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Examination of resistance against Aeromonas hydrophila infection on genetically different common carp variants (preliminary results)
7-11Views:75Septicemia disease caused by the bacterium Aeromonas hydrophila is a major problem for fish farmers around the world. In our experiment resistance to the disease was investigated on carp variants with diferent genetical backgrounds. 96 different genetic variants(„families”) were created by crossing various individuals of 4 carp strains (2 wild and 2 cultured ones). Families were reared until reaching the size of 10 gramms and 100 fish of each families were marked with an individual electronic identifier. Marked fish were divided into 5 groups. Fish from one group were infected with A. hydrophila and mortality were registered during 2 weeks. Based on mortality data, the most resistant and most susceptible families will be selected using population genetics methods.
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Experiments on the Nutrient Removal and Retention of an Integrated Pond System
18-23Views:183A combined intensive-extensive fishpond system developed for the purification and re-use of intensive fishpond effluent water was studied during a three-year experimental period. The investigated pond system consists of five small-size intensive culture ponds of 1 ha total water surface area with 1.5 m water depth and a 20 ha extensive culture pond with 1.0 m average water depth. The water was recirculated between the intensive and extensive ponds with around 60 days retention time in the extensive treatment pond.
Carbon, nitrogen and phosphorus budget and water purifying capacity were described and evaluated by means of regular measurements of nutrient concentrations in the water and sediment. During the three-year test period, 81.5% of organic carbon, 54.7% of nitrogen and 72.2% of phosphorus were retained by the system as a percentage of the total input of each nutrient. A significant amount of the total nitrogen input was removed by the harvested fish, which was much higher than in traditional fishponds or intensive fish culture systems. The efficiency of nutrient removal is clearly indicated by the 27.3% nitrogen assimilation.
Only a small percentage of the total nutrient input was discharged into the environment during fish harvest, which was 9.0% for organic carbon, 13.2% for nitrogen and 12.1% for phosphorus. The combination of intensive and extensive fishponds with water recirculation resulted in significant reduction of nutrient discharge into the surrounding aquatic environment, primarily due to the high nutrient processing and retention capacity of the extensive fishpond ecosystem. -
Survey of the environmental impacts of pond fish farming
19-24Views:71The aim of this study was to survey the nitrogen, phosphorus and organic matter loads and the discharge of fishponds. The inputs and outputs of nutrient amounts of fishponds and their sources are described. The impact of a fishpond on the nutrient loads of receiver waters was determined. The investigations of this study were to determine and evaluate the nitrogen, phosphorus and organic matter budget of fishponds representing different technologies and areas.