Optimization of a protocol for cryopreservation of the spermatophore and sperm mass of the whiteleg shrimp Litopenaeus vannamei (Boone, 1931)

The effect of six cryoprotective solutions based on MgCl2 and methanol, in addtion with sucrose and 10% Aloe vera gel or 10% egg yolk, on the sperm viability in spermatophore and sperm mass of Litopenaeus vannamei was evaluated. Besides, cooling rates of-0.5,-1 and-2 degrees C/min were used until temperature reached-35,-80 and-100 degrees C prior to immersion in liquid nitrogen. The sperm viability rate was determined by eosinnigrosin staining. The results showed that the solutions based on MgCl2, sucrose plus egg yolk or Aloe vera gel better preserved sperm viability in spermatophore (82.8 +/- 2.3% and 72.6 +/- 3.1%) and in sperm mass (83.4 +/- 2.5% and 76 +/- 1.1%) without significant differences with the control group (p>0.05). The freezing curve that presented less damage in spermatophore started from 25 degrees C and reached-35 degrees C with a rate of-1 degrees C/min using a cryoprotective solution with egg yolk and MgCl2, showing a sperm viability greater than 80% without significant differences with the control group (p>0.05), and a rate of-2 degrees C/min in the same temperature range for the group with sperm mass and a solution based on Aloe vera gel. In conclusion, the use of a solution based of MgCl2, sucrose, Aloe vera gel or egg yolk and at a cooling rate of-1 degrees C/min or-2 degrees C/min until reaching-35 degrees C allows a successful freezing of spermatophores or sperm of Litopenaeus vannamei.