Methodology to enhance nutrition and economics of microalgae use as live feeds in marine aquaculture

Culture of microalgae in commercial aquaculture hatcheries is therefore vital, costly, and has room to be optimized.  We believe there are two areas commercial aquaculturists can improve microalgae nutrition and economics: (1) production of live spirulina as a live feed for zooplankton and (2) enhancing the fat content and nutritional fatty acid composition of diatoms through silca fertilization optimization.  

Spirulina has been proven in literature to enhance the survival, growth, and immune system of marine fish and shrimp.  It has extremely high protein content (60-70%) required by fast growing larvae, it lacks cellulose walls meaning it is highly digestible (up to 84%) compared to other algal species,  contains a high amount amino acids such as phenolic acids, tocopherols, carotenes and linolenic acids and has been found to enhance disease resistance through chelating of toxic minerals such as arsneic and heavy metals containing several antiviral and antimicrobial propoerties.  It is also relatively cost effective. Spirulina in powder form has been used extensively as a feed supplement in many aquaculture industries.  However, live spirulina has not been as extensively utilized.  Most likely because spriulina is not a commonly live cultured species in the industry, therefore many culturists are not familar with its husbandry conditions.  At Live Advantage Bait LLC we experimented with culture of live spirulina and found compared to other microalgae species we culture, spirulina can be cultured at extremely high densities at a high pH meaning no additional use of carbon dioxide and at ambient temperatures of South Florida meaning no additional temperature control required.  In addition we have found our isolate of spirulina can be used as a feed for zooplankton (rotifers) at our commercial fish hatchery, producing 2x the culture density of rotifers compared to use of standard practice algae paste products and without need for supplemental oxygen in the rotifer cultures.  These preliminary obeservations demonstate live spirulina culture may enhance both economics and performance of marine aquaculture hatcheries.  

However, literature also demonstrates spirulina must be matched with a high fat microalgae species, such as a diatom, to provide optimal nutrition to marine fish and shellfish larvae.  Unlike culture of flaggelated microalgae, culture of diatoms requires additional fertilization of the culture environment with silica, as diatoms have silica shells.  Literature indicates the nutritional content of diatoms can drastically vary with growth phase of the culture as well as silica availability.  Limiting silica has been found to enhance nutrition content of the culture, however it can also reduce culture growth.  Microalgae is often most nutritious during the exponential growth phase.  Therefore a balance must be made between silicate limitation and growth phase. One way to enahance both production performance and nutrition is to utilize batch culture.  Batch culture of algae starts with innoculating a culture vessel with a small amount of algae and sufficient nutrients to initiate rapid growth and then harvesting the entire vessel when the exponential growth curve, i.e. nutrition, is maximized.  A culturists must therefore understand what the ideal amount of fertilization and silica to use on day 1 to innoculate the culture vessel and on what day the culture will be the most ideal to harvest.  This will require understanding production performance as well as tracking nutritional content of the microalgae over time in order to develop a specific operating procedure (SOP) for the commercial aquaculturist.

In addition, the anticipated variance in nutrition of microalgae species over time and variable culture conditions is invaluable infomration to a farmer who has to make daily decisions on feeding rates and production to maximize margins.  A project that describes anticipated microalgae nutrition as a factor of culture environment and time will be extremely valuable to a economically and environmentally sustainable industry.