gsb_78

I have 3 goldfishes in 50 gallon tank. For the last 6 days i have observed that
(1) A blackish color is developing on their tail fin ends and near their mouth.
Their links are as below:

(2) One goldfish is a little sluggish, remains in the middle tank region, aggressively feeds onto the given food, but gulps out all it has eaten within 1-2 minutes of eating.

Kindly guide as to what the reason could be.

susitna-flower

First, do you have a master test kit? If you do, what are your water parameters? Do you do water changes? The first thing I would suggest is that your fish appear to be developing fin rot, which can be caused by bad water conditions. IF your cycle has not been completed, and ammonia, nitrites or nitrates are too high, this stresses the fish, which could account for all symptoms. I prefer to start with water changes, before any medication is tried. If you can maintain 0 ammonia, 0 nitrites, and no higher than 5 nitrates, the condition should right itself. If you haven't been doing water changes, this might mean you will have to change 50% SEVERAL days in a row.....then keep an eye on the levels to maintain the better water conditions.

gsb_78

Thanks for your prompt response.

My tank readings are as below:
pH - 7.5
Ammonia - 0 mg/l
nitrite - <0.3 mg/l
nitrate - 12.5 mg/l

I have had these goldfish for the last 4 months now. There were no black patches initially, they have appeared very recently.I do vacumming and 10% water changes every week.And feed them 4-5 pellets each, twice a day.

While rest of fishes are all very active, its only this one goldfish which is very sluggish. Today it did not eat anything.Keeps swimming in the middle region of the tank and importantly i have seen it open a mouth very wide(as if it were yawning) since last 3 days.
Its other mates in the tank are:
2 more Goldfish
3 Silver Bala Sharks
4 Parrots
2 Angel
I know its a wrong combination but as i later realised that vendor had given me a wrong combination(When i bought the new tank 4 months back) and neither was he wiling to take them back nor i could find an alternative arrangement for them, so I decided to keep them together.

P.S: On closer observation I have seen these black patches have also started appearing on 1 Parrot.
Their Pics with black patches are given below for your kind reference:

gsb_78

One of my Goldfish which was on fasting for the past 6 days now died today evening. I found it floating bellyup on water surface. Dunno what happened!!!

Chief_waterchanger

By fasting do you mean it stopped eatting or you stopped feeding it?

If it stopped eatting that is probably why it died, but if you stopped feeding it and the container (tank, pond, etc) were well established it would eat on the algae and microfauna.

I would think it to be a bad idea to put a fish on a fast for 6 days.