Bivalve aquaculture production is more dependent on high quality microalgae than any other aquaculture sector. Because bivalves filter-feed almost exclusively on microalgae, the quantity and quality of available microalgae is critical at every life stage, and especially every stage of hatchery production: Broodstock, larvae, hatchery set, remote set, and nursery. Bivalve hatcheries today employ a combination of algae naturally found in local waters with algae produced in their own facilities to meet this demand.
The Microalgae Bottleneck
“The success of a bivalve hatchery depends on the production of algae. Large quantities of high quality algae must be available when needed.” –FAO Bivalve Hatchery Manual
The greatest bottleneck in bivalve production is often an inadequate supply of quality microalgae when it is needed most. Algae production can be compromised by weather and season (where natural sunlight is used), equipment failures, or human error, and it must be timed to match the demands of the hatchery. Short day lengths, low light levels and suboptimal temperatures dramatically reduce winter algae production. To overcome this shortage, hatcheries culture algae, usually indoors, and production of microalgae is responsible for a major fraction of the infrastructure, labor, and other operating costs of a bivalve hatchery.
Algal culture requires specialized equipment and skilled labor, which entail costs with no return during the seasons when algae are not needed. Any shortfall in algae production can result in reduction or even failure of bivalve production. Even when conditions for algae production are good, hatchery cultures can experience unexplained crashes or contamination by unwanted algae or zooplankton, limiting the availability of nutritionally critical microalgal species. Algae that is produced but cannot be used (because timing of production was misjudged, or an anticipated hatch was not successful) is an often overlooked, although significant, contributor to the total cost of algae production. An additional concern is that algae from both local waters and hatchery cultures can be sources of shellfish pathogens.
Fortunately, commercially-available microalgae concentrates provide an economical supplement or replacement for ambient phytoplankton or hatchery-cultured microalgae.
Advantages of Microalgae Concentrates
Easy Control of Feeding Rates
Microalgae concentrates can be formulated with well-defined biomass densities, so the algae can be continuously and accurately dosed into bivalve cultures with a metering pump, matching feed delivery to the demands of the cultures to maximize feeding efficiency. This provides a significant advantage compared to the great difficulty of regulating feed dosing when feeding with hatchery-grown phytoplankton cultures, with their variable growth rates and concentrations.
Broodstock Conditioning with Nutritionally Optimized Blends of Microalgae
Larviculture depends on availability of healthy broodstock. The limited supply of microalgae that often prevails in winter often results in poor broodstock condition. The hatchery production season must be delayed until broodstock animals can consume sufficient microalgae to support development and maturation of gonads, and ultimately gametes. Algae concentrates made with nutritionally optimized blends of microalgae are used to enhance the fecundity of broodstock and accelerate gonad maturation, allowing the production season to be started weeks before wild bivalve populations would be capable of supplying reproductively mature animals.
Partial or Complete Live Algae Replacement for Larviculture
Feeding Spat at Remote-set Sites
Microalgae concentrates are by far the most convenient means to feed spat at remote-set locations distant from a hatchery. Even for hatcheries that culture their own algae for on-site use, use of commercially-available concentrates eliminates the need for equipment and labor to concentrate the algae before transport to a remote site.
Expanded Post Set and Nursery Production at Hatcheries
Specific Pathogen Free (SPF) Feed Source in Challenging Environments
Use of SPF algae concentrates ensures that no dangerous contaminating organisms are introduced with the feed. Use of concentrated feed makes production possible in small volumes of water. It is much more economical to treat small volumes intensively (microfiltration and UV) to prevent introductions of pathogens and parasites, so even small facilities can afford to produce pathogen-free seed.
References
Guedes C, Malcata FX
Nutritional Value and Uses of Microalgae in Aquaculture
In: Muchlisin Z (Ed). Aquaculture. INTECH Open Access Publisher, pp. 59-78. ISBN: 979-953-307-107-6. http://cdn.intechweb.org/pdfs/27104.pdf
Helm M, Bourne N, Lovatelli A. 2004
Hatchery culture of bivalves: a practical manual
Food and Agriculture Organization of the United Nations. 177 pp.
Rikard FS, Walton WC. 2012.
Use of Microalgae Concentrates for Rearing Oyster Larvae, Crassostrea virginica
Mississippi-Alabama Sea Grant Publication No.: MASGP-12-048. nsgl.gso.uri.edu/masgc/masgcg12008.pdf
Shields RJ, Lupatsch I,
Algae for aquaculture and animal feeds
Karlsruher Institut für Technologie--Technikfolgenabschätzung – Theorie und Praxis 2012 21. Jg., Heft 1. http://www.itas.fzk.de/tatup/121/shlu12a.htm
By Eric Henry, Research Scientist, and Tim Reed, Founder and President, Reed Mariculture, Inc., USA (www.reed-mariculture.com)