My goldfish is not in good condition. It is not swimming well showing lethargy and gasping up but other fishes are good in condition they does not gasping so i think the fish have any problem. What should i do?

[Dibyajit sarkar]

 

[Colu]

What are your water parameters ammonia nitrite nitrate temperature with the black on the fins it could be ammonia burn till I no your water parameters it difficult to say for sure I would add an extra air stone and some aquarium salt 1 table spoon for 2 gallons that will aid Gill function and add essential electrolytes till you can test your water parameters 

[Dibyajit sarkar]

My figh has this black spot genetically....and i did a water change immediately.