Fish sperm cryopreservation in France: from laboratory studies to application in selective breeding programs
Application of sperm cryopreservation by the fish farming industry is still limited, despite great interest in optimising genetic resource conservation; limiting risks associated with horizontal disease transmission; increasing genetic progress; and accelerating genetic selection from prime specimens, as in other livestock production. Several factors are listed. With the aim of developing coherent broodstock selection programmes, SYSAAF (Union of the French poultry and aquaculture broodstock industry), INRA and IMV-Technologies, standardised semen cryopreservation procedures between 1994 and 2000. The first step was to develop multispecies (salmonids, turbot, sea bream, sea bass, gold fish, tilapia, European catfish) extenders to collect, induce maturation and conserve (> 7 days) fresh sperm or testicular spermatozoa (StorFish™); to wash ova from faeces and blood (OvaFish™); to freeze sperm (Cryofish™); and to improve fertilisation success (ActiFish™). The second step was to evaluate the practical limits of the technology and to test several potential improvements (GnRH stimulation, anaesthetic, frequency of collection, cryopreservation devices, optimal egg/sperm vol- umes, etc.). The third step was to standardise sperm collection procedures, from the efferent duct or testicular spermatozoa; to ensure absolute traceability by straw printing; to fill and seal a large number of straws by means of an automated filling and sealing machine (MRS1); and to freeze sperm in liquid vapour in adapted container. The entire procedure, using opti- mal extenders and standardised procedures, was transferred to the industry. From 2000 to 2006, 50,080 0.5 ml straws from 1554 males, originating from 26 populations of rainbow trout, sea bream, turbot and sea bass, were frozen by breeding companies. The development of a collective gene bank is in progress, with the aim of securing private gene banks (breed- ing companies, research organisations and Cryobanque Nationale).