As said above.. It will grow back fine... BTW Melafix generally KILLS gars.. so no on that.... Usually even this type of extensive damage will heal fine with the above treatment as long as a fungal situation does not set in. If a fungal situation sets in then other measures need to be taken but right now do none. This fish though should not in any way be put back into that tank.
100% agree. This guy has forgotten more about Gars than most of us will ever know. Again, please do not take this as an insult, but can you please let us know the species of Catfish you had as a tank mate for the gar?
I stress that I have done FAR worse than you. There are a decent number of us "newbie" gar keepers on this forum to "learn" from some of the true experts that frequent the forum. I am surprised that I beat the X-man to the punch, but there is a wealth of information in the stickies that can be very beneficial to new "gar" keepers.
I would particularly suggest reviewing the stickie on gar tank mate experiences. It is important to note that in the "compatibility" area you always find someone who has made the "undoable" combination work out "OK" for them. The stickie in general has the larger catfish species and gar as incompatible.
Pay close attention in these threads to the experts (Pejelajarto & E-Americanus) where posters have included personal experience success stories of gar tank mates that are generally an "exception to the rule". You would have found precious little encouragement to try the catfish/ gar combination.
You have an excellent source of information at your fingertips. Learn to use it, and ask questions first before "experimenting".
It would also help immensely if you DON'T do what a good number of us "newbies" did at first, and ask a question, get excellent advice and that just F'ing do the "WRONG" thing anyway.
I knew alot more than these Gar experts who had the unmitigated gull to inform me that several 14+" Oscar would not be a great environment for a juvenile longnose gar. I don't foresee retrying the Gar/ cichlid combo. anytime soon.