BESUGO has different meanings: 1. The first and most common meaning is a fish (noun) 2. The second meaning is used to call people who are clumsy, innocent and foolish (noun) but I hardly ever use it. For instance: 1. Para cenar he preparado besugo al horno con cebolla y patatas (besugo, fish) 2. Deja de decir tonterías Pablo ¡no seas besugo! There is a SAYING quite common in Spain which is DIÁLOGO DE BESUGOS and it is used when a conversation makes no sense at all because two people are talking about different things because they are not listening to each other, so there is not a proper converstaion. It literally means "Dialogue/conversation of red sea bream" Por ejemplo: - Sergio y Marcos están manteniendo un diálogo de besugos. Hablan a la vez y no se escuchan. ¡Qué aburrimiento!

Yes it is a kind of medium size fish but also it could be an insult related with the intelligence of the person, normally when somebody say something silly "eres un besugo"