Extending the viability of sea urchin gametes

The sea urchin is the material of choice for studying many early developmental events. Methods to extend the viability of sea urchin gametes have not received much attention, but it is well known that the eggs are easily damaged by freezing. This study was designed to extend the viability of Lytechinus pictus eggs and sperm without freezing. Gamete viability measurements were based on relative numbers of fertilized vs unfertilized eggs, percentage fertilization, and on observations of embryonic development. Results indicate that gametes can be stored longer and at lower temperatures than previously described. Sperm were consistently kept viable for at least 12 days with little decrease in viability when stored in glass test tubes or plastic petri dishes and submerged in ice inside a refrigerator at 0 +/- 1 degree C. In one experiment, sperm stored in glass test tubes on ice remained viable up to 20 days after extraction. Eggs were maintained from 1 to 7 days, rather than the 1 day or so previously reported, when stored in glass test tubes submerged in ice in a refrigerator at 0 +/- 1 degree C. Results of egg and sperm experiments varied at different times in the season. Such variations may be caused by seasonal cytoplasmic changes, population differences, or the time mature individuals were maintained unfed in aquaria prior to use. Results from this study should be useful for a variety of research, mariculture, and teaching applications in which sea urchin supplies are limited or when the same gamete population is required for subsequent experiments.