Analysis of water treatment efficiency in factory-based recirculating aquaculture system larval cultivation and pond grow-out for largemouth bass (Micropterus salmoides)

Objective This study aims to investigate the water quality control requirements for factory-based recirculating aquaculture system fry cultivation and pond grow-out of largemouth bass (Micropterus salmoides), providing scientific basis for adapting water quality management techniques. Methods The water treatment efficiency of microfiltration machine, nitrification tanks, and pond application of Bacillus spp. was evaluated based on water quality regulation technology. Results 1) Factory-based recirculating water larval cultivation: Total phosphorus (TP) and total nitrogen (TN) concentrations in the culture tanks were significantly affected by feeding amount (P<0.01), and they increased as the feeding amount increased or decreased as the feeding amount decreased. The microfiltration machines achieved removal rates of (16.26±6.87)% for suspended solids (SS) and (12.94±5.07)% for chemical oxygen demand (COD). The biofilter removed (18.51±7.73)% of total ammonia nitrogen (TAN) and (5.87±3.51)% of nitrite nitrogen (NO₂^--N). The nitrification capacity showed an overall downward trend as the culture time extended. 2) Grow-out pond culture: Within 6 hours after applying Bacillus spp., , the highest removal rates for SS and COD concentrations were observed, with average values of (15.07±3.55)% and (14.22±2.59)%, respectively; The mean TN and TP removal rates were (10.35±2.33)% and (8.71±0.92)%, respectively; The average removal efficiencies for TAN and NO₂^--N were (9.70±2.81)% and (7.76±3.28)%, respectively. Conclusion The study has clarified the relationship between the water treatment methods for larval M. salmoides in industrialized recirculating aquaculture systems and adult fish in pond culture, and the concentrations of TAN, NO₂^--N, TN, TP, SS, and COD in the aquaculture water. It has obtained relevant data on water treatment efficiency, which can provide technological support for the related aquaculture models of M. salmoides.