There are four categories to which one can ascribe to fish when it comes to texture: Soft, Slightly Firm, Moderately Firm, Firm.
Soft can be best desribed as th emeat of fish is extremely flaky (Sea Trout), or that the bones are so soft that one can eat them (Sardines). Firm can be best described as being able to cut the meat into steaks and the bones have to come out. Everything else is somewhere in between.
Soft:American Sole, Anchovies, Atlantic Mackeral, bluefish, buffalofish, butterfish, eulachons, European Sardines, flounder, Freshwater bass, herring, Rainbow smelts, Sea trout, shad, and whiting.
Slightly Firm:Atlantic croaker, Black Sea Bass, fluke, hake, ocean perch, pike, pollack, porgy, rockfish, sablefish, snapper, Spanish mackerel, sunfish, tilapia, tilefish, trout, and walleye.
Moderately Firm:Arctic char, cod, grouper, haddock, halibut, King mackerel, mahimahi, monkfish, mullet, orange roughy, red drum, red mullet, salmon, sea robin, skipjack tuna, striped bass, wahoo, white hake, whitefish, wolffish, and yellow perch.
Firm: Amberjack, Atlantic bonito, bigeye tuna, black drum, blackfish, blowfish, bluefin tuna, carp, catfish, cusk, Dover sole, eel, John Dory, kingclip, lingcod, ocean pout, pompano, shark, skate, sturgeon, swordfish, yellowfin tuna and yellowtail.