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Gold tetra conundrum

rr16

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536
OK, so I haave two different species of tetra, both purchased as gold tetras some time ago. I currently have two fry from one of the species (which of course are silver coloured!).
I'm trying to establish the species that I have. I think one is H. rodwayi, but I don't know what the other is. I'm not sure which is which either as I've seen images of both species labelled as H. rodwayi online and in publications. If anyone could help I'd be very grateful.
Here is the first species.
 

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rr16

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536
And the second species...
 

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Drayden Farci

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I have the same "problem" as you. I have a school of Gold Tetras and it appears as though there may be multiple species. I don't have quality photos, but short descriptions might help:

One group has a green/blue lateral stripe with the black spot near the caudal fin. Some of the fish have white tips in their dorsal and anal fins, though not all of them.
One group has a seemingly red/orange lateral stripe instead of blue/green. Same for the fins.
A few fish in the batch have hints of red bleeding into the anal, caudal, and dorsal fins from the body. Similar, but not quite to the extent of the Silver Tip Tetra, here: https://upload.wikimedia.org/wikipedia/commons/1/18/Kobbertetra_Hasemania_nana.jpg

My theory is that there are many species that are susceptible to the parasite, and occasionally some will get mixed into a school of H. rodwayi. I have seen quite a few different species on FishBase listed as similar to the Gold Tetra, so it's also possible that there are just many incredibly similar species out there. I have seen Green Neon Tetras with gold shine to them, though very rarely.
 

gerald

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For those wondering why Drayden is talking about parasites, the gold color is due to guanine that the tetras make in response to a certain trematode skin parasite they are infected with in the wild. Captive-bred gold tetras (brass tetras) don't have these parasites or the gold color. Several species of tetras can apparently be infected and develop the gold color.
 

rr16

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536
Does anyone have a copy of the original paper that describes this? I think it was by Gery and in TFH. There's a Zarske paper, describing H. filamentosus which shows a few fish in goldform and has an image of what claims to be the trematode metacercaria encysted in the flesh, surrounded with guanine. I'm curious about the research that has gone into this and is now an accepted "fact". I don't disagree with this, but like to look at and analyse info. I may get myself a microscope and wait for one to die, and take some samples, as metacercaria should be easy enough to identify.
It would also be interesting to determine if laying down of the guanine crystals make the fish more visible to bird predators, the likely definitive host of the trematode, as guanine crystals affect the relection or refraction of light. What I have noticed is that when viewed from above, many of the gold form fish have a very concentrated gold area on the head. This in turn would potentially make the fish more visible to predators and increase the chance of the parasite life cycle continuing.
 

rr16

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536
I would be very surprised if this wasn't the case. The claim is thst it's a trematode (a type of flatworm known as a fluke). The adult stage is in piscivorous birds and they reproduce in the bird's intestines. The parasite eggs enter the water in bird faeces when the bird defaecates and hatch out. They then enter copepods which are eaten by fish. The parasite then is activated in the fish intestine, moves into the fish's tissues and becomes a metacercarial cyst (this is, in theory, where the guanine is layed down, around these cysts). In Apistogramma, similar or possibly even the same parasites, cause the "black spotting" seen in some wild specimens, where I think the cyst is surrounded by melanin.
Trematodes are cosmopolitan, so African species will be affected, but whether it causes the deposition of guanine is a different matter.
 

gerald

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Interesting idea RR about the fluke-induced fish color having a benefit to the fluke's reproductive success by making it more visible to birds. There are some fluke species that infect land snails and cause the snails to crawl out into open areas where they're more easily eaten by birds. Let us know what other info you find out.

Linus: I haven't noticed captive-bred Congo tetras having any less iridescence than wild ones, so in that case I wouldn't think their color is due to a trematode parasite. Also, Congos aren't very conspicuous viewed from above, except when they tilt at an angle to display at one another. Are there any African species where captive-bred fish never develop the colors of wild fish (aside from the usual effects of wild-diet and natural sunlight)?
 

rr16

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536
I'll probably never find out, but who knows?
Diplostomum are found in the eyes of fish, in theory, reducing the light in the eye and making them swimcloser to the surface/affect vision, whichmeans they are more likely to be eaten by herons, etc. Toxoplasmosis infection in rats also seems to make rats more attracted to cat urine, where they normally avoid it (the cat is the definitive host of Toxoplasma where the parasite undergoes sexual reproduction). Echinococcus tapeworm cysts are found mostly in the lungs in moose infection (or possibly it's caribou), affecting the ability to run for longer periods of time, meaning they will be targetted as weaker individuals by wolves and the wolves will eat the cysts which develop into adult tapeworms in the wolf's intestine. Parasites are interesting.
 

Linus_Cello

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I

Linus: I haven't noticed captive-bred Congo tetras having any less iridescence than wild ones, so in that case I wouldn't think their color is due to a trematode parasite. Also, Congos aren't very conspicuous viewed from above, except when they tilt at an angle to display at one another. Are there any African species where captive-bred fish never develop the colors of wild fish (aside from the usual effects of wild-diet and natural sunlight)?

Are there any known Congo tetras that occasionally have more gold coloration than usual? As for other species, like Alestopetersius brichardi (red-congo tetra), conventional wisdom is that the red-coloration does go away because of diet. But maybe an alternative hypothesis is that it needs to be reinfected for the red coloration (but then again, the coloration fades also in the fin, suggesting diet)?
 

rr16

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5 Year Member
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536
Get a pet cormorant (an African one, of course) and run some experiments. Keep us posted! ;)
I'm not even allowed more fish tanks so she'd never buy this. Would be cool to run some experiments on this though. You could also use PCR on fish tissue samples to identify parasite species.
 

rr16

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536
Good find. I'm glad my MSc in Parasitology has been useful for something.
 

rr16

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536
Just to add to this thred, I have just seen what appears to be a Nannostomus marginatus with the gold colouration.
 

Drayden Farci

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207
Just to add to this thred, I have just seen what appears to be a Nannostomus marginatus with the gold colouration.
Nice! I've also seen P. simulans, P. axelrodi, Hyp. erythrostigma, Hyphessobrycon sp. "Super Red Line", and a few others that I cannot recall. It's fun to post them on the subreddit r/ShiniesIRL (for the non-Pokemon fans out there, a "Shiny Pokemon" is one that has an alternate color pattern. There is a 1-in-8000 chance of encountering one in the games, making them extremely rare.)
 

rr16

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536
I have also seen a P. simulans in the same shop with the gold colouring. There may have actually been a few in the group, but don't remember properly.
Here's a vid of the pencil.
 

MacZ

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I have also seen a P. simulans in the same shop with the gold colouring. There may have actually been a few in the group, but don't remember properly.
Here's a vid of the pencil.
I'm pretty sure the colouration is washed out due to the lighting and stress. Otherwise I'm torn between a small N. beckfordi or a N. anduzei.
 

rr16

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536
I'm not sure. I feel like it's too stocky and resembles one of the marginatus types. I probably need to go and buy it. May have a look for a suitable tank now.
 

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