|Despite growing consumer demand for organically-produced seafood, less than 1% of farmed seafood products are currently sold under organic labels - a significant lag behind organic production of terrestrial crops and livestock. Although some of the technologies and advances in terrestrial organic agriculture are applicable to aquaculture, research is urgently needed to address the unique challenges of aquatic environments.
Given the environmental impacts associated with excessive exposure to chemicals and antibiotics, many farmers would prefer to utilize more natural methods for pathogen control, but disease outbreaks remain a real concern for aquaculturalists based on fears surrounding mass mortalities and human health risks from pre- and post-harvest bacterial contamination of seafood. In the proposed research, we identify several naturally occurring antimicrobials that show promise as cost-effective and organically-certifiable alternatives for pathogen control. We aim to isolate these compounds and target their delivery in ways that maximize their activity. We then propose to study application at specific points in hatchery and post-harvest aquaculture production to ensure that they provide good protection against losses, and are cost-effective to use.
The project has been underway since 2015, and preliminary results are very promising for the compounds chosen. However, one of the greatest challenges in aquatic environments is delivering feeds or drugs in tanks/pens where there is high water flow, such that dissolution and dispersion of target antimicrobials or feed can be anticipated. Because of this problem, there is often incentive for overdosing of chemicals to ensure effectiveness. When antibiotics are routinely overused, resistance develops among pathogens, thus weakening antibiotic efficiency and ultimately leading to higher dose administration, with subsequent discharge to the surrounding environment and potential trace residuals in seafood produced for human consumption.
One alternative to generalized antibiotic applications is to develop targeted mechanisms to better deliver lower doses of antibacterials directly to the sites of pathogen infection. Micro- and nano-capsules containing minute quantities of an antimicrobial can be designed to interact with pathogens on mucous-covered epithelial surfaces of gills or digestive tract, thus reducing the overall dose concentrations required. In addition to traditional antibiotics, this technology can be used to encapsulate novel new compounds with known antimicrobial properties that do not produce antibacterial resistance. This research focuses on microencapsulation technologies for novel compounds to ensure targeted delivery for high uptake rates. The compounds and the encapsulation materials are biodegradable, easily assimilated by host species, and unlikely to lead to long-term pathogen resistance.
The proliferation of antibiotic-resistant bacteria in fish and shellfish culturing makes it urgent to find alternatives to the use of broad-spectrum antibiotics and chemical disinfection baths. The results of the research have the potential to improve productivity of the aquaculture sector by ensuring better animal health, food safety and economic resilience.