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Thread: Relationship between collecting wilds and evolution

  1. #1
    Administrator brewmaster15's Avatar
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    Default Relationship between collecting wilds and evolution

    I have often wondered how our collecting of wild fish for food and the aquarium trade affects natural selection and trait development in wild populations. Obviously we here are most interested in wild discus but answers to the question of whether collecting wild discus affects natural selection and evolution of discus are likely not going to found due to funding. So we must look towards other aquaculture sectors.

    Theres is a growing body of evidence that shows that , yes, human mediated harvesting Does affect traits and natural selection in Fish populations.

    Some research published in PNAS(Proceedings of National Academy of Sciences) 2021

    https://www.pnas.org/doi/full/10.107...on%20pressures


    The Amazon is a huge system of water ways but collecting areas for discus probably represent a fraction of them.Its probably fair to assume that good accessible sites are revisited each year. As wild discus prices increase and demand grows for Discus with certain traits its very likely that these individual fish are preferentially collected and removed from the population. Over time that really could have serious implications for natural selection and the evolution of Discus Fish. This is probably compounded by habitat loss and fragmentation.

    As I said we have no evidence that collecting wild discus is affecting the natural selection in discus but it would be foolish to assume discus exist outside of rules of evolution simply because it would inconvenient otherwise.


    I have to wonder if it would be better for the overall health of our wild discus populations if we balanced the collecting of wild discus more with a focus on harvesting younger non reproductive fish vs the mature specimens obviously its not likely to happen as theres big money in fancy adult wilds... but It would probably make sense from a fisheries management viewpoint. At some point with over collecting and habitat destruction we may need to do something along these lines to protect the genetic diversity of wild Discus populations.


    Thoughts?

    al


    ps.. please reference the above articles cited sources for more information on the subject.
    Last edited by brewmaster15; 06-07-2024 at 07:51 AM.
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  2. #2
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    Default Re: Relationship between collecting wilds and evolution

    Al, first, happy birthday too Carrie and many more.
    I do think that over harvesting any animal be it fish , mammals, ect. is definitely harmful. Witness the
    declining populations of seafood. Over harvesting decreases the gene pool leading too weaker and less
    healthy animal population.
    But , to think Brazil is going address the issue, not going to happen.Just look at what's going on in the Amazon.
    Deforestation, illegal lumbering, ect and nothing is being done. So, forget discus.
    IT all boils down to one thing, MONEY.
    Jay

  3. #3
    Silver Member Willie's Avatar
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    Default Re: Relationship between collecting wilds and evolution

    The study is done in a stocked lake with Northern Pike, an open swimming top predator, thus it represents a fairly constrained set of parameters. Such constraints means it may not reflect more natural settings, even if they are necessary to generate research data. Discus exist without such constraints. It lives in the Amazon, the largest fresh water system in the world. It forages for food. It hides in root thickets and collection methods are primitive by modern standards.

    The researchers begin with the premise that harvesting northern pike is non-random. Basically they went fishing and kept the larger ones. But they couldn't measure any actual change resulting from their fishing. They reported on a mathematical model that suggest a change would occur, not that it did. At a 95% Confidence Interval, most of the modeled changes were not significant.

    It's hard to imagine how anyone could come up with a definitive answer for discus, especially when there is no evidence that the fish is over-harvested. For example, 200,000,000 cardinal tetras are harvested from the Amazon annually without any measurable genetic impact. Given that harvesting of discus is done individually and by hand, I find it difficult to imagine that harvesting for re-sale has had much effect.

    Of course, the aquarium hobby has caused many other changes to the natural discus populations. The makeshift pens used to hold discus catch often break, leading to discus from different regions released into new ecological niches. We've also read reports of local discus farms flood, releasing large discus populations into the river. The end result is that there are no pure browns, greens even Heckels left. All this is in addition to habitat destruction resulting from construction, farming, pollution and over-population. Climate change, of course, will stress every species in the Amazon - including discus.
    At my age, everything is irritating.

