Effect of freezing/thawing process in different sizes of blue fish in the Mediterranean through lysosomal enzymatic tests.

•AG is a valid marker of the incidence of freezing for all the species of blue fish.•The freezing period after which significant differences become clear in all three lysosomal enzymes is approximately 7days.•The increase of QI was more evident in sardine samples than anchovy, horse mackerel and chub mackerel samples.•In fact a lot of blood in the medulla crystalline of sardines may be correlated to an increase in the opacity of the eye.