Breeding nano fish is where the hobby stops being decoration and starts being biology. A school of chili rasboras in a planted 10 gallon is a nice display; that same school dropping 200 eggs into a breeding tank, the eggs hatching in 24 hours, the fry free-swimming on day three, and the fry hitting 1 cm in three weeks — that is a different kind of satisfaction. This guide is the spawning-strategy framework I use across my nano fishroom, written for the keeper who has kept nano fish for a year and is ready to make more of them. The dedicated nano cichlid breeding guide covers cichlid-specific parental care; this guide covers everything else.
Set up the fry food cultures before you set up the breeders. The single most common reason nano breeding attempts fail is not infertility, not bad water, not egg fungus — it is keepers getting a successful spawn and then realising they have nothing to feed the fry. Infusoria takes 5–7 days to culture. Microworms take 2 weeks to establish. BBS take 24 hours but you need cysts on hand. Have all three going before the breeders go in the tank, and you will not be the keeper staring at 200 free-swimming fry with nothing to feed them.
Why Breed Nano Fish?
The honest answer is that breeding is the deepest engagement you can have with the fish. Keeping is observation; breeding is participation. A pair of Apistogramma that pairs off, claims a cave, defends eggs, and shepherds fry for three weeks is a different animal from the same pair sitting in a community tank — the breeding behaviour unlocks the entire repertoire that the fish evolved to express. Once you have seen it, you will not go back to keeping fish as static display.
The practical answer is that captive-bred fish are the future of the hobby. Wild collection is increasingly restricted, and several nano species (chili rasboras, celestial pearl danios) have been over-collected to the point that wild populations are at risk. Every tank-bred fish you produce is a fish that was not pulled from the wild, and every fry you raise to adulthood and pass on to another keeper expands the captive gene pool. The hobby is a conservation project whether you intended it that way or not.
The economic answer is that breeding offsets the cost of the hobby. A pair of endlers producing 30 fry a month, raised to selling size and traded to the local fish store for store credit, pays for the food and equipment for the rest of the fishroom. A successful spawn of a less-common species (chili rasboras, scarlet badis, pygmy corydoras) trades for credit at a premium because the store cannot get them wholesale. Breeding is not a money-maker, but it can make the hobby self-sustaining.
The 4 Spawning Strategies
Nano fish use four fundamentally different spawning strategies, and each requires a different breeding tank setup, a different conditioning protocol, and a different level of keeper intervention. Knowing which strategy your species uses is the first decision — the rest of the process flows from it.
| Strategy | Example species | Egg location | Parental care | Difficulty |
|---|---|---|---|---|
| Egg scatterer | Tetras, rasboras, barbs | Open water, falls to substrate | None — parents eat eggs | Medium |
| Cave spawner | Apistogramma, rams, kribensis | Cave or crevice | Both parents guard eggs & fry | Medium (covered in cichlid guide) |
| Bubblenester | Bettas, gouramis | Surface bubble nest | Male guards nest & fry | Medium |
| Livebearer | Guppies, endlers, platies | Internal, born free-swimming | None — parents eat fry | Easy |
Egg scatterers are the largest category in the nano hobby. Tetras (ember, neon, glowlight, rummynose), rasboras (chili, harlequin, galaxy), barbs (cherry), and danios (celestial pearl, zebra) all release eggs into the open water column where they fall to the substrate. The parents do not guard the eggs — in fact they eat them as fast as they can find them. The breeding tank for scatterers uses a layer of marbles or a mesh screen on the bottom that lets the eggs fall through where the parents cannot reach them. Conditioning is straightforward: separate the sexes for two weeks, feed heavily with live and frozen food, and put them together in the breeding tank in the evening. Spawning usually happens at dawn.
Cave spawners are the dwarf cichlids — Apistogramma, rams, kribensis, and shell dwellers. The pair claims a cave (coconut shell, PVC pipe, escargot shell) and spawns on the cave roof or wall. Both parents guard the eggs, the wrigglers, and the free-swimming fry for 3–4 weeks. This is the most rewarding spawning strategy to watch because the parental care is visible and dramatic, but it is also the most demanding on water quality. The dedicated nano cichlid breeding guide covers conditioning, the spawn, and fry raising in full detail.
