Farmed fish are a crucial source of protein worldwide, yet disease outbreaks can cause massive losses. The most effective current method uses metal needles: fish must be sedated, lifted out of water, manually injected on a conveyor belt, and quickly returned to the pond. This process is labor‑intensive, risks blood‑borne cross‑contamination, and endangers workers as well as the fish.\ \ Professor Benedetto Marelli’s team at MIT’s Department of Civil and Environmental Engineering, together with the U.S. Department of Agriculture, has created a water‑resistant, food‑grade microneedle system for underwater vaccine delivery. The microneedles are made from silk fibroin and coated with a thin layer of shellac—an insect‑secreted resin already approved for food coatings and pills. The shellac barrier prevents immediate dissolution in water, allowing the needles to penetrate fish skin, stay attached, and later degrade safely.\ \ The platform can load various cargos, including bacterial vaccines and DNA plasmids. By adjusting needle geometry and shellac thickness, release kinetics can be tuned: some formulations release the payload within 15 minutes, others sustain release for 10–24 hours. Notably, DNA plasmids stored dry for four weeks retained about half of their structural integrity, addressing cold‑chain challenges in remote aquaculture operations.\ \ A key advantage is the ability to vaccinate very small fish (1–2 g). In rainbow trout trials, the single‑use microneedles successfully pierced wet skin, remained attached while the fish swam, and delivered vaccines in a controlled manner—something conventional needles cannot achieve until fish reach ~30 g.\ \ While further development is needed for large‑scale deployment, the technology already offers safety for fish and humans, biodegradability, controllable release, and low‑cost manufacturing. It could reduce vaccination expenses, improve worker safety, and enhance fish health, thereby strengthening global food security.\ \ Review