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This Report has been prepared


Miss Bernice Brewster


BSc(Hons), incorporating marine biology, animal physiology, vertebrate anatomy, invertebrate phylogeny, genetics, mammal anatomy and phylogeny.

Fellow of the Linnaean Society

Chartered Biologist

Member of the Society of Biologists

Member of the Institute of Fisheries Management

Chartered Environmentalist

IdQ Freshwater Fish


Natural History Museum, London 10 years in the Fish Section, working with British freshwater and marine fish and the African tiger fish Hydrocynus.

Koi (UK) Ltd pathology and husbandry of ornamental fish from 1987 – 1991

1991 – current self employed fish biologist, Aquatic Consultancy Service

1992 – 2001 Consultant to Tetra

1996 – 1999 part time lecturer Sparsholt College

2005    Temporary part time lecturer Hadlow College

2007 – current part time lecturer Kingston University

2009 – current external examiner University of Greenwich

Research Projects

  1. Information resource on parasites of British Freshwater fish
  2. Distribution of Anguillicoloides crassus in the common eel, Anguilla anguilla
  3. Investigating the life cycle of Eustrongyloides sp. affecting trout in North Wales
  4. Impact of cormorant, Phalacrocorax carbo on the fish parasite Ligula intestinalis

Report for RCAS on the feasibility of growing carp.

This Report is based on discussions held at RCAS Club on 17th April, concerning the feasibility of taking eggs from the fishery and growing carp to approximately 2.25kg (5lb) in weight, a size which are not susceptible to cormorant predation.

1) Mass carp spawning

The first point to be aware is there is no control over the quality of offspring by taking eggs from the lakes.  Whilst the carp may have grown to a large size in the lake, there is no guarantee the genes they pass to their offspring are for similar sized fish. The eggs selected are from mass spawning and does not necessarily mean the offspring will become as good a strain of fish as the parental varieties.

The inheritance of scale pattern in mirror carp includes a lethal, dominant gene which means that some crosses will invariably result in 25% mortalities of the embryos or shortly after hatching.

I believe that during the course of our discussions I was told the eggs would be taken from a lake which is only stocked with carp.  Other mixed stock lakes there is a possibility the eggs taken are from other species of fish.

2) The eggs

Fish eggs are quite delicate and do not respond well to ‘shocks’, which can result in deformities.  In the hatchery environment, the eggs are placed either in Zoug jars or hatchery trays, which are easy to manage and dead eggs removed by water flow.

Outside of a purpose built hatchery, the most suitable means of maintaining the eggs would be an aquarium, as the growing embryos consume significant amounts of oxygen and produce a large amount of nitrogenous waste as ammonias which must be removed from the water or it will kill them.  Most modern aquaria are designed with filtration systems with carbon impregnated foam to remove ammonia when initially stocked and the biological filter foams are often seeded with beneficial nitrifying bacteria to allow the system to start rapidly and without undergoing ‘new tank syndrome’.  

Historically, new tank syndrome killed more fish than true disease.  New tank syndrome arises because the nitrifying bacteria in the biological filter are unable to oxidize the ammonia waste produced by the fish to nitrate in a new tank and filtration system.  Ammonia accumulates in the water and is a potent poison, causing the stocked fish to die.

3) Hatching

Hatching of eggs is temperature and oxygen dependent.  In ideal water temperature (180C +) hatching can take place within 2 – 3 days.  The tiny larvae (on hatching, fish are larvae because the fins and other organs are largely undeveloped) utilize an enzyme on their backs to dissolve the eggs shells as the oxygen concentration drops within the egg.

4) Swim-up

After hatching, the larvae continue to feed using the remains of the yolk from the egg and continue to develop fins and are known as fry.  At the point at which the yolk has been consumed, the fry undergo ‘swim-up’.  The fry swim to the water surface and gulp air, which is swallowed and used to inflate the swimbladder and at this point the fry become active and must start feeding.  At this stage it is essential there is suitably sized food available for the fry.  In the absence of any food, these tiny fry will die within a couple of hours and in the absence of any hard tissues, decomposition is extremely rapid, leaving many people to puzzle over the disappearance of the fish.

5) Foods for fry

Frozen brine shrimp can be purchased from companies such as TMC and used as an initial feed, or alternatively feed manufacturers such as Skretting, produce a feed for fry known as crumb.  Clearly with companies such as Skretting, there is a minimum order usually 1 tonne.  Bear in mind these feeds don’t keep once opened, are expensive and probably the least cost efficient way of raising a few carp.

The final alternative is to prepare live food, known as infusoria.  This must be prepared in advance of the hatch as it takes about two weeks to prepare, using roughly 100 – 200g hay placed in a bucket and boiling water poured in and left to allow microscopic rotifers and other organisms to accumulate to feed on the decaying hay.  The boiling water is used to sterilize the bucket and hay.  The preparation of the live foods must be ongoing to ensure enough food for the rowing fry.

In an emergency, it is possible to feed the fry with hard-boiled egg yolk but this does cause significant water pollution.

Crushed fish pellets are not suitable to feed fry.  The nutrients are carefully balanced for the pellet size.  Crushing or grinding the pellets to feed the fry doesn’t ensure an even mix of essential nutrients and vitamins, which can lead to the development of nutritional disorders as the carp grow, such as spinal deformities or foreshortened gill covers.