Bubblenesters are the labyrinth fish — bettas and gouramis. The male builds a foam nest at the water surface using saliva-coated bubbles, often anchored to a floating plant or a piece of styrofoam. Spawning is the famous "embrace" — the male wraps around the female, squeezes eggs out of her, fertilises them as they fall, then catches them in his mouth and blows them into the nest. The male guards the nest and the fry until they are free-swimming on day 3–4, at which point he should be removed. Betta breeding is the most-documented nano breeding project online; the trap is that betta fry are tiny and require infusoria for the first week.
Livebearers are the easiest nano fish to breed, full stop. Guppies, endlers, platies, and mollies are internally fertilised — the male transfers sperm via a modified anal fin (the gonopodium) and the female gives birth to 20–40 free-swimming fry every 30 days. The fry are large enough to eat crushed flakes from birth, no live food cultures required. The catch is that the parents and any other fish in the tank will eat the fry, so a densely planted tank (Java moss, guppy grass, floating plants) is essential for the fry to hide in. A single female guppy in a heavily planted 10 gallon will produce a self-sustaining population within 6 months.
Conditioning the Breeders
Conditioning is the two-week preparation phase where you get the breeders ready to spawn. The protocol is the same across all four spawning strategies — separate the sexes, feed heavily with live and frozen food, hold pristine water quality — and skipping it is the single most common reason a pair fails to spawn. Fish that have been living together in a community tank are not in breeding condition; they are in maintenance condition. Conditioning flips the switch.
Separate the male and female into different tanks (or a divided tank) for at least two weeks. The visual separation triggers spawning readiness in a way that constant proximity does not — the female develops eggs without being harassed, the male builds sperm reserves, and both fish store energy for the spawning effort. During separation, feed 3–4 times a day with a rotation of live BBS, frozen bloodworms, frozen brine shrimp, and high-quality pellets. The goal is plump, glossy fish with full bellies — not fat fish, but visibly well-fed fish.
Water quality during conditioning has to be pristine — 0 ammonia, 0 nitrite, nitrate under 10 ppm. Do 30% water changes twice a week during the conditioning period, and on the day you put the pair together, do a 50% water change with slightly cooler water (2–3°C cooler than the conditioning tank). The temperature drop simulates the rainy season, which is the natural spawning trigger for most tropical fish. The combination of separation, heavy feeding, pristine water, and a temperature drop is the conditioning protocol that has triggered spawning in every nano species I have kept.
The Breeding Tank Setup
The breeding tank is a 5–10 gallon bare-bottom tank with a sponge filter, a small heater, and species-specific spawning furniture. No substrate — substrate traps eggs and fry and makes cleanup impossible. No light cycle changes — keep the tank on the same 8-hour photoperiod as the conditioning tank. The tank should be cycled before the breeders go in — a seeded sponge filter moved from an established tank is the fastest way to cycle a breeding tank. A bare uncycled breeding tank will kill eggs and fry with ammonia within 24 hours.
For egg scatterers, add a 2 cm layer of glass marbles across the bottom of the tank. The marbles let the eggs fall between them where the parents cannot reach them. After spawning, remove the parents and either siphon the eggs out or leave them in the marbles until they hatch (24–36 hours for most tetras). An alternative to marbles is a mesh screen (plastic canvas from the craft store) raised 1 cm off the bottom with PVC pipe rings — the eggs fall through the mesh, the parents cannot reach them, and you can lift the mesh out to remove the parents.
For cave spawners, add a coconut shell (halved, with a small entrance hole), a PVC pipe elbow (3 cm diameter), or an escargot shell depending on species. Apistogramma prefer caves with a single small entrance; rams prefer flat stones or open caves; shell dwellers need actual snail shells. Add a small piece of driftwood or a low plant (Java fern, Anubias) to break the sight line and give the female a place to retreat if the male gets aggressive. The cichlid breeding guide covers species-specific cave selection.
