The effect of cryoprotectants on the motility and fertilizing capacity of cryopreserved African catfish Clarias gariepinus (Burchell 1822) sperm

The effect of six cryoprotectants was investigated on the cryopreservation of African catfish Clarias gariepinus (Burchell) sperm. Fructose (6%) solut ion buffered with NaHCO3-CO2 was used as the diluent in the experiments. Gl ycerol (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 2 50-mu L straws in a programmable freezer (Cryocell-15, BLS, Hungary) from 3 degrees C to -4 degrees C at 4 degrees C/min and from -4 degrees C to -80 degrees C at 11 degrees C/min. Thawing was carried out in a 40 degrees C wa ter bath for 5 s. Fertilization and hatching trials were performed only wit h DMSO and DMA using 200 and 100 mu L of diluted sperm (100 and 50 mu L of pure sperm) and the dry and the wet fertilization methods. Ethylene glycol, glycerol, methanol and propylene glycol yielded poor results. An average p ost-thaw motility rate of 44.0 +/- 9.7% and 22.6 +/- 18.1% was achieved aft er 10 min equilibration using DMSO and DMA respectively. Highest average fe rtilization (86.8 +/- 3.1%) and hatching (67.1 +/- 11.9%) rates were achiev ed with DMA and DMSO, respectively, 200 mu L of diluted sperm and the wet f ertilization 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 Af rican catfish sperm as DMSO.