Breeding strategies

This is a huge subject. Details of breeding some individual species are given in the list of fishes. But there are some excellent introductory thoughts on breeding strategies, the kind of tanks and other equipment that might be needed, and problems related to raising fish fry, presented in Elaine Thompson's article "Breeding Strategies" at The Krib.  Consistently accurate generous details of breeding, species by species, can be found at Seriously Fish. 
 
Breeding strategies There seem to be so many unusual techniques and requirements for breeding fishes that for a beginner it all looks daunting. In each case some "magical" and quite arbitrary trick seems to be necessary. In fact there are only five basic breeding strategies fishes use, and you can classify them on an ecological basis. If we list the strategies in order of the increasing commitment of energy going into maximizing the survival of each individual egg, they might fall together something like the following. 
 
The egg-scatterers. Mass-spawning egg broadcasters: in which the school's biological cycle is synchronized, and eggs and milt are scattered at random among plants in open water. Egg mortality is high, but this strategy swamps the ability of ovipredators to eat all the eggs suddenly available. Selective egg scatterers: more selective mate selection, in which a similar random-scattering strategy is followed by a pair or a trio of fish.
 
The egg hiders. Clutch hiders: redd builders, like salmon, that sweep gravel over their completed clutch of eggs, but don't guard the nest in a territory. Egg hiders include selective egg placers, in which the female hides eggs singly or a very few at a time, to minimize the possibility that a whole clutch will be found and devoured. (Corydoras spp.)
 
The nest builders. Territorial nest builders buildbubblenests (e.g. Anabantoids) or construct a nest (e.g. sticklebacks). For territorial substrate nesters spawning occurs in an excavation or on a cleaned surface. Territory guarders who select or build a suitable nesting territory  include cave spawners.
 
The brood carriers. Mouthbrooders create a portable "territory." Some fishes carry their eggs in grooves, folds or pouches. Internal carriers: in ovoviviparity the fertilized eggs are merely retained till hatching; in viviparity fertilized eggs are nourished internally.
 
The cheaters. Brood parasites get their eggs and fry guarded by another species. Fish are also capable of acting as streakers, sneakers, even transvestites.
 
Cannibal mothers. Cannibalism on the parents' part doesn't seem like a very effective way to keep a species going. But a cannibal mother can exert a strong selective pressure for quick survival defense reactions among her fry. A guppy female nearing birth seems to feel cumbersome and defenceless; certainly, she retreats into dense planting, as she would if she were temporarily unwell. As the live young are born, their first instinct is to flee into dense cover. Fry that lack this instinct or are slow to move, are swallowed by Mother first. In a natural setting, cannibalism is an effective way of recycling less-well-adapted fry, which are just about to become protein for some predator anyway, into protein that Mother can recycle into a new brood. But then why is the reverse strategy, to tolerate the presence of the young at every stage of their development, so effective for the Molly?
 
Artificial conditions of captivity often increase parental cannibalism among fishes like Cichlids, that ordinarily offer brood-care. Among some artificially-bred fishes, like Angels or Discus, generation after generation have been bred to display color variations and finnage that are considered desirable. For maximal fry-raising, artificial conditions have prevailed. Ineffective parenting no longer has resulted in loss of broods. In effect, aquarists have been "selecting" for glamorous fishes whose parental instincts are no longer "relevant" to survival of the brood.