Vaccination in fish is usually done with a reusable stainless steel needle attached to a multiple injector. The number of fish that can be injected with each needle is 1000 - 5000. This number depends upon the skill of the vaccination team and the size of the fish. Care should be taken to avoid dulling the needle by injecting through scales. Any accumulated scales and debris should be carefully removed from the needle to maximize needle life and avoid reducing the penetration depth. The length of needle chosen will vary depending upon the species and strain of fish being vaccinated. Fish should always be sorted prior to vaccination to ensure that the fish are of a comparable size. This table should be used only as a guide in choosing the appropriate needle for vaccination. Needle diameter should be as small as possible while allowing the vaccine to pass through easily - usual diameters are 0.6 mm and 0.7 mm.