Theo has given great advice although I'm not sure I would have used "esoteric" in it as I had to look it up!
While there is some truth in what you heard from the various hatcheries, there might have also been some efforts to sell you more things, but it would be unfair to say that without the whole picture being put out by any given hatchery or fish seller.
Some kind of food chain has to be created, and feeding pellets can help make the lowest rungs of the food chain more healthy, thus producing better for the higher rungs.
So while pellet feeding is not a necessity as Theo has shown, it can have a role in "jumpstarting" things; pellet feeding can be done many ways and at many cost levels, from throwing feed by hand to automated feeders.
Don't get me wrong though. I'm more talking about feed to clarify what some of the fish sellers might have meant.
