As in red streaking and edges mean septicemia, you will need a bacterial med, what fish is it.
Taken off the board.
As suggested by WuvMyBetta
External Disorders.
All information gleaned from You and Your Aquarium - ISBN 0-7513-0274-0. If this information is useful - please support the author and purchase the book from all good bookstores (and some bad ones too).
Septicaemia
This condition can follow on from skin infections such as finrot or may occur independently as a result of dirty conditions. Bacteria enter the blood stream and circulate through the tissues causing inflammation and damage. Blood vessel and heart tissue damage result in leakage of fluids into the abdomen, prpducing dropsy. Inflamed blood vessels in the skin and at fin bases stand out.
Things To Look Out For
Reddening at the bases of the fins
Small haemorrhages around the eyes
Very dull, listless behavious
Lack of appetite
Treatment
Seek vetinary guidance. The vet will prescribe antibiotics. Check the aquarium for the cause and eliminate it.