HOW CARP GROW IN FISH FARMS

Carp fry start off very small and incredibly fragile. In the wild, very few make it beyond just a few days.

This early period of their lives has the highest mortality rate with less than one in a thousand fish surviving the first few weeks.

From an economic fish farming viewpoint this level of mortality is far too high so it is necessary to intervene in the fry rearing process and offer the baby fish vital protection to ensure more of them survive.

In last month’s Waterlife I detailed how a carp’s egg is collected and fertilised, once hatched out of the egg, the fry has its own yolk to live on for two or three days.

It then needs to start eating.

Carp fry of a few days old are so undeveloped that they cannot digest pelleted foods.

These first-feeding fry need to be fed on live food, on a farm they are fed on tiny shrimp-like creatures called artemia.

These are also just a day or so old and are less than 0.5mm in size which is just perfect for carp to eat.

These tiny shrimps are hatched in large quantities from dried eggs and then fed directly to the carp fry.

However, artemia is very expensive and so it can only be used for a few days t give the baby fish a healthy kick-start.

Beyond this time the carp fry are then stocked out into freshly flooded fish farm ponds. These ponds will have bloomed up with tiny planktonic animals that are the perfect food for the carp fry.

Once in the ponds, the newly stocked carp start hoovering up these tiny animals and grow rapidly.

Once again, by intervening in the early stages of fish growth and ensuring the baby fish have a ready supply of the right kind of food, fish farmers can dramatically increase the survival rates of the young carp.

After just a few weeks the rapidly growing fish will be big enough to enjoy another change of diet as they can start to eat tiny pellets, this will further boost their growth.

These pellets are packed with protein which further enhances the babies growth and survival rate.

One important factor in feeding these small fish is they don’t have stomachs to store and digest food in, this means they prefer their food constantly drip fed to them during the day.

Automatic feeding machines are often used on rearing ponds to govern the feeding of the baby fish.

Believe it or not, experiments have proved that if the fish are fed the same amount of food spread over the day, rather than in two large meals, they will actually grow better by about 20%.

During the summer period the fish grow rapidly in the warm water. There are often a lot of fish in the ponds and the weight of stock can rapidly increase with the growth of the fish.

Once again this can create a problem as the levels of oxygen available to the fish can be reduced by the sheer weight of carp living in there, particularly at night.

To ensure the best survival rate, oxygen levels in the ponds are carefully monitored and aerators are used to keep plenty of oxygen in the ponds.

Once winter sets in, the specially reared young carp will grow much less but they will already have grown sufficiently well enough in the protected environment of the fish farm to be able to survive the cold.

At a time of the year when the natural mortality rate of fish fry peaks again, the farm-reared carp will be big enough to survive until warmer weather returns.

The following spring, these one year old carp are classified as ‘C1 fish’.

The maximum growth potential of carp is rarely achieved in outdoor pond farms, even with the extra feed and good water quality.

It is only in warmer countries than here, or if the carp are grown indoors with the water being heated and constantly maintained, that they reach their maximum potential.

In a trial at Sparsholt College we have managed to grow carp to 20lb in under two years by feeding them good food in warm temperatures!

1. Newly hatched carp fry with a yolk sack attached to them which is full of nutrients. This keeps them alive for two or three days

2. After the yolk has been used, the fry start to form a swim bladder (the clear bubble) and a more fish-like shape

3. The eyes are developing along with a tiny mouth which enables them to eat – these baby carp are known as first feeders

4. This is a microscope-taken shot of a tiny artemia. These tiny shrimps are fed to first-feeding carp when they can’t eat pellets

5. The rapidly growing carp are transferred to a freshly flooded fish farm pond where planktonic life will be blooming

6. Large numbers of fish will be stocked in the pond. An aerator is put in the water to ensure they have enough dissolved oxygen

7. This close-up shows the typical plankton life that the young carp will gorge on in the newly bloomed ponds

8. This tiny plankton is only visible through a microscope which makes it perfect for the small carp to feed on

9. The fish grow rapidly on such nutritious food which helps them survive winter. This is a one-year-old ‘C1’ carp weighing 1.5oz-2oz