Bowlake fish farm was built in 1990 on a 6 hectare site and consists of a hatchery, 34 clay-lined production ponds and 6 clay-lined broodstock ponds. The total surface area of water on the farm is about 39,000m2 at an average depth of 1m. Water is supplied from a biosecure borehole pumped up from the chalk aquifer some 90 meters below ground.
Broodstock are induced to spawn each year to coincide with the rise of pond temperatures and the natural explosion of plankton (algae, rotifers, copepods and daphnia). We stock out our fry into this rich environment and supplement their natural diet to maximise the capacity of the ponds. When the fish reach market size (3-100grams) they are graded, sorted and held in hapas (cages) in the production ponds ready to sale. As orders are made the fish are brought up to the fish house to starve for 24hrs in clean water ready to be distributed across the UK.
Natural production takes place in our static clay-lined outdoor ponds. Every year all our ponds are drained*, dried, disinfected (limed) and fertilised (recycled farm manure) before re-flooding for the new stock.
The static ponds warm up in the Spring sunshine and this allows the growth of natural food (algae and zooplankton) . Our broodstock are spawned over the Spring months and the new fry are introduced into a ‘predator free’ environment. The algae ‘s photosynthesis provides the oxygen for ubiquitous, aquatic bacteria to break down all of the fish’s waste within the pond. Effectively the bio-media for the nitrosomonas bacteria needed for this process is the pond’s soil. Without this soil we cannot breakdown the waste.
Cyprinid fry are so small that they are vulnerable to predation from most aquatic invertebrates and vertebrates. To ensure their survival they need to start their life in a pond that has been disinfected and flooded with ground or filtered water. Ideally the fry are stocked to coincide with the initial production of tiny rotifer zooplankton. Even copepods, some of our smallest zooplankton, will cause severe depletion of swim up fry.
To achieve the maximum production from a static system, supplementary feed is added to the fish’s diet as they grow. The farm uses about 8 tonnes of feed each year to supplement the natural productivity of the ponds. (This works out as an average of 200kg/pond – a little over 1 kg of feed entering each pond daily during the growing season when temperatures are over 15oc.) To increase the pond’s natural, nitrogen cycle’s capacity, an aeration system is integrated and timed to run between 12pm and 4am over the Summer months.
The feed is converted to fish biomass that is regularly harvested for live fish sales during the season. Food and fertilizer in = fish weight out + waste. The waste is broken down within the static clay-lined pond. Ammonia is periodically checked and we have only ever had readings under 0.1ppm. The only exception has been very occasionally during torrential rainfall when slurry has run off from the fields above the site and into a pond. In emergency situations like this we have to run 24 hour aeration to allow the pond to recover it’s natural balance.
Our ponds have feed stations to monitor any uneaten food. Each day these are checked before feeding. O2 and temperature is monitored daily to ensure the correct feed quantities are given. Each pond has a maximum feed rate based on it’s capacity to break down the daily ammonia. If a pond is not actively feeding then a health check is carried out immediately. If necessary, the fish are treated in situ. All treatment comply with Veterinary Medicines Directive (annual inspection) and CEFAS (bi annual inspection). Any medicines used must be able to breakdown naturally in the pond. Fish behaviour is routinely observed twice a day.
Fish are harvested for sale by seine netting the pond.
They are graded in the pond for size and put into holding hapas (cages) that are suspended in the production ponds.
As orders are received the fish are brought up to the fish house where they are starved for 24hours before being put into bags of water and oxygen.
80% of sales are overnight couriered to their destination. The remainder are collected. It is extremely rare for us to deliver fish.
We have an Environmental Management Strategy to help us plan to minimise our impact and alert us to the risks and risk prevention procedures. Overall, as a semi intensive fish farm, it is a very low energy operation.
We abstract 40,000 m2 of water each year from our biosecure ground water which is returned to Bowlake stream. On average each year we require approximately 60,000 kwhrs of electricity to pump water (filing and discharge) and to aerate. We use 8 tonnes of feed that is made from sustainably sourced plant proteins and oils. We use just 500 litres of diesel and 100 litres of petrol each year to run our farmsite machinery. A courier service transports 80% of our product off site and the other 20% is collected by wholesalers and distributers.
Essentially this is a misleading term as we do not have any ‘waste’ production water. Each year we need to restart the production cycle in a predator free environment. So, the purpose of the drainage is to restart the cycle NEVER to remove any waste. (The soil in our ponds acts as the bio media on which the nitrosomonas bacteria live so we do not want to loose any in the drain down.) We will shortly apply for a bespoke discharge license that sets water quality parameters limits when we drain any water into Bowlake Stream. To comply with this we will routinely monitor our suspended solids and other water quality parameters.
There is NEVER any flushing of waste water to aid the nitrification process or to remove any treatments. Every product is broken down and recycled in the pond naturally.
Water that is used to clean nets and cages is resettled in a back-channel before being recycled into our production ponds and water used to hold our fish in our fish house is screened to remove solids before being returned to our production ponds.