How to solve a problem like unexpected fry


Nathan Hill advises how to keep fry safe before they become breakfast for other tank residents.

The biggest issue with spawning is finding hiding places. In the confines of a tank and unusually high stocking densities of captive fish, fry have nowhere to go to evade big mouths…

The fact that most aquaria are painfully sparse of anywhere suited to fry concealment compounds this issue.

So the first thing to do is provide cover. Live plants are best, especially bushy, frondy varieties, but unlikely to be available at short notice — in which case it’s time to improvise!

An immediate way to provide cover is to use marbles or smaller rounded stones densely packed together. These will then make a miniature network of caves that fry can fit among, but the mouths of larger fish can’t. However, this will involve quite a lot of marbles or small stones and, of course, there’s the risk of crushing some fry during 'landslides'.

Transferring fish to a breeding trap is a great way to both monitor numbers and progress, but first you’ll need such a trap!

If you don’t own one, don’t panic, as you can make a temporary one from everyday objects around the home. An old net, free of holes, strategically placed so it has a flow of water passing nearby it will contain fry — but doesn’t leave them immune to fish pecking at the other side of it. Nor does it always keep its shape, sometimes folding and trapping some young.

Alternatively, a margarine tub, or Tupperware-style bowl, will make a superb temporary trap once thoroughly cleaned and rinsed. Tiny holes should be made to allow the passage of water and pollutants into and out of the trap, but not large enough to allow the fry to escape.

If in doubt, then use an old pair of tights to provide a mesh cover over the holes. Slot the tub through a hole cut into some polystyrene to keep it floating, or improvise a way to hold it in place. A couple of small holes with some string running through them usually offers a start at anchoring the trap into place.

Catching fry to transfer them must be performed delicately, as tiny fish bruise and damage easily. If using a net, the mesh must not be so large as to snag around their bodies. Only the finest texture nets should be used, never coarse ones.

Some aquarists prefer to use a very large pipette or a turkey baster to gently suck the fish up and transfer them.

Feeding the fry ideally requires cultured live foods, although some excellent liquid and powder foods are available. If unable to get hold of these, then the powdered yolk of a boiled egg, or dust from a flake food tub will give many livebearers a full belly.

A liquid food for egglayers should be sought at the earliest opportunity — at the least by the time they use up their nutritious yolk sacs. If the laying behaviour is spotted early enough, you might have time to get a mix of infusoria brewing….

Grow your own infusoria

1. Take a jar of water from the aquarium and place it on a windowsill in direct sunlight and without a lid. If using tapwater, ensure it is dechlorinated first.

2. Feed your jar with a bruised lettuce leaf and an algae wafer.

3. Wait. The water will go cloudy as bacteria blooms on the decomposing food.

4. Wait some more. Eventually the water will go clear. This will now be the infusoria feeding on/competing with bacteria.

5. Add a couple drops of the infusoria liquid to the breeding trap. Too much will cause pollution and green water issues.

6. The culture will last for about three or four days, so prepare more than one culture at staggered intervals. Use your infusoria from the existing jars to 'seed' fresh jars.

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