Can reach lengths up to 50 feet and weigh up to 30,000 pounds. Have over 27,300 species. Have colors ranging from green to red to blue. Are able to live in water, something impossible for humans. Can swim up to speeds of almost 70 miles per hour, a little less than three times the speed of the fastest human. Some can detect electrical fields, and yet others can even "fly". Yes, I think we can agree that fish are amazing, not to mention beautiful, creatures. And on February 27th, 2013, 20 kids, including me, walked into a room to partake in a hands-on lab with these animals. Walking into the room, we were divided into groups. Once everyone was settled, we started to delve into the world of water. To start off, we discussed fish farms. What they do, what they are used for, et cetera, but mainly about how disease and other things can spread throughout fish farms and the impact that this may have, whether it is on the fish, the farm, or both. Fish farms, well, farm fish! Hence the name fish farm! They basically breed fish so they can be sent to restaurants and other places for us hungry carnivores to eat! But problems can arise in fish farms as well. Think about it. If one fish has a disease, if there is something wrong with it, then chances are that the other fish will soon have the same problem. This is not good. Some fish may die, and some cannot be taken for restaurants. To prevent this, a report about the fish farm and its fish is filled out at times. By comparing the report to what should be normal, you are able to see if something is wrong. Changes in size and weight, for example, can be clear indicators that there is a problem. What the abnormalities are can lead to discovering what the problem actually is and how to fix it. Our instructor asked us why we would inspect or dissect a dead fish. We came up with two reasons. A) To simply learn more about that type of fish, and b) to try and find out why the fish died. That is exactly what they do at the Shedd, and what our lab was about. We were going to perform a necropsy, meaning we were trying to find the cause of death, by first inspecting the exterior of the fish, and then the interior. The first step was to take the mass and length of the mass. Our group's fish was quite small compared to the others; it only had a mass in the 600's. And while two people were doing that, the other two were finding out what the pH of the water the fish was in was. This can have a big effect on fish. The ideal pH range for them is 6.5-8.0, where numbers above 7 are basic and numbers below are acidic. At first it may seem that only acids are harmful, but this is not true. Bases can be harmful, too. Our fish's water's was over 9. This could easily be a factor that affected the fish. The size of the fish also warns that something may have been wrong. When everybody completed the task, we inspected the scales of the fish. Different things could be associated with the scales, two of which being skin rot and parasites. Our group removed one of the scales and looks at it under a microscope. At such a close view, it reminded us of a fingerprint, with the repeating lines and such. Everything looked just as it should. But when we flipped the fish over, however, we noticed what looked like some skin rot on a part of the fish. The scales here did not have a clear, distinguished pattern as the others did. We recorded our finding on our paper, and then moved on. Next, we had to take a clipping of the tail fin using the scissors. Our tail was not in very good shape. The last part of our exterior examination was to inspect the gills. We had cut a bit to get to them, but when we took a clipping, everything looked pretty good. Obviously, the gills are very important, considering they are the fish's way of breathing. Once, we finished inspecting the outside, it was time to examine the inside. Each group was supposed to cut upward, starting near the anal fin, to the line above the lateral line of the fish. The lateral line of a fish detects vibrations in the water surrounding the fish. This allows the fish to sense things such as nearby movement. Dissecting the fish wasn't easy, though. We had to cut through the fish's ribs, each time hearing a loud "CRUNCH". When we finally peeled down the flap of skin, the organs of the fish were revealed. We combed through the fish, inspecting organs such as the liver, ovaries, intestines, and swim bladder, which controls the fish's buoyancy. We actually removed the stomach, and squeezed it so that the digested food came out onto the tray. Perhaps the strangest part of it all was that a large part of the fish's inside was green. That was definitely not normal, and we wondered why it could be like that and if it might have been a reason as to why the fish died. Later, when the biologist came in, he explained that our fish was female, and was going to lay her eggs. This takes energy, so she was storing up extra fat, and that is what we were seeing. After inspecting the organs, we took the lens out of the fish, which is a hard, clear, circular thing that is located in the eye. To do this, we expunged the fish's eye by cutting around it and then into it, where we had to use the forceps the extract the lens. And that was the end of our dissection. Since we finished our dissection, we had to clean up. We disposed of the fish, and then wiped down our tables. Meanwhile, a fish biologist came into the room. When everybody was settled, he shared his presentation with us. He talked about certain places for endangered fish, and how the fish that live hear in Chicago are not all natives. The American Eel, for example, travels all the way from the Atlantic to here and then back again. Some fish also may only live in certain places. He then talked about ways to fish for fish. One method was to generate a shock in the water, which stuns the fish for a small period of time. The fishers can then scoop up the fish with nets. We also learned about threats to fish, such as eliminating things that may seem unnecessary, but when removed can bring harm to the fish in the area, like small rivers or tributaries. At the end of the presentation, we received guides to fish that live right here in the Chicago area. The guides had pictures and information. Things like how the Lake Sturgeon, which can grow up to eight feet long, were once common in Lake Michigan, but are now rare. And how the Longnose Dace was voted to be the official fish of Chicago by schoolchildren. Overall, I learned a lot about fish anatomy, necropsies, and threats to fish. All that we have left is one more session at the aquarium, which I hope will be as informative as this one was.
