Sustainable aquaculture feed-stock

Environmental and economic sustainability

Fishmeal is very extensively used in feeds for fish as well as other animals. A global survey estimated aquaculture consumption of fishmeal at 3724 thousand tonnes. Now it is becoming increasingly evident that such continued exploitation of this natural resource will ultimately become both environmentally and economically unsustainable.

Any satisfactory alternative feed ingredients must be able to supply comparable nutritional value at competitive cost. Conventional land-based crops, especially grains and oilseeds, have been favoured alternatives due to their low costs, and have proved successful for some applications when they were used as substitutes for a portion of the fishmeal. But, even when these plant-based substitutes can support good growth they can cause significant changes in the nutritional quality of the fish produced.

Why Algae?

The reader may wonder why algae, including both macroalgae (‘seaweeds’) and microalgae (e.g. phytoplankton), and which are popularly thought of as ‘plants’, would be good candidates to serve as alternatives to fishmeal in fish feeds.

One fundamental consideration is that algae are the base of the aquatic food chains that produce the food resources that fish are adapted to consume. But often it is not appreciated that the biochemical diversity among different algae can be vastly greater than among land plants, even when ‘Blue-Green Algae’ (e.g. Spirulina), more properly called Cyanobacteria, are excluded from consideration. This reflects the very early evolutionary divergence of different algal groups in the history of life on earth. Only one of the many algal groups, the Green Algae, produced a line of descent that eventually gave rise to all the land plants.

Therefore it can be difficult to make meaningful generalisations about the nutritional value of this extremely diverse group of organisms; rather it is necessary to consider the particular qualities of specific algae.

Fishmeal is so widely used in feeds largely thanks to its substantial content of high-quality proteins, containing all the essential amino acids. A critical shortcoming of the crop plant proteins commonly used in fish feeds is that they are deficient in certain amino acids such as lysine, methionine, threonine, and tryptophan (Li et al. 2009), whereas analyses of the amino acid content of numerous algae have found that although there is significant variation, they generally contain all the essential amino acids. For example, surveys of 19 tropical seaweeds (Lourenço et al. 2002) and 34 edible seaweed products (Dawczynski et al. 2007) found that all species analysed containedall the essential amino acids, and these findings are consistent with other seaweed analyses (Rosell andSrivastava 1985, Wong and Peter 2000, Ortiz et al. 2006).

Analyses of microalgae have found similar high contents of essential amino acids, as exemplified by a comprehensive study of 40 species of microalgae from seven algal classes that found that, “All species had similar amino acid composition, and were rich in the essential amino acids” (Brown et al. 1997).

Perpetual Biotechnologies is taking actions in this field and soon will be able to provide algae based feed-stock to the Cypriot aquaculture industry.