Eating is the big one, as internal parasites is usually the most common issue you would have, if they are eating that's a good sign. It doesn't mean 100% so you have to give it about 3 weeks, if they did have internal parasites they could appear normal for a few weeks before they took hold. You also take this time to train them to eat with your method of feeding. Releasing into a 360g captive environment they could just disappear into the rocks and not understand what you were trying to feed them is food. Zebra eels are generally pretty tame, but releasing a freshly wild caught eel directly into a display could also pose a risk for other inhabitants.
Flukes; cloudy eyes, shaking head, swimming at the surface. Sometimes it takes a while for these things to show up, once they are in the rocks in a 360g, it would be a nightmare to try and get them out if you had an issue.
Very, very rare, I'd even say just not going to happen, but protozoan diseases like ich or velvet.
If any of issues arise it would also spread to other fish, overall eels are a safe bet if they are eating, but I would at least give it a few feeding cycles.
I wrote a couple of threads on eels if you want to take a look.
Eels and lions have alot in common; I have seen many posts lately concerning eels, so I thought I would pass on some information that I have learned over the years. !st off, know your source, do not get an eel from a source that runs copper in their system. Eels have sensitivity to copper...
www.reef2reef.com
I usually post in Predatory Forum, today I thought I would post here to get exposure. For some reason when people research eels, they fail to realize, these are awesome predators. I've seen alot of interest and failures of late, my lfs told me they sold 3 eels last week, that's alot for eels...
www.reef2reef.com