Recirculating aquaculture system as microbial community and water quality management strategy in the larviculture of Scylla paramamosain

Abstract

The structure and function of the water microbial community can change dramatically between different rearing modes. Yet investigations into the relationships between microbial community and water quality remain obscure. We provide the first evidence that rearing modes alter bacterial community and water quality in the rearing water of the mud crab (Scylla paramamosain) larvae. The juveniles in the recirculating aquaculture system (RAS) had a higher viability than those in the water exchange system (WES). RAS had the significantly lower levels of total ammonia nitrogen (TAN), NH₃, NO₂^--N, total nitrogen (TN), total dissolved solids (TDS), and chemical oxygen demand than those of WES. The number of significantly different amplicon sequence variants between rearing modes increased as the larvae developed. NH₃, TAN, TDS, NO₂^--N, and TN were closely related to the late alterations in water bacterial community. Both the FAPROTAX tool and quantitative PCR analysis showed enhanced nitrogen cycling functional potential of water bacterial community of RAS. Random forest analysis identified the enriched water bacteria especially heterotrophic bacteria such as Phaeodactylibacter, Tenacibaculum, and Hydrogenophaga, which were vital in removing nitrogenous compounds via simultaneous nitrification and denitrification. Notably, RAS could save 18.5 m³ of seawater relative to WES in larviculture on the scale of 2.5 m³. Together, these data indicate that RAS could function as microbial community and water quality management strategy in the larviculture of crab.

Keywords: Larviculture; Nitrogen cycling genes; Recirculating aquaculture system; Scylla paramamosain; Water bacterial community.