Koi, goldfish natural pond diet

The naturally occurring high quality livefood encountered by fish in the natural pond environment is the envy of commercial food manufacturers who try to match the high standard set by nature in an artificial bait. In a totally natural pond or lake situation the success of a fish population (being at the top of the food chain) is governed by the quality, quantity and diversity of its naturally occurring diet lower down the food chain.

So intricate and interdependent are the levels of such a food chain (often aptly called a food web) that the productivity of the more visible and apparent inhabitants (fish and other vertebrates) is largely dependent on the success of the microscopic and less visible plant and invertebrate animal life.

It is said that if you look after the pennies and the pounds will look after themselves, similarly if nutrient levels in the water are high (eutrophic) promoting prolific microscopic phytoplankton growth then it is highly likely that such a water body will support a large biomass of fish. It is as a result of this principle that fish farmers fertilise their ponds prior to stocking, ensuring an abundance of live food for fry.

The carp (Cyprinus carpio) is an omnivorous opportunistic feeder gifted with a keen sense of smell, using its ‘snout’ to dig about on the pond bottom, often making the water turbid. It is a truly wonderful, resilient and adaptable fish capable of high rates of growth and production in a permanently changing and dynamic food environment.

Being omnivorous fish, carp will consume a diversity of invertebrate life from a range of areas be it the water’s surface, within the water column, or from the muddy pond bottom. Carp also eat plants both microscopic phytoplankton (probably inadvertently) and macrophytes such as oxygenating weed. In other words, if an object appears to have some nutritional benefit and it fits in their mouth carp will try it, spitting it out if undesirable. In this way the carp earns its title as ‘the pig of the pond’.

Phytoplankton, the organisms which cause (or rather are) greenwate consist of single or multicellular complexes are pelagic organisms which are highly nutritious. Colonising single-celled diatoms have silica impregnated carbohydrate cells walls and within which is a highly nutritious viscous soup of organelles such as mitochondria, nuclei and chloroplasts (all rich in protein) together with oil droplets and algal pigments (chlorophyll, carotene and xanthopyll). The cytoplasm also contains the products of photosynthesis such as starch, glycogen as well as other sugars and is also a rich source of vitamins, macronutrients (Carbon, oxygen, nitrogen, sulphur and potassium) and micronutrients (iron, manganese, copper and zinc).

The nutritious phytoplankton are consumed by herbivorous zooplankton such as Daphnia which absorb and assimilate these algal nutrients, concentrating the food value of their prey so that they themselves have a higher nutritional value than the algae. Similarly those phytoplankton that die off, sink and biodegrade on the pond bottom, are fed upon by detrivorous invertebrate life. In this way a good supply of food is made available to carp not only be virtue of the increase in size of the organism (single celled algae into zooplankton) but also an increase in quality of the food (plant protein into animal protein).

Carp consume these larger aquatic organisms at different zones within the water column (mosquito larvae – upper, Daphnia – middle, tubifex worms – bottom) and these carp food organisms can be grouped into the following classifications of organisms:


Insects and insect larvae,





Crustacea are mainly aquatic organisms possessing a calcareous exoskeleton.


Water Flea (D. longispina, D. pulex) …. These are small filterfeeding crustacea consuming large quantities of phytoplankton, small infusoria, suspended detritus and even bacteria. These have an interesting lifecycle where an overwintered egg hatches into a female which, without fertilisation, can produce at least 150 liveborn baby daphnia which in turn reproduce parthenogencially. Consequently they proliferate very quickly being clones from a single egg.

Interesting note: At the PROKOI farm recently, daphnia have been shown to filter particles of oxolinc acid from suspension which if desired, can then be fed very reliably to fish as an effective means of administering antibiotic.

Gammarus Freshwater Shrimp (G. pulex) …. Unlike the daphnia this is a benthic organism, feeding on decaying organic matter. It is a filterfeeding organism being found at the mud/water interface in amongst roots and leaf matter.

Asellus. The Water-Hog Louse (A. aquaticus). Again this is a benthic detritivore, being a close relative and very similar in appearance to the terrestrial woodlouse.

Insects and Insect Larvae

Besides the occasional fly taken at the surface, carp will consume insects in their larval form while they inhabit the aquatic environment prior to metamorphosis. Adults are airborne in the final stage of their lifecycle.

