Eels in the Classroom Resources

Tank photo with labels (Photo: R. Shertzer)

Teacher taking tank photo

Supplies Needed for an Eel Tank

• Minimum 10 gallon tank, most used 30-50 gallon tanks
  • Leave enough headspace and use a tight fitting lid so the eels don’t escape
  • Secure top of tank with a screen or glass to prevent escaping
• Filter and filter cartridges
• Hose or siphon for water changes
• Bubbler
• Water treatment/dechloninator
• Water chemical testing kit
• Antibacterial tank treatment to have on hand, such as Melafix or “ick” treatment (found at PetCo or Amazon)
• Substrate
  • Eels need places to hide. Think layers! Rocks from streambeds work well.
  • Gravel/sand to burrow in
  • Plants to rest/climb on

Helpful to Have

Working with your local Conservation District to apply for small grants may help fund these items:

• Full spectrum light for plants
• Automatic feeder for holidays/weekends
• Snails to help reduce algal growth

Tank

Elvers underneath rocks (Photo: Mindy Musser) Elver swimming (Photo: Mindy Musser)

Tank Set-up

• Setting the tank up 1 month in advance allows time for denitrifying bacteria to colonize and a biofilm to develop. This can help keep the nutrient (nitrate) load down.
• Depending on your filtration system, check if mesh needs to be added over the intake to prevent eels from swimming inside.

Disease

Despite best efforts, being a wild animal means eels may arrive with or develop illnesses. Having an antibacterial treatment on hand in case of infection is best and can often clear an infection within a week of treatment. Signs to watch out for include lethargy, disinterest in feeding, white spots on skin, redness and swelling around gills, and extra slime produced around tail fin.

Behavior

• Eels may become more aggressive as they grow larger, this is normal!
• Some eels like to play in the bubbles or rest on the filters/tubes. Some may be very still for long periods of time but they are not dead! The eels come alive at feeding time and some may eventually eat worms out of your hand.
• If you have particularly rambunctious eels, you can use black gorilla tape to cover holes/openings around the filters and tube on the tank lid.

Feeding

• Pellets aren’t the best for food, since they often fall and become moldy when not eaten right away.
• Feeding 2-3 varieties of food is good to keep eels growing at the same rate. Try to avoid a single food source since some eels will grow quickly while others fall behind.
• Incorporating live food is beneficial, since it keeps eel from becoming “lazy” and trains them to hunt for live prey.
• Collecting stream macroinvertebrates during fall field trips offers a great food source for the eels.
• If you can, increase food size as eels grow. For example, start with blood worms and work up to earthworms once they become larger.
• Most importantly, find a feeding schedule that works for your classroom needs, and is easy to remember.

Release Day

The release can be as small or large as you’d like!

• Aim to release the eels from late April-late May. The deadline to release them will be shared via email, usually the end of May.
• Look for a nearby stream you can access with your students during that time of year, and begin field trip permissions/paper work in early spring, or as needed.
• When choosing a release point, try to look for a place where the current isn’t super strong, and try to find a place that appears to have a good amount of natural underwater structures such as rocks, down trees, vegetation, etc. on the bottom. This provides the young elvers safety and food in their new environment.
• Waiting until the latest possible date in the school year to release them is best if possible, as water temperature will be closer to their previous tank environment, minimizing shock associated with acclimating to life in the wild.

Eel release video Eel release, Juniata

Eel Release Day Ideas

• SRBC is happy to join for eel releases if schedules allow. We may be able to provide an electrofishing demo that day (stream flow and weather dependent) and talk about careers in environmental science.
• Some schools create full day events, such as partnering with local Conservation District to create an Envirothon Day with students rotating through water quality related stations.
• Instead of a final project or test, the release day could provide an opportunity for students to demo what they learned about the eels throughout the school year.
• Because the eels are still small and swim away quickly, the release itself can happen quickly and be difficult to see. Try using underwater cameras to capture the release, and make sure to keep students engaged leading up to the release.
• Have plans for after, such as a game or classroom discussion demonstrating what the eels will encounter on their next journey.
• Cross-curriculum ideas:
  • Geography: Mapping their journey back to the Saragasso Sea? How many miles is it?
  • English classes: Graduation speech or a poem for the release date?

Eels video