Exploration of natural cryoprotectants for cryopreservation of African catfish, Clarias gariepinus, Burchell 1822 (Pisces: Clariidae) spermatozoa

Toxicity is a major limitation to successful spermatozoa cryopreservation of fish. Due to this problem, it is critical to find potential cryoprotectants which are more environmental-friendly, non-toxic, easily prepared, and available at affordable prices. Hence, the objective of the present study was to investigate several natural cryoprotectants for optimal cryopreservation of the African catfish, Clarias gariepinus, Burchell 1822 (Pisces: Clariidae) spermatozoa. Three natural cryoprotectants were tested - egg yolk, glucose, and honey, while DMSO was used as a control at different concentrations (5, 10, and 15%). Sperms were diluted with coconut water at a dilution level of 1 : 20 sperm to extender (v/v). Diluted sperms were kept at 4°C for 5 min, then at 0, -4, and -79°C for 5 min respectively, and stored in liquid nitrogen (-196°C) for 45 days. The cryopreserved sperms were thawed in a water bath (37°C) for 5 min and evaluated for fertilization and hatching rates. The data were subjected to analysis of variance (ANOVA), followed by comparison of means using Duncan's Multiple Range Test. The fertilization and hatching rates of African catfish in all cryoprotectants improved with concentration increasing from 5 to 10% but then decreased when concentration was increased to 15%. The ANOVA test showed that the differences in cryoprotectants used significantly affected fertilization and hatching rates of African catfish. Overall, the fertilization and hatching rates were higher in DMSO for all concentrations compared to other cryoprotectants. However, 10% egg yolk resulted in higher fertilization and hatching rates compared to other natural cryoprotectants. It was concluded that 10% egg yolk was the most suitable concentration for African catfish spermatozoa cryopreservation compared to other natural cryoprotectants tested.