Validation of daily microincrement deposition in otoliths of juvenile and adult Peruvian anchovy Engraulis ringens

Wild adult specimens of the Peruvian anchovy Engraulis ringens were captured and reared to validate the daily periodicity of otolith microincrement formation. The postcapture stress generated spontaneous spawning, making it possible to conduct a rearing trial on larvae first in an artificial nutrient-enriched system (ANES) for 52 days followed by an artificial feeding regime in a culture tank until day 115 post-hatch. Microincrements of the sagittal otoliths of sacrificed juveniles [mean±s.d. total length (L_T)=5·13±0·37cm, range 5-6 cm; c.v.=7·5%] showed very distinct light and dark zones. The slope of the relationship between the total number of increments after the hatch check and days elapsed after hatching was not significantly different from 1. The transfer from ANES to the artificial feeding regime induced a mark in the sagittal otoliths. The number of microincrements after this induced mark coincided with the number of days elapsed after the transfer date. In parallel experiments, adult E. ringens (mean±s.d. L_T=14·92±0·55cm, range 13-16cm) were exposed to one of two fluorescent marking immersion treatments with either alizarin red S (ARS; 25 mg l^-1 per 6h) or oxytetracycline hydrochloride (OTC; 200 mg l^-1 per 10h). The microincrements between fluorescent bands were distinct, ranging from 0·89 to 2·75μm (mean±s.d. =1·43±0·28μm; c.v. = 32%) and from 0·71 to 2·89μm (1·53±0·27μm; c.v. = 35%) for ARS and OTC, respectively. The relationship between the number of microincrements between marks and the number of elapsed days for ARS and OCT treatments indicated that there was a significant correspondence between the number of increases observed and the number of days. Hence, daily microincrements of otoliths of E. ringens are likely to be formed in juveniles and adults under natural conditions.