PHOTO: CANVA
Microalgae have the right blend of protein, lipids, and carbohydrates needed to p rotect fish health.
schizochytrium, and 10% N. oculata, respectively compared to fish with the control diet. Although various factors could have contributed to wide differences in the weight gain val- ues in different species, the positive effect of microalgae’s low and moderate inclusion in the diet is evident. Microalgae are a rich source of protein and lipids when compared to other alternative ingredients such as yeast and bacteria (see Table 1). A favourite microalga is spirulina – a filamentous blue-green microalga, which is an excellent source of plant protein that could replace expensive animal-derived proteins in fish feed. So small, less than a millimeter, that it can only be seen through the microscope, spirulina was so named because of its spiral shape. Discovered by the Aztecs, who nourished themselves with its beneficial properties, it has evolved over the centuries and is now increasingly widespread. Spirulina algae is a primordial micro alga, a natural product, and today it is considered to be a “super food” with high protein content (about 60%). It lacks cellulose cell walls and therefore does not require chemical processing in order to become digestible. (The digestibility is 83 – 84 %.) Spirulina is a source of natural ca- rotenoids, containing β-carotene and xanthophylls (zeaxan- thin, echinenone and cryptoxanthin). These carotenoids are integrated into the fish muscle without further modification, producing a more intense red and yellow colouration (i.e. natural dye) of the fillet.
Fast growth occurs in aquatic species when fed a diet con- taining spirulina meal. Spirulina can be used as a partial sup- plementation or complete replacement for protein in aqua feeds for all fish. Giant freshwater prawns, and marine water shrimp improved significantly in terms of growth, survival, immunity, viability, and feed utilisation on a diet of spirulina. It is a cheaper feed ingredient with higher protein than meal of animal origin. Climate change threatens biodiversity and can influence fish populations worldwide. Further, water pollution can be identified as another crucial factor, which has been largely investigated. The intensive use of fishmeal represents a threat to the safeguarding of marine ecosystems. Seawater consumption, the high amount of energy required, and the emission of effluents with a high organic content are some of the reasons why processing raw fish to produce fishmeal is raising environmental concerns. These observations un- derlie the urgent need to identify feasible alternatives to common fishmeal for the aquaculture sector. Microalgae are considered to be more sustainable in terms of resource use than other aquafeed ingredients, and spirulina in particular can also be used to treat wastewater from fish culture activities, as it can efficiently metabolize the nutri- ents and remove the heavy metals contained in aquaculture effluent. Spirulina appears to have considerable potential for development, especially as a small-scale crop for nutritional enhancement.
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