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FAQs on Silver Dollars Selection

Related Articles: Serrasalmine Fishes, Piranhas, Characoids/Tetras & Relatives

FAQs on: Silver Dollars (Metynnis, Mylossoma, Myleus...spp.) 1, Silver Dollars 2,
FAQs on: Silver Dollar Identification, Silver Dollar Behaviour, Silver Dollar Compatibility, Silver Dollar Systems, Silver Dollar Feeding, Silver Dollar Health, Silver Dollar Reproduction, Related FAQs:  Serrasalmine Fishes, PiranhasPacus,

biting Myloplus rubripinnis     11/25/13
I searched for two hours for info re: my problem. You are my last hope.
<Oh? Oh!>
I have a pair of red hooks (Myloplus rubripinnis) in a 55 gallon tank
<Mmm, really need more specimens... like most Serrasalmines, these "silver dollars", live in schools; and much more room for them>

 with 3 African Clawed Frogs,
<Mmm, must be hard to feed here>
1 Convict, 1 plecostomus, and 1 apple snail.
The larger red hook has bitten the smaller red hook on both sides with vigor. The smaller red hook is missing a lot of skin.
<Again; to re-emphasize... need to be kept in a group (dilutes aggression) and bigger world (ditto)>
Is there anything I might use to treat these injuries? 
<Mostly just moving them to a larger system>
Could I add some kind of sedative to the water to calm the large red hook?
<Mmm, no; not really>
Do they make Ritalin for fish?  Ha!
Should I get two more red hooks?
<Three would be better; but only in a hundred plus gallons>
The large red hook is aggressive with everyone in the tank.
I am feeding everybody red worms.
Ph and temp. are normal.
Thank you for any help you might offer.
<I do hope yours recovers... Have you searched, read what is archived on WWM re these fishes? Bob Fenner>
Re: biting Myloplus rubripinnis      11/25/13
Thank you, Bob.
<Welcome Sandran>

Stocking a 55 gallon tank, FW mix   4/25/11
Thank you for all the wonderful things you do, I love your website.
I just acquired a 55 gallon tank and would like advice on how to stock it, so I don't make the wrong choice and end up with unhappy fish. I have heard that silver dollars are a stretch in a 55 gallon, but I would love to have them.
<The problems with Silver Dollars are two-fold. Firstly, they do get rather big, typically 12 cm/5 inches, and secondly, you do need to keep a group of six or more because they're social fish with the potential to become aggressive or nervous when kept in insufficient numbers. On top of these issues, they're both predatory and pronounced plant-eaters, so they're a threat to any small fish in the tank as well as almost all aquarium plants.
So while they're widely sold, they do need to be kept in a very large tank, realistically 180 cm/6 feet from the left to right. In anything smaller they're not going to do well and will likely cause problems. At the very least, they'll simply look stupid wedged into a tank where they can't actively swim about freely.>
What other fish would do best with them?
<In the right aquarium, Silver Dollars mix well with bigger but peaceful companions, typically things like large South American catfish and large barbs. While they may be viable alongside cichlids, this does depend on the cichlid species in question, and some Silver Dollar species can be nippy, so can cause problems with long-finned cichlids if you don't select your Silver Dollar species carefully.>
I tried to find a list of compatible fish with silver dollars but I don't trust what I find on Google (as advice from random people so often conflicts with what you guys say) and I didn't find it on your site (I apologize if it is up there and I overlooked it). Would Tiger barbs work? How many?
<If you have 150 gallons to spare, then sure, half a dozen Silver Dollars alongside 12-20 Tiger Barbs could work. Tiger Barbs can be pronounced fin-nippers, but in large schools this doesn't usually cause serious problems -- it's when people keep fewer than a dozen specimens they find Tiger Barbs trouble.>
I stumbled upon the website aqadvisor.com, do you think I can go by what their recommendations say?
<I have no idea. Don't have the sort of time required to test out this website properly. Looks clever though!>
I basically want a large schooling fish (not Angelfish) that will do well in a community tank. Am I correct in thinking that mollies and silver dollars don't do well together?
<You are indeed correct. Mollies need hard, alkaline water, and ideally slightly brackish water at that. Silver Dollars need soft to moderately hard, slightly acidic to neutral water. There's no real overlap between the requirements of the two species, and a tank that was healthy for one would be stressful for the other.>
I really like mollies too.
<Mollies are best kept in an aquarium that caters to their needs. In a 55 gallon tank that's easy enough to do, and you can then select fish that will tolerate the slightly brackish conditions they appreciate: Brown Hoplo catfish, Blue Acara, Horseface Loaches, Australian Rainbowfish, Glassfish, Spiny Eels, etc.>
I do have experience with freshwater fish tanks but I am by no means an expert. Any and all advice is greatly appreciated. Thank you again,-Amanda
<Hope this helps. Cheers, Neale.>

