Fish are classified not only by appearance but mainly by their fat content, which influences both their nutritional value and culinary qualities. According to experts interviewed by El País, white fish contain less than 3% fat, semi-fatty fish between 2% and 5%, while oily (blue) fish contain more than 5%. Rock fish, however, are classified by the rocky habitats where they live rather than by their nutritional profile.
Common white fish include hake, monkfish and sole, while sardines, mackerel, tuna and bonito are considered oily fish. Sea bass, gilthead seabream, red sea bream and red mullet fall into the semi-fatty category.
Freshness is equally important when choosing seafood. Experts advise looking for shiny skin, bright and bulging eyes, vivid red gills and firm, elastic flesh. As fish lose freshness, the eyes become dull, the gills darken and the flesh softens.
Specialists also encourage consumers to respect seasonal availability, as fish caught in season generally offer better flavour and support more sustainable fishing practices.
