smelt ? good and bad?

[kimbosaur]

"Silversides" can be ambiguous too!

[ConcinusMan]

in the thiamine safe food list, it lists smelt in both good and the bad lists.
Smelt ( fresh water )is in the bad list,
Smelt or "silversides" (Hypomesus olidus)(arctic pond. Also known as silversides, usually frozen available in pet stores) is in the good side.
is it clear on packaging?

No. In fact, you can buy packages of smelt at the store that are called "smelt" or called "silversides" and the packages aren't even necessarily one kind of fish. Sometimes they're mixed species of smelt.

SF Bay Brand "Sally's" and Ocean Nutrition brand (sold in pet stores) are Hypomesus olidus. A type of smelt that does not contain thiaminase.

"Silversides" can be ambiguous too!

Definitely. I can all but guarantee that the "silversides" you buy at bait shops in the U.S. are not Hypomesus olidus but are instead saltwater smelts containing thiaminase (not to mention a heavy parasite load).