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.
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!
…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)
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"
This is not an idiom. It means exactly what it looks like -- you felt the emotion that would lead you to start crying.
The joke is that the clown fish asked "With fronds like these, who needs to BEEP someone?