Most likely, I agree....but to prevent it, nikes, it could have been the crab also...anything fresh caught and given to your stomatopod, or , for that matter, any fish...should be caught far out from the shore to avoid transmitting toxins they can carry or disease. Also, they should be QT'd. A shame, as it seems so good for them and so accessable. I keep Bree's snails and crabs in a QT tank for a couple of weeks before she gets them.
Chin up, buddy, a lesson learned well is not forgotten and won't be made again.
You are brave to have gone through this with us. I commend you for that. We are here to help and support each other.
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Curly