fishing for invasive species

Before we can effectively answer this question, we need more specific information.  Are we talking about a specific species of fish or an invasive crayfish?  We also need to know what body of water you would be fishing and what the final disposition of the fish/wildlife.  For instance, if we are talking about invasive crayfish, you can take as many as you want.  They just can't be alive when they leave the water where they are caught. Clean, drain and dry all your gear to prevent the spread of invasive species.