Gouramis have long pelvic fins that resemble needles. These enlogated fins serve as feelers for navigating their murky home waters. However, these graceful fins are prone to damage. In most cases, they will heal on their own, but you need to identify the cause and correct it to prevent recurrence. In some cases, you may need to take medical action to protect the fish.
First, you need to identify the cause of the damage. Since these pelvic fins are so delicate, many things can harm them. Some species of gourami get into fights. Meanwhile, gouramis' long fins are magnets for fin-nipping by small, active fish like barbs. Some fish just find these long, elegant gourami pelvic fins to be nuisances. Damage during shipping or transport and infection are other possible sources of damage.
Most of the time, a gourami's fins will heal on their own. Just make sure you've removed the original cause of the damage, particularly if it's an aggressive tank mate. Also, keep up on aquarium maintenance like water changes. In sub-optimal conditions, complications like fin rot are more likely to further harm the fins and prevent healing. In fact, if conditions in an aquarium degrade enough, gouramis can develop fin rot spontaneously. Usually the fin will heal on its own; but if the damage is uncommonly severe, the damage may remain. However, if the fish was hatched with a missing or deformed pelvic fin, it is unlikely to ever develop normally.
Signs of Fin Rot
If you see signs of fin rot, the fin will not heal on its own; the situation requires your medical intervention. You will see either a slimy or fuzzy margin to the damaged fin. Sometimes, streaks of blood will appear along the fin. In a narrow fin like a gourami's threadlike pelvic fin, this may require a very close look and great attention to detail for you to notice. If you see these signs, you need to move quickly, since fin rot can spread to the fish's body and kill it within a week.
Treating Fin Rot
The best, most reliable way to treat fin rot is to use commercial aquarium products to do so. These products are usually cheap and effective, especially if you catch fin rot early. Always follow the manufacturers' instructions to the letter. Since fin rot does not readily spread from fish to fish, you can treat your gourami in a separate quarantine aquarium. Remove any activated carbon or zeolite from filters before treating, since these can absorb medications.