The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

Summary (1) Analysis of data from samples of chub taken at monthly intervals from two tributaries of the Herefordshire Wye revealed an annual cycle of scale growth with the formation ofa check during May or June. The frequency distributions of ages deter‐mined from scale checks and the length‐frequency distributions showed close simi‐larities. It was concluded that age determinations based on an examination of the scales were valid, provided care was taken in the identification ofthe first scale cheek. The maximum age observed was 15 years. (2) Examination ofthe population structure revealed an overall sex ratio close to unity but there was a significant increase in the proportion of females in the 11 + and older age groups. Dominant year‐classes were observed. The strongest was 1959, which was attributed to exceptionally warm, dry, sunny weather during the period May‐September. (3) Female chub grew more rapidly and attained greater ultimate size than the males. Changes in the pattern of growth during the life‐span were attributed to the attainment of sexual maturity, especially in the females. The length‐weight relation‐ships of the sexes diflFered slightly but were almost identical for the same sex in the two rivers studied. Seasonal variations in the growth‐rate were followed. Most rapid growth occurred after check formation in May or June and continued until September.