Freshwater angling is one of the nation’s biggest participation sports and is worth about £3.5 billion each year to the economy.  The Government is therefore keen to get even more people involved in the sport as it provides not just environmental benefits but social and economic ones as well.

However, to maintain the sporting viability of many rivers it is often necessary to augment wild fish stocks with farm-reared fertile brown trout (diploid fish).  But in recent years concerns have been expressed that stocking rivers in this way might pose a risk to the wild trout populations through interbreeding.

In 2003, the Environment Agency published its National Trout and Grayling Fisheries Strategy and introduced new policies to help protect and support wild trout populations, including measures to better manage introductions of farm-reared fish. 

Fish farmers are now able to produce brown trout that are infertile through a process that generates all female triploid fish.  Because these triploid fish do not mature sexually they could offer a possible means of avoiding genetic risks to wild stocks.  However, it is possible that using commercially produced triploids could impact on wild stocks in other ways, as they could be more aggressive than conventional diploid fish or they may compromise spawning behaviour.

To discover the implications of this potential change in fisheries management, The Game Conservancy Trust, an independent wildlife research charity, has initiated one of the largest trout management investigations ever conducted in this country.  The project aims to determine the potential impacts of a switch from diploid to triploid stocking on the wild trout population.

The Trust’s two-year study, costing £360,000 is being part funded by the Environment Agency and a private benefactor and will provide evidence about the viability of stocking rivers with infertile trout.

Ian Lindsay, Head of Fisheries Research with the Trust said, “This potential change to stocking management has raised considerable debate in the angling community, particularly as little is known about the performance of these infertile fish. The Trust’s research will provide the science upon which important future management decisions can be based.”

The three aspects of the study include a large-scale electro-fishing programme on stocked and control sites, on upland and lowland rivers; radio tracking to determine the migration and spawning behaviour and an angler survey to measure the catchability and angler perception of farmed diploid and triploid brown trout.

The Game Conservancy Trust has just completed an important three-year study investigating the potential impacts of stocking rivers with farmed fertile trout (diploid fish), and so will take advantage of these sites and utilise the baseline data already gathered to carry out the three aspects of this new study.

The research will take place across 90 sites on six different lowland and upland rivers in the south and west of England.

Ian Lindsay said, “The main purpose of this project is to provide objective information across a range of river types on the performance of stocked triploid trout and their relationship with wild fish.  The Environment Agency’s strategy indicates that further controls on the use of fertile fish for stocking may be necessary to reduce the potential for interbreeding.

The data gathered from our research should help to guide this review, as well as providing practical guidance to fishery managers wishing to use triploid fish in the future.”