Optimization of sperm cryopreservation methods for African Clarias catfish (Clarias gariepinus) for field use in aquaculture enterprises

African sharptooth catfish (Сlarias gariepinus) is one of the promising objects of modern aquaculture. In the natural habitat, the breeding season of catfish correlates with periods of maximum rainfall. Cryopreservation of sperm in aquaculture is widely used to provide gametes for fertilization yearround outside the reproductive seasons. The aim of the research was to optimize the methods of cryopreservation of sharptooth catfish sperm for use in aquaculture enterprises in the south of Russia. Two cryoprotectant compositions and an experimental setup for controlled freezing of catfish sperm in liquid nitrogen vapor were studied. The speed mode of freezing fish sperm is species -specific and is selected for each fish species experimentally. Using an experimental cryochamber made of expanded polystyrene with the internal dimensions (H×W×D) of 21×20×24.5 cm and a wall thickness of 5.5 cm made it possible to deep freeze the reproductive cells of catfish at a cooling rate of 6.5 degrees per minute to a temperature of – 80°C with further immersion in liquid nitrogen (t= –196°C). In the first version of the experiment, the cryoprotector included a basic solution (NaCl, KCl, CaCl2, NaHCO3) and dimethyl sulfoxide at a concentration of 5%. In the second version of the experiment, glucose at a concentration of 18 g/l was added to this composition. The average lifetime of spermatozoa after thawing in the experiment without glucose was 46 sec., which is 5 sec. less than in the experiment with glucose. In the experiment with the addition of glucose, the proportion of motile spermatozoa was 40%, while in the experiment without glucose it was only 20%. It has been shown that addition of glucose to the protector provides the best survival of African catfish sperm in terms of motility after thawing.

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