Black Mosquito Larvae (Culex pipiens). This prolific food occurs seasonally in mid to late summer hanging just under the water surface with its airpipe appendage protruding into the atmosphere. Mosquito larvae are easily disturbed, reacting with an erratic downward movement to avoid possible danger.

Interesting Note: Some fish species have such a high affinity for this larvae (eg the guppy) that they have been introduced as a biological control in Tropical areas against these carriers of malaria.

Bloodworm. Non-stinging Mosquito Larvae/Midge Larvae (Chironomous plumosus).

This is a popular livefood in the aquatic trade, coloured bright scarlet by its high haemoglobin content. Averaging 3/4 inch long it moves vigorously looping its body in a figure of 8 moton. Bloodworms are picked up in the water column and on the pond bottom.

Glassworm. White Mosquito (Chaoborus sp.) … This giant larvae is less abundant than the bloodworm being similar in form but white instead of red. It inhabits the same niches in the pond as the bloodworm, feeding on detritus and small organisms.

Other insects and insect larvae are present as food for the wild carp such as the larvae damselflies, dragonflies and mayflies. These are significant food organisms for adult carp but are predators of carp fry. For this reason carp farmers exclude them from their fry ponds by treating with organophosphate insecticides a week to 10 days prior to stocking out with fry.


These are wholly aquatic invertebrates being largely benthic in location and detrivorous by nature.

Tubifex/Sludgeworm (Tubifex tubifex)

This benthic worm lives in a mucus lined tube excavated in the mud on the pond bottom. It lives head down in the mud wafting its tail in the water to gain oxygen and food (suspended organic matter) from the water current. If undisturbed they will colonise a large area but will retreat into their tubes if disturbed. However the carp’s burrowing snout will detect the worms and readily consume them.

Square-tailed worm (Eiseniella tetrahedra) Relative to the earthworm, burrowing through organic matter exhibiting habits similar to its terrestrial relative. Due to its size the square-tailed worm is more of an important food source for adult carp and is also responsible for breaking down organic matter making it available for smaller detrivores such as protozoa and bacteria.


Briefly, these include all snails, small bivalves and their eggs. Equipped with pharyngeal teeth to the rear of their buccal cavity carp are able to grind, crush and masticate the shelled molluscs and other chitinous invertebrates. This enables them to feed on otherwise indigestible organisms, disintegrating their structure prior to ingestion.

Aquatic Plants and Algae

Plant life plays a significant role in carp nutrition in the provision of roughage, plant proteins and certain vitamins and minerals. Wild fish tend to utilise animal protein rather than plant carbohydrate as a source of energy as there is rarely a limit on the ubiquitous animal protein. However in commercial diets it is cheaper to feed carp artificially on a carbohydrate/protein mix where carp posses the required enzymes to cope with the digestion of starches and disaccharides. This reduces the need for expensive protein resulting in a decrease in the price of food. But if live animal protein is limited in the wild it also means that carp can quite easily switch their diet to one of significant carbohydrate content.

Carp will feed on range of aquatic plants such as the roots, tubers and seeds from marginal plants (reeds, irises, lilies, bogbean, watermint) and the filamentous mass of blanketweed. A plentiful supply of fresh green matter is ideal for the conditioning of broodstock. Even if only partial digestion of such tough plantlife is possible then at least benthic detribores can continue the breakdown of the faecal pellets until they too become valuable food organisms. Submerged plants such as oxygenating plant (Elodea densa) are usually soft and very palatable to carp and are of extra nutritional benefit in that they support a whole range of invertebrate food organisms for other invertebrates to feed on besides carp.

In conclusion, having looked briefly at the natural diet of carp it is important to say that this has only been a simplified account of the natural carp diet in terms of the food species mentioned and the exact nutritional qualities of each food organism. The nutritional status of zooplankton within a pond can fluctuate daily. There can also be differences in flora and fauna between two ponds just a metre apart! The age of the pond and its nutrient status (eutrophic – rich, oligotrophic – poor) determines to a great extent the food species quantity and diversity with older more mature ponds providing a richer and more diverse menu.

Even within a given pond the carp diet is constantly changing with seasonal constraints on algal growth and larval biology. However, what is common to nearly all pond systems is that the food webs are highly complex and intertwined relationships (even within the confines of a pondkeepers external biological filter) where primary production in the form of phytoplankton growth results in the reproduction of a dynamic range of food organisms. It is therefore amazing what nature can achieve through the highly adaptable carp which not only survives, but thrives and goes on to breed in nearly any pond environment.

Kill blanketweed and string algae.