Wednesday, December 20, 2017

21/12/2017: Reducing dependence of hatcheries on on-site production of microalgae

by Victor Chepurnov, PhD, William van der Riet & Marc Temmerman

“Since most artificial substitutes are inferior to live microalgae as feed for the critical stages in the life cycles of several aquacultural species, a growing demand for microalgae will go hand in hand with the expected growth of aquaculture throughout the world.” (Richmond 2007)

Thalapure Shrimp is a microalgae-based product recently developed by Tomalgae CVBA (Belgium, a Benchmark company). Our development is based on decades of experience in experimental studies of microalgae and their mass cultivation, with special emphasis on diatoms (Bacillariophyceae).

Rigorous analysis of the history and current state-of-the-art in the practical field identified as “microalgae for aquaculture”, have allowed us to conclude that despite the fact that “microalgae cultivation has been integral to modern forms of aquaculture for more than 40 years” (Shields & Lupatsch 2012), the experience accumulated is largely empirical rather than science-based leaving a lot of opportunities for improvement.

Our approach is focused, and the focus is on diatoms. At shrimp hatcheries, diatom cultures have become the principal (sometimes, the only) live feed to supply the earliest stages of larval development (zoeae). More precisely, these are a very limited number of species belonging to genera Thalassisosira and Chaetoceros.

“Algae are at the base of the entire aquatic food chain… Therefore, it is not surprising that the microalgae which compose the phytoplankton play a vital role in the rearing of aquatic animals like molluscs, shrimp, and fish, and have a strategic interest for aquaculture” (Muller-Feuga 2000).

Diatoms are the most productive and taxonomically diverse group of marine phytoplankton. They are the principal food source for zooplankton including early planktonic filter-feeding stages of shrimp.

‘Trophic compatibility’ (ingestion, digestibility and sufficiently balanced nutritional quality) of shrimp larvae and diatoms can be explained by millions of years of their coevolution where diatoms have been serving as principal food for shrimp larvae in nature.

“Presently, most aquacultural enterprises produce (albeit with only limited success in many cases) their own supply of microalgae. Since the algal cultures can be often fed directly to the feeding animals, eliminating thereby the necessity for harvesting and processing, such rather small scale on-site production makes economic sense” (Richmond 2007).

However, “mass production of micro-algae has been recognised as a major bottle-neck to many forms of marine hatchery and nursery production… The problem of high costs of individual hatcheries producing their own algae is compounded by the need of scarce expertise, without which crashes of algae at critical periods occur quite commonly” (Heasman et al. 2001).

Theoretically, stability and productivity of microalgae cultures grown on-site could be improved (but still not drastically; see for example Benemann 2013, for more detailed explanations). These would require much better control of abiotic and biotic environments. However, simultaneously this would imply essentially more investment in microalgae. Nowadays, for most shrimp hatcheries, this is an unrealistic scenario.

Read the full article with references, HERE.

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