ANY TIME your skin is broken in an aquarium you SHOULD worry about it. Aside from whether the wound was produced by a venomous animal, there are a number of bacteria and other pathogens that can cause serious infections that can be difficult to treat. In fact, there are infections that are known to only occur when aquarists immerse open wounds in their aquaria. Any time you have a fresh cut, puncture or other wound and it is in contact with an aquarium or marine critter, you should wash it thoroughly with soap and water and consider the use of other antiseptic measures. I would add that to openly engage in behavior that might lead to a bite or scratch is a risk you should seriously reconsider. Believe me, there are things growing in aquaria and particularly in the mouths and on the spines of the animals that you keep that you do not want to introduce into your system.
Roy