I have read that って is the equivalent of the topic marker は. (is これって何ですか just as natural as これは何ですか？)
Are there situations when we can't use って instead of は？
「って 」is an informal equivalent of 「というのは」.Therefore, it is used in the same situations than 「という」in spoken spoken language rather than written.
トロって何ですか トロというのは何ですか "What doesトロ mean?" or "What is トロ?"
When using informal speech, the は particle is sometimes ommitted, and that's why you don't see it in your sentence either.
In this case, というのは indicates the meaning of A, so AというのはB, is asking for the meaning of A, but というのは has also other usages. See it here.
EDIT: turns out that some fonts refer to って as the equivalent of は as well. However, my knowlegde on this is limited.