Flatfish and Spiny-finned fish

Flatfish noun - Any of several families of fishes having flattened bodies that swim along the sea floor on one side of the body with both eyes on the upper side.

Spiny-finned fish and flatfish are semantically related. In some cases you can use "Spiny-finned fish" instead a noun "Flatfish".

Spiny-finned fish noun - A teleost fish with fins that are supported by sharp inflexible rays.

Flatfish and spiny-finned fish are semantically related. Sometimes you can replace term "Flatfish" with "Spiny-finned fish", this terms are similar.