Microbial Resource Management in Indoor Recirculating Shrimp Aquaculture Systems.

Abstract

Indoor recirculating aquaculture systems (RAS) for the production of shrimp are a potentially sustainable alternative to traditional pond culture systems in terms of water conservation and reduced impact on receiving water quality. RAS systems consist of a shrimp production tank and one or more biofilters for water treatment. Microorganisms in the biofilters have a critical role in maintaining water quality in the production tank. Therefore, a better understanding of microbially mediated nitrogen transformation processes in indoor RAS can help improve performance through appropriate operational modifications. Furthermore, a reduction in commercial shrimp feed may be possible through the use of biofilter biofilm as a supplemental feed source for shrimp.

The microbial community was characterized in the trickling filter of a local (Okemos, MI) indoor, zero-discharge RAS used in the production of Pacific white shrimp, Litopanaeus vannamei. Ammonium oxidizing archaea and nitrite-oxidizing nitrospiras were the dominant nitrifying microbes in this system. Clone libraries and quantitative polymerase chain reaction were used to identify and quantify the ammonium-oxidizers and nitrite-oxidizers in the system.

A laboratory-scale indoor, zero-discharge RAS was designed and operated under simulated intensive growth conditions, i.e., at least 100 shrimp per m2 of tank area. The ammonium load to the system was increased to simulate shrimp growth and additional waste production over time to investigate the effect of the ammonium concentration on the population abundance of ammonia-oxidizers and nitrite-oxidizers in the biological aerated filters of this system. A correlation between ammonium concentration and niche differentiation of ammonium oxidizers was not observed but the abundance of ammonia oxidizing bacteria increased, with increasing ammonium concentration. Also Nitrospira nitrite oxidizing bacteria (NOB) were more abundant than Nitrobacter NOB.

The laboratory-scale indoor, zero-discharge RAS was operated to examine the impact of biofilter biofilm as a supplemental feed source on shrimp growth and survival. Supplementing commercial shrimp feed with RAS biofilter biofilm is a viable way to reduce feed costs and improve the sustainability of RAS. Additional research is needed to optimize the level of biofilm supplmentation for increased shrimp growth.