Silver dollars fighting 10/7/2009
I have four silver dollars
<Groups of six or more, please.>
in a 72 gal. They have been together a little over two months. (Other fish: 7 Serpae tetras (starters), 1 turquoise rainbow-3.5", 1 male pearl gourami-4"-starting to become more feisty, 1 platy-2"(starter), 1 bushy nose pleco-4", 1 clown pleco-2.5", 3 bamboo shrimp).
<An interesting mix of fish. Serpae Tetras tend to be nippy, so watch them carefully. The others should be fine, though it goes without saying that as schooling fish, Rainbows are happier in mixed sex groups of six or more.>
The tank has been running almost 5 months and the water quality is good. I do a 10-15% water change weekly, run two 350 Marineland filters, keep the temp. at 79. Two of the silver dollars have red anal fins (I guess they are called anal fins, they are the fins underneath the fish towards the back),
and the other 2 don't really have any color on their anal fins.
<Hmm... if these are Metynnis argenteus or some other Metynnis spp., then it's the males that have red anal fins.>
One of the red anal fins is 4" in diameter and the other is about 3.5". The other 2 have the same measurements. About a month and a half ago, the two colorless ones developed 2 black spots on their sides and the edges of their tail fins/top fins also turned black.
<Do look at Metynnis maculatus, which has black spots on its flanks.
Metynnis argenteus sometimes has very small speckles on its flanks, but not really big spots. Metynnis lippincottianus is another option too; while similar to Metynnis argenteus, it tends to have bigger spots on its flanks. Myleus rubripinnis is also sold as the Silver Dollar sometimes, though its red, hook-shaped anal fin should help tell it apart. Spend a little time on Google comparing photos. While I'd be surprised if you had multiple species in one batch of fish, it's not impossible.>
They have been acting more aggressive towards the other 2 silver dollar, with the bigger one being the most aggressive. These two have often been rubbing against one another. I'm confused, I thought the ones with the red anal fins were the males, but they get chased into corners and they stay out of it when the other 2 are rubbing and fighting.
<Well, yes, the ones with red fins usually are males if we're talking about Metynnis argenteus.>
Are the 2 with the black spots both males fighting for dominance, or male and female?
<Difficult to say. When kept in groups less than six, "all bets are off" when it comes to behaviour: schooling fish simply don't work as they should in too-small groups. In a nutshell, schooling fish try to establish a pecking order. In big groups, no one fish can bully all the others all the time, so a sort of peace reigns. But if you have too few, you make it easy for a bully to cause trouble, and their schooling instinct doesn't work.
Try adding some more and see what happens.>
They are often going at it while the other 2 pick a corner until it's calm again. I have also noticed that the 2 with black spots will periodically go over to the other silver dollars and nudge or nip at it, then go off again to rub and fight. This has been going on for the past 2 months. I assume it is some kind of breeding behavior, but shouldn't it be over with by now? I have not seen any eggs, will they just keep going until some eggs are deposited.? I wasn't to concerned before, however, now I'm starting to see more ragged fins with no end in site. Should I let the behavior run its course, or do I need to do something?
<Do something.>
Thanks for any info
<Cheers, Neale.>
Re: silver dollars fighting 10/7/2009

