Refurbishment of the 130-cover restaurant, which was opened in 1999 by Tony Allan, includes the addition of leather banquette seating with larger round tables designed for groups.
The restaurant, which also has a 70-cover terrace into Borough Market, now features dark marble and a herringbone design seen throughout, as well as a new mirrored dining counter and bar with views of the open kitchen.
Fish! marketing assistant Hollie Allan told BigHospitality the re-design, the first in its 16-year history, was designed to re-position the venue as a destination restaurant where a new generation of diners would come and discover a love of fish.
"We've always had a big appeal with visitors to the market and with tourists looking for good fish & chips, but with the revamp we hope people will now seek the restaurant out as a destination in its own right and spend all evening here, rather than pop in and have a quick bite to eat," she said.
Alongside the refurbishment, Fish! Borough Market, which is run by Hollie's elder sister Charlee Allan, also has a new menu with new raw and salads sections featuring for the first time.
Hollie said the menu's overhaul was designed to highlight the versatility of fish and seafood and tap into more current food trends.
"We haven't got rid of our old classics like fish pie, fish cakes and fish & chips, we have just introduced more dishes like ceviche and sashimi, which just add excitement to the menu and appeal to a younger generation," she said.
"We want to get rid of the perception that fish is something you had for school dinners. We want everyone to be able to enjoy it as there are so many possibilities with fish which I think our new menu shows."