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FAQs on Silver Dollars Identification

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

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

Silver dollar identification 3/30/11
Hello, Jim here. Thanks for your wonderful website. After 50 years of fish keeping, I found your website last November and changed many bad habits. I'd like your help in identifying the silver dollar in the attached photo. The red anal fin led me to the Myleus rubriprinnis, but the second dorsal fin on my fish is about as long as the first.
<Second dorsal fin? Do you mean the adipose fin? This is much smaller than the dorsal fin. Quick reminder: Characins only have a single dorsal fin.>
The finnage seems more like the Metynnis genus.
<Yes, would agree, and something like Myleus rubripinnis rubripinnis, the Red-Hook Metynnis, would seem probable here.>
Two identifying characteristics that don't show up well in the photo are a white tip on the anal fin, and a dark spot about ½' behind the eye and just above the lateral line about the same size as the eye. This spot is almost invisible when the fish is peaceful, but shades to almost black when the school is going through 'pecking order' exercises. It is darkest in the most dominant fish, and fades to very light in the most submissive. There are no other spots on the fish at any time. I Googled a photo of a Metynnis guaporensis that looks close, but the underlying link wanted to search my system for viruses. I didn't find a site that had much information on this species. Fishbase has no photo, but a drawing that seems improbable for a Metynnis.
<There are a great many species in this genus, plus the similar genera Myloplus and Myleus. It is clear that more than a single species have been imported under names like "Red Hook Metynnis" over the years, and the photographs in aquarium books are probably somewhat unreliable. The best approach is to review Fishbase for this family:
In reality, telling some of these species apart depends on microscope work, or at the very least, counting scales and fin rays and other measurements you simply can't do with live fish. The more common species in the trade are sold as Metynnis hypsauchen, Myloplus rubripinnis, Metynnis lippincottianus and Metynnis argenteus.>
I'm most interested in the size this fish will attain, and secondarily in the life expectancy. The fish have about doubled in length in 5 months. If they outgrow their tank I'll have to find them a new home, as I don't intend to install a larger tank.
<Do expect at least 15 cm. Be pleasantly surprised if they stay smaller, but also be wary that 20 cm is not impossible, if unlikely under aquarium conditions. As for lifespan, should be in excess of 5 years, perhaps as much as 10 years if all is well.>
I stocked (overstocked) this tank last November before I found your site, and have since adjusted school sizes for silver dollars and Corys up to present levels, and also added the Otos to help with algae issues that I will get under control without whining. Behavior has been good and improving both within and between all species in the tank. For example, the silver dollars have all but stopped the pecking order exercises that used to occur several times a day. I expect the gouramis will thin out naturally in about a year and a half if they don't fall ill, but all the other tankmates should be around a good while.
Thanks for all I've learned from nosing around your entertaining site.
<Cheers, Neale.><<This is almost certainly a Metynnis sp., likely Metynnis hypsauchen. RMF>>

