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Protecting wild brown trout: It’s all in the genes

Posted by: , Posted on: - Categories: Fisheries and biodiversity

The first fish I caught as a boy was a small wild brown trout in the Lake District. From that moment on, I had a passion for fishing – especially for wild trout.

That passion has shaped my career and, for the past few years, my job as a Fisheries Scientist at the Environment Agency has involved working to protect wild trout stocks and support angling.

The issue

Wild brown trout face a number of threats, both natural and man-made, including pollution, extreme weather events, such as droughts, and predators, such as kingfishers, herons and mink.  

One of the ways in which trout populations are able to respond to these threats is through their genes by evolving to adapt to a range of local environments over thousands of years.  

By spawning at different times of the year, or in different places to maximise the survival of their offspring, wild trout can live and thrive in a variety of habitats.  

We now know that this natural genetic diversity can be reduced by the introduction of farm-bred trout.  

Farm-bred trout are produced with techniques that work differently from the natural selection that occurs in the wild. As a result farm-bred trout have, over a number of generations, lost some of their genetic diversity.

When farm-bred trout are introduced into rivers alongside wild populations and the two interbreed, the resulting offspring have less genetic diversity than their wild parents. This loss of genetic diversity can mean that the progeny are less well equipped to survive in the present habitat, or cope with future changes to their environment. 

Growing up in a safe environment has also led to farm trout becoming more domesticated. Lacking the instinct needed to keep safe from predators, they tend not to survive very well outside of the fish farm.


Rule changes

After an extensive review of research and advice from leading geneticists, the Environment Agency concluded that the continuation of stocking with farm-bred brown trout posed a threat to the native trout populations.  We have decided that stocking with fertile, farm-bred brown trout should be discontinued.

From 1 January 2015 it will not be permitted to stock rivers with fertile farmed brown trout – also known as ‘diploids'. The only brown trout that can be stocked into rivers will be sterile female ‘triploid’ trout or brown trout from breeding programmes that use locally sourced brood-stock.

I’ve been asked a few questions about triploid trout, such as ‘do triploids behave differently to wild brown trout?’ and ‘will they grow too big and predate on native stock?’ We commissioned research into various aspects of triploid trout behaviour and concluded that these trout actually performed the same and will provide anglers with equally as much sport.

Certainly in my own experience as an angler, many of the trout I have caught in the past few years have been triploids and the excitement and thrill of catching a trout is just as intense as it ever was.

Ian Dolben is a fisheries scientist at the Environment Agency. He has worked for the Environment Agency for nearly twenty years.


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  1. Comment by Nigel posted on

    The EA in particular Dr Shields uses the same argument re Atlantic Salmon. Why therefore does the Tyne succeed in having such high runs against other rivers. After all reading Kielder Hatchery own website they release almost a million Salmonoids to the River Tyne Annual. If the degrade theory is correct then surely as night follows day the Tyne is doomed. One thing for sure is that for every scientist view you can get another eminent scientist to contradict there claims.

    To allows this fry feeding triploid trout into Salmon spawning areas does appear to a layman like me rather foolhardy.

    • Replies to Nigel>

      Comment by Ian Dolben posted on

      Nigel - you are confusing two different situations. Kielder hatchery catches salmon broodstock each year from the Tyne, spawning them and stocking the resulting fry back into the Tyne to compensate for the spawning areas lost as a result of Kielder Reservoir being built. The fry are the offsring of wild parents. The aim of the new rules on trout stocking is to prevent damage to wild populations through introducing farm bred trout which have become 'domesticated' through generations of farm breeding and rearing - as the blog outlines.

      Reagrding your point about predation, there are a number of published studies which show that this does not occur - in fact, large, wild brown trout are more likely to predate on salmon smolts.

