it doesnot clarify in rule book-- it tells you you can visit any square of the 8. there is no point of the fish square if it is not possible also it is part of winter??
The rules for New Year’s Day round say (page 7):
On your turn, your Oyakata may stay where it is or jump to any space on Main Street. Once there, you may do business as usual with the shop and/or one of the professionals (occupation cards).
So yes, that would include the Fish Market. Not sure why that needs to be clarified.