Hi! I believe it should be spelled as "stake", which has the exact same pronunciation as "steak". "Steak" is a piece of meat, whereas "stake" has several meanings, including something valuable, such as money or property. In that case, the sentence would be spelled "we used to have just one stake on fish restaurant even then" and it means that they used to have one property, which was a fish restaurant. Hope that is helps, let me know if you have any further questions :)

It can be available but sold or not for sale.so it's on offer,so on sale

He means back then they were still a fish restaurant,providing only one type of steak,not anymore apparently