INJECTION VACCINATION TECHNIQUES

The goal of vaccination is cost-effective control of certain fish diseases. Differences in techniques at critical points in the injection vaccination process can affect both the cost of the disease control program and also the effectiveness. During this workshop, we'd like to look at some of the critical points and some of the considerations in choosing or improving the process at those points to maximize accuracy, speed and safety.

Observations of crews injecting fish at a few different hatcheries will quickly show that there is no "right" or "wrong" way to vaccinate fish. Each crew and each worker develops a technique that works well for them. The discussion during the workshop should help you adapt the experience of others to improve your vaccinations.

Whatever your choice of techniques, I'd recommend that you have a system for monitoring the results of your work. Keeping track of: the number of fish injected by each of your crew; the number and types of problems, if any, after vaccination; the anesthetic and vaccine used; and other information will help you judge how well you're doing and how much improvement you've made.

Delivering fish to the vaccinators

The labour cost of vaccination is largely determined by the speed of the crew and the ability to keep the vaccinators supplied with properly anesthetized fish. Anesthetic techniques were discussed in another session. Efficient delivery of fish to the vaccinators depends on planning and experience with moving totes of fish around the hatchery. Important considerations here are minimizing the amount of time that fish are kept in totes and making the movements from tank to vaccination and back to the new tank as smooth and stress-free as possible. Only experience and trial runs can determine the number and speed of delivering fish to the vaccination table.

Holding the fish for injection

Vaccination machines are the most mechanized way to hold a fish for injection. Machines are not very common in Canada, but are popular in Scotland and Norway. While machines reduce labour costs, the capital cost is obviously much higher. Machines require a rapid supply of fish, graded to tight size ranges to avoid problems with mis-injections.

Injecting by hand is the most common method in Canada. There are two schools of injectors: hold the fish in one hand and inject; or, hold the fish against the table and inject. We'll no doubt be able to get good advice and comments on both methods. With either method, important points are:

• minimize scale loss and abrasion - wear proper gloves, ensure table surfaces are smooth and wet
• hold fish in a position that lets you hit the injection site every time
• avoid self-injection

Injecting

The injection should be made into the abdominal cavity on the midline. The length of the needle will be determined by the size of the fish. A table with suggested needle sizes is provided. Some strains of fish or certain groups of fish might have thicker or thinner body walls, so it's always a good idea to check the depth of penetration of needle sizes before vaccinating a group. Tight grading will make this part of the job easier.

A sharp needle is an important part of reducing problems. Dull needles cause more tissue damage and require more force for injections. The cost of new needles is minor compared with the entire vaccination costs. Ideally, needles should be disinfected between injections to reduce the risk of disease transmission, but there is no practical method of doing this so far.

The needle guard should be adjusted to help place the needle at just the right spot for injection. This will avoid injection into the muscle of the fish, as well as reducing the chances of self-injection.

Syringes are also a matter of personal preference. After a few thousand injections, small differences can become critical. Some injectors have modified the syringes to suit their needs, including one crew that has mounted a counter on each syringe.

The injection should be made only when the needle is fully inserted. Injecting vaccine while the needle is on the way in or on the way out will leave vaccine in the muscle or under the skin. Vaccine in these sites may cause tissue damage and/or poor response. There will be more discussion of this in the section on adverse reactions.