Dark Lump on Corydoras fin

  1. s

    stephers New Member Member

    I have a 20 gallon (long) tank with 3 corydoras (Im guessing they are Swartz corys) a small pleco (about 3 in), and 4 swords. gravel is a mixture of fine and small and smooth.

    I do a quarter water change each month, ph 7.0, temp stays around 72 degrees F. not sure on the ammonia/nitrate levels. I do have some live plants which may be java ferns (they were given to me by someone who didnt know what they were either- they were just passed down thru the family). I rinse out the filter cartridge when it becomes clogged until it seems to be beyond acceptable use. This tank has been running for about 4-5 years with no major issues.

    I bought the 3 corys together as I've had better survival luck when I buy them "with friends" and they have been living happily and growing for about 6 months now. 1 of them (about an 1-1.5 in in length) which I believe is a female has developed a black/maybe dark brown lump on it's pectoral fin. It is located on the front part of the fin that appears to be bone about center and it around a millimeter in diameter. It is not a spot as their pectoral fins are clear and it it raised like a bump. I have no clue what this is, but my cory is exhibiting normal behavior and eating habits. The other two are fine with no lumps.

    All of my google searches have been less than helpful. one site suggested it may be that she is carrying an egg around, but I was under the impression they do that with their pectoral fins. Anyone have some light to shed on this situation?
  2. toosie

    toosie Well Known Member Member

    Welcome to FishLore!!

    A picture if you can get a good shot might help us. At this point it is really hard to say what it could be.

    You could try upping your water changes. Really good clean water can help a fish to heal all sorts of things and supply them with minerals that could be otherwise lacking causing their immune systems to become compromised. Even mild infections can take over a fish under these circumstances. 25% once a month really isn't much fresh water to provide them. Most of us will change out 50% once a week in order to remove toxins that accumulate in the tank, nitrate being one we can test for but there are a lot of toxins we can't test for and to replace the minerals fish require to stay in really good health. It's a thought, and one that won't hurt your fish, but may help them in many ways.