For bubblenesters, fill the tank to 15 cm depth (shallower than the other strategies — the male needs to be able to catch falling eggs before they hit the bottom), add a half-cut styrofoam cup floated on the surface as a nest anchor, and add a small floating plant (Salvinia, Riccia) for additional nest support. Add a small piece of Indian almond leaf to release tannins — the tannins have anti-fungal properties that protect the eggs. For livebearers, add dense plant cover — Java moss, guppy grass (Najas guadalupensis), floating Water Sprite — and the breeding tank is also the grow-out tank because the fry hide in the plants from birth.
The Spawn: Recognising Behaviour and Removing Parents
The spawn itself is fast — usually 1–3 hours from start to finish. Egg scatterers spawn at dawn after a night of courtship chasing; the female releases eggs in batches, the male fertilises them as they fall, and the pair may repeat the spawn cycle 5–10 times over 2 hours. After spawning the parents actively hunt the eggs — this is your cue to remove them. Catch the parents gently with a soft net (a breeder net is too rough on a conditioned female full of eggs), return them to their conditioning tanks, and let the eggs incubate.
Cave spawners behave differently — the spawn happens inside the cave and you may not see it. The signs are the female spending extended time in the cave, the male patrolling the cave entrance and chasing anything that approaches, and the female's colour intensifying (especially the yellow belly on Apistogramma females). Once you see the female fanning water into the cave with her pectoral fins, eggs are present. Leave the parents in — they will guard the eggs. After the fry are free-swimming (day 5–7), you can either leave the parents in for the full parental care period (3–4 weeks) or remove them and raise the fry artificially.
Bubblenester spawning is the most visible. The male builds the nest over 12–24 hours, then courts the female with flaring and dancing. When the female is receptive, the male wraps her in the embrace — she goes limp, he squeezes, eggs fall, he fertilises them, then he catches them in his mouth and blows them into the nest. This repeats 10–20 times over 2–4 hours. After spawning, remove the female — the male will guard the nest alone. Remove the male on day 3–4 when the fry are free-swimming; he may eat them once they start swimming freely. Livebearers do not have a "spawn" — the female gives birth over 2–6 hours, dropping 20–40 fry, and the parents start hunting the fry immediately.
Egg Care: Fungus Prevention and Water Changes
Egg fungus is the second most common reason nano breeding attempts fail (after not having fry food). The fungus is a saprophytic mould (Saprolegnia) that grows on infertile eggs and then spreads to fertile eggs, killing them within 12 hours. The prevention protocol is methylene blue — add it to the egg tank at 2–4 ppm (the water should be tinted light blue, not dark blue), add an air stone for gentle circulation, and remove any eggs that turn white with tweezers within 12 hours. White eggs are infertile or dead — they are the fungus vector.
Methylene blue is the single most effective anti-fungal for fish eggs, and it does not harm the developing embryos. Without it, expect 50–70% egg loss to fungus in a typical nano breeding setup; with it, expect 10–20% loss. A second dose at half strength on day 2 helps if fungus is aggressive. Methylene blue stains everything it touches (silicone, plastic, your hands), so use a dedicated breeding tank, not your display. The stain fades over a few weeks but it is ugly while it lasts.
Water changes during the egg stage are minimal — do 10% daily with aged, temperature-matched water, siphoning carefully around the eggs. The methylene blue will be diluted over the incubation period, which is fine — you want it gone by the time the fry are free-swimming so you can see them clearly. The incubation period varies by species and temperature: most tetra and rasbora eggs hatch in 24–36 hours at 26°C; betta eggs hatch in 36–48 hours; Apistogramma eggs hatch in 3–4 days. Faster at warmer temperatures, slower at cooler ones.
Fry First Foods: Infusoria, Microworms, BBS, Crushed Flakes
Fry first foods are the make-or-break of nano breeding, and the schedule below is the one I use across all egg-laying nano species. Livebearer fry skip the infusoria stage entirely — they are born large enough to eat crushed flakes from day one. Egg-layer fry are tiny (1–2 mm at hatching) and need a graduated food sequence as their mouths grow.
