The use of otolith microstructure in resolving issues of ageing and growth of young Micropogonias furnieri from southern Brazil

The corvina Micropogonias furnieri is a long-lived coastal sciaenid fish that sustains an important demersal fishery from southern Brazil to northern Argentina. The ageing of young corvinas in the Patos Lagoon estuary has been controversial. In former studies, up to six thin opaque bands in their otolith sections were considered annuli, supporting the hypothesis of slow growth and long permanence in the lagoon. However, corvinas caught in coastal waters with the same number of annuli were much larger. This fact raised doubts regarding the periodicity of the band formation in the otoliths of lagoon specimens. To better understand the growth of young corvinas, we examined the microstructure of otoliths. First, we validated the daily periodicity of growth increments using an oxytetracycline marking experiment. Second, 130 wild specimens were aged: 88 from the lagoon (30-285 mm TL, 51-678 days) and 42 from adjacent marine waters (133-275 mm TL, 212-514 days). The thin opaque bands were found to be formed on an average of 159, 269, 341, 418, 477 and 547 days and their number was higher in those corvinas remaining in the lagoon. Specimens of a similar size were older in the lagoon, suggesting slower growth than those that move to the marine environment around the first year of life. These differences may be due to growth constraints on those juveniles that remain in the more variable estuarine environment in the lagoon, or to a larger food supply in the more stable coastal environment.