If you’re talking the Fish tab of the Collections page, that one doesn’t go by the number you ship. It goes by the number you catch, and picking them up off the beach won’t count.
Either craft or buy some Crab Pots, and put them in ocean water with bait, and come back the next day. The first oyster you catch that way, should light it up. I always end up making 8 or so crab pots. Check and reload them in the ocean every day for a week, and then do the same in the town river, and you should get all of the trappable fish.