The higher-end seafood restaurants are typically closed on Mondays, due to shipping and freshness issues with the seafood served. This is not only in Lima, but in many other countries. Anthony Bourdain spoke to this in one of his many Kitchen Confidential books. Here's a link to some information.http://abcnews.go.com/2020/story?id=3140192
El Mercado will also take reservations for parties up to 8 people, but only for the first sitting at 1 pm and they must be made two days in advance. We stopped there on a Friday several weeks ago at about 1:30 and were told there was an hour wait. We didn't wait, drove down to Sonia's in Chorrilos.