic load, so this type application on a full-scale should occupy a sufficiently large volume. Taking into account simplicity of performance, ease of operation and low cost of construction and maintenance, such pretreatment plants based on expanded clay would seem to be a promising tool for the protection of surface waters in catchments of small rivers and streams.