Rainbowfish Fry: Breeding, Egg Collection, and Raising the Young

Q: How long does it take for rainbowfish eggs to hatch, and when are fry free-swimming?

Rainbowfish eggs typically take roughly 7-12 days to hatch, which is longer than many other commonly bred aquarium fish — see our overview of fish egg hatching times for how this compares to faster hatchers like bettas (24-36 hours) and corydoras (3-5 days). Because rainbowfish are continuous spawners, laying small numbers of eggs daily over a period of weeks rather than one large batch, a collection container can end up with eggs at many different stages of development simultaneously if eggs aren't collected and sorted on a regular schedule — which is part of why daily collection is recommended rather than a single end-of-spawn collection.

By Hektor Jorgo Published May 23, 2029 Updated June 15, 2026 4 min read

A pair of brightly colored rainbowfish swimming near fine-leaved aquarium plants

Quick Facts

Species: Melanotaenia spp. and related rainbowfish genera
Spawning Style: Continuous egg-scatterer — small numbers of eggs laid daily among fine-leaved plants or spawning mops
Hatching Time: Roughly 7-12 days per batch of eggs, longer than most egg-scatterers
Egg Collection: Best collected daily — eggs are laid in small numbers continuously, not in one large spawning event
Fry First Food: Infusoria or green water for the first several days — fry mouths are extremely small at hatching
Fry Food (Later): Baby brine shrimp nauplii and microworms once fry are large enough
Parental Care: None — adults will eat both eggs and fry if given the chance
Growth Rate: Relatively fast for a nano fish, but slower than livebearer fry

Rainbowfish are popular for their color, but they're also one of the more approachable egg-scatterers for hobbyists wanting to try breeding — not because spawning itself is hard to trigger, but because the egg-laying pattern and tiny fry food requirements make the process look a bit different from species that spawn in one big event.

Direct Answer: Continuous Spawners With Demanding Fry

Rainbowfish are continuous egg-scatterers — a healthy, well-conditioned group will lay small numbers of sticky eggs daily among fine-leaved plants or a spawning mop, over a period of weeks, rather than producing one large batch and stopping. Eggs take roughly 7-12 days to hatch, on the longer end compared to other commonly bred species (see our guide to fish egg hatching times). The harder part isn't getting eggs — it's that adults provide no parental care and will eat eggs and fry, and newly hatched fry need infusoria or green water, a food size smaller than most fry foods, for their first several days.

Setting Up for Eggs: Fine-Leaved Plants or Spawning Mops

Rainbowfish scatter sticky eggs onto fine surfaces, so providing the right surface is most of the setup:

Fine-leaved plants — dense plants like java moss give eggs somewhere to stick and offer some protection from adults
Spawning mops — a simple bundle of dark yarn, suspended in the tank, mimics fine plant growth and is easy to lift out and inspect or move to a separate container
Conditioning — feeding a varied, high-quality diet (including live or frozen foods where possible) tends to encourage more consistent spawning

Because rainbowfish spawn continuously rather than in one event, daily collection of eggs (moving the mop or a portion of plants to a separate rearing container) is the standard approach — it keeps eggs at roughly similar developmental stages and gets them away from adults that would otherwise eat them.

Hatching and the First Critical Days

Eggs typically hatch in 7-12 days. Once fry emerge, the first few days are the most demanding part of the entire process: rainbowfish fry have very small mouths and need food sized accordingly — infusoria or green water (water dense with cultured single-celled algae) are the standard first foods. This is a smaller food size than many other fry can start on, and fry that don't find enough food in this window often don't make it, even when the eggs themselves hatched without issue. This stage is broadly comparable in difficulty to the food bottleneck faced by otocinclus fry, though for different underlying reasons (mouth size vs. food-type availability). The general progression from infusoria to brine shrimp to crushed adult food, and why mouth size drives all of it, is covered more broadly in our guide to what small fish eat.

Growing On: From Infusoria to Brine Shrimp

After the first several days, fry grow enough to take baby brine shrimp nauplii and microworms — the standard fry foods used across a wide range of species once fry reach an appropriate size. From this point, rainbowfish fry grow at a reasonable pace for a nano species, though still slower than the rapid growth seen in livebearer fry (a useful comparison if you've also kept species covered in our endlers in a 5-gallon tank guide). A separate grow-out tank, away from adults, remains important until fry are large enough not to be seen as food.

