Supple Cow

You may want to get yourself a plastic divider and isolate the swordfish for a week or so to see if more fish disappear. If you can't do this, I would still bet on the sharks being the culprits. I'm not sure this species in particular, but sharks do love their fish meat. Getting bigger fish may just be the equivalent of buying them a bigger lunch. Meaner fish - now that's the ticket.

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"I've missed more than 9000 shots in my career. I've lost almost 300 games. Twenty-six times I've been trusted to take the game winning shot and missed. I've failed over and over and over again in my life. And that is why I succeed."
(Michael Jordan)