Day 1–3: infusoria. Infusoria are microscopic single-celled organisms (paramecium, rotifers, euglena) that are the only food small enough for newly-hatched nano fry. You culture infusoria in a jar of tank water with a piece of hay, banana peel, or boiled lettuce leaf — the micro-organisms bloom in 5–7 days and the culture is ready. Feed 5–10 mL of infusoria-rich water per 5 gallons of fry tank, twice a day. The water will be cloudy — that is the food. You can also buy commercial infusoria starters (Liquid Fry Food, Fry Food Number 1) but they are inferior to live cultures.
Day 3–14: microworms or BBS. Once the fry are 3 days old and have consumed their yolk sacs, they graduate to microworms (live, cultured on oatmeal) or freshly-hatched baby brine shrimp (BBS). Microworms are easier — a starter culture costs $5, you set it up in a plastic tub with oatmeal and yeast, and it produces worms for 3–4 weeks before you need to start a new culture. BBS is more nutritious — the nauplii are bright orange, the fry's bellies turn orange when they eat them, which is how you confirm feeding — but you need to hatch them daily from cysts in a saltwater hatchery. Either works; BBS is the gold standard for growth rate.
Day 14–30: crushed flakes plus microworms/BBS. By day 14, the fry are 4–6 mm long and large enough to start taking finely crushed flake food. Crush Omega One or New Life Spectrum flakes between your fingers to a powder finer than table salt, and feed a tiny pinch twice a day alongside the live food. The transition to dry food takes 1–2 weeks — some fry accept it immediately, others need to be weaned off live food gradually. By day 30, most nano fry are large enough to eat uncrushed micro pellets and to move to a grow-out tank.
Species-Specific Notes
Ember Tetra (Hyphessobrycon amandae): Egg scatterer, easy to breed, 24–36 hour incubation. Condition a pair (or a group of 4–6) for 2 weeks with BBS and bloodworms. Spawn in a 5 gallon with marbles on the bottom, soft acidic water (pH 6.0–6.5, GH 2–5), temperature 26°C. Remove parents after spawning. Eggs hatch in 24–36 hours, fry free-swim on day 3–4. Feed infusoria day 1–3, BBS day 3–14, crushed flakes after. Ember tetra fry are small but robust — expect 30–60 fry from a group spawn.
Chili Rasbora (Boraras brigittae): Egg scatterer, harder to breed than ember tetras because the fry are smaller. Condition a group of 6–8 for 3 weeks — chili rasboras need longer conditioning than tetras. Spawn in a 5 gallon with Java moss on the bottom (the eggs stick to the moss), very soft acidic water (pH 5.0–6.0, GH 1–3), temperature 27°C, dim lighting. Remove parents after 24 hours. Eggs hatch in 36–48 hours, fry are tiny (1 mm) and need infusoria for the first 5–7 days — longer than most nano fry. Expect 20–40 fry from a group spawn, with high early mortality if infusoria is insufficient.
Endler's Livebearer (Poecilia wingei): Livebearer, the easiest nano fish to breed. No conditioning required — a single male and 2–3 females in a 10 gallon with heavy plant cover will produce fry every 30 days. Gestation 24–28 days, brood size 10–30 fry. The parents and any other fish will eat the fry, so dense plant cover (Java moss, guppy grass, floating Water Sprite) is essential. Fry are 6–8 mm at birth and eat crushed flakes from day one. No live food cultures needed. Expect a self-sustaining colony within 6 months if you do not cull.
Betta (Betta splendens): Bubblenester, intermediate difficulty. Condition the male and female separately for 2 weeks with BBS, bloodworms, and high-quality pellets. Set up a 10 gallon with 15 cm water depth, a styrofoam cup half floated for the nest, an Indian almond leaf, and a small sponge filter on low flow. Introduce the female in a clear divider or floating container so the male can see her without attacking; release her after 24 hours. Spawning takes 2–4 hours. Remove the female immediately after — the male will guard the nest. Eggs hatch in 36–48 hours; fry free-swim on day 3–4. Remove the male once fry are free-swimming. Betta fry are tiny (2–3 mm) and need infusoria for the first 5–7 days, then BBS. Expect 100–300 fry from a successful spawn, with high early mortality.
