Development and evaluation of an automated system to deliver a live-attenuated Edwardsiella ictaluri vaccine in commercial catfish production systems

Catfish aquaculture is the largest cultured food fish industry in the United States, accounting for approximately $375 million in sales annually, with Mississippi leading the industry with 36,200 surface acres of production. However, infectious diseases such as enteric septicemia of catfish (ESC) are decreasing production efficiencies, creating losses of $40-60 million annually. Live-attenuated oral ESC vaccines are effective in preventing ESC infections, but have not been widely adopted by the catfish industry due to the lack of a system to administer the oral vaccine at the scale seen in commercial catfish production systems. An automated system was developed to administer a dosage of 220.5 ml of a live-attenuated ESC vaccine per kg of catfish feed, adapting commercial catfish feeder design to include a screw conveyor for mixing vaccine and feed in a continuous process, pulse-width modulated spray nozzle control for precise vaccine application, and a programmable automation controller to regulate and monitor system performance. Initial performance evaluations demonstrated system operation within the desired design specifications. System feed rates were determined to be a function of the rotational speed (RPM) of the screw conveyor and to be linear across the operational range. Feed rates were observed to decrease by 45% over dry feed when applying liquid vaccine to the feed stream at the 220.5 ml/kg (100 ml/lb) rate, resulting in a feed rate range of 6.80-34.02 kg/min (15-75 lb/min) (95% CI). Uniform pellet-level vaccine distribution is crucial to efficacy as pellet consumption is directly correlated with fish size, with more criticality in smaller fish fed at low rates. Pellet vaccine concentrations at 6.80, 20.41, and 34.02 ml/kg were highly variable and vaccine application at all rates were observed to be statistically different (less) than the target 220.5ml/kg rate (95% CI), pointing to potential issues with vaccine delivery system configuration or inadequacies in sampling methodology. Further evaluation at the pellet level with live-attenuated vaccine to obtain viable cell counts within individual pellets would provide data necessary to address uniformity of coverage questions more fully and to develop operational protocols that maximize system capabilities and vaccine efficacy