Anglian Country Inns has opened a fishmonger at the Fox at Willian, in Hertfordshire.
Fish at the Fox is based on the site of the company's recently closed Food Barn behind the pub. Fishmonger Marc Howard is heading up the venture.
A range of fresh fish, shellfish and smoked fish is on offer. Fish dishes made by chefs in the Fox's kitchen are also for sale.
James Nye, Anglian's managing director, said: "We have seen a growing demand for fresh fish on the menu from our customers in the restaurant at the Fox and also from our previous customers from the Food Barn.
"There is a scarcity of fresh fishmongers in north Hertfordshire and we want to fill this gap. We will be sourcing sustainable fish from British waters where possible."
A company spokeswoman said: "The fish side of the Food Barn was successful so we have streamlined to Fish at the Fox. We will be selling associated products when we get up and running."
Fish at the Fox will be open from Wednesday to Saturday.
There is also a customer ordering service available for out-of-hours collection from the Fox.