It's possible, but rarely successful:
* Different species: Generally, fish from different species *cannot* mate successfully. They have different numbers of chromosomes and genes, making it highly unlikely for a viable offspring to be produced.
* Different breeds (within a species): Fish within the same species but different breeds *sometimes* can mate. However, it's often difficult, and the offspring might be less healthy or fertile.
* Hybrids: Occasionally, hybrids do arise. These are the offspring of two different species, like a goldfish and a carp. Hybrids are often sterile, meaning they can't reproduce.
Factors affecting interbreeding:
* Physical compatibility: Fish need to have compatible reproductive organs and mating behaviours.
* Genetic compatibility: Their chromosomes and genes must align somewhat for successful fertilization and development.
* Environmental factors: Water conditions, temperature, and other environmental factors can influence breeding success.
Why it's rare:
* Evolutionary pressures: Fish have evolved to reproduce within their own species, ensuring the survival of their genes.
* Natural barriers: Different species often live in different habitats or have different breeding seasons, preventing them from encountering each other.
In summary:
* Different species: Usually cannot interbreed.
* Different breeds: Sometimes can, but offspring might be less healthy or fertile.
* Hybrids: Rare and often sterile.
If you're interested in breeding fish, it's best to stick to fish of the same species and breed. This will give you the highest chance of success.