Abstract

To service the growing demand for male African giant catfish (Clarias gariepinus) broodstock for aquaculture in Nigeria, and to conserve valuable genetic resources, we improved both short-term (in deep freezer at -35°C) and long-term cryopreservation (in liquid nitrogen at -296°C) of catfish sperm. Catfish sperm cryopreserved at -35°C using three different types of cryodiluents composed of 10% methanol, glycerol or dimethylsulphoxide (DMSO) with 15% non-permeating cryoprotectant (skim milk) and 75% phosphate-buffered saline (PBS) as extender was evaluated at day 1 to 28. Sperm motilities on thawing for the two cryodiluents that contained glycerol and DMSO were the same (p > 0.05) while those for the cryodiluent that contained methanol were significantly lower (p < 0.05). Sperm cryopreserved in DMSO and glycerol provided hatching at least 50% of catfish eggs. Liquid nitrogen (LN₂) was with the same 3 cryoprotectants and one new extender based on glucose and skim milk (Ginzburg fish Ringer, GFR). Two thawing procedures were tried: 1) In the first trial, one set of sperm was frozen with different cryodiluents with extenders in the freezer at -10°C and 2) Stored for up to 8 months in LN₂. Sperm with up to eight months cryopreservation from the first trial when thawed at room temperature at 27°C for 15 min gave 0 - 6.25% fertilization rate (FR). The sperm stored for two months in the second trial when rapidly thawed at 35°C for 5 min gave better results. The FR of 94% was achieved with a cryodiluent of DMSO with 5% glucose solution and PBS when the cryopreserved sperm was thawed at 35°C. Also, DMSO in combination with PBS resulted in a higher FR than either glycerol or methanol. However, sperm cryopreserved with glycerol had the lowest motility rate in the 2 trials (p < 0.05). The use of cryopreserved sperm did not significantly affect (p < 0.05) the survivability of the fry. The use of cryopreserved sperm of the African catfish for fry production will be especially beneficial in Nigeria where reliable sperm supply is a major bottleneck in the catfish aquaculture industry.

Key words: Cryopreservation, sperm motility, Clarias gariepinus, African giant catfish.

Abbreviation

DMSO, Dimethyl sulfoxide; LN₂, liquid nitrogen; PBS, phosphate buffered saline.