In captivity, they can be raised on yeast, bran flour, or dried blood but algae is best. Looking somewhat like terrestrial fleas, they grow up to 0.1 inch with females giving live birth to tiny babies fit for fish fry to eat. Typical lengths are 0.25 to 3 mm for small species. There are many species, and they vary in size. Females lay up to 100 eggs every three days in good conditions.
Females can lay just four days after being born.
If there is a lack of food, oxygen, or space or a drop in temperature, females will lay males. They will breed and produce resting eggs that can dry out just like brine shrimp. For information on rearing daphnia to feed fish, go to the Daphnia FAQ . A visitor pointed out to me that this site no longer works. A drawing of a daphnia can be seen at this water bug site .