Transition period from larva to juvenile in anchoveta Engraulis ringens. Length or age related?

To determine the beginning and end of the transition period from larvae to juveniles in anchoveta Engraulis ringens, seven morphometric measurements were carried out in 333 laboratory-reared and 324 field-caught larvae. Measurements of body morphometrics were employed to calculate the six body ratios selected to show transition changes described in this study. The analysis was carried out with 'dummy variables' (variables that take only one of two possible values: 0 or 1) because a single model was used to indicate the point at which the slope changes in piecewise linear regressions. The regression coefficients of the relationship between ratios of morphometric measurements and body length were not significant in any case (P > 0·05) and, accordingly, a discrete length at which the slope changes could not be estimated. The ratio of the measurements according to the age showed two inflections, corresponding to the beginning and end of the transition period. The first inflection occurred between 32 and 64 days (average 46 days); the second inflection occurred between 81 and 149 days (average 107 days). Therefore, the transition period lasted c. 61 days, starting with a high growth rate, continuing with a slower growth phase, and ending with the onset of a new high growth rate period that corresponded to the start of typical juvenile growth. On the basis of these results, it is hypothesized that the transition from larvae to juveniles in E. ringens is determined more by age than body size.