EFFECTS OF CRYOPROTECTANTS AND FREEZING RATES FOR PRESERVING SPRERMATOGONIAL STEM CELLS OF BLUE CATFISH

In the United States , catfish farming has surpassed 65% of total freshwater  aquaculture production, where the channel catfish ♀ × blue catfish ♂  hybrid constitutes  nearly 70% of the harvest. Unfortunately, sacrificing males is the only way to extract testes to obtain sperm to make hybrids. Thus, our long-term goal is to develop xenogenesis resulting in xenogens to increase reproductive efficiency for catfish hybridization. Having spermatogonial stem cells (SSCs) frozen in germplasm repositories will help facilitate this initiative. In this study, we first examined the effects of permeating cryoprotectants (DMSO, ethylene glycol, glycerol,  methanol) and cryoprotectan t concentrations (1 M, 1.3 M, 1.6 M) on post-thaw cell viability. Secondly, the non-permeating agents, trehalose and lactose, were tested at different concentrations (0.1 M, 0.2  M) in conjunction with egg yolk (10%) and bovine serum albium (1.5%). Finally, different cell freezing rates (-0.5, -1, -5, -10°C/min ) were tested. Our results showed that DMSO 1  M generated the most cells after cryopreservation (Fig. 1A) and had the highest viability recovery index (Fig. 1B). Post-thaw  cell viability increased (70 ± 3.2%) when lactose 0.2  M and egg yolk where incorporated into the cryo-media.  The best freezing rate  was -1°C/min . Together , these finding show that catfish SSCs can be frozen for future  cell transplantation trials. Frozen cells will  also become a valuable resource to conserve genes for  catfish genetic selection programs and conservation efforts.