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Thread: Are some well known discus localities really getting overfished?

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    Moderator Team Paul Sabucchi's Avatar
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    Default Are some well known discus localities really getting overfished?

    I confess to being a subscriber to Santarem Discus YouTube channel, lately besides the videos from NADA (congrats for another clean sweep in the Wild category) there is one of a short chat between Victor and Jack Wattley. Interesting to hear Victor's opinion that the prolonged removal of the best individuals from certain areas (Manacapuru, Alenquer) may have resulted in the "reverse selection" of gradually more misshapen fish. Ok Discus have been captured for the best part of 90 years but the sheer vastness of these areas compared to the limited extent of the bits that can be enclosed with nets should maintain a healthy population. I understand Victor is only human and may tend to emphasize aspects advantageous to his business BUT his fish seem to always win, he does get around a lot (both in the Amazon basin and the world in general) and has a good vantage point and generally I think he is a straight shooter. What are your thoughts?

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    Default Re: Are some well known discus localities really getting overfished?

    I think its possible that overfishing in those areas has had negative effect. Its true they are huge areas but I wonder how much of it is actually fished for discus...if certain areas are more heavily fished because of ease of access its likely the gene pool is affected in some way locally

    Unfortunately whats needed is more natural history studies of discus in the wild. We really know little about how far discus travel in an average lifetime or season to season. If they tend not to move much the effect of collecting on a particular area would have the potential of having a greater influence on the genetic diversity and health of local populations. If Discus are largely transient and cover lots of area the effect will be minimized greatly due to the influx of new individuals to the collection areas.

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    Default Re: Are some well known discus localities really getting overfished?

    Hawaii shut down ornamental fish trade and there have been species hit hard in Lake Malawi from over fishing, so it is possible. If you consider fallen trees to be like a reef to a Discus, you could impact a population by catching the entire school and removing the reef in the process.

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    Default Re: Are some well known discus localities really getting overfished?

    I agree with both the points above, if the discus population tends to stay put or the netting disturbs if not damages their habitat, this could have an impact on these populations. So I have little trouble believing there could potentially be an issue with overfishing, just wondering if it is to the extent described by Victor. Elsewhere he also said that a fair number of Asian discus breeders are having serious problems arising from excessive inbreeding. As this and the above affirmations are quite controversial I would be curious to know where the truth lies.
    I also agree that overfishing of some species in lake Malawi has definitely had an impact, particularly on Chindongo (formerly Pseudotropheus) saulosi, a species that inhabits only a small territory at Taiwanee Reef. I understand the allure of wild caught discus (but doubt I will go down that road), less that of wild Malawi's; I have two big tanks full of domestic mbuna and don't think they have nothing to envy their wild cousins (here are my saulosi and Maingano boys)
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    Default Re: Are some well known discus localities really getting overfished?

    When I was surveying Lake Wanam, it became apparent that wild rainbowfish come in all shapes and sizes. In captivity, we breed for a certain shape and colour, believing we are reflecting the true wild form. It would not surprise me if the buyers in the Amazon reject the not so round fish in preference for our view of the perfect discus.

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    Default Re: Are some well known discus localities really getting overfished?

    I’ve been wondering about this, too. When you look at the major (or best known) exporters in Brazil, their advertised fish are mostly flawless. However, a lot of fish that hit the market are nowhere near that “quality”. Say you order 100 red and semi royals without hand picking them from the exporter’s catalogue, quite a few will be harder to sell, at least to people who care a lot about objectively high quality. You get broken bars, less desirable eye colour, funny shapes and also poorly conditioned examples. This seems to be especially true for the greens in my experience so far, with those it’s difficult to even find a few good specimens amongst many which have been exported already.
    And given that most collection locations have a set quota per season, I doubt it has such a negative impact on the diversity and quality of the remaining reproducing population.

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    Default Re: Are some well known discus localities really getting overfished?

    Also a valid point, it may be perfectly natural for there to be less than round wild discus. I just keep wondering if there really is some substance to the alleged impact in the population of prolonged removal of the best looking individuals. The impact of human interference can be far greater in a small self contained ecosystem such as the lake you surveyed, the Amazon is a huge network of interconnected waterways so if this artificial selection was really taking place it would also imply that those populations are also sedentary, with little exchange with other populations. Again mbuna spring to mind, a certain species may be present along most of the shores of the lake but with very distinct characteristics in the different areas. Although they share the same body of water they are separated by their adversity to cross stretches of open water

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    Default Re: Are some well known discus localities really getting overfished?

