INJECTION VACCINATION TECHNIQUES

Melanie Hoare, Syndel International;
Dr. Jim Brackett, Syndel International;
Mark Lennox, Alpharma Aquatic Animal Health

The goal of vaccination is cost-effective control of certain fish diseases. Differences in techniques at different stages 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 considerations in choosing or improving techniques 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.

Monitoring

Whatever your choice of techniques, we 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.

One person should be responsible for overall observation of the vaccination process. This person should monitor the flow of fish, the supply of vaccine, the quality of water in the anesthetic bath, the recovery of fish and all other activities. Unless one person is responsible for the overview, it is easy to concentrate on one part of the process and miss problems developing at another point.

At any time, if there is noticeable scale loss, stop the operation until the cause of the scale loss is identified and corrected. Fish with scales removed have been seriously injured and are unlikely to respond well to vaccination or handling. Scale loss is probably the number one cause of post-vaccination mortality.

Delivering fish to the injectors

The labour cost of vaccination is largely determined by the speed of the crew and the ability to keep the injectors supplied with properly anesthetized fish. Anesthetic techniques were discussed in another session. Efficient delivery of fish to the injectors depends on planning and experience with anesthetics and 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. The lay-out of the hatchery will determine the best methods of moving fish.

Only experience and trial runs can determine the number and speed of delivering fish to the vaccination table. The anesthetist should make sure that the groups of fish are only large enough to keep the injectors working smoothly. Fish should be injected and off the table as quickly as possible. Care should be taken to make sure that one group of fish is entirely removed from the table before the next group is added from the anesthetic. Mixing new groups with old risks leaving some fish out of water for extended times.

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 you should always check the depth of penetration of needle sizes before vaccinating a group. Tight grading will make this part of the job easier. If all the fish in a batch are the same size, you can be more sure they all need the same size needle.

A sharp needle is an important part of reducing problems. Dull needles cause more tissue damage and require more force for injections. The large, rough injection site made by a dull needle may allow vaccine to leak back out of the abdominal cavity. This may lead to loss of the vaccine or inflammation and melanization in the muscle. Dull needles can also lead to self-injection. 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. You should have something handy, e.g. a wedge or a sponge, to remove scales every so often.

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. Be aware of safety policies and work safely.

Injectors 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 injector.

The injection should be made only when the needle is fully inserted. Pressure on the trigger should be released only when the needle is removed. 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.

Recovery and return to tanks

Many farms use a gravity return system from a raised vaccination platform. This greatly reduces the amount of handling that's needed. The pipes can lead back to a recovery tote, a transport tote or directly to the rearing tanks.

Stainless or plastic pipes are commonly used, but whatever the material, it is very important that all joints and fittings be filed and sanded smooth on the inside surfaces. Even minor burrs can scrape off a large area of scales. Plastic or epoxy paint is a good idea on any wood surfaces.

Saltwater vaccination and injections

Vaccination and treatment of fish in saltwater pens is now more common than it was a few years ago. These procedures can be safe and cost-effective, but require more planning than operations on land. All of the considerations for preparation, handling and monitoring are similar to those discussed for hatcheries, but the method of crowding and pumping or brailing the fish out of the pens is an added critical stage. Careful monitoring for the effect of tide and current changes, avoiding pockets in the net, crowding only as many fish and as densely as necessary and constant alertness for scale loss are required.

All equipment used in saltwater handling should be designed to minimize trauma and abrasion, and water flows should be set so that the fish are always wet. Pescalator pumps are very popular and function with minimal crowding. Special modifications can be made to recycle anesthetic water for small fish. Other pumps and brails are used effectively by trained crews.

A tarp suspended in the recovery pen allows the fish to recover before sinking to the bottom and lets you monitor the rate of recovery from the anesthetic. When vaccinating at sea it is very important to thoroughly disinfect all gear before bringing it to the site and after use, especially if it's going to be used at a different site.

Broodstock injections

Broodstock in many areas are routinely treated with erythromycin for control of BKD. These injections are usually given into the dorsal sinus just in front of the dorsal fin. This is not an easy injection to give. The fish should be anesthetized well, because large fish are difficult to handle. The needle should be at least 1 to 1 1/2 inches long, and 18 or 20 gauge. The needle is inserted just in front of the dorsal fin and follows the angle of the fins. The injection must be made exactly on the midline to avoid abscesses caused by muscle damage from the antibiotic preparation. lntraperitoneal injections are equally effective, but some consider that there is a risk of damage to the eggs.

Spawning compounds are usually injected intraperitoneally. Fish are anesthetized and can be injected while they are held head down or lying flat. The pectoral fin is lifted and the injection is made through the thinly scaled body wall under the fin.

COMMONLY USED NEEDLE SIZES

Always sample a few fish: cut them open and MAKE SURE the needle is going where you think it should be going.