Why is it that white fish do not have as strong of a "fishy" taste as other fish?

Kudos to your wife for giving it another shot!

Let me start with what I feel is the most important part of my answer: find a good fish monger and make friends. If the supermarket is the best you can find, so be it, but learn the name of the person behind the counter, ask about the fish, be interested. Ask what's just in, ask what's fresh. If the fish is frozen at sea, ask if you can get some from the freezer instead of the stock in the case that's been thawed and sitting all day.

Ask to touch and smell the fish. Look at the stock - do the whole fish have clear eyes? Does it smell like a dumpster? Getting the freshest, best fish will help you and your wife enjoy it more. Some good suggestions here on shopping for fish.

Now, on to your bullet points. Fish should never smell or taste "fishy". Fishy smelling fish is a sign of bad fish.

I find that a lot of my friends who say they don't like fish have had experiences with poorly handled or old fish. Fish must be fresh (or frozen at sea and handled properly afterward) to be good. I've stopped ordering fish in restaurants unless it specializes in fish (and I don't mean Red Lobster) or is well known for their freshness.

That said, some fish is certainly more strongly flavored than others. I found this nice chart here with a few varieties of mildly flavored fish. I do agree that flaky, white-fleshed fish is generally the mildest. Flatfish, like sole or flounder tend to be consistently mild. Tilapia has become an extremely popular fish lately.

However if you do find a good fish monger, talk to him about it and you should be able to find plenty of interesting venues: monkfish has been called the poor man's lobster, and I had some arctic char the other night that knocked my socks off.

As for why white fish tends to be less strongly flavored than meatier fishes, I can't really answer authoritatively. My guess would be that meatier fishes tend to be more oily and fatty, which equals more/stronger flavor.

Fishy is a good word for it.

JoeFish's answer about freshness, etc. is excellent and my answer is intended to suppliment it.

Darker-fleshed fish, including salmon and tuna, have much higher fat content in their flesh. This fat content adds a great deal of flavor, as well as vitamins and other nutrients. However, this fat also causes these fish to spoil faster than non-fatty "white" fish such as halibut, cod, and "snapper".

Fish in the herring family, such as mackerel, pilchards, sardines and any of the miscellaneous small fish which go under the name "anchovies", are very fatty indeed (up to 30% by weight), so much so they are called "oily fish". While this makes these fish very nutritious and tasty when fresh, it also causes them to spoil very rapidly and become "fishy". They also freeze poorly, decomposing rapidly when thawed.

For example, I won't buy sardines which were caught more than 36 hours ago, and cook them the day I buy them. For this reason, I don't recommend buying fresh sardines or mackerel ever if you live inland.

Even if they are fresh, oily fish have a stronger, more assertive flavor than other fish. People who are not that keen on fish generally dislike them.

It seems like most of the answers didn't seem to really address the root of the question - what makes some fish stronger vs milder when it's not an issue of freshness -

the fish with a higher oil/fat content have a stronger "fish" flavor to them. So, for instance, if you look at a list of fish that have the highest/healthiest amounts of Omega-3 oils, they will also tend to be stronger-flavored fish.

I've always been told that a fishy flavor to fish is due to what a fish eats, and that typically bottom feeders are the fishiest. It doesn't seem to be perfect, but it's often correct. For instance, catfish is a fishy fish.

Overall, you'll be much better off eating lake fish than ocean fish. I'm not a big fan of fishy fish either, and some of the fish I like are yellow lake perch, bluegill, flounder, tilapia, cod, whitefish, and salmon (among others). Yellow Lake Perch is my all-time favorite.

I grew up in a fishing community in the province of Newfoundland on Canada's east coast and later in life I was a commercial fisherman for National Sea Products which is best known as Highliner Seafoods. I have also fished on smaller boats called inshore fishing and from my experience the darker the fish the oilier it is and therefore the stronger it tastes.

Its the type of blood that the fish has in its body that determines the fishy tase