    Let's remember that "quality" is a man-made definition. The fish evolve to best suit their environment. Removing individual fish should not impact the survive-ability of the local populations unless the numbers are excessive. Other possible concerns would be methods for catching the fish and other human activities in the local area.
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    Default Re: Are some well known discus localities really getting overfished?

    The fish evolve to best suit their environment which puts round discus at a disadvantage because they are taken out of the reproduction pool. Meaning fewer round discus to reproduce, fewer round babies and eventually fewer round adults to be collected.

    It shouldn't impact the population size unless round discus, in the absence of human fishing, survive better than discus of less perfect roundness.

    How old are the discus that do get netted and kept? I wonder if there should be a size limit such that only fish that are 2+ years old and have bred a number of times before they are taken out of the wild gene pool.

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    Default Re: Are some well known discus localities really getting overfished?

    I don't think we can assume that the size of the Amazon eliminates the risk. We already know that certain locations have distinct colour strains (meaning they don't necessarily travel large distances frequently) and that in the dry season (collection time) the local fish come together around fallen vegetation. Hit those locations hard enough and you would likely have an impact.
    The distribution across the Amazon may have taken hundreds or more likely thousands of years.

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    Default Re: Are some well known discus localities really getting overfished?

    Quote Originally Posted by JamesW View Post
    The fish evolve to best suit their environment which puts round discus at a disadvantage because they are taken out of the reproduction pool. Meaning fewer round discus to reproduce, fewer round babies and eventually fewer round adults to be collected.

    It shouldn't impact the population size unless round discus, in the absence of human fishing, survive better than discus of less perfect roundness.

    How old are the discus that do get netted and kept? I wonder if there should be a size limit such that only fish that are 2+ years old and have bred a number of times before they are taken out of the wild gene pool.
    I think the fish that are netted are seldom older than 2 years (the audio of Victor's talk at NADA was very poor)

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    Default Re: Are some well known discus localities really getting overfished?

    I always thought about this and I'm glad it was brought up on the forum.
    Let's not forget what happened to the oceans. Because of it's size it was thought to be a never
    ending supply of fish. Well looked what happened-cod, sword fish,wales and many others that have been
    become severely depleted come to mind. Some to the point that there ability to continue the species
    is in serious doubt.
    So we might want to rethink our thinking.
    Jay

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    Default Re: Are some well known discus localities really getting overfished?

    Sea fishing and discus collections are not a good comparison. First one is with the advent of modern trawler nets, sonars and other modern techniques etremly efficent in catcthing all individuals and is quickly depleting stock to the implosion of fish populations. Beside that there is a lot of bycatch reisdues, so not only are the target species depleting but also other species. Freshwater equivelant of this is fishing with gill nets/mosquito nets, wich cathces all the fish, even the smallest fry in particular area. Discus collection is done with two methods, first one with large nets aroud submerged wood/under the trees (the so called galhadas or wast 100groups of discus). The other is more precise with night collections by picking one individual after another. So discus collection is more akin to trophy hunting, which removes only the best individuals which can be alpha animals with best fitness. Wild discus do have some migration both in the lenght (down/up the river) and between igapos and main river/lake. The cost of colections on national population is thus depended on species distribution, breeding strategy (a lot of eggs or just few, aka r and k strategy), general biology (time needed to suplement population with natural recruitment). So large collections could influence local populations of some wild discus. As far as i know, there were times when some locations are off limits for collections so the natural populations can recover. At least one, Hudson collects green wilds under strict quota from Mineura biological station. Partial closing of some collection sites for few years are also the reason. why the big three now offer new locations, that were previously not exploited.

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    Default Re: Are some well known discus localities really getting overfished?

    We need more scientific research in the Amazon, such as this one (PhD dissertation in Portuguese with abstract in English):

    http://bdtd.inpa.gov.br/handle/tede/2423

    We cold could create a crowdfunding account (such as GoFundMe) to support scientific research about wild discus in the Amazon. NADA could establish a committee to manage the account and select the project that would receive funds. But that would work only if this community is committed to the project.
    Mauro
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