Setting up a bubble-nest spawn, conditioning the pair and raising the fry through their fragile first weeks.
By Zhao Min · 2026-08-19
Macropodus opercularis has been bred in Chinese households for centuries, and it shows: the fish is forgiving, spawns readily in tap water, and the male does most of the work. Success depends less on equipment than on three things — a conditioned pair, warm still water, and patience during the fry's first month.
Paradise fish are bubble-nest builders: the male constructs a floating raft of mucus-coated bubbles at the surface, courts the female beneath it, and gathers every falling egg into the nest. Watching this behaviour is one of the great gateways into fish breeding.
Choose a male with strong colour and a female with a clearly rounded belly — gravid females show a thicker profile and a lighter, almost pinkish vent. House them apart for ten to fourteen days where they can see each other through glass, feeding heavily on live and frozen foods.
Cooler holding water (20–22 °C) followed by a spawning tank at 26–28 °C mimics the spring warm-up that triggers spawning in the wild. The temperature shift, plus rich food, is the most reliable trigger.
A 20–30 litre tank, filled to 15 cm, at 26–28 °C, works well. Add a clump of floating plants or a piece of styrofoam for the nest anchor, some fine-leaved cover for the female to retreat into, and gentle filtration — a small sponge filter with an airstone set low.
Introduce the pair in the evening. Courtship begins with flaring and circling; spawning wraps, where the male squeezes the female as eggs and milt release, repeat for one to three hours and can yield 200–600 eggs.
Eggs hatch in 24–36 hours depending on temperature. The male tends the nest for another two to three days, returning fry that fall out — remove him once the fry are free-swimming and horizontal, or he may begin eating them.
First foods decide survival: infusoria or commercial liquid fry food for the first week, then newly hatched brine shrimp. Feed small amounts three to four times daily, and keep the water pristine with daily 10–15% changes using matched-temperature water.
Growth is steady on live baby brine shrimp. By week four the labyrinth organ develops and juveniles begin gulping air — keep the tank covered with cling film or glass so the air above the water stays warm and humid while the organ matures.
24–36 hours at 26–28 °C, with fry becoming free-swimming about three days later. The male guards the nest the whole time; remove him once the fry swim horizontally or he may start eating them.
Infusoria or liquid fry food for the first five to seven days, then newly hatched brine shrimp three to four times a day. The first food is the bottleneck: fry that get live food from day five grow twice as fast as those kept on prepared foods alone.
Usually one of three causes: the female was left in too long and disturbed the nest, a sudden noise or light change stressed him, or the nest simply failed and he recycled the eggs as food. First-time males often lose their first spawn — give the pair a week and try again.
They may spawn, but fry survival in a community tank is near zero — other fish eat eggs and fry, and the flow scatters the nest. A dedicated shallow spawning tank takes an hour to set up and transforms success rates.
Around two months, at 2.5–3 cm, once the labyrinth organ is fully developed and they take crushed flake. Before that, abrupt temperature swings and poor air quality above the water are the main risks during any move.