Silver Dollar Fish spots and possibly bad water.  1/4/09 Hi, I recently discovered your site and my head is spinning from all the recommends and good information! I wrote you this week to ask about my Gourami's nipped fin and you were extremely helpful. Now I have just discovered I probably have two new problems. My Silver Dollars appear to be developing spots. They are round dark gray spots that don't seem to change the fish surface texture in any way. See the attached pictures. The fish appear healthy in every other way; good social life and very good appetites. And I really thought my tank was cycled, but it's not and I'm fearing for the safety of the fish. I relied upon unreliable chemical measurement devices; quick dips. And used a lot of chemical products. Now, I'm wondering if my two problems could be the same problem--bad tank water causing Silver Dollar spots. All my other fish are doing well, except for one of the Cory cats who is obviously very lonely; eats well, but hides a lot. But I won't add more fish until all these problems are resolved. To sum up, here are My Questions 1. What do my Silver Dollars have? 2. How do I fix whatever it is they have? 3. Where did I go wrong with tank upgrade cycling? 4. How do I fix the tank upgrade cycling situation? The Story. I thought the spots were natural coloring on the two largest of my Silver Dollars; I have three of them. Then today I visited my LFS and spent some time observing their Silver Dollars--none of them had spots. When I returned home, I noticed the smallest of my three now had spots when there hadn't been any before. Plus I realized the spots on the other two had become more numerous. I guess that means it's more than natural coloring. I'd like to know if this is a sort of disease and what I can do about it. General information regarding the tank is below. But here is some history that can be helpful in diagnosis, I hope. A month ago, I upgraded from a 10 gallon tank to a 50 gallon tank. To cycle the new water, I transferred about 7 gallons of water from the 10-gallon tank into the new 50-gallon tank, inserted filter material from the 10-gallon tank into the new tank filter system and used the Stability product (described below) as directed--except I extended it's use from one week to two & a half weeks. So as to let the good bacteria build up, I've only done one partial water change with the new tank--I vacuumed the bottom and changed out about five gallons of water. I'm wondering if my Silver Dollars have a bacterial infection from overuse of the Stability product. But that's confusing because the bottle specifically stated there was no danger in over use. Stability-New Tank Stabilization System. What follows is a quote from the bottle. "a synergistic blend of aerobic, anaerobic and facultative bacteria which facilitate the breakdown of waste organics, ammonia, nitrite, and nitrate. The bacteria employed by Stability are non-sulfur fixing and will not produce toxic hydrogen sulfide. Stability is completely harmless to all aquatic organisms as well as aquatic plants, thus there is no danger of over use." Using the quick-dip test sticks left over from my smaller tank, I thought my upgraded tank was cycled. After reading your web site I decided a more precise measure of tank chemicals was in order and bought some test kits today, (that's what I was doing at the LFS). I learned two things. One, the color charts on these kits are very hard to read. Two, my tank has NOT cycled. I obtained the following readings. Nitrite NO2 = 1.0 ppm NO3 = 5.0 ppm So now I'm thinking maybe the Silver Dollars have been stressed out all this time and the stress led to the development of a bacterial infection OR that the high level of NO2 has done something to the fish. I really thought adding the old water from the 10-gallon tank and old filter material would have sped the cycling process along. The final thing I can think of is that I had a ph problem for 4-6 weeks, the water was acidic, around 6.2. About one and a half weeks ago, two heavy doses (about 5 days apart) of a ph regulator brought it up to 7. Could the spots be related to water acidity? After much reading on WWM I've decided I'm probably overfeeding and will reduce feedings to one type of food once daily and cut out the proteinaceous shrimp until tank properly cycles. My LFS owner told me that my fish will survive the high NO2 and NO3 and that the tank will probably finish the cycling within 2 or 3 days. I'm not as confident as he is and am worried about the toxicity of my tank and the health of the fish in it. Tank information. 50 gallon tank: 19" high, 48" long, 12" wide; Ph=7 ; Lots of hiding places-huts/caves/arranged stones; Lots of fake plants of differing texture, height and density; No live plants; Filtration=two Aqua Clear filters, each for 40-70 gallon tank; Temp: 79 degrees; Food: Daily, Aqueon tropical flakes and Hikari tropical micro pellets; weekly, frozen brine shrimp; most days, spinach, romaine lettuce or other nutritious greens. Fish transferred from 10-gallon tank to 50-gallon tank 9 Neon Tetras (one died since) 3 Rainbow Tetras 3 Emperor Tetras 3 Albino Cory Catfish (one died since) Fish added to above fish in 50-Gallon upgrade 1 Pearl Gourami 3 Silver Dollars 3 Buenos Aires <Greetings. The short answer is that several "Silver Dollar" species are on sale, and some of them have black spots. Yours may well be Metynnis maculatus, the Spotted Metynnis, a species that gets to 18 cm in length and according to Fishbase at least is known to give serious bites, so be careful! Silver Dollars are vegetarians to be sure, but they have strong jaws just like their very close relatives the Piranhas. http://www.wetwebmedia.com/FWSubWebIndex/serrasalminae1.htm Anyway, as for cycling. The truth is that these "bacteria in a bottle" products are often very hit-and-miss, and cynic that I am, any product that advertises itself with the word "synergistic" rings all kinds of alarm bells with me. It's one of those buzzwords used by marketers rather than engineers most of the time, like "holistic" and "wholesome". So if you went "wrong" anywhere, it was probably in assuming that this product would do what it said it would. The reality of life is that cycling tanks is best done by introducing obviously live biological media -- e.g., live rock (in marine tanks) or mature filter media (all types of tanks). Assuming you have at least one mature filter from the 10 gallon tank, dividing up its biological media into the two large filters on the big tank should jump start them very effectively, and I'd expect these new filters to settle down within a week if "seeded" this way. In the interim, don't feed the fish much (if at all) and do lots of generous water changes to keep nitrite below 0.5 mg/l. With luck, that'll get you through the worst of things, and you'll be fine. Cheers, Neale.> Thank you. There's a wonderful place for you fish-guys in heaven! <What a kind thought! Happy to help, Neale.>


