Microalgae for aquaculture: Opportunities and constraints

Abstract

The aquaculture of macroand micro-algae is a valuable global industry. Macroalgae are farmed for their hydrocolloids as well as for food (Abbott, 1996; Bixler, 1996), and microalgae are cultured commercially for use as health food and as a source of valuable chemicals such as betacarotene (Belay et al., 1994; Borowitzka, 1994). Microalgae are also an important food source and feed additive in the commercial rearing of many aquatic animals, especially the larvae and spat of bivalve molluscs, penaeid prawn larvae and live food organisms such as rotifers which, in turn, are used to rear the larvae of marine finfish and crustaceans. The importance of algae in aquaculture is not surprising as algae are the natural food source of these animals. Although several alternatives for algae exist such as yeasts and microencapsulated feeds (Jones et al., 1987; Nell, 1993; Heras et al., 1994; Nell et al., 1996), live algae are still the best and the preferred food source. The decline in fish stocks and in the catch from ‘wild’ fisheries in recent years has lead to an ever increasing focus on aquaculture. The increased importance of aquaculture is well illustrated by the shrimp industry. The world shrimp supply increased from 1925 103 t in 1984 to 3080 103 t in 1994, an increase of 60% (Ling et al., 1997). The bulk of this increase was in cultured shrimp, which increased 420% in the same period to a total of 921 103 t in 1994 which represents 29.9% of the total harvest. With increasing aquaculture of animal species there is an increasing need for suitable microalgae in the production of these animals. This paper will review the main problems and constraints faced by aquaculturalists in algal production and will consider the main advances being made to improve algal supply for aquaculture. Table 1. Microalgal species commonly used in aquaculture and the animals to which they are usually fed.