A histological study of gonads and a statistical analysis of biometric variables were used to study the biology of scad, Trachurus mediterraneus. The reproductive cycle was subdivided into three phases: a pre-reproductive phase from January to April, a reproductive phase from May to August and a post-reproductive phase from September to December. Five sexual maturity stages could be described in both males and females. The gonosomatic index reached its maximum value in June–July. In both sexes size and age at sexual maturity averaged 16 cm and 2 years, respectively. At the end of the reproductive period, gonadal regression was observed first in females. The analysis of the length–weight relationship showed conditions of positive allometry in May–June, negative allometry in July and October, and isometry in the other months.