Author: Matt H.
This week at the Shedd we were doing fish dissection! We began the lesson talking a bit about fish farms, and how there was sometimes disease in the fish. We then began to look at the fish (Atlantic Striped Bass) externally, taking samples and looking at them under a microscope. We compared the samples to different pictures and descriptions that described different diseases and parasites that might be found. We also measured the pH of water to see if the fish were not in the right pH range (which was about 6.5 to 8), and we measured and weighed the fish to find any abnormalities in size. In our fish we found a sort of skin rot in some of the scales, though this could have been from freezing the fish prior to the lab. After the external examination of scales, fins, and gills (which should have been very red if they were healthy), we cut the fish open after talking briefly about the function of the lateral line, to sense movement/vibration in the water. We inspected different organs, taking out the liver, and again compared them to the given pictures and charts. We also looked at th size of the liver in comparison to that of the other fish. After the internal inspection was over, we popped out the eye so that we could look at the lens. This was the last bit of dissection that we did. We then watched a presentation about fish in the Chicago region. We learned how fish biologists study the populations and habits of the many fish in the region, which tends to be by dragging nets through the water to capture fish to study or by setting traps in deeper water. We learned how some “hotspots” of endangered populations or species were formed. For example, we learned about how a lake had a natural dam made of ice holding it in. When the ice broke, a massive flood changed the land greatly and spread fish in certain places. We also learned about threats to the fish, such as the elimination of small, seemingly unimportant creeks, and irrigation channels that spread cow manure and fertilizer into creeks, resulting in deadly algae or bacterial blooms. We all got to take home a guide to a few fish in the Chicago area, including the American Eel, which comes all the way from the Atlantic, the Burbot, a relative of carp that lives deep in Lake Michigan and tastes wonderful, and the Longnose Dace, a fish chosen by schoolchildren to be Chicago’s city fish. After that, we asked questions about the presentation before the end of class. I think that this was a really valuable lesson and that I learned a lot about fish, especially those nearby.
As we entered the room, we were assigned each to an animal. We got together with the people
who were the same animal. I was a sea otter. We were taught a little about MPAs. MPAs are Marine
Protected Areas. There are different levels of protection. For example, all MPAs ban fishing. More
protected MPAs would ban swimming or diving, and extremely protected MPAs would ban boating in
Each of our tables had boxes with information on our animal. Our main objective was to find a good
area to serve as an MPA for our otters. Our boxes had charts and papers about sea otters and their diets
and population and the like. There was an interactive map of the ocean off the west coast of the US. It
showed the population of sea otters (and the other animals) in specific areas. We had an empty chart
in which we wrote the population of the sea otters in each section. Once we had written the current
population of the sites, we rolled a die to decide what would happen to each population. There was a
sheet that had different events for each number on the die.
When we finished our activity, a scientist who had studied sea grasses in the Caribbean came up and
gave a talk on sea grasses. Acres of sea grass can be clones of one organism. The scientist talked more in depth about MPAsand the difficulties of convincing fishermen to help. MPAs help protect and replenish the fish for fishing. They take a section of the ocean, and don’t let anyone fish, swim, dive, or boat in that area. In time, the fish in that area grow in population and then in size. Several years later, there is spillover: some fish go out of the protected area, and get caught by the fishermen. So by protecting one area of the ocean, fish are constantly being replenished.
Last week at my Shedd Aquarium class, I learned about protected areas in oceans and lakes, and how there were degrees of protection for these areas.
Ten arms/tentacles, lined with toothy suckers and each thought to be controlled by an individual nerve center. Capable of swimming at speeds of up to 2.5 body lengths per second. Muscle-bound pigment cells called chromatophores that allow their skin to change in color. A sharp beak and a spiky organ called a radula for ripping and tearing flesh. These sound like the attributes of a space alien, but in fact these are all characteristics of species of the class Cephalopoda (squids, octopuses, cuttlefish and nautiluses). Last Wednesday, we dissected Longfin Squid and learned about their anatomy and morphological adaptations for life in the sea.
We began by talking a little bit about squid and octopuses, and developing some research questions we wanted to answer. The specimens for dissection were earlier destined for restaurant use – longfins have been commercially harvested, and thanks to their fast growth and high reproductive rates are considered a sustainable dining choice (learn more about the sustainability of Longfin Squid as seafood here). We talked about the anatomical differences between squid and other, more familiar organisms. We discussed adaptations like statocysts that let squid replicate auditory perception. We discussed as a group some subjects that we all wanted to learn more about through the dissection, including squid senses and respiration.
