Ask about the method of catch.
You should also know how a fish was caught. Cimarusti says you should ask fishmongers or restaurateurs if it was caught on a hook and line (preferable), a long line, or if it was netted. Netting is often accomplished by a large boat launching a smaller boat along with its net. "Once they've encircled a school of fish, they pull that line up, and the net draws together like a purse. This is relevant because there are certain fish deemed sustainable, but only if they are caught on a hook and line or rod and reel" (like albacore tuna). The purse method results in more so-called "bycatch" and habitat destruction.