First year ponds
We stock out the first-fed larvae into specially prepared ponds which have an abundance of natural food of the correct type and size. The ponds range in size from 100m2 to 350m2 and have an average depth of 0.8m. They are filled 2 to 4 weeks before the predicted stock-out date of the larvae, allowing time for the natural food to develop. We use dried poultry waste to manure the ponds at a rate of 1000 to 2000 kg/ha. This promotes the growth of phytoplankton, which are in turn preyed upon by the small zooplankton such as rotifers and protozoans. These small zooplankton are the ideal first food for the larvae and numbers of them quickly multiply under the right conditions.
The development of the pond, its food size and abundance, is closely monitored to ensure that ponds are in a perfect condition to receive the larvae.
Polythene covered horticultural tunnels are used to elevate the water temperatures, a technique which greatly increase the growth and survival rates of the larvae. The effect the polytunnels can have is to raise the water temperature by as much as 5 or 60C over that of outside uncovered ponds.
The first fed larvae are stocked out at between 1,000,000 and 1,500,000 larvae/hectare. Survival rates up to the end of the first summer usually range between 60% and 85% depending on species.
Second year ponds
Ponds used for growing the fish for their second summer are larger and deeper than those used for larval rearing ranging in size from 400m2 to 5,000m2 and an average depth of 1.5m. Although the ponds are larger, they are prepared in much the same way.
The ponds are left empty over the winter during which time the pond bottoms dry out. We clear drainage channels and outlet chambers of excessive silt, which has built up during the previous growing season. To speed up the drying of the pond bottom, the silt deposits are raked either by hand or machine to a depth 5cm to 10cm. This also helps to oxidise the bottom deposits and release nutrients locked up in the muds. Exposure of the bottom to frost further breaks up and loosens the silt by freeze-thaw action.
2 to 3 weeks before we fill the ponds, the bottom and banks are treated with 1,000kg/ha of CaOH (76% CaO) which further improves the mud and ensures that all pathogens and invertebrate predators are killed off.
When the ponds are filled in early spring, we add dried poultry waste at a rate of 2,000 to 3,000 kg/ha and this ensures that a dense daphnia and zooplankton culture develops in 8 to 10 weeks.
When the zooplankton bloom has matured we introduce the fish for the start of their second growing season, usually at densities of between 50,000 and 150,000 fish/ha.
