Effect of Cryoprotectants on Walking Catfish (Clarias batrachus) Embryos

Abstract

The purpose of this study was to examine the toxicity of cryoprotectant (CPA) on the embryos of walking catfish (Clarias batrachus), a small-sized fresh water fish which may constitute a suitable experimental material for the development of cryopreservation methods for walking catfish embryos. This study also observed the suitability of ultrasound in embryo cryopreservation studies. Exposure of morula, six-somites and tail elongation stages embryos to 10%, 15%, 20% and 25% solutions of propylene glycol (PG), methanol (MeOH), dimethyl sulfoxide (DMSO), dimethylformamide (DFA) and ethylene glycol (EG) for 20 min revealed that CPA toxicity for walking catfish embryos increased in the order of PG < DMSO < MeOH < EG < DFA. Twelve mixture solution, prepared based on the toxicity of single CPA were used at different concentration to test the toxicity to embryos. Mixture solution, MS1 (mixture of 15% PG, 10% DMSO, 10% EG, 5% MeOH, 5% DFA and 55% YRS solution), MS7 (mixture of 20% PG, 10% DMSO, 10% EG, 5% MeOH, 0% DFA and 55% YRS solution) and MS10 (mixture of 25% PG, 10% DMSO, 10% EG, 5% MeOH, 0% DFA and 50% YRS solution) were found less toxic to embryos than other mixture solutions. Embryos exposed to ultrasound in mixture solutions (MS1, MS7 and MS10) for 2 min could be effective for cryopreservation studies of walking catfish embryos. This study also proved that tail elongation stage was more tolerated to CPA solution than other developmental stages. However, further study is needed to investigate the use of these protocols when combined with cooling or vitrification of this high valued catfish species.