  2. Comment by Dave posted on

    There is more to game angling than merely sport.
    While we welcome any measures that encourage real wild trout populations, there are grave worries about the future of our Salmon stocks.
    The decline on the west coast rivers over the recent years has been truly alarming.
    My local rivers are absolutely full of Parr and Smolt in the upper reaches. As soon as they begin their sea journey they are decimated by Pike and Cormorants in the lower reaches.
    We aren't giving them a chance.
    Prevention is better than cure and until something is done with the predation of our stocks, then I fear we are simply ignoring the real issue.

  3. Comment by Nigel posted on

    Dave... which river are you alluding re the Pike ?

  4. Comment by john posted on

    Not all stocking is done with what you call 'farm bred trout'. To suggest as you do that fish reared from in river parents are genetically inferior is to insult our intelligence. They are one and the same. the likes of you and the Kyle Young's of this world have a lot to answer for. Have you or he personally ever done anything to improve the stocks of trout or salmon in any river.
    Career suicide in the NRW now to go against current prejudices so wouldn't expect anything alse from anyone now in that organisation

  5. Comment by peter posted on

    The Wye was once one of the greatest salmon rivers in England & Wales; that is no longer the case. Our objective at Wye Salmon Association is to return it to its former pre-eminence. Success in this undertaking would produce a valuable river for owners, leaseholders and anglers alike.
    Recent decisions by NRW have not blunted our enthusiasm and we therefore propose a new agenda.

    Request government agencies enable private initiative and allow us to determine recovery strategies rather than dictating them themselves

    Adoption of a privately-led Semi-natural Release (SNR) programme

    Adoption of a privately-led egg box release programme.

    Continued support for proven habitat improvement projects through the Wye & Usk Foundation

    Our first step is to ask you, to demonstrate support for these efforts. The support will start in the form of a petition, requesting government agencies remove restrictions on private, third party, stocking initiatives and restrict their involvement to reasonable licencing of such work.

    • Replies to peter>

      Comment by Tom johnson posted on

      Your salmon have gone cause they are being harvested at sea in huge numbers.
      It's not complicated.

  6. Comment by Environment Agency posted on


    ‘Wild’ brown trout are those that hatched from eggs spawned by wild parents, as opposed to farm-bred trout, hatched from eggs artificially stripped on a trout farm and raised in ponds prior to stocking. Wild trout are genetically diverse, as opposed to farm bred trout which have a limited genetic makeup due to years of line breeding. The evidence we produced in support of the new rules showed that, whilst there is no evidence of reduced genetic diversity in trout stocks in England (although there is evidence from elsewhere in Europe), by acting now we can reduce the risk to trout populations in future.
    With regard to your second point, there is no evidence that triploid trout are more aggressive than wild brown trout. If introduced triploids are more catchable than wild trout, then in fisheries which stock with triploids this should improve catches for those anglers who wish to catch fish easily, leaving the more difficult to catch wild fish to survive and spawn.


  7. Comment by Bernard Sunderlanhd posted on

    " ‘Wild’ brown trout are those that hatched from eggs spawned by wild parents" -
    Here is a fine example of sophistry. Sorry, this does not define 'wild'. According to this, the 'wildness' of the parents depends on the 'wildness' of their parents and so on back through antiquity. Therefore if any trout has a farm-bred ancestor, it is not wild. So it can not knowingly be claimed that any wild trout exists in any water which has been stocked. If the EA wishes to devise some policy regarding wild trout, it must have a clear and workable definition of 'wild' otherwise the exercise is just nonsense. Does a more valid definition exist?

    If eggs are stripped from a wild trout (by any definition) and raised in a farm, are they wild or not?

    "Wild trout are genetically diverse" -
    I am not sure if this means even within any isolated (natural) environment. I have seen a number of trout in a small and almost certainly untouched and self-contained environment which had exceptionally bright colouring. I do not know much about genetics but this seems to indicate a distinct genetic code. And surely, any animal living in a naturally isolated community (one lake, or one river system) must be inbred.

