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Gender Reveal: Fish

“Is that fish a girl or a boy?” is a common question we get asked at the Aquarium.  With some species it is a very easy question to address but with others it can be a bit more complicated.  (Sometimes the answer can even be both!)

If a species is sexually dimorphic, males and females will look different from each other.  Sometimes this is just a subtle variation in color or shape but it can also mean the two sexes look radically different from one another. A good example of this is a species of angler fish. The females of this species can grow to over a foot long, while males only grow to about half an inch!

Some species of fish show no sexual dimorphism and it can be impossible to tell the difference between males and females without looking inside the animal’s body.  For some species at the Aquarium we can make an educated guess based on mating behaviors, but for others we just don’t know. The green moray eels in the Shark Gallery are one example of a fish that has no sexual dimorphic traits. Both sexes look identical.

Adding another layer of complication is the fact that some fish have the ability to switch sexes throughout their lifetime while others are both male and female at the same time. This is known as hermaphroditism, and there are many different forms. There’s simultaneous hermaphroditism, seen in species of hamlets, where the animal has both male and female reproductive organs and can play either role in mating. A more common type is sequential hermaphroditism, where an animal changes from one sex to the other at some point in its life.  This can be further broken down into more categories: changing from male to female (protandry), female to male (protogyny), male to hermaphrodite (protandrous hermaphroditism) or female to hermaphrodite (protandrous hermaphroditism).  This phenomena is not uncommon and you may be surprised at how many fish you know that fall under one of these categories.

One of the most recognizable fish at the Aquarium is the clownfish.  What some people don’t know is that clownfish are actually sequential hermaphrodites—protandry to be exact. When it comes to clownfish hierarchy, the female is dominant.  She is the largest fish in the group and the next largest is her male mate. The remaining fish in the group are smaller, undeveloped and unable to breed. If the female dies, the largest male then grows and becomes female and the next fish in line matures to assume the role of breeding male.

Groupers, angelfish, gobies, damselfish and wrasses (my favorite being the rooster hogfish) all fall under the protogynous category.  This means that these species start out as females and can quickly switch and become males if the dominate male leaves.  This type of hermaphroditism is more common and benefits the fish by allowing them to produce the maximum number of offspring.  It is a size-based reproductive strategy with large, strong males protecting the nesting sites of many smaller females.  For these species it is beneficial for females to produce many offspring while small and then become males when they themselves are bigger.  It is also beneficial because it’s a big ocean out there and sometimes difficult to find another member of your species let alone one of the correct sex. The ability to switch sexes means these fish have more opportunities to find a mate.

Hermaphroditism has evolved independently in fish many times and has proven to be a successful reproductive strategy throughout the animal kingdom.

 

Rooster hogfish are both sequential hermaphrodites and sexually dimorphic.  Can you spot the differences between the female (top) and the male (bottom)?

– Kelsey Scheutzow, Greater Cleveland Aquarium Diver

Scuba Cylinders

Scuba equipment is absolutely critical to keeping divers protected and alive. Today, I want to talk about the one piece of gear that we divers need and is often overlooked—the scuba cylinder. Scuba cylinders supply air, enabling us to explore the underwater world that we have come to love. They come in many different shapes and sizes to serve different needs.

Back when the sport of scuba diving started, many innovative divers would actually take, used fire extinguishers and convert them for diving purposes. Today, we know this is not the best option, but just 40 or 50 years ago there was not much in the way of “dive shops” to go to. In fact back in those days a person could just walk into a local department store and buy most of what he or she needed to dive. It wasn’t until the creation of the first dive training and certification agencies that the sport started to become a little more like what you may recognize today.

Modern scuba cylinders come in two main materials: steel and aluminum. Each of those has their place within the industry. Steel is really the preferred choice of technical divers that go into the darkest reaches of the underwater world. It is more durable, has a better weight balance and can be more easily filled to higher pressures–all the way up to 5000 PSI (pounds per square inch).

Aluminum on the other hand is lighter and cheaper, so for the recreational diver or for the dive operation that needs a large supply of them, this becomes the better choice. Aluminum is not as forgiving when it comes to its durability and cannot be filled to as high a pressure. Aluminum cylinders can be bought in almost any color your heart desires. While, steel are usually galvanized dipped and look just like your neighbor’s chain link fence…lol.

