Food-Grade Biomaterials-Based Microneedles for Fish Vaccination in Aquaculture

To meet the rising seafood demand driven by rapid population growth, an expanded aquaculture industry is essential. Over the last 60 years, the consumption of aquatic food per capita has increased from 9.9kg to 20.5kg, with a projected 15% increase by 2030. Salmon and trout exports account for 18.4% of the value of all exported aquatic products in 2020, compared with 5.1% in 1976. Despite various factors that cause fish loss, such as environmental changes (e.g., temperature fluctuations, water quality, and farming density) exacerbated by climate change, disease outbreaks remain the most significant challenge. Beyond the immediate ecological impacts of fish loss caused by disease outbreaks, there are ongoing concerns about the long-term impact of antibiotic resistance and the bi-directional spread of infectious disease between farmed and wild salmonid populations.<br/>Early-stage vaccination is crucial for preventing disease outbreaks in aquaculture, ensuring food security, and reducing antibiotic overuse. Among current vaccine administration methods–oral, immersion, and injection, injection using hypodermic needles offers the highest protection with minimal vaccine usage. For fish above 25 g, injection is done for individual sedated fish with a human-operated vaccine gun. However, for juvenile fish that are 1-2 g in size, it is challenging for such a setup to operate as manual handling such small fish is difficult. Thus, for fingerlings at this size vaccination is commonly done with individual manual injections. However, the anesthesia process is costly and labor-intensive for the workers and stressful for the fish. Additionally, using fine needles on juvenile fish presents a risk of needlestick injuries to farm workers. This practice also generates needle waste which is costly and energy-intensive to process. Stakeholders are interested in innovations that can vaccinate small fish in an automated manner without needing to take them out of the water.<br/>To address these challenges, we developed microneedles based on food-grade biomaterials. To be able to be deployed in aquatic environments, these microneedles need to be waterproofed to maintain their mechanical strength to penetrate fish skin. At the same time, the microneedles can release loaded vaccines. We demonstrate easy fabrication for hollow microneedles that can be easily loaded with vaccines and released without barriers. Inactivated bacteria and DNA vaccines are loaded and preserved. We tested injecting our microneedle using both zebra model fish and juvenile rainbow trout. After microneedle injection, the fish can swim with the microneedles attached to them to continue vaccine release. In our pilot test with 60 rainbow trout in each group, upon <i>Yersinia ruckeri</i> pathogen challenge 32 days after the vaccination, the microneedle-vaccinated group had a 65% mortality compared with 85% mortality in the PBS-injected negative control group. Although more optimization is needed to achieve &lt;30% mortality for on-farm efficacy, our initial results show that immunity protection for juvenile fish can be achieved with this microneedle technology. It opens the possibility of having fish vaccination automatically deployed underwater without stressful fish anesthesia and labor-intensive manual injection.