It is also written: … and they shall be a detestable thing unto you. (3M 11:11)
The subsequent sentence of this verse clarifies the sense of the Hebrew word שֶׁרֶץ; it is a ban of consumption and contact with the carcass.

We should keep our distance from this type of animal from the water, and not contaminate our food through them, because it is written: … ye shall not eat of their flesh, and their carcasses ye shall have in detestation. (3M 11:11)
And it is also written: Whatsoever hath no fins nor scales in the waters, that is a detestable thing unto you. (3M 11:12)
This verse repeats the earlier prohibition.

This verse highlights the condition Whatsoever …  in the waters, it means, that we must scorn all animals from the water that do not have fins and scales during their life in the water.
There is one type of fish known as Kena'at *, which, after pulling out of the water, loses its scales, however because in water it has scales and fins, it belongs to the allowed fish.

* Kena'at - it could be the Spanish mackerel Scomberomorus maculatus; in Arabic سمك الكنعد ((samak) al kanad - translator's note)

The above verse explains why is this particular species, is permitted the same as other fishes belonging to the same genus.
Through this verse, Allah ** wanted to remove all the doubts that might arise.

** This work is written in Judeo-Arabic language, and from this reason the author uses the Arabic word الله אללה Allah; he uses the word Allah as the Arab word for the One God, not as the name of the One God - the translator's note.

Keep in mind that, although a rule for water animals meeting only one of two criteria is not mentioned, the same principle must be applied as for terrestrial animals that do not meet all three criteria, ie it is not permissible to consume them.

The rules regarding water animals is included also in the fifth book of Moses, only the expression detestable שֶׁרֶץ is replaced by the expression unclean (impure) טָמֵא: These ye may eat of all that are in the waters: whatsoever hath fins and scales may ye eat. (5M 14: 9)
And whatsoever hath not fins and scales ye shall not eat; it is unclean unto you. (5M 14:10)
The term טָמֵא has the same meaning as שֶׁרֶץ.
The sense of the word שֶׁרֶץ is explained at the beginning of this chapter.
Keep in mind that the expression טָמֵא, very often associated with food, has almost the same meaning as שֶׁרֶץ.
But if the term טָמֵא is connected with a person who has touched a kind of impurity, it means that this person has became impure.
Therefore, the word טָמֵא needs to be interpreted on the basis of the context.
Its meanings depend on the word to which it is bound.