Cylinder capacity is dictated by several factors. First, divers have to consider just how long you intend to stay underwater and the depth, since the deeper you are the more air you will use. Your breathing rate is the last piece of information to consider. Cylinder capacity is measured in cubic feet, and they can range from 3 cubic feet to more than 120 cubic feet. An average recreational aluminum scuba cylinder has a capacity of 80 cubic feet and generally weighs about 35 pounds and more than 42 pounds when full.

What do we put in scuba cylinders? That’s actually a bit of a trick question. Many people think that cylinders are full of oxygen but that is relatively unusual, most cylinders have air. What is air? Air is 78% nitrogen, 21% oxygen and 1% trace elements. It is very important for a diver to know what is in his or her scuba cylinder because diving with a gas mixture different from air can have consequences. Diving pure oxygen at depth can be a fatal mistake! One alternative gas some divers use is nitrox, which is similar to air but with less nitrogen and more oxygen. Using nitrox in our cylinders allows diver to stay at depth for longer and we divers love that.

So next time you are thinking “awwww . . . it’s just a cylinder,” you may want to ponder just a bit longer. Cylinder purchases and fills are important and if you are buying the lime green cylinder because it’s cool, there may be more to think about.

– Matthew Ballish

Mistaken Monsters

Many of the aquatic species we know and love today were once believed to be sea monsters. Stories were told and retold through many generations about “sea monsters” that threatened sailors who dared to enter the dangerous, unknown waters. While the tales still live on as spooky stories, today we know these animals are not monsters at all… Let’s take a closer look at some of these “monster-ous” and intriguing animals!

A Multi-Armed, Transparent Monster AKA a Jellyfish

Jellyfish have some decidedly un-human traits. For example, they function without a heart or brain. They also have the ability to clone themselves. And, in a zombie-like twist, it’s even been discovered that the Turritpsis dohrnii jellyfish are biologically immortal. Luckily we know now that jellyfish do not intend to hurt humans and their uniqueness is more intriguing than frightening. (Pictured: an upside-down jellyfish)

A Creature unlike Any Other AKA a Giant Pacific Octopus

A Giant Pacific Octopus’s eight large arms made them easy targets for folklore and scary tales. It is well known today that octopus have DNA unlike any other species on this planet. We also know that octopuses have three hearts, blue blood, a keratin beak and the ability to squeeze into extremely small spaces. It’s pretty easy to imagine how an octopus’s alien appearance could have scared sailors who had never seen one before. Now these highly intelligent creatures are much better understood and appreciated.

A Scaleless Fish AKA an Oyster Toadfish

It seems silly that a moderately sized fish would seem scary, but people generally become frightened by the unusual or unknown, not what is actually threatening and the oyster toadfish is different. For example, it can survive out of water for a lengthy period of time. If that wasn’t startling enough, oyster toadfish flattened heads are scaleless and they have fleshy flaps on their cheeks and jaws.

Sharp Toothed Creatures AKA Sharks

Sharks’ size and sharp teeth earned them the nickname “man-eaters” and made them the basis of many horror stories. In truth, sharks are not interested in preying on humans. People are a bigger threat to sharks than sharks are to us by a long shot. In fact, while people kill an estimated 100 million sharks every year there were only 5 shark-related human deaths in 2017. From their sandpaper-like dermal denticle skin (designed to protect and reduce friction) to their flouride-coated teeth, there’s a lot more to revere than fear when it comes to sharks.

Named Like a Fire-Breathing Fairy Tale Monster AKA Seadragons

While old legends of dragons swimming across the Mediterranean to countries like Italy and Greece might have sent chills down a few spines, clearly these seadragons are not dangerous monsters. The weedy seadragons pictured below are well camouflaged because they are poor swimmers that lack stomachs or teeth.

We’ve come a long way from believing that every unfamiliar underwater animal is a monster ready to cause harm. While so much of the ocean is still to be explored, any discoveries we will make promise to be more fascinating than frightening. Discover these and other curious creatures on your next visit to the Greater Cleveland Aquarium.

