A lot of what one does in this hobby depends on ones goals. Certainly there are ways to get larger/quicker gains in growth, and/or greater fecundity in female breeders - but that does not necessarily equate to healthier fish.
If ones only concern is large gains in growth, feed a generic trout chow. If one cares about the longevity & overall health of their fish, then that's not something they'll want to be doing long term, because in most species of fish kept in an aquarium it will result in fatty deposition of the liver.
A local breeder that I know that has been keeping & breeding various species of fish for the past 40 or so odd years, likes to "feed to breed", which basically is what some people refer to as power feeding. His females are larger than what one would ever see in the wild, and they produce tons of eggs/fry, but they are also generally spent within a few years from that type of growth and egg production. But his goal is to maximize egg production, maximize the growth in his fry, and maximize his sales. His goals are the same as most commercial aquaculture facilities, such as salmon farms, trout farms, tilapia farms, etc. Longevity is not a factor, maximizing growth & reproduction is the main focus of their operations, as that equates to maximizing profits.
In the wild the vast majority of fish go through seasonal swings of feast or famine, mostly borderline famine, yet in home aquariums I personally find that the vast majority of hobbyists overfeed their fish, offering them far more nutrients than what the fish can utilize without resulting in excess storage of fat. Anyone that has ever spent any time around a commercial importers operation will tell you that you will never see chubby "wild" fish arriving from SA, CA, Africa, or anywhere else on the planet. Overfeeding on a regular basis is IMO far more detrimental to the health of captive fish, than what one chooses to feed. Fish are one of the most efficient animals on the planet for converting food to flesh, and from what I see from many of the photos shared here on MFK, a LOT of hobbyists fail to understand that. It seems as though the BIGGER the "Monster" fish, the greater the praise they receive. Ironically those fish are probably having years shaved off of their natural lifespan from overcare.
As far as color, and overall health, I have yet to see a single example of any species of fish that doesn't look as good/healthy as a wild fish swimming in their native habitat, as one fed an exclusive diet of high quality pellets. Not one, including both freshwater, and marine species. I have heard this many a times over the years, from people who are actually diving, photographing, and collecting various species of wild fish in their native habitat.
Being nutritionally balanced does not mean it is the best nutrient source, same with dogs and people plants and just about any living thing.
I agree completely, which is exactly why a food manufacturer that keeps this in mind will use a "wide variety" of sources for his food. Not just amino acids (protein) from a single raw ingredient, or fatty acids from one source, or aquatic plant matter from one source. They will use
numerous sources, and then top off the natural vitamins/minerals & various natural bioactive compounds found in those raw ingredients. Naturally occuring compounds that have been shown to have biological effects in fish such as growth promotion, immunostimulation, anti-stress, anti-bacterial, anti-fungal, anti-virals, and appetite stimulators. I can tell you that not many fish manufacturers understand that concept, or at least don't practice it when formulating their feeds. (because it ain't cheap!)
Having said all that, my advice has always been - they're your fish, do what you are personally most comfortable with.
