Implantation of a New Micro Acoustic Tag in Juvenile Pacific Lamprey and American Eel

The overall goal of this procedure is to implant miniature acoustic tags within the body cavities of juvenile Pacific lamprey and American eel and to monitor their behavior and physical effects after the tagging process. Numerous studies have been conducted to understand fish survival, behavior and movements near river structures, such as hydropower dams, that may impede upstream or downstream migration routes. To help address this ongoing and usage need, Pacific Northwest National Lab developed a new miniature acoustic tag that specifically designed for the use in juvenile lamprey and eels called the lamprey and eel tag.

This method identifies the protocols for using acceptable dose rates, handling fish without injury or undo stress and identifying the optimal location where tags can be implanted. The main advantage of this tagging technique is the speed of the process, because no sutures are required. The location of the tag within the body cavity minimizes physiological stress, promotes tag retention and does not cause any detrimental effects to the fishes'swimming ability or behavior.

To begin, prepare the tags for implantation by disinfecting them. Place tags in 70%ethanol solution from 20 minutes. Then remove tags using plastic tweezers and place in a small glass dish containing sterile water.

Next, remove tags and place in a sterile pill cup. The next step involves preparing the anesthetic bath which enables fish to be handled and tagged. In a small plastic cup, weight 40 grams of tricaine.

Dissolve powder into a 500-milliliter beaker of tap water on a stir plate and mixer bar. Then transfer to a 500-milliliter plastic bottle to achieve an 80-grams-per-liter stock solution. Repeat the same procedure with sodium bicarbonate and add to a separate 500-milliliter bottle.

Fill a 10-liter plastic tub with five liters of water from the same source as the fish to be tagged. Add 6.25 milliliters of tricaine solution and 6.25 milliliters sodium bicarbonate, using a measuring pouring gauge attached to the top of the 500-milliliter bottles. This results in a 100 milligrams-per-liter dose to the tub.

The sodium bicarbonate is added at an equal dose to the tricaine to keep the pH balanced, because tricaine is acidic. Stir to mix solution thoroughly, in the tub, and have a lid available to cover the tub to ensure lamprey do not escape while in the anesthetic solution. This completes the anesthetic solution preparation.

Place an individual lamprey into the anesthetic bath, using a small dip net. Wait four to five minutes for lamprey to become fully demobilized and stop swimming, while maintaining a slow but steady gill movement. Use a dip net to remove lamprey.

Take length and weight measurement and record the unique identification code of the acoustic tag. Meanwhile, prepare a 1.3 centimeter-thick, closed-cell foam pad, saturated with water first, and then 150 microliters-per-liter of protective coating solution. The coating helps to counteract the disruption of mucus membranes during the surgical procedure.

Place the lamprey ventral side up on the prepared foam. Position a small section of tubing so that a regulated supply of water from an elevated water tank flows through the lamprey's mouth region. This allows for respiration while fish is undergoing tag implantation.

Next, locate where the incision is to be made, approximately 20 millimeters posterior to the gill pores on the left or right lateral side. A ruler can be used for reference or markers placed on the foam pad. Using a sterile 3.0-millimeter microsurgical scalpel with a 15-degree blade, carefully make a 2.5-to three-millimeter opening in the lateral direction, ensuring that the scalpel is cutting just through the inner skin wall.

Then carefully place the disinfected tag anteriorly into the body cavity, by hand. Apply slight pressure to the tagging site to ensure tag has moved into the body cavity. Next, place tagged lamprey into a recovery bucket, containing fresh river water supply with an oxygen pump tubing and air stone.

Ensure that lamprey have recovered from the anesthetic and transfer to holding tank for future study. Follow the same steps to tag yellow-phase American eel with these differences. To achieve a dose rate of 240 milligrams-per-liter, use the previously described anesthetic solution of 80 grams-per-liter tricaine and sodium bicarbonate.

Add 15 milliliters of each to the five-liter water bath. The incision is to be made 25 millimeters to the base of the pectoral fin on the left or right lateral side or approximately 1/3 of the total length of the eel. Ensure fish are swimming normally in the recovery container.

This figure illustrates the duration to impingement in a constant-water-velocity swimming tube for the four size groups tested, from 120 to 160 millimeters. The results show no statistical difference between the tagged and untagged control groups. This figure illustrates the critical swimming speed in body lengths per second for tests conducted in a swim chamber.

The size groups range from 111 to 120 to 161 to 175 millimeters. The results show that there is no statistical difference between the tagged and untagged control groups. This figure shows the median swimming speed in body lengths per second for all size groups tested.

The speeds were 4.12 body lengths per second for tagged and 3.88 for the control group. Again, there is no statistical difference between the tagged and control groups. The results of these laboratory studies demonstrate that the tagging procedure and tagging effects do not have adverse impacts to fish survivability or swimming ability.

The tag implantation procedure was effective at placing tags in the body cavity without causing significant hemorrhaging or infections at the tagging site. The duration of the tagging process, less than 60 seconds, is beneficial in that it reduces stress associated with the fish being anesthetized. These findings characterize a new tool for juvenile lamprey and eel passage research and can be utilized in future studies.

This technology will allow researchers to track lamprey and eel movements within the river systems as they approach hydroelectric dams or other structures that may impede fish passage. In turn, the results can better inform management decisions to help conserve these species throughout their juvenile life stages.