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Guppy fry are born fully formed and capable of swimming immediately — but they are tiny, vulnerable, and will be eaten by adult fish if not protected. With the right setup and feeding routine, guppy fry are straightforward to raise. This guide covers everything from the first hours after birth through the juvenile stage.
Guppy Fry at a Glance
| Size at birth | Approximately 6mm (0.25 inches) |
| Time to juvenile size | 4–6 weeks |
| Time to adult size | 3–6 months |
| Sexable at | 3–4 weeks (anal fin shape visible) |
| Feeding frequency | 3–5 times daily |
| Safe to add to main tank | When too large to fit in adult mouths (approx. 1 inch) |
Immediate Steps After Birth
Guppy fry are at highest risk in the first few hours after birth. Adult guppies — including the mother — will eat fry on sight. If fry are born in the main tank, they will instinctively seek cover in plants and decor. In a heavily planted tank, a portion of fry will survive without intervention. If you want to maximize survival, move fry to a separate grow-out tank as soon as possible after birth.
If you used a breeding box, remove the mother immediately after she finishes giving birth. Leaving her in the box causes unnecessary stress and she will eat fry if given the opportunity.
Grow-Out Tank Setup
A dedicated grow-out tank gives fry the best chance of survival and healthy development. Recommended setup:
- Tank size: 10 gallons is ideal for a single brood. Larger tanks support faster growth.
- Filter: Sponge filter only. Standard hang-on-back filters will suck up fry. A sponge filter provides gentle biological filtration and is completely safe for newborns.
- Heater: Maintain 76–78°F for general growth. Some breeders raise temperatures slightly (around 80°F) to encourage faster growth, though this may slightly increase metabolism and reduce long-term lifespan.
- Plants: Java moss, hornwort, or floating plants provide hiding spots and harbor infusoria that fry can graze on.
- Lighting: Standard aquarium lighting on a normal schedule.
- Water quality: Fry are sensitive to ammonia and nitrite. Perform small, frequent water changes (10–15% every 2–3 days) to keep parameters stable without causing temperature swings.
What to Feed Guppy Fry
Fry need appropriately sized food from day one. Their mouths are very small — standard flake food must be crushed to near-powder consistency before they can eat it.
Best Foods for Guppy Fry
- Finely crushed flake food: Crush between your fingers until almost powder-fine. The most accessible option for most keepers.
- Baby brine shrimp (BBS): Newly hatched live baby brine shrimp are the gold standard for fry growth. They are nutritionally complete, the right size, and trigger strong feeding responses. Frozen BBS also works well.
- Micro-worms: Easy to culture at home, excellent nutritional profile, and a good size for fry from day one.
- Infusoria or liquid fry food: Useful for the first few days when fry are at their smallest. Commercial liquid fry foods are a convenient alternative to culturing infusoria.
- Vinegar eels: Another easy-to-culture live food that works well for small fry.
Feeding Schedule for Fry
Feed fry 3–5 times daily in very small amounts. Fry have tiny stomachs and need frequent feeding to grow well. Feed only what they consume within a few minutes and remove uneaten food to maintain water quality. Consistent feeding frequency has a significant impact on growth rate — fry fed more often grow noticeably faster than those fed once or twice daily.
Fry Growth Stages
- Week 1–2: Fry are tiny and vulnerable. Focus on frequent feeding and stable water quality. Keep them separate from adults.
- Week 3–4: Fry begin to show color and fin development. Sexing becomes possible by anal fin shape. Males begin to develop color; females remain plainer.
- Week 5–6: Many fry are approaching a size where they are less vulnerable, but introduction to the main tank depends on the size of the adult fish present. Continue growing them out if there is any risk they can still fit in an adult’s mouth.
- Month 3–6: Fry reach adult size and full coloration. Males are sexually mature by 2–3 months; females typically around 2–3 months as well, depending on temperature and growth rate.
When Can Fry Join the Main Tank?
Fry can be safely introduced to the main tank when they are too large to fit in the mouths of adult fish — generally around 1 inch in length. Introduce them gradually and monitor for any aggression or predation. If the main tank contains large or aggressive fish, wait until fry are closer to adult size before introducing them.
Separating Males and Females
If you don’t want uncontrolled breeding, separate males and females before they reach sexual maturity at 2–3 months. Males can be identified by their pointed gonopodium (anal fin) from around 3–4 weeks of age. Separating early prevents unwanted pregnancies and population explosions.
See our Male vs. Female Guppy guide for identification help.