Lake Erie: Under the Waves

Written by: Halle Minshall & Ray Danner

 

There’s more to Lake Erie than meets the eye. We talked to one of the Greater Cleveland Aquarium’s divers about his experiences exploring this Great Lake’s hidden depths while surveying historical shipwrecks.

Lake Erie has a long history of shipping traffic and ideal water conditions for preservation. Still, you might be surprised to know that there are an estimated 1,400 shipwrecks in Lake Erie alone. With an average depth of just 62 feet and a maximum depth of 210 feet, the wrecks of schooners, barges, tugs and sidewheel steamers are mostly accessible to SCUBA divers.

How did you get involved in Lake Erie shipwreck diving?

Ray: I am always looking for interesting dive opportunities. I began volunteering with the Maritime Archaeological Survey Team (MAST), a nonprofit group founded in 2000 and dedicated to documentation, study and education pertaining to the underwater resources in the Great Lakes. MAST trains divers of any skill and experience level in the finer points of underwater surveys so that they can join the field teams in Lake Erie. We use a lot of the same skills to survey a shipwreck as we do diving at the Aquarium.

How many shipwrecks have been surveyed?

Ray: So far ONLY five have been surveyed and registered as official archaeological sites with the State of Ohio, meaning there are lots of unrealized survey opportunities. The freshwater of Lake Erie aids in the preservation of these shipwrecks so there are a good number yet to be located and identified.

 

What do you do when you survey the wrecks?

Ray: We lay a tape measure as a baseline running the length of the wreck. From there, we use a method called trilateration to nail down the distances from one object to another and determine the relative position and size of all items on the wreck. It can be challenging to do underwater measurements in three dimensional space, especially in cold water with low visibility. Learning underwater communication techniques and task-loading strategies is very important for all of the divers. Each dive team is assigned a small section of the wreck to survey and it can take several dives to cover even a 5-foot section of a shipwreck. After each dive all of the diver teams come together to input there new data onto a working map and sort out what data points are of priority for the subsequent dives. Through this tedious process an image is slowly formed of the bits and pieces of shipwreck lying on the lake bottom.

Two divers measuring the hatch cover of the Schooner the Dundee in Laker Erie. The diver on the left is recording the distance from the baseline to the interior edge of the hatch cover. The diver on the right is holding position on the baseline as a reference point. (Photo Credit: Jack Papes)

That sounds really interesting can I get involved?

Ray: Yes, MAST hosts a workshop every spring at the Great Lakes Museum, which trains local divers and non-divers alike. During the classroom training workshops, you’ll practice using mock surveys and the trilateration method for measuring and mapping a wreck. A final lesson is held in the waters of the White Star Quarry where divers put their new skills to the test.

Why is this important?

Ray: Lake Erie is closely tied to the lives and livelihoods of many Ohioans and it is a great resource. I think it is extremely interesting to take a look at how we used this resource in our past with the shipping and transporting of goods along the lakes shores. In learning about these shipwrecks we also learn how much we need to protect the lake they rest within.

Shark Teeth

Did you know that some shark species lose upwards of 30,000 teeth in their lifetime? Due to a strong bite and lack of a hard jawbone anchor, sharks’ teeth constantly break off or fall out. But do not worry! Sharks can have 5 to 15 rows of teeth. When a shark loses a tooth, a new one moves forward to fill in the empty spot. A shark’s first, or working, teeth are the largest. As you go back in its mouth, these teeth get smaller.

Like human teeth, shark teeth are made out of dentin. However, unlike ours, shark teeth are coated with a layer of cavity-preventing fluoride . . . so pass the candy!

Shark teeth come in a variety of shapes and sizes. Often the teeth their upper jaw are shaped differently than those in their lower jaw. The actual shape and structure of a shark’s teeth is related to the diet and hunting style of the species. For example, tiger sharks are known to eat sea turtles, seals and more or less anything that fits in their mouths, so they have large wide serrated teeth well suited to that varied diet. Meanwhile lemon sharks are primarily piscivores, or fish eaters, so their pointed rather than serrated teeth make it easier for them to grab fish and swallow them whole.

