Rare silverdollar ID

[Xeno]

Hey,
now that's an impressive in depth analysis.
Thank you so much for taking the time to write down such an informative post!

But one thing is not clear to me:
FRom what I know M.asterias almost looks identical to M.rubripinnis, M.ternetzi and M.torquatus but the juveniles of both species look very different to the ones being sold as Tometes/Mylesinus right now.
For example these fish do look like what's also knows as Myleus rubripinnis "luna":

https://www.facebook.com/panta.rhei.50/posts/894464653965823

This specimen which was supposed to be a juvenile M.asterias sure looks similar but it is lacking the striping and red coloration:

https://www.facebook.com/Deister-Aquaristik-123380451081984/photos/2266631276756880

I still do think that M.setiger is more plausible than M.asterias (if the pictures found of M.asterias really are showing this species).
One option could be that the importer was screwed over and those fish are all captive bred specimen from Asia which would open up the possibility of these fish being hybrids.

 

[kno4te]

Get permission from the person on YouTube who happens to be a member here on the forum. tcav88

 

[FJB]

Thanks.

• YES, Myloplus asterias is externally (and molecularly) most similar to Myloplus rubripinnis. In fact, in their re-assessment of M. asterias, Jegu & Dos Santos (2004) conclude this, and for that reason they included a detailed comparison of both. Currently (Kolmann et al 2020) it appears that our common red hook SD, “M. rubripinnis” is actually a complex of at least two, possibly more, closely related and morphological similar taxa, and a similar situation appears to occur with M. asterias.
• I regrettably neglected to include a comparison with Myleus setiger, so I am doing so now.

I am going to conclude that M. setiger is a very good candidate, although there are some important differences between the Glaser +2 and verified photos of immature setiger (see below). Some characters may be said to fit (zebra stripes in juveniles, lower lip somewhat protruding over upper) , others do not (size and shape of anal and caudal fins).

Myleus setiger Muller & Troschel 1844. [Information below from original description, and from Jegu & Dos Santos (2002) - Révision du statut de Myleus setiger et de Myleus knerii. Cybium].


Distribution: Guianian and Central Brazilian shields Basin, in the Amazonian basin, the Orinoco basin and the Guianian coastal rivers. As such, it is one of the most widely distributes species in this group.


Dorsal and Anal Fins: In immature fish and female fish ranging 53-150mm (~2-6 in), the first 4-6 rays of dorsal, and 5-8 rays of anal extended, forming long lobes  Glaser +2 DO NOT have dorsal and anal fins remotely comparable to what shown for immature setiger.
Extensions on both fins reduced or disappear in mature specimens. --> Not possible to compare with Glaser +2. We don’t know the actual size of Glaser +2 (I believe they are young), or how they will look like as adults.

Coloration (preserved):

• “In [immature] specimens~ 70mm (2.7 in) lateral side patches divide into 12-15 narrow vertical bars, which remain present to 140mm (5.5 in) in some specimens, and disappear in most adult specimens.--> These can be interpreted as the ‘tiger’ or ‘zebra’ stripes in Glaser +2. -->setiger?, or another species that also has this character?
• Edge of dorsal and anal fins with black border--> similar to that seen in Glaser +2, but also several other species.
• A round humeral spot (pupil-sized) on 2-3 scales, located between scales 5-9 along the lateral line. Present in fish 50-100mm , and up to 140mm (less frequently).--> Glaser +2 photos DO HAVE a black humeral spot, of about that size, and in about that position. Interestingly, the much larger RED Blotch on Glaser +2 is not mentioned for either preserved, or fresh coloration.

Coloration (fresh):

• Young fish 2-4in: Silvery on sides (no mention of zebra stripes). With humeral black (sometimes) --> Again, no mention of large red blotch.

All in all, I would say there are some similarities, but also some important differences, that makes it impossible to be certain (or even fairly confident) that Glaser +2 are actually Myleus setiger.

The possibility of a hybrid is always there but I consider it unlikely. However, there are of course precedents such as the blackberry silver dollars. It should be possibly to obtain better certainty of whether the fish are indeed wild-caught, of produced under domestication.

The critical piece of information missing is:
HOW WILL THESE FISH (Glaser +2) LOOK WHEN THEY ARE ADULT?

 

[Xeno]

Hey,
Thank you again for this in depth analysis!
Sadly I have no clue how these specimen will look like in a few months.
50 bucks a piece is a little expensive for me personally to end up with luna red hooks so I am very hesitant about getting 4 of these fish.

Let's make it even MORE confusing:
An importer who lives near me is selling some larger specimen as M.setiger and these fish do look super similar to the ones glaser and the other fishdealer are selling.
He does NOT get his stock from Glaser.

 

[FJB]

What size is the fish at center in the second of your last pictures?
I do see similarity on the shape of that fish (and less so but still others in those photos) with the two immatures in the paper by Jegu & Dos Santos (2002). The fins are not as long as in the paper, but similarly shaped.

I wish I could afford fish like these (big SDs). I don’t even have the large tanks required for that. For the time being, I will just continue to play with my little Metynnis.