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Daphnia as a Fish Food and in Nature

Daphnia is a small fresh water crustacean, sometimes called a Water Flea.  They have the  name 'flea' because of their jerky motion in the water, but they are not even insects, and they do not bite.  There are many different species, but they have some clear similarities. There are also related species in different genera.

The smallest Daphnia may only grow to a millimetre (a twenty fifth of an inch) long, and the biggest may approach ten times this size.

Filter Feeders

Daphnia filter the water, eating the small things they remove.  Their main food is algae, but they will eat things like yeast and bacteria.

Water Purity

Although the water Daphnia grow in often appears dirty, they cannot tolerate pollution. They are used scientifically to make sure water in not polluted.

Breeding

Under good conditions Daphnia can breed at an enormous rate.  A baby Daphniod may be having babies itself at less than a week old. They are are short lived animals, often dying of old age before they are two months old, but they can have a lot of babies in their short life.

Parthenogenesis

When Daphnia are being grown under good conditions, the population is often all female. These females have live young which look like miniature adults.  They are genetically identical to their mothers.

Eggs

When the conditions become less favourable, the Daphnia produce some males.  After mating, the Daphnia produce eggs.  These eggs are very resistant to conditions like heat, drying and cold which would kill the active Daphnia.

When the conditions are favourable again, the eggs hatch.  The babies produced are not normally genetically identical to the mother Daphnia that laid the eggs.  This allows for the mothers more capable of surviving under the conditions of the water body they are in leaving more eggs, and allows gradual, or sometimes quite rapid, change to suit the conditions.

Species and Strains

There are a lot of different species of Daphnia and similar animals, but in addition to this, within each species there are many different strains.  These would still be able to interbreed if they came into contact with each other, but they are distinctly different.

In a single body of water there might be twenty or more different species, as well as variations between different families.

As the weather changes with different seasons, different species or strains of Daphnia become dominant.

Fish Food

Live Daphnia is a good fish food.  Daphnia from water that has no fish in causes less trouble than nearly all types of live food.

Although, some people believe that Daphnia can harbour some types of fish parasite, they are not the main host for these parasites. If there are no fish in the water the Daphnia come from, no parasites will be introduced with the Daphnia.

Food Value

Typically, live Daphnia contain about 50 percent protein and 20 percent fat (expressed as a dry matter percentage).  This is quite high.

Size

Naturally, you want live food of a suitable size for your fish.  In my experience, fish are quite good at eating Daphnia.

 Even small fish like Neon Tetras will eat quite big Daphnia.

Feeding Fry

Once baby fish are big enough to eat them, the fish benefit considerably by even the occasional feed with Daphnia. 

Screened Daphnia and Feeding Fry

In many of the older books on keeping fish, there are mentions of screened Daphnia.  All this means it that they are sieved by passing through a sieve of the right size, separating them into smaller and larger ones.

I often use this method. I catch the Daphnia from the containers we are breeding them in with a fine aquarium net.  Then I pour them through a coarse aquarium net into the fry tank.  The small Daphnia go in to give the fry a good meal. The larger Daphnia left on the coarse net are fed to the larger fish.

If larger Daphnia are put into the fry tank, they will not harm the fry, and will both filter the water and have babies which are the right size for the baby fish to eat.

Frozen Daphnia

This is sometimes available but although it is a reasonable fish food it is not as nearly good as the live form.

Dry Daphnia

This is less commonly available now than it used to be.  Much of the food value seems to be lost.  I assume that this is because of the methods of drying often used for this food.  Personally, I would not use it.

Algae Control

Daphnia will eat large quantities of the sort of algae that makes the water look green.  If you have a bloom of this sort of Algae, adding sufficient Daphnia can get rid of the algae quickly.  However, this method often does not work, simply because the fish eat the Daphnia before they have had time to eat much algae.

Some success has been achieved by putting the Daphnia in a netting box with mesh to fine for the Daphnia to get through, but which allows the water with the algae to go through.

Daphnia and Axolotls

Axolotls of all ages will eat Daphnia and it is one of the best foods of all for raising baby Axolotls.
 


 
 
 
 
 
Live Daphnia for sale
 


 
 
 
 
Female Daphnia Magna (A Large species)
 
 
 
Daphnia pulex (A small species)
By (Photo: Paul Hebert) [<a href="www.creativecommons.org/licenses/by/2.5">CC-BY-2.5</a>], <a href='http://commons.wikimedia.org/wiki/File:Daphnia_pulex.png'>via Wikimedia Commons</a>