    I am certainly in favour of severely limiting restocking, which has been indiscriminate and, I think, wrong for many years.
    When I regularly fished local rivers during my teens, 50 to 60 years ago, the takeable limit for a trout was 10". To catch a takeable trout was the goal for all anglers, and this was good because it was achievable but only occasionally. In the Wharfe, the average grayling was somewhat larger than the average trout and both were present in large numbers. When I returned to angling 25 years ago I found the trout limit raised to 12" and these were common. Anglers now appear to expect to catch big fat trout from the rivers and many clubs provide them. In my view it is very likely that the grayling stocks and probably the 'wild' (by some arbitrary definition) trout stocks have been decimated by the constant introduction of trout which are much larger than nature decreed they should be in these waters. Diploid or triploid, they all eat anything which moves. I am not convinced that restocking was ever necessary but if it is to happen, should be of immature fish only, raised from the local population (though, of course, with all its introduced imperfections).

  8. Comment by Fred Hefford posted on

    Ian I believe there is much danger in the Triploid approach. Reports from the USA indicate that some of the attempts fail to produce Triploids, it is a difficult and costly process, some will die about 1 in 10 will remain diploid. Never-the-less, due to mans interference with the reproductive system of the fish, we could be endangering the wild fish population of the rivers. USA reports indicate that the Triploids grow more quickly and achieve greater weight than the natural Diploids. I understand that they believe it is due to the Triploids not going through the reproductive process. It will be too late when we find that the added growth is due to the fact that they are cannibals. Surely, a safer and better way to increase the Wild trout population is to capture Wild trout, Strip the Hens and Milt the cocks allow the eggs to fertiise and mature in river conditions, until at a stage when they can be released alongside other wild fish. I have witnessed this being done for Salmon in the Test and Itchen. At least, then, we wouldn't be playing God, but assisting Him.

    Another approach would be to improve in river conditions and in particular, flow, habitat and river bed, which all good River Keepers do, when allowed.

  9. Comment by Bernard Sunderlanhd posted on

    Ian, thank you for your considered reply to my comments. I follow the reasoning leading to final recommendations but I remain sceptical of all restocking schemes. When all is said and done, the proof of the pudding is ONLY in the eating. One thing I have learned is that as a generality, it is easy to instigate a change but the result is rarely what was intended.

    I am convinced that stocking mature fish which are larger than the rivers naturally support is the first contributing factor in the ruination of our river habitats. Of course, there are many others. Anglers who expect to easily catch big trout from the rivers should not be catered for. Let them go to the commercial still waters. Why should their greed influence policy with regard to protection of our natural habitats?

    I believe that the only sensible way to move toward a reliable understanding of trout populations is to cease stocking altogether and return all trout and grayling caught for a number of years, whilst making it mandatory to return catch records when renewing licences. It might turn out that natural stocks are self-maintaining!

  10. Comment by Nigel rainton posted on

    Where can I find the Regulations that enforce the stocking of triploid brown trout?

  11. Comment by Alan timms posted on

    Hi I live in tameside Manchester and fish the river tame who can I talk to about stocking the tame all we have here is a few brown trout not like Stockport up the road which as barbel Chubb grayling but they can't get up this end due to a massive weir we are a growing group on Facebook called the river tame hunters and we really could do with the river tame stocking with barbel Chubb grayling ect starting at Hyde then dukinfield and staylebridge thanks

    • Replies to Alan timms>

      Comment by Environment Agency posted on

      Hello Alan, We have passed your comments to the local team for the River Tame and will reply once we have more information, regards Jayne

      • Replies to Environment Agency>

        Comment by Johnathan Wayne posted on


        Any news on the barbel being stocked in the river Tame in Dukinfield and Hyde as requested by Alan in May.

        Kind regards.

