Cryopreservation of embryos of humpback grouper (Cromileptes altivelis) using combinations of non-permeating cryoprotectants

In this study, Cromileptes altivelis embryos were successfully preserved using non-permeable cryoprotectants for the first time. We compared the toxicity of single non-permeable cryoprotectants and combination of nonpermeable cryoprotectants on C. altivelis embryos. Five non-permeable cryoprotectants at 1 M (i.e., trehalose, sucrose, lactose, fructose, and glucose) were used to treat embryos in the somite, tail-bud, or heart-beating stages for 1 h. Survival rates and rates of normal embryonic development after treatment with trehalose, sucrose, or lactose were all greater than 86.97% and 86.01%, respectively. Levels of toxicity of trehalose, sucrose, and lactose were lower than those of fructose and glucose in C. altivelis embryos. Sucrose and trehalose were combined at different ratios (total concentration 1 M) and used to treat embryos for 1 h. Rates of survival and normal development for the somite, tail-bud, or heart-beating stages did not significantly differ among groups treated with sucrose + trehalose at ratios of 1:1 (S1T1), 1:3 (S1T3), and 3:1 (S3T1). Embryos treated with S1T1 had a little higher survival rate than those of the other treatment ratios(P > 0.05). Survival rates of embryos treated with T1S1, sucrose, and trehalose were 93.86 +/- 4.17%, 91.58 +/- 3.15%, and 92.79 +/- 2.45%, respectively. S1T1 was less toxic than sucrose or trehalose alone under the same conditions. Various cryopreservation-related factors (e.g., the cryoprotectant solution, embryonic stage, equilibrium time, thawing temperature, and time) were screened. The optimal protocol was the treatment of embryos at the tail-bud and heart-beating stages with 1 M S1T1 for 2-10 min and thawing at 26 degrees C for 10 s after freezing. In total, 21 viable embryos were recovered after freezing and thawing, with a survival rate of 0.21-7.55% and maximum survival time of 5 days. Our results demonstrate that it is feasible to cryopreserve C. altivelis embryos using non-permeable cryoprotectants and provide a reference for the use of combinations of cryoprotectants for the species.

Automated summary

The study successfully preserved Cromileptes altivelis embryos using non-permeable cryoprotectants for the first time. Trehalose, sucrose, and lactose were found to be less toxic to the embryos compared to fructose and glucose. Combining sucrose and trehalose at a 1:1 ratio resulted in higher survival rates.