Why Egg-Scatterers Need a Different Approach Than Livebearers

If you've raised livebearer fry — guppies, mollies, platies — rainbowfish breeding will feel like a different process entirely. Livebearer fry are born free-swimming and large enough to take crushed flake or baby brine shrimp immediately, with no egg stage at all. Rainbowfish (and other egg-scatterers, including corydoras) require managing an egg stage, collecting eggs away from adults, and feeding fry foods smaller than what livebearer fry need on day one. If you're newer to breeding generally, our guide to the easiest freshwater fish to breed is a useful starting point for understanding where rainbowfish sit on that difficulty spectrum.

Quick Reference

Rainbowfish are continuous spawners — small numbers of eggs laid daily over weeks
Eggs are laid on fine-leaved plants or spawning mops; collect daily for best results
Eggs hatch in roughly 7-12 days, longer than many other egg-scatterers
Newly hatched fry need infusoria or green water — very small initial food
Adults provide no parental care and will eat eggs and fry
After several days, fry move on to baby brine shrimp and microworms

Frequently Asked Questions

How do you get rainbowfish to spawn in the first place?

Rainbowfish are one of the more cooperative egg-scatterers — a well-fed, healthy group in good water conditions will often spawn without much special intervention. The main thing to provide is somewhere for eggs to be laid: fine-leaved plants (like java moss or similar dense foliage) or an artificial spawning mop (a bundle of yarn that mimics fine plant growth) both work well, since rainbowfish scatter sticky eggs onto whatever fine surfaces are available. Conditioning the group with high-quality and varied foods (including live or frozen foods) tends to encourage spawning, but unlike species that need a specific triggering event, rainbowfish in good condition with adequate fine-leaved surfaces often spawn fairly readily on their own — the harder part is usually the next stage: collection and rearing.

What do rainbowfish fry eat, and when?

In the first several days after hatching, rainbowfish fry have extremely small mouths and need correspondingly tiny food — typically infusoria (a mix of microscopic organisms) or 'green water' (water cultured to be dense with single-celled algae). This is a meaningfully smaller food size than what fry of many other species can start on, and it's one of the more failure-prone stages of rainbowfish breeding — fry that don't find enough food in their first few days often don't survive even if eggs hatched successfully. After this initial period, fry grow enough to take baby brine shrimp nauplii and microworms, which are the standard fry foods for a much wider range of species once fry reach that size.

How long does it take for rainbowfish eggs to hatch, and when are fry free-swimming?

Rainbowfish eggs typically take roughly 7-12 days to hatch, which is longer than many other commonly bred aquarium fish — see our overview of fish egg hatching times for how this compares to faster hatchers like bettas (24-36 hours) and corydoras (3-5 days). Because rainbowfish are continuous spawners, laying small numbers of eggs daily over a period of weeks rather than one large batch, a collection container can end up with eggs at many different stages of development simultaneously if eggs aren't collected and sorted on a regular schedule — which is part of why daily collection is recommended rather than a single end-of-spawn collection.

Will adult rainbowfish eat their own eggs and fry?

Yes — rainbowfish provide no parental care, and adults will readily eat both eggs and fry if given the opportunity, the same as most other egg-scattering species. This is the main reason daily egg collection (removing eggs from the main tank to a separate rearing container) is recommended rather than hoping fry survive in the community tank. This pattern — egg-scatterers with no parental care needing eggs separated from adults — is shared with species like corydoras, though corydoras spawn in larger batches less frequently rather than continuously. If raising a meaningful number of fry is the goal, a dedicated rearing setup separate from the adult tank is close to essential for rainbowfish.

Sources & Further Reading

About the Author: Hektor Jorgo

Co-Founder & Marine Biologist

Hektor is a co-founder of Sea Life Planet and has kept reef and freshwater aquariums for over 15 years. He holds a background in marine biology and focuses on species care accuracy, water chemistry, and tank husbandry.