Studies on cryopreservation of eggs from rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kisutch)

The effect of pre-freezing treatments as well as freezing of inseminated, not water-activated eggs from rainbow trout Salmo gairdneri, and coho salmon, Oncorhynchus kisutch, was investigated in relation to survival and further development.Effects above freezing temperatures included: the temperature at insemination, viability of inseminated and unactivated eggs after storage, suitability of an incubation medium and the tolerance of eggs to various levels of the cryoprotectant dimethylsulfoxide (DMSO). Freezing experiments included: investigating the action of DMSO (0, 1, 2 mole) and the tolerance of coho eggs to temperatures between ?4.6 to ?30°C. Insemination temperatures between 0.5°C and 9.8°C (coho eggs) as well as incubation in an artifical medium (1-0°C) for 80 min (rainbow trout eggs) and 170 min (coho eggs) did not influence subsequent fertility. Storage of inseminated and unactivated rainbow trout eggs for 135 min and beyond reduced egg fertility. DMSO at 2 and 4 mole was detrimental to coho eggs (1-0°C). One mole DMSO had no (coho) or reduced (rainbow trout) influence on egg fertility when it was added gradually.In the presence of 1 mole DMSO most eggs remained unfrozen (67–89%) when kept for 10 min in frozen artificial medium (?4.6%) and 27–32% subsequently reached the eyed stage (control = 100). Further cooling (0.3°C/min) to ?10°C was still tolerated (62% unfrozen, 22% eyed eggs) but not to ?20°C (6% unfrozen, no development) and ?30°C (no survival). Use of 2 mole DMSO did not improve the results.