Dr. Urzua-Osorio, Angel

In the aquaculture of prawns in inland facilities, the supply with natural seawater is technically difficult and expensive, while the use of artificial salt may be suboptimal due to unfavorable ionic composition. In the present study, Amazon River prawn, Macrobrachium amazonicum, were reared from hatching through nine larval stages to the first juvenile instar, comparing four experimental conditions with two salinities (5, 10) and two different types of salt (artificial, natural). Larval biomass growth was measured in terms of changes in dry weight (W), contents of carbon and nitrogen (C, N), and proximate biochemical composition (lipid, protein); moreover, body size (carapace length, CL) was measured in first-stage juveniles. After passing through the nonfeeding first larval stage, later stages showed an exponential increase in values of biomass per individual. Rates of increase differed significantly among treatments, showing generally lower growth in experiments with artificial vs. natural salt, and at 5 vs. 10. The same response pattern was found also in CL of early juvenile shrimps. Similar but mostly weaker effects were observed in the percentage C, N, lipid, and protein values (in % of W), and in the C: N mass ratio. Our data indicate that larval rearing of M. amazonicum is feasible with artificial salts and at lower than commonly used standard salinity (10). This makes the cultivation of this species feasible also in aquaculture facilities located at large distance from the coast, where a reduction of costs and logistic investments may compensate for reduced larval growth and production of smaller juveniles. However, these salinity effects on offspring production have to be taken into account in comparisons of growth data from different laboratories and locations.

In marine invertebrates, the modes of development at early stages are related to the type and capacity of larval feeding to achieve growth. Therefore, studying the factors that determine larval feeding strategies can help to understand the diversity of life histories and evolution of marine invertebrates. The polychaete Boccardia wellingtonensis is a poecilogonous species that encapsulates and incubates its offspring. This species produces two types of larvae: (1) larvae that do not feed within the capsule and hatch as planktotrophic larvae (indirect development), and (2) adelphophagic larvae that feed on nurse eggs and other larvae inside the capsule to hatch as advanced larvae or juveniles (direct development). Otherwise, the larval types are indistinguishable at the same stage of development. The non-apparent morphological differences between both types of larvae suggest that other factors are influencing their feeding behavior. This work studied the potential role of the activity of 19 digestive enzymes on the different feeding capacities of planktotrophic and adelphophagic larvae of B. wellingtonensis. Also, differences in larval feeding structures and the larval capacity to feed from intracapsular fluid were evaluated by electron and fluorescence microscopy. Results showed that both types of larvae present similar feeding structures and had the capacity to ingest intracapsular fluid protein. Adelphophagic larvae showed overall the highest activities of digestive enzymes. Significant differences between larval types were observed in nine enzymes related to the use of internal and external nutritional sources. Given that larval feeding is closely related to larval development in species with encapsulation, this work supports that the study of the digestive enzymatic machinery of larvae may contribute to understanding the evolution of developmental modes.