Why are my Silver Dollars so f***ing tense ?

[Ansorgii]

Could it be that there is more than one species being sold als M. Hypsauchen ?
Because that is the most commonly sold species here, and they look way different beyond just male and female. Kept them too, but I dont like their shape. (Example pic below, not mine)

In my (and my friends) experience Silverdollars do not discriminate at when it comes to forming groups or mating as long as they arent completely different. At worst they are indifferent to each other.

6 Redhooks 3-3 and that one in 720l. The tank is Ok since it has a lot of room and current, but bigger is always better.

 

[FJB]

Yes, current hobby naming is a mess. What is being sold under each name is a mixture of a few common species, and even some of the most reputable sellers have a mess of taxonomy in the names they use. Even among the common species the names seem to be used haphazardly. I have pointed out errors in several websites (privately) and have not gotten much response or even a thank you.

In Metynnis (long adipose fin silver dollars) - Out of 14 currently recognized species, only 6 are commonly seen in the hobby (argenteus, lippincotianus, altidorsalis, maculatus, fasciatus, hypsauchen). The rest are basically know only by ichthyologists (anisurus, cuiaba, guaporensis, longipinnis, melanogrammus, luna, mola, otuquensis).

Among the first group of 6, only fasciatus and hypsauchen are very similar to each other, except for coloration. They will do pretend mating among them. The other 4, are most similar to each other, and different than the former two, and will also do pretend matings among them. But the two first species will not do sexual displays to the members of the foursome. They are just different. All six of them will of course school together and form multi species packs, but not sexual stuff. Wonky among members of the two groups defined above.
Regarding the other 8 species that are just not seen in the hobby - we just don’t know enough about their behavior in captivity. However, morphologically, both hypsauchen and fasciatus appear to be more similar to cuiaba and guaporensis than they are to other species.
Interestingly, recent improved molecular understanding of relationships within Metynnis appear to be at least not inconsistent with the groupings I mentioned above.

Regarding your single Metynnis dollar- with the extended anal fin it has, it looks more like hypsauchen (and fasciatus) than like any other species. The only other plain silver species (argenteus) has a different fin shape. That is why I believe it is hypsauchen.

 

[FJB]

Could it be that there is more than one species being sold als M. Hypsauchen ?
Because that is the most commonly sold species here, and they look way different beyond just male and female. Kept them too, but I dont like their shape. (Example pic below, not mine)

In my (and my friends) experience Silverdollars do not discriminate at when it comes to forming groups or mating as long as they arent completely different. At worst they are indifferent to each other.

6 Redhooks 3-3 and that one in 720l. The tank is Ok since it has a lot of room and current, but bigger is always better.

View attachment 1516323

I should have mentioned:
In the last picture your posted (from your friend's tank), it appears that there are at least two species of Metynnis silver dollars shown: M. argenteus, and M. altidorsalis. There could be more- It is hard to say since only 2 fish are shown more of less complete, and it is clear there is a larger group in the tank.
Those two species would of course readily school together, act as a pack and develop group dynamics, including inter-specific mock breeding behaviors. Nice fish!