Pygmy Corydoras (Corydoras pygmaeus): Egg scatterer that attaches eggs to plants and glass rather than dropping them. Condition a group of 6–8 for 2 weeks with BBS, bloodworms, and pellets. Spawn in a 10 gallon with Java moss and broad-leaf plants (Anubias), slightly cooler water (22–24°C, a 2°C drop from conditioning triggers spawning), pH 6.5–7.5. The female carries eggs in her pelvic fins and deposits them on plant leaves and the tank glass — you will see 1–3 eggs per deposit, with a total of 30–60 eggs per spawn. Remove the adults after spawning. Eggs hatch in 3–5 days; fry free-swim immediately and eat microworms and BBS from day one (no infusoria needed — pygmy cory fry are larger than tetra fry).
Common Failures
1. No fry food cultures ready. Already covered in the callout — this is the #1 killer of nano breeding attempts. Set up infusoria and microworm cultures 2 weeks before the breeders go in the tank.
2. Egg fungus. Already covered — methylene blue at 2–4 ppm prevents 80% of fungus losses. Without it, expect to lose half the eggs.
3. Parents eating eggs. Egg scatterers and livebearers eat their own eggs and fry. Remove parents from scatterers within 2 hours of spawning; for livebearers, provide dense plant cover and either remove the female to a separate tank to drop or remove the fry to a grow-out tank as you spot them.
4. Breeding tank not cycled. A bare uncycled breeding tank with eggs and fry will spike ammonia in 24 hours. Seed the sponge filter in an established tank for 2 weeks before setting up the breeding tank.
5. Wrong water parameters. Chili rasboras will not spawn in hard alkaline water; Apistogramma will not spawn in hard water. Test your tap, and if it does not match the species' spawning parameters, use RO water reconstituted with the right minerals. Forcing soft-water fish to spawn in hard water wastes the conditioning effort.
6. Overfeeding fry. Fry tanks crash from overfeeding just like display tanks do, but faster. Feed tiny amounts 3–4 times a day, and siphon uneaten food daily with a turkey baster. A 25% daily water change is mandatory in a fry tank.
Frequently Asked Questions
What is the easiest nano fish to breed?
Livebearers are the easiest nano fish to breed. Endler's livebearers, guppies, and platies give birth to free-swimming fry that eat crushed flakes from day one — no live food cultures, no egg fungus, no special tank setup beyond heavy plant cover for the fry to hide in. Egg-laying nano fish are significantly harder because the fry are too small for any commercial food and require infusoria or green water for the first week.
How do I stop nano fish eggs from fungus?
Add methylene blue to the egg tank at 2–4 ppm (water tinted light blue), add an air stone for circulation, and remove any eggs that turn white with tweezers within 12 hours. Methylene blue is the single most effective anti-fungal for fish eggs and it does not harm the developing embryos. A second dose at half strength on day 2 helps if fungus is aggressive. Without methylene blue, expect 50–70% egg loss to fungus in a typical nano breeding setup.
What do you feed newly-hatched nano fish fry?
Day 1–3: infusoria (paramecium, cultured in a jar with hay or banana peel) — the only food small enough for newly-hatched egg-layer fry. Day 3–14: microworms or freshly-hatched baby brine shrimp (BBS). Day 14–30: crushed flakes or commercial fry food in addition to microworms/BBS. Livebearer fry skip the infusoria stage — they are large enough to eat crushed flakes from day one.
Should I remove the parents after nano fish spawn?
Yes, for egg scatterers and bubblenesters. Tetras, rasboras, and bettas will eat their own eggs and fry — remove them as soon as spawning is complete. Cave spawners (Apistogramma, rams) and livebearers are the exceptions — dwarf cichlids guard the eggs and fry, and livebearers do not guard anything but the fry are born mobile. The dedicated nano cichlid breeding guide covers the parental-care case in detail.
How big of a tank do I need to breed nano fish?
A 5–10 gallon bare-bottom tank with a sponge filter is the standard nano breeding tank. For egg scatterers, add a layer of marbles on the bottom to let the eggs fall where the parents cannot reach them. For cave spawners, add a coconut shell or PVC pipe cave. For bubblenesters, add a small floating plant cup and reduce water depth to 15 cm. For livebearers, add heavy plant cover (Java moss, guppy grass) for the fry to hide in.