The usual fish tank aquarium is set up for the enjoyment of the observer. An aquarist will often buy a pair of fish, a male and a female. As with other creatures when a male and a female get together the natural impulse is to breed. A natural question might be, ”Why doesn’t the aquarium soon over flow with fish?” One of the answers to such a question is related to the breeding needs of tropical fish.
In some cases, fishes in captivity do not acclimate to aquarium conditions. Even though they may be kept alive and in good health there is “something” missing. The missing element could be one thing or a combination of things. It might be that the water pressure is not right for that breed of fish to spawn. For some fish there is a need for a lot of surface water and even a large fish tank cannot provide enough surface water. Some fish are rendered sterile under normal shipping conditions. Not all the reasons are known and most are speculation.
For the fish that do breed in a fish tank aquarium, the usual community tank does not give enough protection for many of the fry to survive. This is especially true for the egg scatterers.
Egg scatterers comprise a large portion of the commonly used tropical fish population. Included in this group are the Tetras, Pencilfish, most of the Barbs, some of the Minnows, Hatchet, and Catfish as well as many others. The process is just as the name implies. The female swims and scatters her eggs; the male follows behind her and fertilizes them. An observer sees this behavior as a chase. Other fish in the tank see this as a feeding. Even the parent fish will enjoy the roe once the spawning is completed.
A few of the fertilized eggs may make it to the bottom of the tank and find shelter in the aquarium gravel. The eggs differ in degrees of stickiness to none at all. The sticky eggs may adhere to an aquarium ornament or plant; some of the eggs may float. All of the eggs in this group are abandoned by the parent fish making them susceptible to scavengers. Even the eggs that make it to the safety of aquarium sand or gravel have only a slight chance of maturing into fry. Bottom feeders and scavenger fish will eat most of them. If an egg should be able to hatch their chances of survival are next to nothing. The fry are non-swimmers until the yolk sac is absorbed and a lack of an appropriate food source will also inhibit the small fish’s chances of survival.