Carp aquaponics involves the most widely farmed fish in the world for many excellent reasons. They should be close to the top of your list of fish when deciding what species to grow in any large UK aquaponic system.
Carp are able to survive low winter as well as high summer temperatures. They grow very quickly in warm water and consequently, benefit greatly from greenhouse and polytunnel installations. There is a small but established market for table, restocking and ornamental fish. Most importantly, fry and fingerlings are available at a reasonable cost from a number of specialist breeders. All things considered, carp is an ideal species choice for the larger aquaponic system.
Controlled carp breeding over the centuries has resulted in many different varieties but they all belong to the same species, Cyprinus carpio. The three most important species are;
a) Mirror Carp, Cyprinus carpio
Table producers have concentrated on mirror carp that are characterised by a small number of large mirror-like scales on their flanks. They tend to be more dumpy in shape with a reduced number of fine bones. Early growth, in particular, tends to be rapid but they have tendency to lose shape when grown to specimen sizes.
b) Common Carp, Cyprinus carpio
Common carp tend to be fully-scaled and have a more torpedo-like shape. They resemble more closely the early forms of wild carp. Although carp can thrive in our climate they are not a native species. They were probably introduced by the monks in the Middle Ages and were farmed for the table in local ponds.
c) Koi, Cyprinus carpio
Coloured variations of the common carp have been selectively bred in the Far East for a few hundred years. This has resulted in the development of the modern day koi carp industry. Their beauty and continued popularity has ensured that this remains an attractive and lucrative industry. Primarily based in Japan, koi production has spread far and wide with farms now in Israel, USA and the UK. In respect of their growth and importance I have written a separate fact sheet covering koi aquaponics.
It is important to remember that koi are still the same species as mirror and common carp and will freely interbreed. In fact a cross of mirror carp and koi results in what has become known as ghost koi, named on account of their skull-like markings on their heads. This variety has also become very popular with pond keepers on account of their hardiness, fast growth rates and affordability. Over the years I have produced many thousands ghost koi. The design principles behind carp aquaponics apply equally to all species.
Carp Aquaponics Culture Conditions.
- Water temperature. Carp are generally referred to as a warm water species along with tilapia and catfish. They are able to adapt to temperatures in the range of 0 – 32° C. However their ideal range for growth in 24 – 28 °C with the formed the optimum for food conversion and the latter the optimum for growth. For further information see my article on fish tank temperature.
- Dissolved oxygen. Carp are able to survive comparatively low oxygen levels of around 4mg/l. that can exist in warm static ponds. However, under warm water conditions they consume much higher levels of oxygen than trout. This is an important consideration particularly when stocking and feeding levels are high. See my article on Do fish need oxygen?
- pH. In common with many fish carp are able to thrive in waters of pH 6 – 8. There is no need to attempt to control pH too accurately by adding chemicals, in spite of what many would like us to believe. Buffering nevertheless, is still an important consideration if pH crashes are to be avoided.
- Ammonia. In common with other fish this toxic waste product should be maintained below 0.02mg/l NH3-N. this is not TAN (Total ammoniacal nitrogen) and the two shouldn’t be confused. I explain the difference more fully in this article on fish ammonia.
- Nitrite. Nitrite is also toxic to carp but less so than ammonia. A maximum level of 0.2mg/l is a reasonable guideline for carp. It is not directly produced by carp. Rather it is a result of successful biofiltration and is an intermediate step in the Nitrogen Cycle.
- Nitrate. Carp aquaponics depends upon the production of nitrate to feed the plants. Nitrate is very much less toxic to fish than either ammonia or nitrite. As such a level of 100mg/l. should not be cause for concern. Like nitrite it is not directly produced by fish and results from the successful breakdown of nitrite.
Table Carp Production
In 2013 world carp production exceeded 4.2million tonnes. This represented a 51% increase from 2006 to 2013. 72% of this production occurred in China. In the EU production remains relatively stable at around 78,000 tonnes per annum. The Czech Republic and Poland are the biggest producers with Hungary and Germany also significant. The market is primarily for live fish that are subsequently prepared at home. There is only a tiny market for processed carp. This would need addressing if younger consumers are to be attracted. The market also shows strong seasonality with peak consumption at Easter and Christmas.
