A multi-step nitrifying microbial enrichment to remove ammonia and nitrite in brackish aquaculture systems.

One of the most important advancements in harnessing the biological nitrification in the field is enrichment solution of nitrifying microbial consortia. In the current study, we developed an improved multi-step enrichment to amplify a targeted microbial consortium from a sediment sample collected in tropical mangrove, Vietnam. The results showed that it took 122 culturing days with five unique continuous enrichment steps, the microbial consortium consumed total 5665 mgN L-1. Relative substrate removal rate increased rapidly from 0.114 mgN L-1 h-1 at the end of the first-step enrichment up to 3.58 mgN L-1 h-1 at the end of the fifth-step enrichment. High-throughput sequencing revealed that Nitrospirae, Proteobacteria and Bacteroidetes were the dominant taxa at the phylum level while Nitrospira, Marinobacter, Denitromonas and Nitrosomonas were the dominant taxa at the genus level in the enriched consortia. A pilot-scale experiment for shrimp cultivation of L. vannamei in 84 day-period proved the efficiency of Total ammonium nitrogen and nitrite removal in the consortium-activated treatment was much higher than the control.

Distribution and density of Lutraria rhynchaena Jonas, 1844 relate to sediment while reproduction shows multiple peaks per year in Cat Ba-Ha Long Bay, Vietnam.

Lutraria rhynchaena Jonas, 1844 is of great commercial interest, but its reserves have dramatically declined over recent decades. Therefore, there is an urgent need of scientific basis to propose effective fishery management measures and improve artificial aquaculture of the clam. In this study, we investigated the distribution and density of L. rhynchaena, sediment characteristics, and established the clam's reproductive cycle through monthly observations from August 2017 to July 2018. The study results showed that distribution and density of clams are related to sediment types, and the sediment type of medium sand is likely the best benthic substrate for the clams. The spawning of clams occurred throughout the year with three spawning peaks in January, April and September. For the sustainable management of the clam resource in Cat Ba-Ha Long Bay, the fishery authorities can issue a ban on harvest of the clam in spawning peak months in January, April and September.