With this mod, when a fishery improvement is built, the tile no longer gets worked by a citizen. This means the base resources for that tile are not available.

The upshot is that placing a fishery could be, and often is, detrimental to the city. it means you have to examine the surrounding area to see if placing a fishery is what you want.

The mod needs to be changed so that a fishery can be worked for the base resources. It should never be that improving a tile is detrimental.