Plastic growth of the herbivorous reef fish Sparisoma viride: field evidence for a trade-off between growth and reproduction

The growth of different Life phases and social categories of the protogynous parrotfish Sparisoma viride was studied on a fringing reef on Bonaire (Netherlands Antilles) using mark-recapture procedures and by taking repeated stereographic measurements of free-swimming fish. Weight-growth was best described by the Putter/von Bertalanffy growth equation for all categories, allowing comparison of specific growth rates (dW/Wdt) using analysis of covariance with W-(1/3) as the covariate. Growth was retarded by Peterson discs, but no effect of fin clips was detected. Adjusted for size differences, growth of juveniles was fastest, followed by sexually inactive terminal phase (TP) males living in groups. Initial phase (IP) females and territorial TP males (spawning daily) showed the lowest growth rates. Growth rate of territorial males was negatively correlated with their average spawning rate. All adult categories showed seasonal variations in growth, the highest rates occurring in the warmest season (August to October). A possible effect of depth on growth is confounded by differences in social and reproductive status. Growth of group TP males showed a weak positive correlation with their condition. Gross growth efficiencies were estimated by combining data on growth and body composition with previously published data on food intake and assimilation. Growth efficiency is highest for protein, ranging from 50.6% of food intake for juveniles to 0.12% for territorial males. Corresponding values are 6.25 to 0.01% for ash-free dry weight and 7.9 to 0.01% for energy. The high abundance of small, sexually inactive group TP males (early sex-changers) in our S. viride population is related to their fast growth. We suggest that these 'bachelors' trade growth against current reproduction and thereby enhance their chance to acquire the status of a territorial male with high reproductive success. Insight into intraspecific variation in growth improves the accuracy of trophodynamic models and increases our understanding of complex Life history patterns in fish.