(Source: C. Walker and G. Streisinger from Zebrafish Book 5th Edition)
Sperm may be frozen and thawed later for in vitro fertilization. This method is well suited for "backing up" genetic stocks against accidental loss or for reducing the number of tanks used to house different lines.
To freeze sperm
...
9 ml Ginsburg Fish Ringers
1 ml Methanol
1.5 g Carnation Powdered Skim Milk
Note: This order is important to prevent
precipitation of milk