As a diver at the Greater Cleveland Aquarium, there are days when I find dozens of sandtiger, sandbar and nurse shark teeth. These three shark species have different types of teeth. The most visible of those belong to the sandtiger sharks. They have large, imposing and very sharp pointed teeth that jut out in all directions. Sandtigers can only eat things that fit within their mouths and swallow whole. Perfect for grabbing and holding prey, sandtigers use their teeth like the tines on a fork.

The smaller sandbar sharks have triangular teeth with serrated edges. They have teeth similar to a great white shark. These teeth allow sandbars to rip and cut food into bite-sized pieces.

Meanwhile, nurse sharks’ powerful jaws allow them to create suction and pull prey from hiding places in rocks and coral. Nurse sharks then use their dense and flattened teeth to crush their prey before swallowing, similar to the way humans use our molars to crunch and grind food. Their teeth are relatively small when compared to their body size.

The next time you visit the Aquarium and look up at that shark in the seatube you will know there is a lot more to a shark’s smile!

– Stephanie Q., Diver 

Fear the Frill

Did you know that the coloration of a frilled lizard depends on where it lives? Fortunately I had the opportunity to talk to Bethany Hickey, a Greater Cleveland Aquarium Aquarist, to learn all about one of the aquarium’s newest residents.

Check out the video below, and come visit the Greater Cleveland Aquarium to see the frilled lizard for yourself… if you can spot it!

Nature. It’s a curious thing.

Shark Spotlight: Sandtiger Sharks

It’s that time of year again—Fin Fest! Sharks are already on our minds 24/7, but this week-long celebration of sharks (July 22 – 29, 2018) gives us an excuse to really show how much we appreciate these jaw-some animals.

Of the three shark species in the Shark Gallery, sandtiger sharks are often the first ones you notice and the ones you remember long after you visit for a number of reasons. They tend to cruise around near the water’s surface, positioning themselves above the nurse and sandbar sharks at the top of the gallery’s vertical hierarchy. The aesthetics, too, are enough to drop a few jaws. Row upon row of ragged, razor-sharp teeth reveal themselves even while the shark’s mouth is at rest, lending an aggressive edge to an already imposing body that can grow to 10½ feet and more than 350 pounds.

However, the voracious behavior implied by these fearsome features couldn’t be further from the truth. In fact, sandtiger sharks are a very docile species known to attack humans only when bothered first. They’d much rather spend their time swimming at depths of about 60 to 100 feet, coasting around obstacles and looking for their next meal of small fish, crustaceans or squid. “You’ll find them around a lot of shipwrecks on the Carolina coast,” says aquarist Ray Popik. “They hang out around the top of the wreck … they don’t like to get down low and navigate between things.”

The sandtiger’s docility, though, develops only after it’s born. The pre-birth behavior of the species is just about the most brutal example of natural selection in the entire ocean. Along with several other shark species, the sandtiger has been known to practice intrauterine cannibalism — during pregnancy, the first pup to hatch uses the other eggs and embryos in the mother’s uterus as a food source. “The first egg that hatches wins,” says Popik. “It’s a pretty gnarly process, but in the end it allows them to provide the most amount of nutrition to put out the largest, most well-developed shark possible as a newborn.”

The sandtiger shark is also the only shark species that exhibits a certain hunting behavior: They are known to swim to the surface and gulp air into their stomachs, giving their bodies more buoyancy. This enables them to hover in the water with ease and stalk their prey by remaining completely motionless until the right time to strike. So, while they may not be the most aggressive swimmers or the most ravenous eaters, but when the time comes to feed they can put all those teeth to good use.

It doesn’t take long to find a sandtiger shark on a typical visit to the Aquarium. Their awe-inspiring stature and protruding rows of teeth catch the eyes of guests almost immediately as they enter the shark gallery. Popik agrees that their appearance combined with their behavior gives them an air of quiet dignity. “They have a presence in the exhibit,” he says. “The way they just cruise around; you can tell nothing bothers them.” Indeed, simply watching a sandtiger glide by or even overhead in the sea tube inspires a sense of respect for ocean life few other creatures can match.