        • Replies to Johnathan Wayne>

          Comment by daveferguson posted on

          Hi, sorry for the delay in replying. The River Tame in and around Dukinfield, Hyde and Stalybridge has always been predominantly populated with Brown Trout and the odd Chub in residence, this has always been the case for the last twenty to thirty years but as things have improved with water quality etc some other species have started to appear.
          As for stocking the river we have stocked the mid to lower river at various points upstream of Harrisons weir at Tiviot Dale with Chub, Dace and some Barbel in 2012 with a view to them populating the river upstream of Harrisons weir which is an impassable barrier to the upstream migration of fish.
          At present there are no future plans to carry out further stocking of the river, but this may change in the future should mitigating circumstances arise.

  12. Comment by William Forbes posted on

    Hi could you advise me if the above regulation is in Scotland and does it apply to stocking in lochs at billy

  13. Comment by Trevor posted on

    As rivers continue to improve in water quality must we wait for brown trout to enter these systems naturally, or is there an argument to give them a 'hand up'?
    I grew up in North Yorkshire, where most streams were trout streams, but now live in Bedfordshire, near a clear, gravel stream that supports chub, bream and pike. I would love to introduce native brown trout to this stream. Can anyone justify why this would be a bad idea?

    • Replies to Trevor>

      Comment by daveferguson posted on

      Hello Trevor, We passed your question to the author of the blog, Ian Dolben, and he has replied as follows:

      Although you suggest that the stream currently only supports chub, bream and pike, it may be that brown trout are present, but in low numbers due to limited habitat. Alternatively, the presence of those three species is typical of a lowland tributary stream, which do not always support trout.

      It may be the case that trout are present in the main river, but are unable to move upstream due to the presence of impassable weirs. We have put considerable effort over the past few years into investigating the reasons for limited fish populations and investing in improvements such as fish passes and weir removal.

      I suggest you contact your local Fisheries, Biodiversity and Geomorphology team who may be able to give you detailed information about the fish stocks present, and will be able to update you on the potential or planned improvements. Assuming your stream is suitable for brown trout, removal of any factors limiting trout populations should enable trout to re-colonise the stream naturally – which is the ideal solution.

      For waters where natural re-colonisation is impossible due to lack of access (but suitable habitat exists) it would be possible to re-establish trout populations using broodstock obtained from populations in nearby waters (a local broodstock scheme) – but this needs to be carried out using strict protocols to ensure that the offspring will thrive in their new environment.

      I hope this helps – please contact me again if you would like to discuss further

  14. Comment by Dave D. posted on

    Trout eggs and fry are being decimated by the introduction of Barbel,which are bottom feeders sucking up eggs and fry of all other fish.The wye 45 years ago had loads of trout.Very rare now in area around Ross.

  15. Comment by Bill Sowerbutts posted on

    When it comes to stocking there's never a truer saying than "if its not our friend , its our enemy". Every fish we stock that predates potentially reduces ova and fry. So I'm sorry but that bloke from the EA is frankly missing the point, if he doesn't realise that any sterile trout will still need to eat - and that as a predator, they won't lose condition and so any trout (fertile or infertile) not caught and removed will simply feed on what little there is in the river over the winter. And of course -being trout- will be right there with the breeding fish to scoop up whatever they produce.

  16. Comment by Sam posted on

    Hi to all . I have read many of your comments , views , facts and ideas and take all on board .
    I live East of Edinburgh in East Lothian .
    The river Tyne which runs into the forth estuary is my local river , it is home to brown trout , sea trout and the occasional salmon and graying , eel are also in numbers .our members opted to stop stocking trout about 15 yrs back , after about 7 yrs the numbers of larger fish dropped fairly quick but the amount of smaller fish stayed around the same , now 15 yrs on the fish numbers are fairly steady but there are fewer larger fish to be readily caught , I have seen some really nice fish but they are very wary of the surroundings. We have an advised catch and release but never stop anyone from taking the odd one for supper , 95% of anglers return all fish with the other 5% returning more than 1 in 10 .
    Fishing is great on our river now as long as you are not expecting monster trout and happy to be content with returning fish and not expecting 1 1/2 lb fish every night . I have blanked only once in the last 50 days out and fish average 7-11 inches . Sometimes it’s better to be patient and let nature take its course .


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