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

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Commodities

• Animals: fish, shellfish

Practices

• Animal Production: aquaculture

Culture of microalgae in commercial aquaculture hatcheries is vital, but 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.

This project will include three objectives (1) demonstration of live spirulina culture and use as a live feeds in marine fish and shellfish hatcheries; (2) development of a SOP for diatom culture to enhance production performance and nutrition; and (3) outreach/education 

(1) Live Spirulina culture optimization as an aquaculture live feeds

Spirulina will be cultured at Live Advantage Bait LLC in 18inch diameter 4 foot high suntubes in 4-5 day batches.  Production performance metrics will be recorded including cell density and size over time and temperature through three triplicate production runs at ambient temperature in South Florida summer, fall, winter, and spring conditions (daily production performance x 3, 5 day batches x 4 seasons).  Mature spirulina cultures will also be utilized to culture rotifers in triplicate batches.  Samples of the spriulina and rotifers, on day 2, 4, and 6 of culture will be sent to the New Jersey Feed Lab for proximate nutritional analysis (3 sample times x 2 sample types x triplicate samples = 18 samples).   Spriulina will then be used as a live feed for Mercinaria mercinaria (hard clam) culture, greenwater in larval fish culture and the rotifers fed spriulina will be used as a live feed for Lagodon rhombiodes (pinfish, a marine baitfish) aquaculture in duplicate side-by-side experiments and production performance compared to standard commercial methods. Mercinaria culture will take place at Great Florida Shellfish, a commecial shellfish hatchery and collaborative partner on this project.

(2) Diatom culture optimization as an aquaculture live feed

Thalassiosira weissflogii (TW) is a large diatom (6-20µm x 8-15µm) that is used in the shrimp and shellfish larviculture industry.  TW will be cultured at Live Advantage Bait LLC in 18 inch diameter 4 foot high suntubes.  Known, and standard amounts of f/2 fertilizer medium and silica, will be used to culture 4 day batches of TW in triplicate, tracking cell density over time. The trial replicated reducing the amount of silica utilized by 20% each round until cell density, i.e. growth, is compromised.  Samples of TW cutlures utilizing silica concentrations just above and at compromised growth (2 treatments) will be sent to the New Jersey Feed Lab for proximate nutrational analysis on day 2, 3, 4, and 5 of culture (2 treatments x 4 time periods = 8 samples).  A SOP manual will then be developed on batch culture of TW for optimized nutritional performance.  

(3) Outreach.  Techniques for live spirulina culture and production performance metrics from Objective 1 and diatom SOP for Objective 2 will be developed into white papers and presented to industry through the Southern regional extension services as well as Aquacontacts and National Aquaculture Association (NAA) listserves and directly through minority groups within aquaculture. A webinar will also be organized to present these white papers, advertized through the same groups as mentioned prior.  The papers will also be posted on the Live Advantage Bait LLC website for download.  In addition, cultures of spirulina will be made available for 12 months post the completion of the project.