  4. #4
    Administrator brewmaster15's Avatar
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    Default Re: Relationship between collecting wilds and evolution

    Quote Originally Posted by Willie View Post
    The study is done in a stocked lake with Northern Pike, an open swimming top predator, thus it represents a fairly constrained set of parameters. Such constraints means it may not reflect more natural settings, even if they are necessary to generate research data. Discus exist without such constraints. It lives in the Amazon, the largest fresh water system in the world. It forages for food. It hides in root thickets and collection methods are primitive by modern standards.

    The researchers begin with the premise that harvesting northern pike is non-random. Basically they went fishing and kept the larger ones. But they couldn't measure any actual change resulting from their fishing. They reported on a mathematical model that suggest a change would occur, not that it did. At a 95% Confidence Interval, most of the modeled changes were not significant.

    It's hard to imagine how anyone could come up with a definitive answer for discus, especially when there is no evidence that the fish is over-harvested. For example, 200,000,000 cardinal tetras are harvested from the Amazon annually without any measurable genetic impact. Given that harvesting of discus is done individually and by hand, I find it difficult to imagine that harvesting for re-sale has had much effect.

    Of course, the aquarium hobby has caused many other changes to the natural discus populations. The makeshift pens used to hold discus catch often break, leading to discus from different regions released into new ecological niches. We've also read reports of local discus farms flood, releasing large discus populations into the river. The end result is that there are no pure browns, greens even Heckels left. All this is in addition to habitat destruction resulting from construction, farming, pollution and over-population. Climate change, of course, will stress every species in the Amazon - including discus.

    Willie I draw your attention to the studies sited sources again. This isn't a one study paper by an unknown institution. Its a legitimate concern in aquaculture across many fish species.



    I realize that the Amazon is huge.. but discus are not migratory fish. Theres a very good indication that certain areas have certain populations that have certain traits. Its really not unreasonable to think that a population in a specific area could be fished out given the financial incentive of several hundred dollars a fish and ease of access year after year.
    Add that incentive to climate change and habitat loss and I see it being an issue in the future. I suppose I could take the position that that the Amazon is so big that theres no way collecting prime specimens from populations year after year will have any effect on genetic diversity except for the fact that scientifically we know thats not true in many many species. Its part of the reason why in the North east we have slot limits for wild fish.

    We may feel a few fish taken from the Amazon here and there is nothing to worry about. We felt that way with marine fish from reefs too..until we learned otherwise.

    The body of research clearly shows we do affect the diversity of wild species.. why would discus be any different other than it inconveniences us to recognize it?
    I do realize that there is no proof this is happening with Discus and stated that but much of what we know about our tropical fish comes from researchon other species where there is funding... to ignore that makes no sense to me.
    Looking at the long term survival of discus and other
    South American Cichlids given climate change and habitat loss and over collection/unmanaged collection for the aquarium trade does anyone truly think its not Possible we could be doing great harm by how we are going about all this. We Humans tend to be short sighted when it comes to resource management..We manage species of interest well after the warning signs or after a population crashed.. I see this as an example of that.

    ps.. The cardinal example is not really a good one.. every cardinal I have seen is the same color and pattern and lives a year or two.. really no comparison to discus with lifespans of a decade and many many patterns and forms.
    Last edited by brewmaster15; 06-07-2024 at 07:41 PM.
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    Registered Member gimaal's Avatar
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    Default Re: Relationship between collecting wilds and evolution

    Interesting thread. Al, it is true of course that cardinals live only a year or two in the wild. I read one serious article that described them as annuals. But do we know what the lifespan is for wild Discus? Yes, we can keep them going for a decade or more in our tanks but I had always assumed, perhaps erroneously, that their lives in the wild were shorter.


