Cryopreservation of medaka sperm (in six steps). (1) Isolate the testis from an adult male, and prepare the sperm suspension on ice using two pairs of sharp forceps. (2) Collect 10-μL aliquots of the suspension in glass capillaries. (3) Distribute the capillaries in plastic cryotubes. (4) Place the tubes in a larger plastic tube embedded in crushed dry ice, and allow the suspension to freeze for 20 min. (5) Further cool the cryotubes in liquid nitrogen, first in a Dewar flask, and then in a large storage container. (6) Examine motility of the remaining sperm using an inverted phase contrast microscope.