Thanks for the quick response,
The tetras have been behaving and only fight amongst themselves and the Gourami has taken over the tank.
<Well, okay.>
The Gourami doesn't beat up any one fish but they all know whose boss.
<For now.>
I attached a few photos, maybe they can help with identification.
<Actually, they look rather odd, and not any species I'm familiar with.
Myleus schomburgkii has a black vertical band on the flanks, but a bit further back along the body. They certainly aren't the Red-Hook Metynnis, Myloplus rubripinnis; the anal fin is all wrong for them. The two common Silver Dollars, Metynnis hypsauchen and Metynnis argenteus, have the right body shape and the red anal fin, but not the spots on the shoulder like yours. Metynnis maculatus has lots of spots, all over its body.>
The two that develop the spots (also red throats and black edges on fins) don't always them. They seem to change almost instantly when they are ready to do battle, which most of the time during the day. I was afraid of adding more because I didn't know if there was enough room left. I'm not getting a bigger tank any time soon, however, if adding more with bring peace, then I'll do it.
<I suspect adding a couple more will be helpful.>
Thanks again
<Cheers, Neale.>

All plastic plants... I'd feed some greens. RMF

Re: silver dollars fighting  10/9/09
I plan to pick up 2 more silvers dollars. If there is a selection, should I get 2 like the aggressive ones with the spots or 2 like the others? Does it matter?
<I'd get two of the *less aggressive* sort, on the assumption this will minimise bullying by dividing up the attentions of the aggressive fish among a larger number of non-aggressive fish. Cheers, Neale.>
Re: silver dollars fighting  10/22/09

hello again,
I recently added two more silver dollar. The store had one large red hook and three small common ones. I bought two of the common ones. They are only about a fifth the size of my current guys. They haven't schooled with my big guys yet, but they are starting to become more comfortable.
<Only members of the same species school, so it's important to make sure you buy the same kind as whichever ones you already have.>
The turquoise rainbowfish is bossing them around a bit. He doesn't nip, he's just pushy. I guess he wants to show them that he was there first and he's bigger and badder.
<Rainbowfish should be kept in schools as well, and kept singly, yes, their behaviour can be aberrant.>
The first day they were in corners, now they just move when he comes by then go back to doing what they doing. I was wondering if I could add one more fish - an angelfish.
<I wouldn't mix Angels with Serpae Tetras; Serpae Tetras are notorious fin-nippers, and I wouldn't ever keep them in a community tank. These were my first ever tropical fish -- and I learned about their shortcomings the hard way!>
Would the pearl Gourami not like that?
<Usually, Gouramis and Angels get along fine, given adequate space.>
Would the angelfish become a problem as it grows?
<Pairs certainly become territorial, and single mature males possibly so, though not usually.>
I'm looking to add one more nice looking fish, the angelfish fits that description. If the angelfish wouldn't be a good idea, do you know of one that would work?
here's my community again: 6 silver dollars-4.5",4",2@3.5",2@1.5", 7 long-fin Serpae tetras, 1 turquoise rainbow-3.5", 1 male pearl gourami-4", 1 platy-2", 1 bushy nose pleco-4", 1 clown pleco-2.5", 3 bamboo
<Hope this helps, Neale.>
Re: silver dollars fighting  10/27/09

me again,
<Hello Curtis,>
I had to remove my turquoise rainbow fish. I put him in my 10 gal.
quarantine tank. He immediately attacked the 2 new small silver dollars, then preceded to harass 3 of the other 4 silver dollars. I had noticed him hanging with my silver dollars lately. Maybe he thinks he's a part of their group. Anyway, he would not let the 2 new guys school with the other 4.
When I removed him, the 2 new guys looked so relieved they explored every corner of the tank and began mingling with the big guys and the big guys immediately started becoming more friendly to one an other.
<Yikes! Sounds quite the disaster story.>
What do I do about the rainbowfish? I would really like to keep it - it looks quite nice, but I don't want a rampaging fish. I would consider selling it. Would it calm down after a few weeks in quarantine?
<Often this does indeed happen. As Bob says, "a spell in solitary takes the fight out of them". Put in more biological terms, he's removed from the social group and from a familiar environment. When returned, he has to re-learn his position in the pecking order, and usually the fish that are already there will have the advantage. So yes, it's well worth a shot.>
or go back on the attack? I'm at my stocking limit as far as the inch per gallon rule goes, so I don't have room for 5 more.
<Indeed, adding a few more, maybe even 3-4, would help.>
<Cheers, Neale.>

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