Freshwater

In the home aquarium, you can duplicate a rainstorm to some degree by
doing frequent water changes (about 20 percent per day in a breeding tank).
Clean, demineralized water stimulates most species into entering their seasonal
spawning cycle.
Another way to duplicate the rainy season is by showering the surface of the
water in your spawning tank with drops of water. You can do this quite easily
by using an inexpensive plastic watering can purchased at almost any garden
shop. No, you don’t have to stand there all day imitating a stone fountain.
Just run one full can of water slowly over the surface each hour when you
have time. (Don’t forget to remove some water first!) You can also try pouring
water slowly through a plastic fine-holed colander or fine plastic mesh.
The barometric pressure advantage
In the wild, an increase in atmospheric pressure (the weight of air as measured
by a barometer) often makes fish more lovable and loving. Many hobbyists
report that their fish breed more actively right before or during a rain or
snowstorm. Follow the local weather conditions and you may be able to
introduce pairs to the breeding tank during a barometric pressure drop
and have a successful spawning.
The old change the temperature ploy
If you go backpacking out to your species’ natural environment, you soon find
that they do not live in an area that remains the same temperature 24 hours
per day. (If you don’t believe us, pitch a tent for a night out there.) Try fluctuating
the temperature of the breeding tank overnight. Slowly drop the temperature
3 degrees at night by adjusting the heater, and then slowly raise it back
up in the morning. Now don’t get carried away and start tossing ice cubes into
the tank or anything. All temperature changes must be done slowly!
The new guy next door approach
Chapter 19: The Breeding Room
If you have a beautifully colored male that is being really stubborn and refusing
to breed, you can always try introducing a second male (the meanest,
ugliest one that you can find) in close proximity. This is kind of like sending
your fish to a singles bar. Placing the rival male in a glass holding container
near the spawning tank often inspires the stubborn spawner to breed when
he suddenly realizes that there may be competition for his female.
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