Patterns of larval growth and chemical composition in the Amazon River prawn, Macrobrachium amazonicum

The Amazon River prawn, Macrobrachium amazonicum (Heller, 1862), is a target species for regional fisheries in Brazil and a candidate for aquaculture. Under controlled laboratory conditions (29 °C, 10‰), the larval phase of this species shows variability in the morphology and number of successive stages (mostly 9–10, occasionally 8 to > 12). In the most commonly observed developmental pathway (9 stages, taking approximately 20–22 days from hatching to the first juvenile stage), we studied patterns of larval growth in terms of total body length (TL), carapace length (CL), dry mass (W), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN). At hatching, about 12% of late embryonic W, 15–18% of C and H, but only 7% of N were lost, indicating higher losses of lipids and/or carbohydrates than proteins. Significant variability was observed in the initial biomass and elemental composition of newly hatched larvae from 20 different egg batches. This may cause variation in the endotrophic potential of the early stages, as the zoea I of this species is a non-feeding stage, and also the zoea II may still utilize internal energy stores remaining from the egg yolk. Lacking or low larval feeding activity from hatching through stage II coincided with low initial growth. Concomitantly, the proportions of C and H (in % of W) as well as the C:N ratio decreased from hatching through stage IV, indicating a utilization of stored lipids. The percentage of N showed an opposite pattern, reflecting protein synthesis associated with morphogenesis. Size growth showed maximum increments per moult in the late zoeal stages (III–VI), followed by lower increments in the subsequent decapodid stages (VII–IX). This sigmoidal growth pattern may reflect ontogenetic changes in morphometric relationships. Biomass showed exponential patterns of increase from zoeal stage III throughout later larval development and in the first two juvenile stages. Furthermore, patterns of larval growth in M. amazonicum are characterized as linear relationships between larval W in stage n and that in stage n + 1 (Hiatt diagram), between larval size (CL) and biomass (W, C), and between W and either C or N. Using CHN data, we also provide estimates of the protein and lipid contents of larval biomass (ca. 38–46% and 10–12% of W, respectively). High survival, rapid development, and predictable patterns of larval growth support the assumption that M. amazonicum should be a suitable species for production in aquaculture.