Publication Abstract

Importance of microbial ecology in managing a biosecure, zero-exchange shrimp technology(BioZEST) system

F. Azam, D. Verner-Jeffreys, B. Basilio, F. Malfatti, and S. Moss

Most recirculating aquaculture systems rely on the provision of clean, oligotrophic water for the production of high-value target species. These systems depend on various types of filters to remove suspended solids and other organic and inorganic compounds that can damage fragile gill tissue, increase biological oxygen demand, and contribute to the accumulation of toxic nitrogenous wastes. However, shrimp reared in eutrophic water containing high abundance of bacteria, microalgae, and microbial-detrital aggregates grow almost twice as fast as shrimp grown in clean, filtered seawater. This microbial ecology-based approach to the production of aquatic animals in zero-exchange systems represents a major paradigm shift from current methods and has the potential to significantly increase production and profitability for shrimp farmers. In addition to a direct nutritional benefit, in situ microbes mediate important biogeochemical processes in the culture environment and have a profound impact on water quality. Importantly, microbes play a critical role in maintaining a balanced ecosystem where host, beneficial microbes, and opportunistic pathogens co-exist. For BioZEST systems to be economically viable they must support rapid shrimp growth and high survival by providing an environment that promotes the persistence of a beneficial microbial community.

Interrelationships among various functional groups within the microbial community are poorly understood and relationships between microbes, system inputs, water quality, and shrimp health are complex. Shrimp culture systems can exhibit rapid changes in ambient nutrient concentrations that result in unpredictable blooms and crashes of eukaryotic microalgae. Nutrient fluxes result from the periodic additions of exogenous inputs and poorly understood changes in microbial biogeochemical cycling. In addition, shifts in heterotrophic bacterial community structure can favor opportunistic pathogens, thereby creating animal health problems. A potential obstacle to increasing production and profitability of the BioZEST system is the inability to maintain the persistence of beneficial microbes that enhance shrimp growth and survival and promote acceptable water quality. However, if such microbes can be identified and maintained in the culture environment throughout the growout period, shrimp production can increase to levels that are unattainable with existing technologies.

In light of the importance of understanding microbial ecology in BioZEST systems, culture-dependent as well as culture-independent approaches (molecular phylogeny, population dynamics and community-level biochemical process rate measurements) are being employed to understand and model the microbial regulation of system behavior. This information will be used towards the design of BioZEST systems with increased shrimp survival, higher stocking densities, efficient feed utilization and low environmental impact.

F. Azam, D. Verner-Jeffreys, B. Basilio, F. Malfatti, and S. Moss. 2004. Importance of microbial ecology in managing a biosecure, zero-exchange shrimp technology(BioZEST) system. World Aquaculture Society Meeting, 1-5 March 2004, Honolulu, Hawaii, USA