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Diatoms as hatchery feed on-site cultivation and alternatives By Viktor Chepurnov, PhD., Claas G. Steigüber and Philipp Siegel
At shrimp hatcheries, microalgal cultures grown on-site play a pivotal role as the principal feed for the early stages of larval development (zoea). Cultivated algae are predominantly, or often exclusively, diatoms (Bacillariophyceae). However, sustainable growth of high-quality diatoms in sufficient amounts remains a challenge: “Cultures will fail to grow, will become overly contaminated with competing microorganisms or will crash even in the best-run hatcheries“ (Shoji & Ajithkumar 2013).
Among possible alternatives to onsite microalgae production, we (Tomalgae, a Benchmark company), in accordance with our experience and expertise, chose for production of high quality diatoms analogous to those currently grown at hatcheries. We have also developed procedures for processing the biomass and manufacturing a diatom-based product, Thalapure Shrimp, with prolonged shelf-life and efficient rehydration and resuspension method. In a recent publication characterizing our technology and the product in detail (Chepurnov et al. 2017), we made the following statement: “Theoretically, stability and productivity of microalgae cultures grown on-site could be improved … However, simultaneously this would imply essentially more investment in microalgae. Nowadays, for most shrimp hatcheries, this is an unrealistic scenario.” Here we shall try to evaluate this statement. Various literature sources are used, with quotes, to show our judgements are not unique. Hopefully, our arguments will help hatchery
managers make more informed choices when faced with the dilemma of whether to invest in modification of on-site microalgae production, or to investigate alternatives.
Methods of on-site production of microalgae were developed rapidly, from initiating phytoplankton blooms in larval-rearing tanks to, already in the 1970s, culturing selected algal species “in specialised facilities and then transported to larval or live prey rearing tanks…” (Muller-Feuga et al. 2003). However, “the culture techniques developed then have remained relatively unchanged” (MullerFeuga et al. 2003, see also De Pauw et al. 1984, Shields & Lupatsch 2012). “Starting with sterile testtubes the algae are inoculated in large glass containers and carboys, then to bigger vessels or plastic bags and finally to large, indoor or outdoor tanks” (Dhert & Sorgeloos 1991). It was quickly defined which abiotic parameters are the most important in regulating algal growth: “nutrient quantity and quality, light, pH, turbulence,
