The Literal Commandment
These you may eat, whatever is in the water: all that have fins and scales, those in the water, in the seas or in the rivers, you may eat. But whatever is in the seas and in the rivers that does not have fins and scales among all the teeming life of the water, and among all the living creatures that are in the water, they are detestable things to you, and they shall be abhorrent to you; you may not eat of their flesh, and their carcasses you shall detest. Whatever in the water does not have fins and scales is abhorrent to you. (Leviticus 11:9-12)
The literal commandment is that we should not eat water creatures that do not have fins and scales.