    And as for this from Willie:

    <<The end result is that there are no pure browns, greens even Heckels left.>>

    It's been a while since I read the most recent mtdna study of the genus that, among other things, affirmed the status of the green Discus, S. tarzoo, but I seem to recall that the green Discus was cited as the only evolutionary unit in the genus for which there was no evidence of hybridization, further supporting its status as a reproductively isolated species on its own individuated evolutionary path.

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    Default Re: Relationship between collecting wilds and evolution

    Quote Originally Posted by gimaal View Post
    Interesting thread. Al, it is true of course that cardinals live only a year or two in the wild. I read one serious article that described them as annuals. But do we know what the lifespan is for wild Discus? Yes, we can keep them going for a decade or more in our tanks but I had always assumed, perhaps erroneously, that their lives in the wild were shorter.


    And as for this from Willie:

    <<The end result is that there are no pure browns, greens even Heckels left.>>

    It's been a while since I read the most recent mtdna study of the genus that, among other things, affirmed the status of the green Discus, S. tarzoo, but I seem to recall that the green Discus was cited as the only evolutionary unit in the genus for which there was no evidence of hybridization, further supporting its status as a reproductively isolated species on its own individuated evolutionary path.
    I will also add to this that discus as a group are thought to be in the process of speciation evolutionarily. .. not that they are becoming one species.

    Releasing a few albino discus into a wild population doesnt pollute the whole population. Those fish still need to out compete the native population to breed... easier said than done in many cases.


    Breed two random wild greens and you arent going get heckels.... breed two heckels(good luck there) wont give you a green or a heckel with spots.

    I disagree with this
    <<The end result is that there are no pure browns, greens even Heckels left.>>
    As a keeper of many wilds over the years.. Heckels are still Heckels, greens greens and browns and blues still breed true in the vast majority of cases...


    side note..approx 3% of modern humans contain neandertal genes.. Yet we don't consider that an issue on the purity of the human Race.

    https://humanorigins.si.edu/evidence...0al.%2C%202015).
    .
    Last edited by brewmaster15; 06-07-2024 at 09:28 PM.
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  7. #7
    Administrator brewmaster15's Avatar
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    Default Re: Relationship between collecting wilds and evolution

    But do we know what the lifespan is for wild Discus? Yes, we can keep them going for a decade or more in our tanks but I had always assumed, perhaps erroneously, that their lives in the wild were shorter.
    Aaron I think to answer that definitively we would need a serious tagging study in a particular location. That kind of study would be unlikely. But we can infer a few thing from Our Domestics. The first being the fact that Males tend to mature slower...often taking 2+ years to become fertile.To me this indicates at the very least wilds probably reach 3 plus years age.

    Next inference is on specimens collected .. their sizes. some specimens are very large... size like that probably takes a few years. to reach.

    A thread here on the forum years Back indicated that 5 years max was likely per Heiko.

    Screenshot_20240608-041119~2.jpg
    Last edited by brewmaster15; 06-08-2024 at 08:32 AM.
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  8. #8
    Registered Member gimaal's Avatar
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    Default Re: Relationship between collecting wilds and evolution

    Thanks, Al. Surprised to hear Heiko say he never knew anyone who kept them more than ten years. I have, several of them, and I am sure I'm not the only one.

    And I'm glad you underscored the point that Discus are thought to be on the path of speciation, not the reverse. That certainly was the thrust of the findings of the most recent (2011) mtdna research in which they proffered fours species, ones we commonly refer to as Heckel, brown, blue, and green, and suggested there's a fifth 'significant evolutionary unit' in the form of the Xingu population. They acknowledged that hybridization has occurred between the brown and some of its neighbors but maintained that each species remained on individual 'evolutionary trajectories.'

    As you know this 2011 revision has been widely adopted and has not been seriously refuted since then, which, in what is often the chaotic world of taxonomy, is meaningful.

  9. #9
    Silver Member Willie's Avatar
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    Default Re: Relationship between collecting wilds and evolution

    Heiko can tell the age of a discus just by looking at it...
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