Different types of fish are known for their coordinated movements that make themselves look like one big, shimmering blur. This behavior, known as schooling, is an effective way of avoiding predators! It’s very difficult for predators to pick out one fish, separate it from the group and chase it down. And while visitors can see this behavior in lots of exhibits, it’s on full display in the Schooling exhibit!

Close-up of the school. How many fish do you see?

Blueback herring, Alosa aestivalis, have been a staple of the Schooling exhibit, showcasing the ability of a fish species to act as one collective unit. After a recent group of herring grew too big for the exhibit, they were moved to a larger exhibit at the Montreal Biodome (where some of our young researchers studied wolffish). This made way for a new school!

In October of 2012, Aquarium staff and volunteers headed to Buzzards Bay to collect some new exhibit animals. After being granted a special permit by the Massachusetts Division of Fisheries, the crew used seine nets to catch close to 2,500 young fish! Having lived and grown behind the scenes for over a year, it was time for them to make their big splash.


How do you move approximately 2,500 fish from one tank to another? With lots of help! Fortunately, the holding tank and exhibit are only a few short steps away from each other, making the process a little easier. Two aquarists would gather small batches of fish inside the holding tank. Once a batch was collected, the fish were transferred in bags to a waiting group of helpful staff and volunteers. With some quick, careful steps the fish were at their final destination.

Ready to move!

Once the humans, and the fish, reached the exhibit, the bags of fish were gently lowered into the water. In position, the bags were opened and the new inhabitants would be off—the fish quickly swimming to join the rest of the school. It was then back to the holding tank to repeat the process many times over!

And they are off!

The new herring getting used to their new home!

There are some incredibly fascinating animals behind the scenes at the Aquarium right now. We're talking mind-bending amazing. An animal that defies the natural order of life and death, packaged in an animal the size of your pinky nail. Meet...the immortal jelly.

The immortal jelly: An impressive name for an animal the size of a pinky nail

Now you won't be able to see these animals when you visit. They are staying behind the scenes under the watchful eyes of our sea jelly aquarists. Right now our jellies exhibits are chock-full of other interesting animals—like the moon jellies, flowerhat jellies and comb jellies. But we think these jellies are so cool that we just had to tell you all about them.

The immortal jellies actually spend most of their time laying about at the bottom of their tank

These guys eat a diet of brine shrimp (note their pinkish-orange insides, that was lunch). They send out their tiny tentacles to snatch a shrimp then pull it toward their mouths. While they're active during feeding time, these specimens actually spend a lot of time just lazing about on the bottom of their tank.

The jellies extend their tiny tentacles around feeding time, when they snack on brine shrimp

But before we answer the question "How did these jellies get their name?" let's quickly review jelly reproduction. "True jellies" from the class Scyphozoa can reproduce asexually by budding, or sexually through a process called strobilation. That's when the fertilized egg becomes a planula larva and lands on a surface and becomes a polyp. The polyp becomes a strobila—almost looking like a stack of coffee filters. Each of these detaches and becomes an ephyra which then transitions into either a male or female medusa to begin the process all over again. (Check out the fancy diagram here for more help understanding this process.)

What makes an immortal jelly (Turritopsis dohrnii) so amazing is that as soon as a sexually mature jelly encounters hardship—environmental threats, old age and the like—it can revert back to its polyp stage and start all over. From what we now know, there's no other animal in the animal kingdom that can similarly age in reverse. Call it the Benjamin Button effect.

Senior Aquarist Chris Doller feeds and cares for the immortal jellies

There's a lot we don't know about immortal jellies. They may have originated in Mediterranean, maybe the Caribbean, but they are now distributed in tropical oceans throughout the world. No single specimen has been observed long-term so scientists don't know how old an individual can be. Also, it's important to note that most of these animals probably succumb to predation or disease before they revert to the polyp stage. That means no jelly invasion, just yet.

These jellies are not on exhibit, but amazing enough that we just had to tell you about 'em!

So. Call them creepy, call them fascinating, you've just met one of our blue planet's more mysterious creatures. Even though you can't see these guys, you can come visit its relatives at the Aquarium.