In the 1980’s I supplied live carp to the Eastern European and Chinese markets for many years. Although much of this involved live fish I also carried out extensive research into developing a market of processed smoked carp products. A purple built carp processing plant was built to supply smoked carp fillets and smoked carp pate to local restaurants. These products were well received by local and national chains but needed far greater production capability than existed at the time if the market was to be fully developed.
In the UK at least, the table market could not achieve the same selling price as that enjoyed by the more lucrative restocking market that existed for private angling fisheries. Here the bigger the fish the better the price. The problem as far as the small producer is concerned relates to the requirement to sacrifice several fish for disease evaluation in order to satisfy the legal requirements of fish movements in and out of fisheries.
Carp are omnivorous fish and generally require medium levels of protein in their diets compared to carnivorous salmonids. Typically a protein level of 35 – 45% is ideal. Carp are a very adaptable species and can make good use of a wide variety of feeds. In an enclosed aquaponics system there is very some natural food production but this doesn’t really amount to very much. It is wise to feed a complete pelleted food. However, it is an excellent idea to supplement a diet of dry pellets with plants grown in an aquaponic system. In a more open pond carp would immediately eat and destroy the plants thus preventing any further production.
Carp do not have a stomach as such and benefit for a ‘little but often’ feeding regime. As with all fish species the smaller fish eat a higher ration per unit body weight than larger fish. They also have a higher requirement for protein. A large carp of 1kg would probably eat around 2% BWD (body weight per day) where a carp of 1g could eat over 10%BWD.
Carp Fish Tank Design
Carp thrive in moderate to low water flow rates. They can survive well in warm, static ponds in common with tilapia and catfish. Nevertheless, if they are to grow to their full potential under warm water conditions the demand much greater quantities of dissolved oxygen. For this, and other reasons, I would recommend the home operator keep stocking densities below 20 kg/m3.
With regards tank shape I would recommend a round tank. The flow velocity can be controlled by the angle of the water inlet whilst still maintaining a self cleaning ability. Stock capture and grading may be more problematic than a rectangular tank but the wide range of acceptable harvesting weights make this less of a regular task.
Economics play more of a role the larger the fish farm. Small producers are more concerned with quality of product than production costs. The following figures can be used as a yardstick to judge different species and different production systems. Of course carp aquaponics have the great advantages that a significant crop of fresh plants are also produced.
|EU production Costs||1.12 – 1.44 EUR/kg|
|Ex farm||1.95 – 1.97 EUR/kg|
Table 1: Prices achieved in EU Carp Ponds 2013
Prices achievable in the UK are considerably higher than those shown in Table 1. Dead whole carp are regularly offered on a market stall at Ipswich market for £7/kg.(2019). Live carp would command a much higher selling price. If you do not intend to consume your home production yourself I would suggest that you invetigate the market for live fish in the local Chinese and Eastern European communities.
As already mentioned, the angling market presently dominates the UK carp farming sector. Here the bigger the fish the higher the income per unit weight. Fish values jump significantly as weights exceed 10lbs. and even more so if over 20lbs. A 30lb fish would be exceptional and priced individually. The going rate (2019) for fish over 20lbs is £15 -£20/kg making an individual fish fish worth something approaching £1,000.
Much of this information, although interesting, is of little relevance to the home producer. The important thing to remember is that carp grow rapidly and make excellent eating. Fears of muddy flavours should not be taken seriously as fish kept in clean water for a few days rapidly lose any off flavour.
One important consideration when selecting any species of fish for home production is the availability of young fry or fingerlings. Carp score highly on this count , more so than tilapia. When choosing a supplier it is preferable to pick one that carries out their own breeding as small fish cost quite a bit less and grow quickly in an aquaponic system. Fish of 1″ would be ideal but most breeders offer a minimum size of 2′ – 3″. The following farms are able to supply 2″ – 3″. Expect to pay 30 – 40p each for 2″ – 3″ fish or 50 – 60p each for 3″ – 4″ fish. (2019 prices)
It is vitally important for purchasers of live fish and operators of aquaculture and aquaponic systems to familiarise themselves with the legal requirements of fish movements. These are not difficult to comply with and cost very little, if anything. They do however, help protect all fish stocks from the spread of disease. Reputable fish suppliers will be only too pleased to offer advice and assistance. The future of carp aquaponics in the UK is dependent upon upholding excellent biosecurity measures.