Black Marks On Silver Dollars?

[redSG]

Hello all...we're looking for a bit of advice on some newly noted markings/behaviour with our silver dollars.
We have four SD's in a 190 litre tank. Two have been reared by us from a small size (one's a red-hook, if that makes any difference) for about 10 months; two were purchased grown about 4 months ago. They're all currently about 2-2.5 inches round, and had been quietly schooling and getting on til recently.
In the past few days, the two newer SD's have developed black patches near the gill region, and a blackened tinge to the edge of their tail and dorsal fin. They also seem to be chasing each other/the other SDs. The older SD also has developed these dark areas, but not as intense/constant, and without the aggression. The Red-Hook hasn't developed any darkness and is docile as ever.
I've tried to research, but the only thing that seems to come up is a black-spot disease that doesn't resemble this at all. Does anyone have a clue as to what's going on? Conditions in the tank have been constant since it's been set up about 10 months ago, and the only other problems we've had with the SD's was a touch a white-spot when we added the newer two. Tankmates include an earth-eater, a parrot cichlid, a couple of gouramis, a rainbow shark, a couple of angelfish, a sailfin plec and a chinese algae eater. The tankmates seem to leave the SD alone and vice versa.
I'd appreciate any help/advice on the matter.

 

[WILDER]

Black patches can be ammonia burns that are healing.
Will get you some info to take a look at.
Look under black patches.
[URL="http/www.fish-disease.net/diseases.htm"]http/www.fish-disease.net/diseases.htm[/URL]
http/puffernet.tripod.com/myxobacteriosis.html

 

[redSG]

Thanks for the links. I'm not sure if this is ammonia poisoning, as the fish aren't gasping and gills look fine. Plus, the levels are nil. I'll keep checking, though.
One new thing I noticed today, it appears that one of the regular SD's was trying to rub up/shimmy against the red-hook (who I think is a female--it's a bit rounder than the others). Could it be that the fish are trying to spawn? Forgive my ignorance, but I've no experience in breeding egg-layers.

 

[WILDER]

Black patches can be due to ammonia in the tank but when you see the black patches it means that the fish has healed nothing to worry about.
Not sure if its mating behavour as I have never kept them,.
But someone will know on the forum.
Good luck.

 

[cheesy feet]

Thanks for the links. I'm not sure if this is ammonia poisoning, as the fish aren't gasping and gills look fine. Plus, the levels are nil. I'll keep checking, though.
One new thing I noticed today, it appears that one of the regular SD's was trying to rub up/shimmy against the red-hook (who I think is a female--it's a bit rounder than the others). Could it be that the fish are trying to spawn? Forgive my ignorance, but I've no experience in breeding egg-layers.

Yup they're breeding, mine do that and get that (the black marks) when they're in the mood.Nothing to worry about.

However your tank will become a bit overstocked,If not slightly already, the parrot cichlid and sailfin should both really have a larger tank.The silver dollars should be much bigger then 2 1/2 In 4 months.What are you feeding them?
In 4 months mine were like 5' or so, I think.Massive now anyhow.I've been feeding catfish pellets, courgette, peas, tetra prima, bloodworms, glassworm, beefheart and prawns
I've never bred mine but it they usually do the shimmering dance at night, my fish must eat the eggs they drop though, I've never spotted them.

Good luck!

 

[redSG]

Thanks for all the help guys. At least I know it's nothing to be worried about! They actually seemed to have calmed down a bit, so maybe they got it out of their system for a while.

That size was a typo...the guys are about 3.5 inches (the red hook's a bit bigger), not counting fins. It's a bit hard to get an accurate measurement, as they haven't been staying still much lately, and the glass is curved. They love eating catfish wafers/pellets, and also eat just about anything else we throw at them (flake, prima pellets, bloodworm, brine, shrimp sticks, our broad leaf plants). We've tried feeding them peas and spinach, but they didn't seem too keen.

We're well aware of the size/stocking issues with some of the fish. When we were first starting out, we were told by the lfs that our pleco would be fine in a 60L tank. Imagine our surprise when we picked up an encyclopedia and found out how big they can get! We moved him within a couple months of that to the 190L, and he seems okay for now. With the Parrot Cichlid, he's still pretty small, but we know they get bigger too. Currently, everything seems to be going quite good, knock on wood, but it's certainly in the cards to upgrade eventually.

 

[cheesy feet]

Nice one, sounds like you've been giving them excellent care.

Suprises me that they wouldn't eat peas...