Shrimp grow out systems under zero water exchange mode demand constant remediation of total ammonia nitrogen (TAN) and NO 2 −-N to protect the crop. To address this issue, an inexpensive and user-friendly technology using immobilized nitrifying bacterial consortia (NBC) as bioaugmentors has been developed and proposed for adoption in shrimp culture systems. Indigenous NBC stored at 4°C were activated at room temperature (28°C) and cultured in a 2 L bench top fermentor. The consortia, after enumeration by epifluorescence microscopy, were immobilized on delignified wood particles of a soft wood tree Ailantus altissima (300-1500 μm) having a surface area of 1.87 m 2 g − 1. Selection of wood particle as substratum was based on adsorption of NBC on to the particles, biofilm formation, and their subsequent nitrification potential. The immobilization could be achieved within 72 h with an initial cell density of 1 × 10 5 cells mL − 1. On experimenting with the lowest dosage of 0.2 g (wet weight) immobilized NBC in 20 L seawater, a TAN removal rate of 2.4 mg L − 1 within three days was observed. An NBC immobilization device could be developed for on site generation of the bioaugmentor preparation as per requirement. The product of immobilization never exhibited lag phase when transferred to fresh medium. The extent of nitrification in a simulated system was two times the rate observed in the control systems suggesting the efficacy in real life situations. The products of nitrification in all experiments were undetectable due to denitrifying potency, which made the NBC an ideal option for biological nitrogen removal. The immobilized NBC thus generated has been named TANOX (Total Ammonia Nitrogen Oxidizer).

Nitrate reducing potency of 88 bacterial isolates segregated from marine and brackish water nitrifying bacterial consortia (NBC), generated for activation of nitrifying bioreactors, was confirmed by determining the nitrate reducing capability under aerobic conditions as maintained in nitrifying bioreactors. All the isolates had the potential to be used as bio‐augmentors for activating nitrate dissimilation in recirculating aquaculture system. The existence of nitrate reducers with nitrifiers in NBC and in the reactor configuration negates the requirement of integrating anoxic denitrifying system for effective removal of NO3−‐N. Phylogenetic analyses of representative isolates from each cluster of the dendrograms generated based on phenotypic characterization and amplified ribosomal DNA restriction analysis revealed profound diversity of nitrate reducing bacterial flora in the NBC. They were composed of Streptomyces enissocaesilis, Marinobacter sp., Pseudomonas sp., Microbacterium oxydans, Pelagibacterium halotolerans and Alcanivorax dieselolei from marine NBC and Streptomyces tendae, Nesterenkonia sp., Bacillus cereus, Microbacterium oxydans and Brevibacterium sp. from brackish water NBC. The diversity indices of the consortia were calculated using Mega 5.0, primer 7 and VITCOMIC softwares. Marine NBC exhibited higher Shannon wiener diversity and mean population diversity than brackish water NBC. The study delineated higher species richness and diversity in marine NBC than in its brackish water counterpart, a possible reflection of the higher biodiversity of marine systems, and hence, the former is more promising to be used as start‐up cultures for the activation of nitrifying bioreactors after appropriate acclimatization to the desired salinity.

Two distinct nitrifying bacterial consortia, namely an ammonia oxidizing non-penaeid culture (AMO NPCU-1) and an ammonia oxidizing penaeid culture (AMOPCU-1), have been mass produced in a nitrifying bacterial consortia production unit (NBCPU). The consortia, maintained at 4°C were activated and cultured in a 2 l fermentor initially. At this stage the net biomass (0.105 and 0.112 g/l), maximum specific growth rate (0.112 and 0.105/h) and yield coefficients (1.315 and 2.08) were calculated respectively, for AMONPCU-1 and AMOPCU-1 on attaining stationary growth phase. Subsequently on mass production in a 200 l NBCPU under optimized culture conditions, the total amounts of NH 4 ? -N removed by AMONPCU-1 and AMOPCU-1 were 1.948 and 1.242 g/l within 160 and 270 days, respectively. Total alkalinity reduction of 11.7-14.4 and 7.5-9.1 g/l were observed which led to the consumption of 78 and 62 g Na 2 CO 3 . The yield coefficient and biomass of AMONPCU-1 were 0.67 and 125.3 g/l and those of AMOPCU-1 were 1.23 and 165 g/l. The higher yield coefficient and growth rate of AMOPCU-1 suggest better energy conversion efficiency and higher CO 2 fixation potential. Both of the consortia were dominated by Nitrosomonas-like organisms. The consortia may find application in the establishment of nitrification within marine and brackish water culture systems.

A packed bed bioreactor (PBBR) was developed for rapid establishment of nitrification in brackish water hatchery systems in the tropics. The reactors were activated by immobilizing ammonia-oxidizing (AMON-PCU-1) and nitrite-oxidizing (NIONPCU-1) bacterial consortia on polystyrene and low-density polyethylene beads, respectively. Fluorescence in situ hybridization demonstrated the presence of autotrophic nitrifiers belong to Nitrosococcus mobilis, lineage of b ammonia oxidizers and nitrite oxidizer Nitrobacter sp. in the consortia. The activated reactors upon integration to the hatchery system resulted in significant ammonia removal (P \ 0.01) culminating to its undetectable levels. Consequently, a significantly higher percent survival of larvae was observed in the larval production systems. With spent water the reactors could establish nitrification with high percentage removal of ammonia (78%), nitrite (79%) and BOD (56%) within 7 days of initiation of the process. PBBR is configured in such a way to minimize the energy requirements for continuous operation by limiting the energy inputs to a single stage pumping of water and aeration to the aeration cells. The PBBR shall enable hatchery systems to operate under closed recirculating mode and pave the way for better water management in the aquaculture industry.

For establishing nitrification in prawn (non-penaeid, salinity 10-15 ppt) and shrimp (penaeid, salinity 30-35 ppt) larval production systems, a stringed bed suspended bioreactor (SBSBR) was designed, fabricated, and validated. It was fabricated with 5 mm polystyrene and low density polyethylene beads as the substrata for ammonia and nitrite oxidizing bacterial consortia, respectively, with an overall surface area of 684 cm 2 . The reactors were activated in a prototype activator and were transported in polythene bags to the site of testing. Performance of the reactors activated with the nitrifying bacterial consortia AMONPCU-1 (ammonia oxidizers for non-penaeid culture) and NIONPCU-1 (nitrite oxidizers for non-penaeid culture) was evaluated in a Macrobrachium rosenbergii larval rearing system and those activated with AMOPCU-1 (ammonia oxidizers for penaeid culture) and NIOPCU-1 (nitrite oxidizers for penaeid culture) in a Penaeus monodon seed production system. Rapid setting up of nitrification could be observed in both the static systems which resulted in a higher relative per cent survival of larvae.Keywords Closed system shrimp hatchery Á Immobilization Á Nitrification Á Nitrifying bioreactors Á Nitrifying consortia Á Shrimp/prawn larval production Abbreviations AMONPCU-1 Ammonia oxidizers for non-penaeid culture AMOPCU-1 Ammonia oxidizers for penaeid culture IHHNV Infectious hypodermal and hematopoietic necrosis virus