Methodologies for the Bioenrichment of Plankton

Abstract

Aquaculture is expanding worldwide to meet the protein requirements of humans. The basic requirement in culture practice is seed production, while the major constraint is larval nutrition (Imelda 2003). Larviculture—specifically, the initiation of feeding in early larval stages—is a major bottleneck for the industrial scale-up of fish and shellfish cultures. Larval survival also varies with the type of organism, with a rate of <10% in finfish, <1% in mud crabs, <20–40% in shrimp and <20% in molluscs. Evolutionarily, most fish and crustacean larvae are motile prey organisms and encounter problems with the initiation of inert/dry diets. Even if they accept the diets, their poor enzymatic activity and non-functional stomachs will not allow them to digest the existing formulated diets (Pedersen et al. 1987; Pedersen and Hjelmeland 1988; Agh and Sorgeloos 2005). Thus, improving the acceptance of dry diets for fish larvae and formulating more digestible and less polluting diets are important tasks for aquaculturists. The challenge in larval nutrition lies in the fact that live feeds are not completely replaced in hatchery operations. Therefore, once this is achieved, live food (phytoplankton and zooplankton) will remain an important food source for the starting of feeding in the early larval stages. Among the important starter feeds used in larviculture are newly hatched nauplii of Artemia and rotifer Brachionus plicatilis. The successful development of commercial hatcheries and farms has been made possible by several improvements in the production techniques of this live food (Candreva et al. 1996; Dehasque et al. 1998; Agh and Sorgeloos 2005). When compared to rotifers and Artemia nauplii, the traditional live feeds provided to marine fish larvae, copepods can improve larval growth and survival and the ratio of normally pigmented juveniles when fed either alone or as a supplement (Kraul 1983; McEvoy et al. 1998; Nanton and Castell 1999). Thus, the ability to culture these organisms at a scale adequate for marine larviculture would present a major step forward for the production of many marine species that require a better suited diet nutritionally than that provided by the traditional live prey (Josianna and Stottup 2006). It is believed that the optimal formulations for the first feeding of larvae should simulate the yolk composition and, to some extent, reflect the nutrient requirements and metabolic capacities of pre-feeding finfish and shellfish of other organisms (Imelda 2003).