(Source: E. Sullivan from Zebrafish Book 5th Edition)
This method requires more work, but is especially well-suited for production of large numbers of embryos (upwards of 1000 embryos per tank) once or twice a week. A continuous supply of embryos can be obtained with this method by adding more tanks of fish and rotating the schedule among the tanks. Although zebrafish reach sexual maturity at 10-12 weeks, the breeding fish should be between 7 and 18 months of age. Keep males and females in separate tanks with up to 8 females or 16 males per 10 gallon tank. The tanks should be cleaned at least once per day by siphoning, replacing about 1/3 of the water. Feed the fish 2-3 times per day. On the day before you want embryos, 1-2 hours before the end of the light period, feed the fish and clean the tanks. Then transfer the males into the tank with the females at a ratio of 1 male to 2 females (excellent results come from 4 males and 8 females). Add marbles to cover the bottom of the tank a single layer deep. After the beginning of the next light cycle, collect the embryos by siphoning the bottom of the tank (see Embryo Collection).
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