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

The effect of extenders was studied on the cryopreservation of sperm from A frican catfish, Clarias gariepinus (Burchell). The following six basic exte nders were tested: fructose, glucose, sucrose, NaCl, KCl solutions and the artificial seminal plasma of the African catfish, Each of these extenders w as tested both with and without buffer systems (i.e. NaHCO3-CO2 and Tris-HC l) 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 moti lity (25%) was achieved with 333 mmol L-1 fructose solution and NaHCO3 buff er. 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 w ith 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 fertil ized 96% of all eggs.