Heston Blumenthal's Fat Duck restaurant will re-open today with the blessing of environmental health officers – but without shellfish dishes.

As a "precaution", the chef has taken all oysters, langoustine, mussels and other shellfish – which are notorious for causing food poisoning – off the menu until the Government health watchdog concludes its investigation.

Several test results are yet to come back but no evidence has been found during the 15-day inquiry that could link the illness to food poisoning – a gastro bug could be the cause.

Health Protection Agency officials gave the Fat Duck the all-clear after testing its kitchen and ingredients to get to the root of the illness mystery. About 400 diners reported falling ill after eating at the Fat Duck between the end of January and the end of February.

Blumenthal is not commenting until the investigation is over. His spokeswoman said: "We are very excited to be re-opening. We will be open at lunchtime tomorrow and we are hoping to be back to normal as soon as possible."

The Health Protection Agency said Fat Duck management agreed to comply with all the recommendations that environmental health officers made after conducting a risk assessment of the premises. It would not specify what the recommendations were.

"Preliminary findings... have informed the advice given so far, but the investigation is ongoing. So far no one source has been identified.

"The detailed questioning of people who reported illness is likely to continue for some weeks in order to build a more complete picture."

Blumenthal is thought to have lost more than £100,000 in earnings during the closure.

Up to 1,000 diners who had their bookings cancelled will be offered new ones.

Blumenthal's spokeswoman said he would consider whether any compensation should be paid to diners once the HPA investigation was complete.