I am a bit of a broken record with my imploring of people to always take a closer look at the natural world, as what may seem already familiar so often holds new discoveries. So, without apology, I have another mystery creature to introduce this week — one that I have never seen or even heard of before.

Two young banded rudderfish swim in Casco Bay. Kristin Peterson photo

The banded rudderfish looks more like a fish someone accidentally let out of its aquarium than one you would expect to see in Casco Bay. Its docile nature made it seem even more out of place, as it lolled about just beneath the surface right off the dock of a local boatyard. That stood in contrast to its shark-like form with its white-tipped elongated top tail lobe. Whether it was an aquarium escapee, it certainly couldn’t be a native species. My friend who discovered it is an avid boater and has been all over Casco Bay for many years but had never come across one of these unusually zebra-striped swimmers. As I have done many times with marine life I’ve been unable to identify, she too sent a photo of these fish out to other friends and fishermen to see who might recognize what they were. The replies were mostly perplexed. But finally, she got a reply that suggested it was a banded rudderfish. And to her surprise, while not a common species, it was not an invasive one.

The banded rudderfish (Seriola zonata) has a wide geographic range from the Gulf of Maine all the way to South America. It is more commonly seen in the more southerly part of that range and resembles several other warm-water fish that have similar bands. But the thing that distinguishes the rudderfish is that those bands are only visible in its juvenile years. That means that not only was this an unusual sighting because of its species but also because of its particular age group. Once they get to be about a foot long, they lose their stripes (zonata is Latin for banded) and are simply bluish or greenish in color. What wasn’t unusual was the fact that it was seen close to a boat. As adults, rudderfish spawn offshore and have been seen following boats, and as juveniles, they also seem to have an affinity for boats and prefer warmer waters closer to shore.

Knowing that the rudderfish is, although rare, native to Maine, I wondered what other, more common fish it might be related to. One of its other common names, banded mackerel, offered a clue. Maine is home to plenty of mackerel, which share the rudderfish’s banded pattern. But our more common Atlantic mackerel belong to a different genus — Scomber. The banded rudderfish is more closely related to the jacks like the amberjack and yellowtail jack, which are found in the southern part of their range. Like these jacks, rudderfish are tasty to eat. There are both commercial and recreational fisheries for them in the South Atlantic and the Gulf of Mexico where they are typically caught with a longline or a gill net.

Finding a new species to appreciate is one of my favorite things about spending time in Maine on or near the water. No matter how much we think we know and how old-hat things may seem to be, there is always more to discover. Things are also changing so that we are seeing shifts in species, and new arrivals are making their homes along the Maine coast. Perhaps this is a fitting last column before the school year — a lesson for us all to be constant students of the natural world in an effort to more fully understand it and all that it provides.

Susan Olcott is director of strategic initiatives for Maine Coast Fishermen’s Association.