It means that the thing which is being referred to is totally unnecessary, just like a bicycle is not needed by a fish.
metaphor
The reference to "fish" in a conversation could be a euphemism to change the topic or introduce a non-sequitur. Similarly, the idiom "like a fish out of water" describes feeling uncomfortable or out of place in a particular situation.
idiom means expression like a page in a book
It's not an idiom. It means exactly what it looks like.
…and just then the sea cucumber looks over to the mollusk and says: With fronds like these, who needs anemones? (with friends like these, who needs enemies)
if you mean Big fish in a little pond, then that is like the oldest people in that society, like say if you are in yr6 at primary school, than someone can say that your a big fish in a little pond. When you go into secondary school, then that same person can say, now your a big fish in a big ocean!
idiom is like discribe e.g as light as a feather
It is an idiom, because it does not use the term "like" or "as".
That is not an idiom. When you see the word LIKE, you're looking at a simile.
no an idiom would be like "it's raining cats and dogs"
The joke is that the clown fish asked "With fronds like these, who needs to BEEP someone?
This is not an idiom. It means exactly what it looks like -- you felt the emotion that would lead you to start crying.