Feeder Fish. What is the deal here?

Gfishery popped their head over the parapet saw what was going on and
said
I went to a local pet store (one of the major chains) and bought a
Red Cap Oranda and an Orange Fantail recently.

Goldfish:
Red Cap Orandas retail for $2.99
Orange Fantails retail for $3.49

Feeder fish:
Some retail for $0.12 each
Others retail for $0.29 each

Couple of days later, I saw a worker moving a goldfish from the
goldfish tank to the feeder fish tank.
Did the price for that particular goldfish decrease by 90% in just 10
seconds?
I notice some other Orandas and Fantails in the feeder fish tank.
Why did they do this?

Should I have waited for the "price drop" instead of paying full
price?

"Feeder fish" are exactly that they are fish that are going to get fed
to something, so they (the LFS) may realise that the fish in question
is going to die shortly, and selling a lot of fish that die soon after
they
are sold is bad business, hence moving it to the "feeder fish tank",
hence the reduction in cost. There are those who like the challenge
and buy "feeder fish" and "nurse" them so that they live a long time.

--
yours S

Nihil curo de ista tua stulta superstitione