Someone explain reason behind this

I have always been told never to feed freshwater fish..sal****er
foods, and never to feed sal****er fish freshwater foods...be it
frozen or prepared items. Was always told its to keep from
introducing foreign critters into the environemnt that the fish are
not used to.

So whats the difference when it comes to feeding brine shrimp or
krill or any other number of frozen foods that say Fresh or salt water
fish on them. I often acclimate mollys or guppies to SW and feed
varous SW fish live foods. Last I read sw micro organisms do not
survive in FW anbd visa versa, so I am having a hard time reasoning
with the no to feed sw to fw etc etc.

I have fed what I wanted to feed all the time and as long as the fish
etc eat what I give them thats fine.......and have never had problems.
So whats everyone else's take on this? I have a bunch of cichlids that
will tear up my home brew frozen SW ifsh food which is mainly chopped
and diced and pureeded shrimp, krill, mysid, scallops, clams and
muscles and squid and assorted what ever is cheapest at the time some
kind of SW fish.



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I forgot more about ponds and koi than I'll ever know!