Calverton covers 4 Hectares and has 35 mature ponds ranging in size from 100m2 to 5000m2. Each pond has its own inlet fed by an underground 9" main and has between 1 and 4 outlet drains. These drains allow Harvesting to be done in a controlled manner and ponds can be dried out over the winter.
Ponds up to 350m2 are aerated using large diameter porous pipe linked to an underground air supply. For the larger ponds, single or multiple "paddle wheel" aerators are used. These units also provide a substantial horizontal flow, which helps to increase the "fitness" of the fish.
All water is supplied by borehole with a maximum flow of 4500 m3/day (1 million galls/day). The advantage of the borehole is that no "second hand" water is used and the risk of parasitic, bacterial and viral infection is removed. The quality of the water is very good with a pH of 8, and an annual temperature range between 9.5 and 10.50C. The oxygen content is quite low (65% saturation), therefore liquid oxygen is used to bring the DO level up to 100% saturation.
The site has a warm water hatchery that is used to produce eggs and larvae in the spring. The unit also has a thermostatically controlled diesel burner, which supplies 100 lit/min of 250C water. When this is mixed with the cool bore hole water it enables the temperature in the tanks and troughs to be adjusted between 10 and 250C depending on the particular species requirement.
To increase production of certain species, a large recirculation system has been built. This system uses biofilter technology to "re-condition" the water and fish grow very quickly due to the warm clean water, abundant food, and high oxygen levels. At the unit we can produce more than 4 tonnes of fast growing fish each year.
We have also built a Research Unit where we can study the effects of sewage effluent on fish.
In the event of electricity supply interruption, all of the electrical equipment is connected to an emergency 210 kva standby generator. In addition, we have fitted alarms to all the essential items of equipment to give early indication of any system failure. The site also includes a caretakers house, and is manned 24 hours/day. Five full time members of staff are employed on the farm, along with various part-time students.
Very few brood fish are kept on site. Experience has shown that fecundity, egg quality and larvae survival is usually lower when captive brood fish are used. Another problem is the potential lack of genetic variation if a small number of adult fish are repetitively spawned.
Adults in spawning condition are taken by electric fishing from carefully chosen sites. They are selected according to condition, and transported back to Calverton. Here they are quarantined in holding tanks, injected with varying doses of carp hormone, and hand stripped in the normal way. The adults are kept in good condition and returned to the river 2 or 3 days later.
There is usually a surplus of larvae when the eggs hatch and these are reared for 2 to 3 weeks before being stocked back into the same stretch of river. This ensures that there is minimal impact from brood stock collection activities.
