I'm not familiar with the song you refer to, so I looked up the lyrics:
I want you back for the rhythm-attack
Coming down on the floor like a maniac
I want you back, so clean up the dish
By the way, how much is the fish?
How much is the fish?
I wouldn't necessarily assume that the lyric "how much is the fish" directly relates to the English expression "what's that got to do with the price of fish", for a number of reasons.
Firstly, the expression you refer to isn't always fish. I've heard it used with eggs, rice (perhaps because it rhymes with 'price'), and tea in China.
Secondly, the reason for using any of the above expressions beginning with "what's that got to do with the price of..." is said as a response to suggest that a statement made by someone else is a non sequitur, or irrelevant to the matter at hand. It is not said to make a discussion irrelevant. The Scooter lyrics do not appear to be in the form of a discussion, rather they seem all to be in the first person.
Lastly, although I think the lyric is probably just meant to be an aberration, representing a shift in thought, as if the person is distracted, if it is meant to relate to a popular saying there are probably more relevant cultural references, such as the saying "try the fish", which is sometimes tagged onto the end of a monologue to suggest the speaking style of a stand-up comedian who may be contractually obliged to recommend the special dish at the venue he is performing at. As stated, I don't think that is the case.