The effect of six cryoprotectants was investigated on the cryopreservation of African catfish Clarias gariepinus (Burchell) sperm. Fructose (6%) solution buffered with NaHCO3-CO2 was used as the diluent in the experiments. Glycerol (5-11%), ethylene glycol, methanol and propylene glycol (5-15%) and, finally, dimethyl sulphoxide (DMSO) and dimethylacetamide (DMA) (10%) were tested using various equilibration times (2-30 min). Sperm was frozen in 250-μL straws in a programmable freezer (Cryocell-15, BLS, Hungary) from 3°C to -4°C at 4°C/min and from -4°C to -80°C at 11 °C/min. Thawing was carried out in a 40°C water bath for 5 s. Fertilization and hatching trials were performed only with DMSO and DMA using 200 and 100 μL of diluted sperm (100 and 50 μL of pure sperm) and the dry and the wet fertilization methods. Ethylene glycol, glycerol, methanol and propylene glycol yielded poor results. An average post-thaw motility rate of 44.0 ± 9.7% and 22.6 ± 18.1% was achieved after 10 min equilibration using DMSO and DMA respectively. Highest average fertilization (86.8 ± 3.1%) and hatching (67.1 ± 11.9%) rates were achieved with DMA and DMSO, respectively, 200 μL of diluted sperm and the wet fertilization technique. The use of cryoprotectants increased the percentage of malformed larvae compared with the control groups. We found that DMA at a 10% concentration was equally as suitable for the cryopreservation of African catfish sperm as DMSO.
ASJC Scopus subject areas
- Aquatic Science