Daphnia and fishing

Daphnia fly

So what is Daphnia? Daphnia is an aquatic crustacean commonly called water fleas because of their swimming style which resembles the movements of fleas. Daphnia live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers. An individual Daphnia’s life span is dependant on certain factors, water temperature and the amount of available food and predators. They can live for 12 to14 months if water temperature remains favourable.

Predation can also have a large impact on life span. In the UK due to low seasonal variations the life span is 5 to 8 months. Towards the end of the growing season the females produce tough resting eggs or winter eggs which can endure extreme cold, drought and low food levels. These resting eggs are protected by a hardened shell and emerge when conditions are more favourable, mild water temperature etc...

Daphnia Clouds


Daphnia cloud

At certain times of the year on some lakes in the UK vast clouds of immature Daphnia proliferate. During the later stages their of development these baby Daphnia can easily be observed form above. In the early stages the immature Daphnia are almost transparent and hard to see, as they mature however their coloration becomes darker and orange in appearance. Like a huge shrimp soup the Daphnia will drift in the upper layers of water especially on sunny days, they will change depth as the weather becomes dull. On lakes where Daphnia is abundant the fish in the lake will take full advantage of this food source. Usually beginning in May and lasting through to July (depending on water temperature)

Daphnia will go through stages of development until eventually becoming almost adult size and sinking. They will then seek sanctuary in weed and bottom debris. On a particular lake that I spent many years fishing I used to observe this Daphnia life cycle. Many fish less nights and days passed before I realised that the carp (and others) were totally pre-occupied on the Daphnia. At dusk and on bright nights carp could be seen moving amongst the orange clouds with their heads protruding above the water surface as they cruised along sucking in the shrimp soup. The lake in question was over 90 acres with a carp stock estimated at around 100. With such a low stock density could it be that there just was not enough carp to have any impact on the Daphnia, I am not sure but what I do know was that it was a waist of time for me to carp fish from May to July.

So, what can we do if Daphnia are effecting our fishing. Go Bream fishing! Only joking, no but seriously I do have a trick up my sleeve which has caught me a couple when all else has failed. I looked to fly fishing for some inspiration and realised that fly fishermen have known about the effect that Daphnia can have on Trout and they have devised flies to act as imitation Daphnia or rather a group of Daphnia. I normally use an orange Blob fly for times when they're feeding heavily on daphnia. You will need a Fly Rod which is adequate for playing carp and a heavy fly line. Just cast it out on a slow sinking line. Straighten the fly line. And then use an ultra-slow, figure-of-eight retrieve in order to stay in touch with the Blob as the fly line slowly pulls it beneath the surface and to greater depths.

Stock density and other factors mean that on many lakes the Daphnia doesn't have the chance to regenerate to such an extent. If the fish stock density is high then Daphnia numbers will be reduced substantially and the vast clouds will not have the same chance to establish. This phenomenon seems to occur on large, low stocked waters.