Dedicated to Fancy Guppy breeding in the UK
‘Food for thought’ © – by David Rodgers
Why feed live daphnia?
The benefits of feeding live daphnia have long since been recognised by fishkeepers. I was aware of this fact for some time; however, just how important daphnia were from a historical perspective was totally unknown to me.
It was only recently when browsing at a charity car boot sale that I stumbled across a book ‘Exotic Aquarium Fishes’, by Dr. W. Innes.
Reading through the chapter on live foods, I was particularly interested in a photograph showing American aquarists netting their own daphnia. Judging by the makes of cars in the background, the photo dates to post 1932, incidentally, around the year that the first edition of the book was published. It was remarkable to see that pioneering fishkeepers from this era had already realised that they were on to a good thing with live daphnia.
Back then, processed dried foods of good quality were not available, there was a high dependency on daphnia as a regular food source.
Thankfully, nutritional technology has come on a long way since then and modern dried foods do contain the majority of nutrients required by fish.
However, feeding fish on a balanced diet of proprietary dried foods and live daphnia will yield results that only speak for themselves. Fish will display greater health, vitality and vibrancy of colours when fed on a balanced diet.
So what are some of these benefits of daphnia?
There are many sources of published information on ‘red daphnia’ containing a higher haemoglobin content which accounts for an increased percentage in protein. This is mainly the case when daphnia are grown in water with low to moderate dissolved oxygen content.
The redness colouration in daphnia is also associated with lipid based carotenoids. Fish are only able to derive these caretonoids from their foods (Evans, 1998). The caretonoids in fish food leads to deposition of brightly coloured polyene pigments in the yellow/orange and red pigmented skin cells in fish, otherwise known as xanthophores and erythrophores.
The hard shell of daphnia is made of chitin and has usually been dismissed as indigestible. Chitin has limited digestibility when fed in controlled amounts, this is especially the case in carnivorous fish (Lindsay, 1985). Chitin has also been identified as an immuno-stimulant, thereby aiding the natural immune response of the fish (
Why feed live daphnia as opposed to frozen daphnia?
For both the novice and the professional fish breeder, intensive fish culturing requires intensive feeding regimes. For this reason the fishkeeper may have to rely upon frozen daphnia to bulk up daily feed intake. There are commercial suppliers of good quality frozen daphnia, however, during the freezing process ice crystals lyse the cellular tissue in the food and destroy cell membrane integrity. Upon thawing some of the essential nutrients and vitamins leach out from the tissue and into the surrounding water.
This has several implications, excess leaching of nutrients into the water will cause havoc on biological filters due to the organic overload. For the enclosed aquarium slight fluctuations in excess organic nitrogen will only lead to subsequent surges in ammonia and nitrite levels.
Additionally, the fish are deprived of these essential nutrients that leach out and only defeats the purpose of feeding freshly prepared foods.
In contrast to frozen daphnia, live daphnia can only be described as pre-packaged morsels of food containing those additional nutrients and they are non-polluting in the enclosed aquarium. This is particularly useful when feeding gravid female livebearers within the breeding tank. Swarms of live daphnia can be added to the breeding tank and during this time she will happily consume live daphnia at her leisure. Any surplus daphnia in the tank will remain alive for many weeks after their introduction to the breeding tank, thereby not polluting the water or overloading the filter.
Live daphnia can also serve as a useful food when trying to acclimatise wild fish to captivity. Very often newly acquired fish will not readily feed on dried or frozen foods.
Supplementing the diet with live daphnia will also bring fish into breeding condition. In some cases the feeding frenzy associated with live daphnia will even induce spawning in egg laying fish.
Why culture daphnia as opposed to collection of wild daphnia?
My only advice to collecting wild daphnia is not to take unnecessary risks. Daphnia from wild sources serve as a sole food source for many native fishes, especially for the fry and juvenile stages. You can rest assured that for the majority of water bodies that contain daphnia will also contain fish. Wild fish stocks have many diseases that are endemic to the population.
Epistylis sp and Vorticella sp are just some of the most common parasites associated with wild daphnia. The daphnia from wild sources will also harbour pathogenic bacteria, mainly Aeromonas and Pseudomonas sp of which there are several different pathotypes.
Even for daphnia sourced from ponds that are ‘fish free’ there are risks involved. Many amphibians will be resident in such ponds and they are carriers of a protozoan Tetrahymena pyriformis. During my time as a student I had encountered a prolonged problem with Tetrahymena pyriformis in livebearers. Ironically, this is also referred to as Guppy Disease (Glass, S., Aquarium Quarterly - Guppies) Tetrahymena will decimate fish fry stocks and the disease is usually attributed to poor water quality, however manifestations will even occur in the most pristine conditions.
Successful artificial culturing of daphnia can be achieved all year round, whereas wild populations tend to flourish only in the spring and autumn. Wild daphnia are self limiting in that accelerated numbers cause depletion of the food supply, therefore the pond is no longer able to sustain such high numbers. For propagation of daphnia in culture it is possible to attain several thousand daphnia per litre of water. (Pillay, 1990). There are complex mathematical models for growth kinetics of daphnia, although in layman’s terms you simply need to feed the critters.
Cultured daphnia fed on a diet of mixed algae and supplements will also have higher protein content and higher fecundity (Murphy, 1970).
References
Baldwin, G. (2000) Practical Fishkeeping Magazine, December issue.
Evans, D.H. (1998) The physiology of Fishes, 2nd edition
Glass, S., Aquarium Quarterly – Guppies (YB-032), T.F.H. Publications
Innes, W. (1966) Exotic Aquarium Fishes, nth edition
Lindsay, G.J.H. (1985) Chitinolytic enzymes and the bacterial microflora in the digestive tract of cod,
Gadus morhua. Journal of Fish Biology, 26, 255-65
Murphy, J.S. (1970) A general method for the monoxenic cultivation of the Daphnidae,
Bio..Bull., (2):321-332
Pillay, T.V.R. (1990) Aquaculture, Principle and Practices,
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