We can also conclude that:
If a non-fish sea creature was considered as a fish by the early Arabs, then we will consider it as a fish, e.g. a Whale.
If a non-fish sea creature was unknown or never mentioned by the early Arab community then we will either use Analogy or we will use a modern biologically definition, i.e. we will say it is not a fish biologically therefore haram.
If the sea creature is a fish, regardless of size or predatory nature, it will be halal.