Survival of Macrobrachium amazonicum embryos submitted to cooling

Cooling techniques have several applications for reproduction in aquaculture. However, few studies have sought to create protocols for cooling and cryopreservation of Macrobrachium amazonicum embryos. Thus, the objective of this work was to verify the survival of M. amazonicum embryos and the correlation between embryonic volume and mortality of M. amazonicum embryos after cooling. Embryo pools were collected from three females and divided into two treatment groups: dimethyl sulfoxide (DMSO) 3% and ethylene glycol (EG) 0.5%, both of them associated with 2 M sucrose. Positive and negative control groups consisted of seawater 10%. Aliquots of 10 µg of embryos were placed in Falcon® tubes containing a cryoprotectant solution and submitted directly to the test temperature of 2°C for 2 and 6 h of cooling. Further analysis of survival and embryonic volume were performed under a stereoscopic microscope. Data were subjected to analysis of variance (ANOVA), and means were compared using the Tukey test at 5%. The highest embryonic survival rate was observed after the shortest storage time for both the DMSO 3% and the 0.5% EG groups, with survival rates of 84.8 ± 3.9 and 79.7 ± 2.8%, respectively. There was a reduction in survival after 24 h, with the DMSO 3% group presenting a survival rate of 71.7 ± 6.6%, and the EG 0.5% group, 66 ± 6.9%. Survival showed a statistically significant difference when compared with the positive controls after 2 h and 24 h of cooling, with 99 ± 0.5% and 95.8 ± 1.5% survival rates, respectively. There was no significant statistical difference in the embryonic volume, but it was possible to observe a change in the appearance of the embryos, from a translucent coloration to an opaque white or brownish coloration, after 24 h in incubators. Thus, it can be concluded that survival is inversely proportional to storage time and that, although there was no change in the embryonic volume after cooling, a change in the appearance of embryos could be observed.