Sick Silver Dollars (no, they're really not!)  8/18/08 Hello Robert I am having some problems again.. You've been extremely helpful in the past.. I have a small shoal of silver dollars, 15 total.. 2-3 of the fish have reddish spots or splotchiness on their bodies. <Normal for sexually mature (male) Myloplus rubripinnis "luna".> 1 in particular has it bad.. They have been that way for approx. 18 months or so.. When I got them I had quarantined for 3 months due to some Ich and what looked to be some sort of secondary infection from the Ich.. The red spots have always been there just less noticeable at times.. 1 fish has it particularly bad.. It hasn't affected his/her behaviour at all. He swims with the rest and eats like crazy.. They are living in a 240 with misc other fish.. Bichirs, Endlis, Distichodus, Niger Cats, Asian Redtail Cats, Assorted Cichla and a large Flagtail Prochilodus.. <Nothing to worry about.> I have attached links to where I have some pics of them saved on the net to reduce the size of this email.. If you want the originals you can take them in whatever size you want from my Flickr link or let me know and I can attach them in whatever size you need.. Thanks Doug Here is the link to the picture set. http://www.flickr.com/photos/fishnfst/sets/72157608166578919/  <Nice photos! Cheers, Neale.>
Re: Sick Silver Dollars (no, they're really not!)   10/19/08
Wow thanks for the quick reply.. I'm glad that they aren't sick :) I saw some with the same markings at the California academy of sciences today.. <Sounds a fun day!> I thought maybe theirs were sick as well.. Now I know... Those are the males... <Indeed.> Thanks Again Neale.. Doug <Happy to help. Enjoy your fish! Cheers, Neale.>

Tom... need titles to find/match prev. corr... 9/28/06 ? Pacus, Serrasalmine IDs... Tom, <<Hi, Lisa.>> Oh, I'm so confused! Well, my cousin said that I had a cichlid? I know for sure that I had at least one I know for sure is a silver dollar. . . ( I had two) But maybe it's a Pacu? <<Could be... These two, and Piranhas, are sometimes confused at the juvenile stage. As they mature, the differences become more obvious.>> Is there any kind of difference between a Pacu and a Silver Dollar? <<Oh, Lord, yes! Sorry about the emphasis but if you have a Pacu as opposed to a Silver Dollar, you'll need a 300-gallon aquarium to keep it. Not likely, I'm thinking. :) Now, a Piranha might have a distinct taste for your other fish.>> I know for a fact it was eating my fish because one day I saw parts of what was left of my fish chomping on it! I really did get the memo.. Just its wrong.. ( haha) Yes, its very 'nervous' I can't even turn on the light in the tank and it goes crazy. <<Again, this is common of Pacus, which is why they fall into the "tank buster" category. They can/will "frenzy" themselves into anything and everything in the tank. Not what you want in a fish that reaches 30+ inches in length and can weigh upwards of 55 lbs. or more.>> My fish is not typical in any way. Oh, I think this is kind of funny. When I was cleaning my tank I noticed my fake plant had gnawing marks all over them. I wonder who that was from'¦ <<Silver Dollars and Pacus, both, will eat aquarium plants of just about any variety. (There are some plants that folks have found that won't get devoured but most of those that you'll find readily at the fish store will be turned into "lunch" sooner or later.)>> Okay for the filters'¦ even if you have charcoal, they don't get the bad stuff out- thought it got the 'invisible solids' out? <<Activated carbon does a very nice job of "polishing" the water of hard-to-eliminate solids but does nothing for ammonia and nitrites.>> Um, I usually clean the filter when it gets kind of bad. Hard to get the stuff out, I change it. I'm such a bad fish keeper! Definitely getting an F'¦ (haha) I'm guessing you are an aquarist yourself? <<Yes, indeed.>> If so fresh or saltwater? <<Strictly freshwater at this point in time, Lisa.>> Yes, I do wish there was more time in the day. That would be nice'¦ Lately I been going to bed kind of early 9-10. I guess my body isn't in the swing of school yet. Should I tell the person about the worms? Or keep and eye out on the tank? ( I'm scared to tell him.) <<As I suggested, Lisa, the problem is with the tank, not the fish. If your friend's tank comes down with Planaria, it will be due to water conditions in his aquarium, not the fish you gave him. You're off the hook! :)>> I'm sorry I'm bombarding with a lot of questions. <<Any time, Lisa. Tom>>

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