And then the dissection began. Ben M. and I worked together with Zola and Ezra to answer two assigned research questions about how squids catch food and how they ingest and process it. Our instructor helped us by letting us know where certain parts of the squid were, where we might want to cut, and what we might want to take a closer look at under the microscope. It was an exciting and messy process, with split ink sacs and an accidental decapitation of one of the specimens. We conducted the dissections using metal probes, scissors and tweezers, and we were provided with squid anatomy charts that aided us in locating the squids' internal physiological features.
One of the squid's key predatory adaptations is its speed. Squid swim backwards, jetting along by releasing water from a siphon positioned at the anterior end of the body. Squid are able to seal off their mantle cavity, forcing the water out of the siphon. Wing-like swimming fins just from the posterior of the mantle, aiding in steering. While swimming, the decapodal squid conceals its two long, club-like tentacles within its eight arms. Once within striking range of a prey animal, the squid lashes out, ensnaring the poor creature in its tentacles and grasping it in its arms, laden with suction cups reinforced with calcareous sucker rings (we were able to remove and take a close look at some of our squid's sucker rings). The prey is passed off to the tearing, beak-like mouth, and bites of flesh are chewed up and shredded by a spiky structure called a radula inside the squid's mouth. The squid's visceral mass (containing the stomach and digestive tract, as well as other organs) is long, thin, and streamlined, in keeping with the squid's general form and function. We removed our squids' beaks (made of two interlocking pieces of chitin, a nitrogen-containing polysaccharide that is found in combination with calcium carbonate in the exoskeletons of arthropods), and we cut open our squids' mantles to take a look at the stomach.
At the end of the workshop, we looked at some videos of cephalopods releasing ink clouds and changing their color and shape to counter threats. Some of the groups also presented their findings to the class. One of the tables came around and showed everyone how to remove the lenses of our squid's eyes (squids' retina-equipped camera-type eyes are closely analogous to vertebrate eyes an example of convergent evolution). Another table came around and helped us locate and remove our squids' feathery gills.
15 (fifteen) of us, ranging in age from 9 (nine) to 17 (seventeen) filled a nautically inclined
classroom deep in the nautically inclined bowels of the Shedd Aquarium, 3-4 to a table, one 30
cm Longfin inshore squid to every two nautically inclined individuals. The decapodal specimens
had been provided by a nautically inclined and unnamed restaurant supplier.
Our appointed teacher spoke generally about squid. These cephalopods of the order Teuthida
boast bilateral symmetry, a mantle, and eight short, grasping arms assisted in the hunt by two
long, grasping tentacles. The primary body is enclosed in the mantle, which has a swimming
fin along each side, and the skin is coated in color shifting chromatophores, white signaling
aggression. When courting a female, the male maintains the heartily comforting red of the side
facing the female and the furious white of the side facing outwards, toward other males.
The squid’s underside is always lighter than the topside to provide camouflage from the
predators cruising above and the prey cruising below. They have vastly differentiated from their
mollusk ancestors, their bodies lengthening and condensing into a slim, aerodynamic predator
with advanced eyes similar to vertebrates and no ancestral shells. Instead, the squid’s structure
is supplied by a feather shaped pen made of chitin. Under the body are openings to the mantle
cavity, which contains the gills and openings to the excretory and reproductive systems. At the
front of the mantle cavity one finds the siphon, which the squid uses for locomotion via precise
jet propulsion. In this form of locomotion, water is sucked into the mantle cavity and expelled
out of the siphon in a fast, strong jet. The direction of the siphon can be changed, to suit the
direction of travel.
Post preamble, each group of two was supplied with an assignment, a secret to unlock from
their limply defrosted squid carcass. Our mission was to determine the method by which squid
hunted down their prey; our tools—probes, medical scissors, and tweezers. The exterior of a
longfin squid is obviously built for the hunt, its slimly lateral backwards mode of high speed
travel allows it to swoop down upon its prey from above, while its two tentacles, kept hidden by
its arms during travel, dart out and snag a small fish or crustacean, encasing it in its cartilaginous
suction ringed arms and tearing away flesh with its hard, sharp beak.
When a squid’s natural speed and ability is not enough to evade predators, it resorts to the sack
of ink it carries in its body, a dark pigment comprised of melanin and released into water when
the squid is threatened. The release of ink takes place in two stages—massive amounts of ink to
create a smoke screen, then a second release of pseudomorphic smaller clouds of ink with greater
mucus content which are attacked while the squid speedily slips away.
So here we are, hopefully having learned about squid and the wonderfully wacky ways in which
they work. Yessiree Bob, I tried to deliver straightforward information about squid, fascinating
animals that they are. There’s something slightly mystical and compelling about the squid
physiology. Fascinating animals.
Author: Ben M.
With Every Drop is a Chicago-based blog, published by CR² team members, that focuses on the biodiversity, ecology, and conservation of marine and freshwater ecosystems.
“Even if you never have the chance to see or touch the ocean, the ocean touches you with every breath you take, every drop of water you drink, every bite you consume. Everyone, everywhere is inextricably connected to and utterly dependent upon the existence of the sea.” – Dr. Sylvia Earle