"A woman needs a man like a fish needs a bicycle" was a line from the U2 song "Trying to throw your arms around the world" from Achtung baby. I think Guinness used the line in one of their 'ironic' adverts a fe years back
Sorry to disappoint any U2 fans who still believe this is a product of Bono's lyrical genius, but "a woman needs a man like a fish needs a bicycle" is a very old feminist slogan from long before Achtung Baby came out.
Presumably, the aim of every advertiser is to get people to remember their product. So any image which is unusual or bizarre is more likely to achieve this and that could be the reason for the fish and the bicycle.