FISH FLAVOR
Fish, contrary to meat, are pale and much more tender. The reason is simply that they don't need hard-working muscles filled with oxygen deposits of myoglobin (the red pigment in meat). If the fish cruises the waters, it doesn't consume much energy. Just a part of the large muscle, typically just under the skin, is colored brown/red. Fish do however need to sprint from time to time, and that's the reason why they have the fast white muscle fibers in their bodies. Of course, some exceptions exist, the most famous would probably be the pink meat of a tuna fish. From the perspective of muscle to total body volume, fish are also very efficient "producers" of the meat. Certainly a fine sort of food, yes?
So, there we have, nice tender and white fish meat. Why doesn't it taste like the "land" meat? As with animals, the flavor of the fish depends a lot on what they eat and where they live. Notice that sea water is salt, in fact it is so salt that fish wouldn't normally survive in it unless it could balance this saltiness against its own body fluids (that are not that salt). The way they do it is responsible for the flavor they get. Fish meat is filled with tasteful amino acids (glycine which is sweet, and glutamate which is flavorsome) that counter the influx of salt, so to speak. The more of these amino acids they have, the more tasteful will the fish be. Especially shellfish, e.g. scallops, are known for their flavorsome and sweet taste - it's because they contain the nicely tasting amino acids. Fish may also contain more or less of the not-so-nice molecules that become transformed by microbes and enzymes into smelly, bad old fish, odors. One major compound in this category is TMAO, a tasteless substance, that becomes a smelly TMA when the fish is left to stand for a longer while. What about fish from lakes and rivers? Since the water is not salt, they don't need that many amino acids to counterbalance the osmotic pressure from salt, and so they taste milder than sea fish.
Then, there is more to the sea water than just salt. It is also quite cold, which results in another necessary adaptation of fish to their environment. One is that they need to produce unsaturated fatty acids (the healthy ones!) so they won't solidify in the cold. Saturated fats will solidify in cold water, so they are of no use. Second, fish also have digestive enzymes as well as parasites and bacteria that thrive in cold temperatures. This means, you cannot keep fish in cold for too long (as opposed to meat). The best bet is to put fish on ice, and try to avoid freezing them (for the sake of texture and flavor). You can have a fresh fish on ice for some days, although it is always best to eat it as soon as possible.
Before you buy some fish, also consider this. A fish, even if it has the same name, is not always the same. It depends on their life cycle. If they are caught during their growth phase, they taste wonderful. However, if they are in process of getting babies and migrating, they use their muscle proteins as energy depots! If you eat such fish meat, it will be spongy and mushy. It is good to learn which fishes are at their best in the region where you live.
Fish meat, since it is best in cold, is not easily cooked. The heat may transform it so quickly into a dry lumpy mass! In fact, some fish proteins are starting to denature in room temperature. It is obvious then that the fish should be prepared quickly, not allowed to stand in room temperature for too long before it's cooked, and when it is cooked - make it gently and carefully. It is a fragile meat and it should be treated with care.