What's the difference between butterfish and stromateid?

Butterfish

Definition:

(n.) A name given to several different fishes, in allusion to their slippery coating of mucus, as the Stromateus triacanthus of the Atlantic coast, the Epinephelus punctatus of the southern coast, the rock eel, and the kelpfish of New Zealand.

Example Sentences:

(1) While we sat on the shore eating our lunch we watched the otter tucking into a butterfish with the same enthusiasm – and completely oblivious to our presence.
(2) In the butterfish, cod and rockling, all the oxygen absorbed by the skin is consumed by the skin tissue itself, whereas in the other species there is a net inward transcutaneous oxygen flux.
(3) were investigated in seven species of teleosts in normoxic sea water: butterfish (Pholis gunnellus L.), cod (Gadus morhua L.), five-bearded rockling (Ciliata mustela L), shanny (Blennius pholis L.), flounder (Platichthys flesus L.), sole (Solea solea L.) and eel (Anguilla anguilla L.).
(4) Although MPS-II possessed many radiologic similarities to MPS-I, the former presented certain characteristic features such as butterfish-like vertebra, and small triangular malformation of carpal bones and tarsal scaphoid etc.
(5) Bacterial decomposition of butterfish and smelts in small sealed jars containing seawater and other solutions, for periods ranging from 65 to 205 days, results in a large increase in concentrations of dissolved bicarbonate, carbonate, and ammonia (plus volatile amines).