• age and growth;
  • age validation;
  • micro-increment;
  • oxytetracycline dyes

The daily periodicity of micro-increments in the otoliths of Atlantic thread herring Opisthonema oglinum was demonstrated from juveniles injected with oxytetracycline and reared for up to 62 days. Micro-increments ranged from 26 to 358 in the overall sample. Von Bertalanffy growth function (VBGF) using micro-increment counts were: L= 337 mm fork length (LF) (s.e. = 31 mm); K = 1·2 (s.e. = 0·2) and t0= 0·04 years (s.e. = 0·01 years). The otolith-based growth was corroborated using the LF frequency analysis. Observed lengths of increments were considered unsuitable for VBGF derivation, as no increase in size was obtained from them. Furthermore, the high percentage of unreadable otoliths suggests that increment analysis is unreliable for age estimation. Most growth occurs within the first year, differing from previous longevity estimates of 4–8 years. In contrast with published information, O. oglinum is a fast-growing and short-lived species.