Development of extended shelf-life microalgae concentrate diets harvested by centrifugation for bivalve molluscs - a summary

Abstract

On the basis of initial harvesting efficiency trials and screening trials to evaluate apparent cell damage and viability, high-speed centrifugation was selected as the most appropriate microalgae harvesting method for developing extended shelf-life concentrates that would collectively meet the requirements of marine hatcheries and nurseries. Bioassay evaluation of stored microalgae concentrates revealed major discrepancies between closely related species of microalgae with regard to the impact of harvesting method on both short-term nutritional quality and shelf-life of stored concentrates. At one extreme, very good retention of nutritional quality was exhibited by high-speed-centrifuged concentrates of Tetraselmis spp. and Chaetoceros calcitrans beyond 8 weeks storage. In contrast, the naked flagellates Pavlova lutheri and Tahitian Isochrysis and the diatom Chaetoceros muelleri exhibited rapid and profound losses in nutritional quality as a consequence of supercentrifugation. Likewise, the impact of storage conditions and the effects of preservatives and other common food additives on the quality and extended shelf-life of stored concentrates was found to be unpredictable and highly species specific. Accordingly, optimum combinations of harvesting and storage, including optimum cell densities, presence or absence of food additives, temperature and, in some cases, gaseous atmosphere and light, had to be specifically tailored to individual species of microalgae in order to maximize the effective shelf-life of their concentrates. Data are presented demonstrating that the best binary concentrate diets developed during the course of this study could sustain growth and survival of larval and juvenile bivalves at rates similar to fresh microalgae culture even after storage periods of 6–8 weeks.