Much of the difference boils down to diet and physiology, but there are a few key things that make fish different from other types of meat. While beef and pork store their fat in tasty little pockets, fish fat is contained in their oil and distributed throughout their body. It's like the difference between keeping your money in your wallet or wearing it like clothing. Fish muscles are also flakier than other types of meat because they're segmented in order for them to swim efficiently, as well as flop back and forth furiously after they're caught.
To give a little more insight into why fish taste the way they do, we've broken down five of the most popular foods of the sea with some tasty science nuggets on why they make for such tasty nuggets. LEARN THINGS AND BE AMAZED!
CATFISH Diet: Dead fish, mud, worms, animal feces, bugs, rotting plant vegetation. Anything, really. They're like the sluts of the sea. Physiology: Catfish are nearly blind and use their mouth to explore the world around them, so they're putting quite a bit of gross stuff in there. Again, we could make a pretty accurate slut of the sea reference. Taste: When you cut open a catfish, you'll typically find mud -- this is why some people consider the meat to taste "muddy" or "dirty" or "like a fish that's been eating gross old stuff all its life", especially in the middle, but sweeter towards the ends. It's also why people fry the sh*t out of catfish.
SHRIMP Diet: Plankton, worms, small shellfish Physiology: The "sand vein", aka the digestive tract, is actually mostly flavorless. The exoskeleton does hold a ton of flavor, however, as well as help in lowering cholesterol. Taste: A study in Fisheries Science compared freshwater to saltwater shrimp and showed that the saltwater increased the levels of umami, sweetness, and overall flavors. But the New Kitchen Science adds that if there's too much iodine in the saltwater, it can lead to a metallic taste, and that smoother tasting shrimp can be found at the mouths of rivers because of the lower salt content in the water.
SALMON Diet: Smelt, herring, krill, anchovies, mackerel, shellfish Physiology: Salmon is actually a white fish, but the diet of krill colors the meat orange. The muscles are stronger because of longer swimming distances, but less firm due to less interaction with tides. Taste: The higher the fat content, the more powerful the taste, as evidenced in appropriately named species like King Salmon. Colder water increases this fat content and therefore the level of deliciousness. The diet of small, salty fish also contributes to the rich flavor, as opposed to a ska fan, who survives on a diet of Reel Big Fish.
TUNA Diet: Sardines, herring, mackerel, squid, crustaceans Physiology: The red color comes from a higher level of hemoglobin, and the meat is firmer because of the thicker muscles necessary to swim in high tides. Taste: Across the nine species of tuna there is a ton of variation in quality, with the littlest tunny having the cutest name and the coarsest texture due to its small size and low percentage of edible meat. Bluefin's gigantic size means it's consuming exorbitant amounts of small, salty fish that give the meat its unparalleled flavor.
OYSTERS Diet: Algae, plankton, sea water Physiology: Oysters store starch as an energy supply, instilling their meat with a sweet taste. Taste: An oyster's flavor depends largely on the ecosystem in which it's raised. Fanatics consider the terroir as important as it is to wine. The type and amount of algae in an area can swing a flavor from melon-y to cucumber-like, and the mineral and salt content of the water determines whether it tastes briny or earthy. There are over 200 appellations of oyster, and their aphrodisiac qualities mostly depend on the terroir of the person sitting across from you.
Dan Gentile is a staff writer on Thrillist's national food/drink team who recently purchased a very nice toaster oven and is excited about exploring the world of crispy reheated food. He also enjoys hating mustard. Follow him to pots of gold/Twitter at @Dannosphere.