Effect of extenders on sperm cryopreservation of African catfish, Clarias gariepinus (Burchell)

The effect of extenders was studied on the cryopreservation of sperm from African catfish, Clarias gariepinus (Burchell). The following six basic extenders were tested: fructose, glucose, sucrose, NaCl, KCl solutions and the artificial seminal plasma of the African catfish, Each of these extenders was tested both with and without buffer systems (i.e. NaHCO3-CO2 and Tris-HCl) by using 10% dimethylsulphoxide (DMSO) as a cryoprotectant. The two-step freezing was carried out in a programmable freezer by using the following freezing rates: (1) 4 degrees C min(-1) between 3 and -4 degrees C; (2) and 11 degrees C min(-1) between -4 and -80 degrees C. The best post-thaw motility (25%) was achieved with 333 mmol L-1 fructose solution and NaHCO3 buffer. The fertilization experiments were carried out with unbuffered fructose and glucose extenders using various amounts of sperm and two fertilization methods: (1) dry and (2) wet, The best fertilization rates were achieved with 75 mu L of sperm and wet fertilization with glucose extender, or 100 mu L of sperm and dry fertilization in case of fructose - both methods fertilized 96% of all eggs.