Individual study: Cryopreservation of sperm of Xenopus laevis and Xenopus tropicalis
Sargent M.G. & Mohun T.J. (2005) Cryopreservation of sperm of Xenopus laevis and Xenopus tropicalis. Genesis, 41, 41–46
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Freeze sperm or eggs for future use
A replicated, controlled study in 2004 of captive African clawed frog Xenopus laevis and western clawed frog Xenopus tropicalis in the UK (Sargent & Mohun 2005) found that although sperm lost viability following freezing to −80°C, sufficient survived to fertilize eggs. Relative sperm motility after freezing, compared to a control was 30–40% (141–178 days) for African clawed frog and 39–70% (22–182 days) for western clawed frog. Optimum motility was obtained with a cooling rate of 10°C/minute in 0.2 m sucrose. Sodium bicarbonate was less effective and pentoxyfylline not effective at protecting sperm during a freeze-thaw cycle. Frozen sperm half-life was approximately one year for both species. Fertilization efficiency was greater in sodium chloride solution concentrations of 0.4 compared to 0.1 for western clawed frogs. Fertilization was similar with varying concentrations (4–40 mM) for African clawed frogs. Testes were macerated in sodium chloride solutions. Cryoprotectants (with egg yolk) were: 0.2, 0.4 or 0.6M sucrose, sodium bicarbonate or pentoxyfylline. Sperm was frozen to −80°C at rates of 0.5–50°C/minute. Samples were defrosted rapidly in a water bath at 30°C. Fresh eggs (40–100/test) were fertilized and success recorded after 5 hours.