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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

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.

PADI International Women’s Dive Day

As a dive instructor and the Greater Cleveland Aquarium’s Dive Safety Coordinator, PADI International Women’s Dive Day is a special time to share what I love. From my perspective, SCUBA diving has great value. It is a lifelong skill and a key to a hidden world. Diving also helps to build confidence, foster new relationships and cultivate a sense of independence.

What else is out there in the two-thirds of our planet covered by water? The sea provides a limitless number of new experiences. As a dive professional who does hundreds of dives a year, you may think I have become immune to the wonder and amazement diving provides, but I am constantly marveling over new sights and new interactions. For example, I was diving with sharks when a large, fully grown female tiger shark swam over to me, looking into my eyes with her massive ones before nudging me out of her way. Interactions like these, while being REALLY COOL, also cause a change in perspective. This mighty creature wasn’t interested in confrontation. We were able to coexist peacefully in her world. Intuitively, I knew she was not seeking to harm me but now I have lived it. I have had experiences many only dream of and from them I have learned to think for myself to form my own opinions. I now relish the times where my comfort level is exceeded by a large shark’s close encounter.

Diving is all about personal growth and development. In challenging you to do things you find uncomfortable and allowing you to struggle until you learn to put all of the pieces together, diving helps you build confidence. When teaching someone how to dive, there inevitably are skills that give each student difficulty. Coaching them through and past these difficulties is rewarding for both me and them. For example, the fundamental SCUBA skill of clearing your mask is not as simple as it might seem for new students. While it’s not a technically tricky skill, it requires mental strength to overcome the discomfort of having water on your face. This breakdown—when our brain tricks our body into panicking—must be controlled from within. This self-governing, self-control aspect of SCUBA diving sets a foundation for learning how to overcome mental obstacles in everyday life.

There is no strict phenotype on who can and cannot become a great diver. Historically, SCUBA diving has been a male-dominated industry. This needs to change. Women can become fantastic divers. Children (ages 10 and older) can become fantastic divers. You don’t have to be an amazing swimmer to become a fantastic diver. You don’t have to be wealthy to become a fantastic diver. You don’t even have to live near an ocean to become a fantastic diver. For SCUBA diving to continue to grow it must become more open and inclusive. For this reason, the Aquarium’s dive team wants to share our experiences, answer your questions, and encourage your participation in learning about SCUBA diving on July 21. Come join us!

– Halle Minshall

International Women’s Dive Day

Let’s take a look at our women divers in action!

Our diver suiting up for a swim with the sharks.

Getting the diving gear ready to go!

Heading into the tank for one of our four daily dives for the day!

Twice a day, our divers will do a maintenance dive as well as two full face mask dives.

Our divers do an outstanding job cleaning our exhibits and keeping them looking squeaky clean for our guests.

Dive shows are a great way to learn more about our divers and what their job entails. Guests are able to interact with the divers and get to experience some of their daily tasks.

Our divers sanitize after every dive to make sure they don’t contaminate the water when going from fresh to salt water or vice versa. The divers also clean the corridor exhibits, in addition to the sea tube pictured above.

5 Things More Dangerous Than Sharks When You’re 47 Meters Down: A Diver’s Perspective

We recently saw 47 Meters Down. The new shark thriller starring Mandy Moore is designed to get your heart pumping, for sure. The fact that the silver screen has a habit of making us unnecessarily scared of sharks aside, the things that made us fear for the survival of the novice diving duo at the center of this horror flick had nothing to do with the animals that surrounded their dive cage.

1. Inexperienced divers going to significantly deeper depths than those for which they are trained can be a recipe for disaster even without a shark in the mix. Due to the effects of pressure, the volume of air a diver consumes in a given time typically increases with their depth—go deeper breath more. Other factors can also cause a diver’s air consumption rate to increase including exertion while swimming, speaking and cold water, just to name a few. Stress is also a major contributor to air consumption so two inexperienced divers being harassed by sharks like those portrayed in the film would result in a drastic increase in air consumption. At 47 meters even an experienced diver with a fantastic air consumption rate would quickly drain their scuba cylinder, probably in less than 20 minutes. An inexperienced diver swimming, talking and being harassed by sharks MIGHT make it five minutes at that depth.

2. The full face mask system used in the movie would be extremely dangerous for these inexperienced divers. Humans convert 5% of the oxygen we breathe into carbon dioxide which is then exhaled. The masks in the film do not have separate chambers for new and exhaled gas which would result in the diver breathing in carbon dioxide. The effects of breathing carbon dioxide on the surface are rapid breathing, rapid heart rate, fatigue, nausea and headache. Other, more severe effects can develop if the carbon dioxide exposure is not reversed. Underwater all of these effects would be more even sudden and life threatening.

3. According to the US Navy dive decompression tables a diver may spend up to five minutes at 160’ (47 meters) without needing to decompress during their ascent. The longer a diver stays underwater the greater their exposure to “the bends” becomes. The bends is a layman’s term for decompression sickness, which is caused by the accumulation of nitrogen breathed under pressure. This does not pose a problem until a diver begins to surface and nitrogen bubbles form in the bloodstream. The bubbles can cause the bends. The amount of time it would take a diver to safely surface increases as the amount of time s/he spends at that depth increases. It would actually take more than four hours to safely surface from a 60-minute dive at a depth of 160 feet.

4. Another risk often faced by divers at depths exceeding 80 feet is nitrogen narcosis. Commonly referred to as “rapture of the deep,” nitrogen narcosis makes a diver feel and act like they are inebriated, lacking inhibitions and generally numb to any concerns. Luckily nitrogen narcosis has not been known to leave any lasting effect so long as divers recognize it and ascend enough to limit its effects. It is easy to imagine the havoc nitrogen narcosis could play on a diver who needs to be very mindful of their surroundings and sharks!

5. Even in warm water hypothermia is a risk. Not wearing a proper fitting full coverage wetsuit can set up a diver for problems. Water can pull heat away from a diver’s body 25 times faster than air. Hypothermia’s effects on the body start with shivering which can become violent and lead to loss of coordination and function. In bikini-style suits the likelihood divers at 47 meters down would experience more than just a mild hypothermia is high.
Given the depth, equipment, clothing and stress factors, it would be a challenge for the most experienced divers to survive under these circumstances.

— Halle Minshall, Dive Safety Coordinator, & Erik Helgesen, Exhibit Diver