Why Do Guppies Eat Their Babies? Causes and Fixes

Why do guppies eat their babies? Picture this. One evening you see that your full-figured female guppy is hiding near the heater. In the morning she is skinny. You move closer to a plant and notice three small baby fish, or "fry" attached to it.

Just three. But a guppy is capable of dropping a much larger brood.

Where did the rest go, then? For most tanks, the truth is, it's an uncomfortable one. The adults fed on them. Occasionally the mother joined in herself.

It feels cruel. Still, it is not. So why do guppies eat their babies? This is how it was typically run.

Guppies are livebearers. The female does not lay eggs, but instead gives birth to free-swimming fry. She does this quietly quite frequently. Numerous owners overlook the birth entirely.

The fry are very small, hesitant and slow. Most dart right up to the surface or go into the plants. Any fry remaining in open water stay exposed.

Guppies do not provide any care after birth. There is no instinct which tells the mother to protect her young. A small moving speck is merely a food item to the adult guppy.

This behaviour has a name: filial cannibalism.

There are a number of theories about it in the hobby guides, and they don't line up nicely. Hunger, particularly in a recently-delivered female. Discarding less vigorous fry that are unable to escape. Mother building up body reserves. But none of these is completely adequate to explain it. Male guppies eat fry as well. The best guess is that it is simple instinct.

This is something that many owners don't think about. Not all the missing fry ended up inside a fish.

The filter is another unheralded culprit. An unguarded filter intake can suck fry in at night. Also, strong water flow can exhaust fry, forcing them into open water where the adults find them.

Some fry starve slowly. Easy to miss, this one. Adults finish food in seconds. Fry should have smaller portions of food throughout the day. They are also more vulnerable to ammonia and nitrite than adults are, and water thought to be suitable for adult fish may quietly harm a brood, without making a single ripple.

So if they go missing, don't blame the mother just yet. Look at the filter, water flow and water first.

If you make a couple of changes, the subsequent birth in the same tank can be different.

Plant densely near the surface. Fry can enter fine-leafed plants like java moss, hornwort and guppy grass, which the adults do not follow so easily. Floating plants over part of the surface conceal fry from above. However, do leave some water open to allow light and air to circulate.

Then the filter. Gentler or guarded. The gentlest option is a sponge filter. If using a hang-on-back or canister filter, cover the intake with a sponge.

Maintain a more subdued atmosphere in the tank, and keep the adults well fed. Offer them small meals one or two times a day. Hungry fish are more aggressive in their search for food. Do not overcrowd, as this increases stress and competition.

If used wisely, a birth space can help. A breeder box or a separate planted tank is best. However, only move the female when she appears to be near giving birth. A long stay in a box would stress her, and problems with the birth can occur if she stays there too long. Return her to the main tank as soon as she delivers, so she cannot consume the fry. A few guides caution that you should not keep fry in a breeder box for more than approximately 2 weeks.

When you observe new fry, remain calm. Do not disturb the tank. Feed the adults a small meal to keep them occupied with food.

Do you need to relocate the fry? Avoid using a net as this can injure them, use a small cup or spoon instead. Use water from the same tank, of the same temperature, not fresh tap water.

Offer dry, crushed flakes or fry food to fry several times daily.

There is no certain age to be safe. Unfortunately, no neat number. The general rule is that fry should be too big to fit in the mouth of all fish in the tank. Even in that case, be extra vigilant about them following their relocation. If adults continue to pursue them, move the youngsters back.

It is not a bad mother if a guppy eats their babies, it is normal fish behaviour. You will not save all the fry. In a nutshell, however, three survivors can be a healthy little school, with the help of plants and a safe filter, steady water and well-fed adults.

This is your first time keeping fish in India? Visit our beginner's guide to setting up a fish tank. Interested in another mystery on the tank? Read why betta fish make bubble nests.