1 - Yes, it is illegal per TPWD.
2 - Stay focused to the question.
I was asked this today and I wasn't sure of the correct answer.

*** If you bought trout at the local grocery store, would that fish be exempt to the rule if you were using the purchased trout as bait? ***

Of course, I think it would be a good idea to keep your receipt. But with the trout stockings that the TPWD does at this time of the year, would it fly with the wardens if you bought from a grocer store?
Or, are trout (game fish) illegal to use as bait, period?

It is illegal trout is classified as a game fish and TP&W states No game fish or parts of gamefish can be used for bait!

Those giant stripers love the stocking size. The whole fish. Grocery store fish I have seen are all dressed. I guess if you had the receipt, it would be interesting to explain to GW you just needed some cut bait.

Illegal, since it is still the same species whether it comes from a waterbody or a store.

Could a person use bought trout in private waters?

In private waters you could use any bait you like just lock the gate and keep it to yourself!

Sounds like everyone is voting for still illegal - even if they come from the store. Even on private waters

Yep!

I had a "friend" back in the 90's that caught some HUGE striper below the Canyon Lake dam using stock trout for bait. This was back before we really had swim baits that looked like trout.

Same friend caught the state record striper out in the same spot until it was confirmed the fish was caught using live trout and stripped the record.

Big ones below the dam at Lake Hamilton. Been issues in the past of using as bait.

Yeah, even if you have a receipt it won't matter. There's no way to prove you didn't catch some trout and use those in addition to the ones you bought so they can't allow that.

Private pond on private land you would be ok.

If your fishing a private lake or pond there are no state regulations in Texas. Now if your fishing on private property on a public lake, that's a different story.

back in about 1980 or so I used trout below canyon, horseshoe falls was a guaranteed big striper hole. gw told me back then that the trout were legal since they were not native.
best day I had was 5 striper over 20# and 2 of those were over 30#. we had one heck of a fish fry at whitewater sports

I had a guide up in Arkansas tell me that he would catch some trout in the white river then go down where the Buffalo runs into the white and use the trout to catch double digit LM Bass. Big fine if you are caught but stripers and LM Bass eat lots of them. There are some big stripers below PK along with huge gar and flatheads so any trout they stock are going to get reduced by those predators.

I had a game and fish warden in Arkansas tell me they sometimes have to remove big stripers from below beaver if they come up river and start eating the trout.