CRYOPRESERVATION OF MEMBERS OF THE GENUS TETRASELMIS USED IN AQUACULTURE

Commercially important members of the genus Tetraselmis were cryopreserved with high levels of post-thaw viability. Levels of post-thaw viability > 50% for T. suecica (Kylin) Butcher were achieved by employing a simple protocol using glycerol as a cryoprotectant; samples were placed in a cooling-bath preset at - 30 degrees C for 30 min, followed by plunging into liquid nitrogen. This was found to be less satisfactory for T. chui Butcher. The highest levels of viability were obtained using cultures grown at 20 degrees C, preincubated in 10% (v/v) glycerol, Followed by a two-stage cooling process, using a cooling rate of 1 degrees Cmin(-1) to - 30 degrees C and then plunging the samples into liquid nitrogen. Viability levels were higher in all the strains tested when they were grown under ambient conditions (15-20 degrees C) and were species-dependent, with T. suecica (Kylin) Butcher strains having higher levels of viability ( > 70%) than T. chui Butcher (28-40%).