Someone who has a fish tank at home bought Kosher L’Pesach fish food to give to the fishes over Pesach. The fish food before Pesach cost around 12 shekels (normally it would cost half that or even less.) Someone came along and threw away the food (purposely) Subsequently the fish didn’t have what to eat over Pesach (they didn’t like Matzah…Perhaps because it was grebucks) and died. Is the person who threw away the fish obligated to pay according to the price of the fish food before Pesach, or the price of the fish food now? What about the fish themselves: is he chayiv to pay for the loss of them?
I don’t think fish have a problem with gebrochts.
The person who threw away the fish food has to pay the value at the time he threw it away (like a person who is mazik an esrog; although there is a great and renowned dispute over paying for the value of the hiddur, all agree that after Sukkos the damager can’t simply give the person a new and highly inexpensive esrog).
He isn’t obligated to pay for the fish, though there might be an obligation latzeis yedei shamayim, because he caused their untimely demise.