Help my poor fish!

It is difficult to determine from the photo what it is.

Is it like a slimy looking spot or an ich-like spot?

Could just be small wounds from being netted and moved. Hopefully, Melafix will fix your fishy up. But without the info rbishop requested, there is little we can determine.

Was the 55g tank he was moved into cycled prior to his introduction? Are there any other fish in that tank? The pH is rather acidic, and dropping pH for fish can be extremely stressful. What is the pH of the tank he came from, and how long did you drip acclimate him to his new tank? Your ammonia seems to be within the realm of possibly being lethal... you need to do a huge (50-75%) water change and possibly keep doing them once or twice daily until that number comes down. IMHO, a 55g tank is not an appropriate size tank for a fish which is a foot in length, but that aside, I would like to see your fish pull through this. What is the temperature in the 55g vs the 35g, and what kind of filtration do you have on the tank? (asking to determine the water turn-over rate, not so much for what brand of filter it is)

the fins look like they may have some nitrite burn. you need to get the ammoina and nitrite levels down; do a 50% water change.

what else is in the tank and what size is the tank?

I'd like to make a few suggestions for you, and I believe it will help you out in the long run. (and I believe I have a few questions yet too)

The 55 gallon tank you have would be better suited with at least one more filter, rated for at least double the flow rate of your current filter. Ideally speaking, you want the water in the tank to be processed 5-10 times per hour. (also keep in mind, the flow rate quoted on the packaging is not what the actual flow rate is... so long as the filter is maintained, I would say actual flow rate is 60-75% of listed flow rate.) That having been said, I'd recommend getting a large aquaclear filter (like the Aquaclear 70) which is rated for 300 gph. The combined quoted power of your filters would be 420 gph, and 60% of 420 would be 252 gph. In my opinion, that would provide adequate circulation for the tank, as the turn-over rate would be at least 5-1, and possibly a little higher. You would also want to have the filters on opposite ends of the tank (they can both be on the back of the tank, just one on each end) so that you can minimize or eliminate dead spots in the water. (areas with no flow)

What is the wattage rating of the heater you have? Ideally to keep a 55g tank at 78-80 degrees in an otherwise cool environment (assuming it can drop to low 60's) you would want a 300 watt heater, or to ensure more thorough heating, 2 150 watt heaters, one placed near each filter to disperse the heat with the water flow.

The fish you showed us, is it a wild caught native fish? If so, you may want to check with local laws as far as releasing him back into the wild, as well as check his water requirements if you are able to find them. It is illegal in most (if not all) states to release any captively kept animal (fish, bird, mammal, etc.) into the wild, for fear of introducing new bacteria, disease, etc. and damaging the ecosystem.

I was a little unclear as to whether or not your fish had any other tank mates. Were there other fish/invertebrates in the 55g with him, or was the the only inhabitant?

I'm very glad to see that you are concerned about your fish's well being, and that you want to provide the best care for him you can. All too many people view fish as disposable entertainment, and that ideology is something I would love to break one day. I have the utmost respect and compassion for all of the pets I've ever kept, and I always strive to take care of them to the best of my abilities. Best luck to you and your fish.