That sounds right, now that I see others on the web. Thanks for the ID. He was caught with a trap in a canal in the Keys, oddly enough. Here's some info from the web about them:
Common name: Soap Fish
Scientific name: Family Rypticus
Depth found: 5' to 100'
Size: 3" to 8"
Compatibility: Will eat small fish
How common: somewhat
Notes: These fish are toxic to other fish when frightened.