Shark Spotlight: Sandbar Sharks

It’s that time of year again—Fin Fest! Sharks are already on our minds 24/7, but this week-long celebration of sharks (July 22 – 29, 2018) gives us an excuse to really show how much we appreciate these jaw-some animals.

Also known as the “brown shark” due to their muddy-gray appearance, the sandbar shark is most commonly found in shallow coastal waters with a population distribution that touches every continent except Antarctica. Despite being prevalent on an international scale, some of the largest groups of sandbars can be found relatively close to Northeast Ohio. In fact, they’re the most common species of shark in the western Atlantic Ocean. Large nursery grounds in the Chesapeake Bay, Delaware Bay and in parts of the Carolina coast make them a very common shark species around popular beach vacation spots for Clevelanders. Their population in these areas takes a huge hit in the winter, however, as their migration patterns take them as far south as the Gulf of Mexico in search of warmer water.

At the Aquarium, sandbar sharks are a perennial favorite due to their more active, agile swimming habits. Their tendency to traverse a lot of vertical space in the exhibit and make sharp, sudden turns shows off their distinctive body shape and makes them exciting to watch. Their shape in particular is what aquarist Ray Popik describes as a “classic shark look.” Their uncommonly tall dorsal fins, short snouts and wide pectoral fins give them a sleek profile that draws a lot of attention. “Sandbars are very stereotypical and jet fighter-looking,” says Popik. “They’ve got that nice, tall dorsal fin which gives them the look you picture when you think about a shark.”

Showing off their athletic swimming ability and undeniably cool appearance, sandbar sharks don’t just bridge the gap between the nurse and sandtiger — they’re proof that even the most common shark species are something truly extraordinary.

Shark Spotlight: Nurse Sharks

It’s that time of year again! Fin Fest is only a few weeks away, and we can’t wait to welcome shark lovers of all ages to the Aquarium to celebrate with us. Sharks are already on our minds 24/7, but Fin Fest gives us an excuse to really show how much we appreciate these jaw-some animals.

This week we’re covering the nurse shark, the sedentary bottom-dweller that can be found hanging around the lower, more secluded areas of the shark gallery. There are a few theories on how nurse sharks got their unusual common name. Most agree that it comes from the old English word “hurse,” meaning “seafloor shark,” but others argue the name was inspired by the sound they make while hunting which is often compared to a nursing baby.

The unique noise comes from their feeding technique, which involves sucking their prey up from the seafloor like a vacuum. Their mouths are just big enough to eat things that live near the bottom, like snails, crustaceans and mollusks, but too small to hunt for larger fish like their fellow sharks do. Being nocturnal hunters, they’ll begin to prowl the seafloor for food at night using the the whisker-like barbels that extend from their face to feel around for things to eat. “Here in Ohio, we think ‘Oh, that looks like a catfish,’” says aquarist Ray Popik of the nurse shark’s appearance, “and they actually do fill a bit of the same ecological niche.”

According to Popik, all of these characteristics go hand-in-hand. “During the daytime you’ll see them underneath ledges and in crevices hiding out. Then at night they’ll cruise the bottom scavenging for food,” he says. “Typically the more bottom-oriented the shark is, the more nocturnal it is. The opposite is true for sharks that are more active hunters, and nurse sharks are usually scavengers in the wild.”

Contrary to the popular belief that all sharks have to remain constantly swimming in order to breathe, nurse sharks and their seafloor-inhabiting peers can push water over their gills themselves without having to move much. They can circulate water through their systems by opening and closing their mouths, which allows them to stay put. The nurse shark’s bottom-dwelling habits usually catch the eye of Aquarium guests, as their behavior differs from the constant cruising of their “gallery mates” the sandtiger and sandbar sharks. However, Popik says their behavior is relatively common for seafloor shark species. “[Their behavior] is unique out of our three species,” he explains, “but it’s not terribly unique in the wild.”

Hanging out in the lower regions of their exhibit, the calm-and-collected nurse shark shows us how varied shark behavior can be in nature. Next week we’ll be talking about the sandbar shark, whose agile swimming and striking silhouette make it one of the most fun to watch animals here at the Aquarium — and don’t forget, Fin Fest is happening right here every day from July 22nd through the 29th. If you love sharks as much as we do, it’s the place to be, so don’t miss out.