Breeding starts not with a spawning tank but with an honest answer to the question of what the fry are for and where they will go. A pair can produce hundreds of eggs, and a month later those fry need volume, food and grading. Everything else is technique.

How fish spawn

The mode of reproduction determines the whole preparation, and it is given in every species profile.

  • Livebearers (poeciliids, some halfbeaks) carry the eggs internally and release fully formed fry. A female can produce several broods from a single mating.
  • Egg scatterers (barbs, danios, tetras, rasboras) release eggs into open water or over plants and start eating them at once. Their eggs have to be protected.
  • Substrate spawners (angelfish, apistogramma, loricariids) clean a stone, a leaf or a cave and guard the clutch themselves.
  • Bubble-nest builders (bettas, gouramis, paradise fish) build a nest at the surface, and the male tends the eggs.
  • Mouthbrooders (many Malawi and Tanganyika cichlids) carry eggs and fry in the mouth, eating nothing meanwhile.
  • Seasonal killifish (nothobranchius, annual aphyosemion) lay eggs in the substrate, and those eggs need a drying period — a diapause.

The breeding tank

A separate tank is nearly always needed: in a community aquarium the eggs are eaten within hours.

  • Volume — from 10–20 litres for small egg layers; more for cichlids.
  • Bare bottom. It keeps the eggs visible and leftovers easy to remove.
  • Egg protection for scatterers: a mesh above the bottom, a layer of glass marbles, a dense clump of java moss.
  • Sponge filter on an air pump only. Internal and external filters draw in eggs and fry.
  • A heater and shade. Many species need subdued light, and the eggs of several are sensitive to bright lighting.
  • Water from the main tank, or specially prepared if the species needs softer and more acidic water to spawn; how to prepare it is described in the Water chemistry section.

Conditioning the breeders

For a week or two males and females are kept apart and fed live or frozen food — bloodworm, glassworm, daphnia, brine shrimp. A varied protein diet is the main stimulus for eggs to ripen. A ready female fills out visibly, while the males colour up and become more active.

Take adult, healthy fish, and not the smallest ones. Weakened fish, and any that have recently been ill, are not bred.

What triggers spawning

In most tropical species spawning is tied to the rainy season, and in the aquarium that season is imitated:

  • a 30–50 % change to softer water, a degree or two cooler;
  • lowering the water level and then raising it back slowly;
  • stronger aeration and flow;
  • morning light — many species spawn at dawn.

If a pair will not spawn, the cause is more often the conditioning or the age of the fish than a lack of "triggers". Raising the temperature above the species' upper limit is not an option: it does not hasten spawning, it shortens the fish's life.

After spawning

Scatterers are removed immediately. With a bubble nest the female is taken out at once and the male once the fry are free-swimming. Cichlids and loricariids are usually left alone — they raise a clutch better than any keeper.

Inspect the eggs daily and remove the white, unfertilised ones: fungus settles on them quickly and spreads to the living eggs.

Raising the fry

For the first days fry live on the yolk sac and need no food. Feeding starts as soon as they swim horizontally.

  • First foods: infusoria, "green water", vinegar eels, microworms.
  • A few days later — newly hatched brine shrimp, the best food for growth.
  • Then — crushed dry foods, chopped tubifex, cyclops.

Feed little and often, four to six times a day. The main danger in a grow-out tank is not hunger but spoiled water: uneaten food decays fast. A daily change of 10–20 % and siphoning of the bottom are needed throughout the growing period.

Common mistakes

  • Overfeeding the fry, and with it ammonia in a small volume.
  • Too strong a filter or flow — fry are drawn in or worn out.
  • A cramped grow-out tank. Crowding stunts growth irreversibly: the small fry never catch up with the large ones.
  • Crossing closely related species. Hybrids survive and look much like their parents, then spread from tank to tank as a "pure species". That is how lines are lost that are already scarce in the wild.
  • Moving fry to the community tank too early: a youngster smaller than a tank mate's mouth becomes food.

When breeding will not work

Some aquarium species do not reproduce in captivity at all. Others need conditions you cannot create at home: seasonal swings, enormous volumes, hormonal induction. When a species profile says the fish is not bred in aquaria, that is not cautious wording but a fact: such fish reach the trade from the wild or from commercial farms.