Aquaculture Africa 2024

November 19 - 22, 2024

Hammamet, Tunisia

CRYOPRESERVATION OF AFRICAN CATFISH Clarias gariepinus SPERM USING A STATIC LIQUID NITROGEN VAPOUR VITRIFICATION METHOD WITH TREHALOSE AND DIMETHYL SULFOXIDE AS CRYOPROTECTIVES

Mark Goodman* and Chris H. Fouche

Department of Forestry, Fisheries and the Environment

South Africa

 



Captive breeding of Clarias gariepinus entails stripping of mature females, while males must be killed - or testes partially excised - to obtain spermatozoa. Sperm cryopreservation could significantly improve the reproductive potential of male catfish. In this study, Ginzburg Fish Ringer (GFR) was the common extender in all protocols with or without 0.3M trehalose. Dimethyl sulfoxide (DMSO) and methanol were tested to determine the preferred equilibration period for the complex before cryofreezing. The cryopreservation method and sperm fertilisation capacity were assessed in terms of hatchability rate. A feasible semen rationing protocol for maximised fertilisation was also evaluated. A customised freezing chamber was constructed to induce vitrification of the sperm with static liquid nitrogen (LN2) vapour. LN2 vapour-induced freezing rates ranged from -2.7 to -5⁰C.min⁻¹, and cryovials/straws were immersed in the LN2 when -41⁰C was reached. Straws significantly outperformed cryovials in cryopreservation efficacy. Optimal fertilisation occurred with trehalose and DMSO-treated cryostored sperm, comparable to fresh semen. 0.05mL diluted semen was required to fertilise 35g eggs, compared with a similar volume efficacy for undiluted sperm. The inclusion of trehalose enhanced fertilisation for both fresh and thawed DMSO-treated sperm. All methods produced healthy larvae to 21 days post-hatch. The validated method can yield 60 straws (0.5mL) from 3mL semen, fertilising approximately 2.1kg eggs (~ 162 × 10⁴ eggs). The LN2 vapour vitrification method was shown to be as effective as - and more cost-efficient - than controlled rate freezing equipment.