Cryopreservation and sperm storage of the white shrimp

Abstract

This study was performed to evaluate a protocol for sperm cryopreservation of the marine shrimp Litopenaeus schmitti, an important species in Brazilian commercial fisheries. No studies or protocols were found for cryopreservation of its spermatic mass. This paper provides information about the technique of semen storage based on protocols applied to other penaeid species. Two cryoprotectants, glycerol and dimethylsulfoxide (DMSO), were tested for sperm cells toxicity in two concentrations (5 and 10%), and two exposure times (10 and 30 minutes). Influence of liquid nitrogen storage in apparent sperm viability (ASV) was also tested in 1, 15 and 30 days of storage. The cryopreservation was performed in a two-step (2 and 0.5°C min^-1) freezing protocol. After freezing until temperature of -32°C, sperm mass was immersed in liquid nitrogen (-196°C). Thus, glycerol and DMSO was not toxic to sperm in both concentrations and equilibration times. For all toxicological tests, ASV was up to 79.8% after exposure. Liquid nitrogen storage tests indicated no significant difference between glycerol 5 and 10%. Results were significantly different over time between days 15 and 30 of storage in liquid nitrogen, in which ASV was around 42.8% and 16.3% respectively. Thus, it is suggested glycerol 5% (10 minutes) as cryoprotectant for L. schmitti spermatic mass cryopreservation. It is also suggested that the L. schmitti spermatic mass can be stored during 15 days in liquid nitrogen, using a two-step (2 and 0.5°C min^-1) freezing protocol.