The storage of plaice (Pleuronectes platessa) sperm at low temperatures

Plaice (Pleuronectes platessa) sperm were deep-frozen at −79°C and −196°C, using the sodium chloride extension medium of Mounib et al. (1968). Hand-stripped semen was diluted 1 : 3 and the sperm were frozen without prior washing by centrifugation. After 315 days storage at −196°C thawed samples from 3 different fish showed strong sperm motility and mean fertilisation and hatching successes of 39 and 20%, compared with 41 and 25% for fresh sperm using eggs from the same female. Sperm stored aat −79°C showed little or no motility on thawing and were incapable of fertilisation.