Items you will need
Aquarium or pond thermometer
When fish have babies, it is known as “spawning.” The baby fish produced from spawning are called “fry.” As long as there is a male and a female, pond fish will spawn if conditions are right for rearing fry. There will be signs leading up to the event, but the actual spawning can easily be missed since it may only last for 20 to 30 minutes (see Reference 1). Eggs should appear in the pond if the fish are successful, and the fry can be raised if desired.
Check the calendar. Pond fish begin their breeding cycle when the days begin to get longer and the water temperature is starting to rise. The long days of early summer stimulate the females to prepare her eggs for spawning (see Reference 1).
Get a pond or aquarium thermometer and test the water’s temperature. Koi fish will breed at 68 degrees Fahrenheit (see Reference 1), but both goldfish and koi will spawn if the water temperature is gradually raised (see Reference 2), signaling the warm season.
Determine the age of the pond fish. Koi should be old enough to have reached sexual maturity at around two years old (see Reference 3).
Look at the females carefully for any signs of swelling, which could indicate that maturing eggs are inside her. Females will also eat more food than the males during this time so that they can produce successful eggs (see Reference 1).
Watch the male fish behavior. Around the time of spawning, they may swim in groups along the surface of the water or the edges of the pond (see Reference 1).
The males will chase the females around the pond and attempt to beat the eggs out of her when the fish begin spawning (see Reference 1).
Check the water for clear eggs. They may be under plants or cling to other things in the pond water. The adult fish may eat a number of the eggs before there is a chance to check the water. Spawning mops can be used to catch the eggs.
To keep the eggs alive, they must be removed from the adult fish’s pond to protect them from being eaten. The eggs should be put into a separate rearing tank or pond.
Female fish may become very stressed and even injured during this time due to the aggression from the males (see Reference 1).