Fish in a fish tank... why don't they multiply?

Factual Questions
1

Why no new fish?

2

I´m not a fish how do i know?

3

My mistake.

From here, you looked like a fish.

Again, my apologies.

4

Maybe they aren’t sexually mature.

Maybe the water isn’t the right chemistry or temperature to trigger them to spawn.

Maybe they’re malnourished or stressed to the point where they’re not healthy enough to generate eggs.

Maybe they are breeding, but the tank is overcrowde enough that the eggs are all getting eaten before they can get a chance to hatch.

Maybe they’re descended from factory-like production lines and are incapable of breeding normally without having the right hormones artificially added to the water.

Maybe they’re all males, or all females.

More information is needed to answer your question.

5

You obviously do not have Guppies, or else you wouldn’t ask this question.

Many kinds of fish will breed in a fish tank. Reasons they may not:

  1. Tank is too small.
  2. Tank is too crowded.
  3. Not enough or the wrong kind of food.
  4. Fish are not mature.
  5. Water is wrong temperature.
  6. Other fish in the tank eat the eggs or young.
  7. They’re not in the mood.
  8. Any one of a dozen other factors.
6
  1. The tank does not closely duplicate their native habitat: they may need to attach their eggs to the stems of aquatic plants; they may need to construct some sort of ‘nest’ (like Sticklebacks) and the materials to do so may be absent; the tank substrate may not be suitable for them to bury their eggs in (they may want mud or fine sand instead of chippings or gravel).
7

…because different species have multiple requirements for “setting the mood.”

  1. Guppies (and pretty much any members of the live bearing family) have virtually no requirements. As previously mentioned, put male and female in tank, and voila! Hundreds of little baby mollies, guppies, platys, or swordtails.

  2. Goldfish, meanwhile, require large amounts of space and need to be allowed to reach the size of sexual maturity. This is impossible in commerical tanks.

  3. Bettas (“Siamese Fighting Fish”) have many requirements: tank must be 10 gallons, minimum; water must be at least 80 degrees F; water needs to be fairly shallow, no more than about 6" deep; there needs to be numerous floating plants; the female must be “ripe”; the male needs to be introduced first so he can first construct his bubble nest, indicating sexual maturity…etc.

  4. Some South American cichlids (Jack Dempseys are my experience) require space–in my case, a 60gal tank–to establish territory. They also require what are commonly called “target fish.” Those are fish of a different species that are essentially targets of aggression. They also need a flat surface, like smooth rocks, to lay their eggs on.

  5. Other South American cichlids, such as the more docile angelfish and discus, require high temperatures, acidic water, and large amounts of plants (preferably live, not plastic).

And so on. You get the idea. :slight_smile:

8

You beat me to it.

As a kid, I was distraught to learn that guppies ate their young. After they crowded the other fish out of our tank, I concluded that the problem was that they didn’t eat enough of their young. Guppies are the cockroaches of the tropical fish world.
Read up on the requirements of your species. There are plenty of fish care books out there.