The amazing Daphnia water flea

by Owen James

Daphnia are fascinating under magnification, not that your fish will wait two seconds before swallowing them!

Daphnia are fascinating - not that your fish will look twice before swallowing them!

Today’s tropical fish foods are a world away from those of even my youth. And my father’s generation had to make do with biscuit-based dried foods as the staple of choice for their fish.

The huge variety of flake, pelleted and freeze-dried food we enjoy today is a real treat for modern fishkeepers (or rather, our fish!). Add in a smorgasbord of frozen foods and it’s pretty easy to keep tropical fish in top condition.

Old-time aquarists were much more familiar with feeding and breeding live foods such as Daphnia water fleas, however, and I believe this was to the benefit of their fishes.

Wives (or husbands!) might not have appreciated shoe boxes of nasty-sounding grindalworms or vinegar eels tucked into the linen closet, but their fish often did.

Early tropical fishkeepers put much of their breeding success down to feeding a wide range of live foods. Dried foods of the day just didn’t cut it.

Even today, fish breeders swear by live foods as a method of getting their fishes in the mood.

Introducing Daphnia: The water flea that isn’t

Feed your tropical fish Daphnia just once, and you’ll never again say live foods aren’t worth the effort.

It’s true tropical fish can grow, live and die on flake food, but variety is the spice of life and their lives are undoubtedly spicier for the occasional treat of Daphnia.

Daphnia are small water-born crustaceans, between 0.2mm and 0.5mm in length. They’re not fleas; the name comes from the way they seem to ‘hop’ through the water as they swim.

Daphnia aren’t particularly pretty to look at, but if you do put them under a magnifying glass you’ll find their rounded, fused bodies are usually completely translucent, so you can see everything from eggs to their beating heart. (They are used in the study of alcohol poisoning on the body for this reason). You’ll also see the legs that most Daphnia use to filter algae from the water for food.

Almost any body of freshwater in temperate regions is liable to contain Daphnia, particularly water rich in organic matter and yet low in predators, such as a muddy wallow in a farm.

If you’ve got a wildlife pond in your garden, you’ll almost certainly see Daphnia in summer – assuming your sticklebacks and minnows don’t snap them up first.

Although as aquarists we lump all Daphnia under that single name, there are actually a great many species. Some are carnivorous, preying on other water fleas. A few species with very restricted local distributions are threatened in the wild.

Feeding Daphnia to your fish

Common Daphnia is abundant in nature and in the fish trade. You can catch your own from a local pond in spring or summer, but the easiest way to start feeding Daphnia is to buy some at your local aquarium shop, where they are sold in small bags.

Unpack a bag of Daphnia as soon as you get home, since the tiny creatures can easily die from lack of oxygen or over-heating.

Either feed them to your fish immediately, or else pour the bag and water into a shallow vessel, such as an old ice-cream tub. Put the Daphnia in a cool part of the house until you’re ready to feed your fish, which you should do within 24 hours.

Before feeding Daphnia to your fish, do a quick check to ensure there are no obvious predators in the water.

Here in Europe you sometimes find water boatmen mixed in with Daphnia. These hard-shelled crustaceans are predators, and should be removed before feeding, especially if you’re feeding Daphnia to small fry. Look out for leeches, too. The odd stray tubifex worm or similar will be eagerly eaten, but remove anything you can’t identify.

If you’ve transferred your Daphnia to a tub, then a fine-meshed fish net will enable you to capture a fraction at a time for feeding. You can even use meshes of different sizes to grade your Daphnia if you’re feeding fy.

Grow your own Daphnia

Daphnia is very easy to farm in your own garden.

Get a big wide tub, or construct a small nature pond, and strew some old vegetable peelings across the base. Wait a week or two for the water to turn green. Add shop-bought Daphnia or some you’ve captured from a local pond and watch the population explode.

One problem with backyard culturing is it can encourage mosquito and gnats, which will lay their eggs on the surface. The simplest solution is to run your net over the surface of the water every few days to capture the mosquito larvae before they wriggle to the bottom or hatch.

Feed the larvae to your fish, too. They’ll devour them eagerly.

Is Daphnia safe to feed fishes?

Daphnia is about as natural as live food for tropical fish comes, unlike say worm cultures, which can be very fatty and present dietary problems in excess. You can feed your fish all the Daphnia you can find.

People are often worried about introducing fish diseases, which in folklore can be introduced to aquariums with live food.

I’ve never had problems feeding Daphnia, and I suspect that most incidents of diseases arising in aquariums that do have issues after feeding live foods come from pollution.

That said, fish diseases are strange things, with the larval stages of some parasites using other creatures in the ecosystem as hosts.

Personally I wouldn’t worry too much – professional fish farmers feed Daphnia to their fish by the bucket load. If you culture your own Daphnia on your doorstep in a fishless pond or tub, you won’t have any problems.

Incidentally, marine fishkeepers can feed Daphnia, too. It won’t last long in saltwater, so only feed small quantities that are snapped up as soon as they hit the water.

Further reading on Daphnia

Give Daphnia a try. You might just find your fish reward you with renewed vigour and maybe even breeding.

Check out Katy's Tropical Fish Guide for more aquarium info.

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{ 1 comment… read it below or add one }

su xi tian 07.20.09 at 1:36 pm

Dear madam, sir:

I’m very interested in culturing Daphnia magna, but I couldn’t find it at all.

Do you have the resting eggs of Daphnia magna? Could you please send me

some? Thank you very much! Have a good day.

My address

2, Jalan Midori 3,
Taman Midori, 86200
Simpang Renggam, Johor
Malaysia

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