CHILLING SENSITIVITY OF CARP (CYPRINUS-CARPIO) EMBRYOS AT DIFFERENT DEVELOPMENTAL STAGES IN THE PRESENCE OR ABSENCE OF CRYOPROTECTANTS - WORK-IN-PROGRESS

The unsolved problem of cryopreservation of the yolk-rich teleost embr yos may be related, in part, to their sensitivity to chilling and cryo protective agents. The aim of this study was to gain data on the sensi tivity of carp embryos to low temperatures at different developmental stages and on the possible protective and toxic effects of cryoprotect ants. A total of 86,400 morulae, half-epiboly and heartbeat-stage embr yos was selected and then placed in water or in 1 M methanol dimethyl sulfoxide (Me2SO), glycerol or 0.1 M sucrose solution at 0, 4 or 24 de grees C for 5 min or 1 h. Following these treatments, the embryos were held in a 24 degrees C water bath until the evaluation of hatching ra tes. In every developmental stage a significant decrease of hatching r ates following exposure to 4 or 0 degrees C was detected. Sensitivity to chilling changed significantly with development (heartbeat<morula<h alf-epiboly). Half-epiboly stage embryos were less sensitive to a shor t period of exposure to cryoprotectants than morula and heartbeat stag es. A l-h exposure to cryoprotectants revealed a stage dependent sensi tivity. Toxicity increased in the order of methanol<Me2SO<glycerol in morula and half-epiboly stages, and methanol<glycerol<Me2SO in the hea rtbeat stage. The results show morulae are partially protected against chilling in Me2SO and sucrose, half-epiboly in Me2SO, sucrose and met hanol, and heartbeat-stage in methanol and glycerol. The results furth er suggest that carp embryos are sensitive to chilling and that toxici ty and protective effects against chilling of cryoprotectants are stag e-dependent. The finding on the low chilling sensitivity of heartbeat- stage embryos and the protective effect of certain cryoprotectants may be useful in designing cryopreservation protocols. (C) 1998 by Elsevi er Science Inc.