Taking plant material from the one of the lakes which may have suitable rotifers and other microscopic food attached is potentially risky as it will include bacteria and fungal spores, which can potentially wipe out the entire population of fry as their immunity is undeveloped at this stage.  Effectively they will have been reared in isolation from the natural pathogens in a lake.

6) Cannibalism

As the carp fry grow, some will start to feed on their siblings and will grow at a much faster rate – the finest feed for any growing fish, is fish protein.  Cannibalism is common within a confined environment such as an aquarium, as the prey find it difficult to find refuge.  

It is quite possible in an aquarium environment to start with 100+ fry and end up with less than 10 big carp fry.  The expenditure of aquaria and food doesn’t really justify the cost of rearing approximately ten fish.

7) Growing fry – juveniles

The only effective way to keep carp growing is by constantly thinning out the stocks, reducing competition for dissolved oxygen and feed and maintenance of good water quality.  The more carp maintained in any one aquarium or vat the greater management input is required.

The more carp contained within one area, the more likely there will be an instance of disease outbreak, for example white spot.  Contained fish stocks need to be regularly assessed for signs of disease and it must be dealt with quickly.

8) Disease outbreak

It is a certainty that at some point, there will be an outbreak of disease.  Can the disease be identified, appropriate treatment applied and most importantly considers the disposal of treated water.

Personally, I have great anxieties surrounding an outbreak of disease within this cultivated stock and the potential to transfer disease to the stocks in your lake by accidental cross-contamination, or even a well-meaning desire to help by transferring sick fish to a lake.

Disease happens - it is an important issue which you should consider carefully.

9) Vats and filtration

The alternative to rearing in an aquarium is simply placing eggs and plants into a vat and hoping a suitable number will hatch and become fry.  Initially the volume of water in the vat will be adequate to maintain the water quality but as the fish grow and ammonia production increases, there must be some means of filtering vat water or, arranging a flow through system, clean water in, waste water out.  Unmonitored flow through systems always have the potential for a disaster, where the vat either overflows and the fish will leave with the water, or it drains down, leaving the fish stranded.

Considering the cost of vats, Aquosis are the best on the market, I use these myself for temporarily holding fish.  Vats with an11,000 litre (3,000 gallon) capacity start at about £1500 prices rising to over £5,000 for 45,500 litre (12,000 gallons).  Alternatively, Aquosis will quote for custom made vats.

Web site: www.aquosis.co.uk

In the initial stage of growing the carp a single 11,000 litre vat may be suitable but to achieve carp of 2.25 kg (5lb) will require thinning the stock out.  Assuming you wish to produce 25 fish, once they reach about 500g in weight, after about 18 months, the carp will need to be separated into further vats or ponds.

Filtering the water may be a viable alternative.  There are numerous pond filters on the market with differing levels of maintenance but be assured there is no such thing as maintenance free and blocked filters can also lead to overflowing or drained vats.

The price of filtration systems can vary from a few hundred pounds to systems such as the Nexus range (and which would be my recommendation) produced by Evolution Aqua and which start at about £1,000.

Web address: http://evolutionaquamarketing.co.uk

Finally, there is an additional ongoing cost of electrical supply for pumps and aeration systems, plus essential pipe work, air lines and diffusers.

9) Clay lined natural pond

We also discussed the excavation of a purpose built pond, lined with clay.  I would suggest the area shown to me may be large enough to finally produce perhaps 6 or 7 carp up to 2.25kg but is not sufficient for production of 25 carp of this size.

I would also point out that it will take perhaps 4 – 5 years to attain the 25 carp of this size, before starting again to rear a further 25, which really seems an inefficient means of production.

Sources of clay suitable for lining ponds are available from the following:

Puddling Clay www.puddlingclay.co.uk any size order taken.

1t bag £40

1,000t £6.00 per tone

Moore & Sons Ltd

www.mooreandsons.co.uk.  Tel. 01782 563470


10) Carp sourced from farm reared fish

From our discussion it is clear there is great anxiety with regard to the sourcing of carp for further stocking of Rickmansworth Conservative Angling Society lakes, particularly as some of the extant stocks are ageing.

I am at great pains to state that any fish stocking is an unquantifiable risk, including the addition of any fish that you have reared yourself.  My advice will always be to find a reputable source and stick with these suppliers, even if it may entail a waiting period of a few years before the required sized become available.  By sourcing from one supplier the risks are minimized.

Koi Herpesvirus (KHV) is an apparent major cause for concern.  Farmed carp are the most likely source of disease free fish.  It is not in the interests of any reputable carp farmer to produce stock which may be carrying an infection, the result to the business would be disastrous I would say that any reputable fish farm will not entertain carp movements onto the site and there is little chance of introduction of disease.  If you are unsure of a supplier ask for references, where have the fish been stocked, contact the owners of the fishery and ask about the quality of fish supplied.  Any decent supplier will provide you with this information.

Concluding remarks

I really question the cost effectiveness of producing a handful of carp for re-stocking at Rickmansworth Conservatives, I do believe it to be a better proposition to buy carp of the specified size from a reputable supplier.  Additionally, rearing carp is long term and a dedicated activity, turning out all weathers and times of the day or night to ensure the welfare of these captive fish.

If there are matters arising, please do not hesitate to contact me.

Bernice Brewster BSc, FLS, MSB, CBiol, MIFM, C.Env

Aquatic Consultancy

9 Charlton Lane

West Farleigh



ME15 0NX