Some pecularities of feeding of paddlefish (Polyodon spathula (Walbaum, 1792)) in the process of its growing to the marketable weight in ponds of Ukranian Polissia

Abstract

Purpose. To investigate peculiarities of feeding of paddlefish during the second year of life in polyculture with carp fish in ponds of Ukrainian Polissia. Methodology. A North American zooplanktophage belonging to sturgeons, the paddlefish was reared in polyculture with carp, hybrids of silver and bighead carps, as well as grass carp in pond with areas of 1 hectare on natural food supply. Development of the natural food supply was stimulated by applying cattle manure into ponds at an amount of 1 ton/ha. The stocking density of age‒1 paddlefish with an average weight of 143 g was 150 ind./ha, The total stocking density of all polyculture objects was 520 ind./ha. The determination of the nutritional and growth characteristics of fish, the qualitative composition of forage aquatic organisms and their biomass was carried out using well‒known methods. The main physicochemical parameters of water quality were investigated during fish rearing using generally accepted recommendations in fish farming and hydrochemistry. Findings. The environmental conditions of the pond mainly met the biological requirements for the studied aquaculture objects. A periodic decrease in dissolved oxygen concentration to 1.5‒2.0 mgO2/dm3 was observed, which could slow down fish growth. During sampling to determine the feeding habits of paddlefish, the zooplankton biomass in the pond varied within 1.11‒6.44 g/m3, with the predominance of Cladocera and Copepoda. At the end of the study period, age‒1+ paddlefish reached an average weight of 979.0 g with a fish production of 120.4 kg/ha and a survival rate of 82.0%. The total fish production for all polyculture objects was 502.3 kg/ha. The average digestive tract fullness index of paddlefish varied within 199.72‒459.0030/000. The diet of paddlefish was dominated by lower crustaceans with a predominance of Cladocera (65.28‒86.23%). The role of Copepoda in paddlefish nutrition increased at the end of the culture season (up to 32.76%). Rotifera and other forage aquatic organisms did not have a significant value in the paddlefish diet (up to 3.85%). A significant amount of detritus swallowed by fish was observed (13.43‒31.31% of the digestive tract content). A selectivity in the consumption of paddlefish of various groups of zooplankton organisms was noted with the selectivity index for Cladocera at the level of 1.23‒1.48. Originality. New data were obtained on the feeding habits of paddlefish in Ukrainian Polissia. Practical value. The study results are an integral part of the database for the development of improved technologies for pond fish farming in Ukraine. Key words: paddlefish, pond aquaculture, fish polyculture, natural food supply, fish feeding.