What lives in Casco Bay?
City Fish or Country Fish Activity
Learning objective: Explore the oceans’ diversity by comparing how cold-water marine fishes, such as those found in the Gulf of Maine, to the fishes that live on coral reefs.
Like the classic tale of The City Mouse and the Country Mouse, the fishes that live in cold “country” waters and “city” coral reefs are adapted to the challenges and opportunities of their own ecosystem.
Some people, like us Mainers, live where the seasons change. In the fall, the leaves turn red and orange. In the winter, snowstorms offer sledding, skiing, and unscheduled school holidays. Others live where it is warm all year long, and they can go fishing, biking, or swimming any time.
Some people live in the country, close to the land. They take long walks and enjoy the peace and quiet. Others wouldn’t trade their apartments in the city for anything. They love the hustle and bustle of the crowds and that they can order a pizza any time, day or night.
In the ocean, too, there are places that cool and warm with the seasons and other places that stay warm year-round. You might be surprised to learn that these are a lot like the country and the city on land.
If you were to ask people to picture where in the world oceans they would find the largest number of fishes, most would say the tropical seas, conjuring up images of a vivid, bustling coral reef. But consider the locations of the major fisheries of the world, which depend on netting huge quantities of fish in each tow; they are all in cold waters. Temperate and cold seas are home to relatively few species of fishes but many individuals, and while tropical waters offer a staggering variety of life, there are far fewer individuals of each species.
“Country Fish”: The fishes of cold and temperate waters
The cold waters of temperate and frigid seas may look murky, but not from pollution. It’s the rich sea soup of plankton that reduces visibility under water to a few feet and makes it appear green from above. Advantage: Abundant food
- Live close to the earth, in fact, many varieties, such as cod, haddock, and flounder, are called “groundfish” because they live on or near the ocean floor
- Their colors are earth tones—tan, speckled, brown, or black—to match their surroundings, or silvery to reflect back the light on the waves
- Their bodies are robust and hardy for swimming long distances. Most have the classic, streamlined submarine shape built for the long haul
- Shaped to fit: some lie flat to fit against ocean floor (flounder)
- These travel in schools across broad expanses of ocean, as opposed to “City Fish” that tend to stay concentrated in cramped quarters
- Their defenses are speed and/or camouflage
- The rhythm of life here is tied to the changing seasons, with spawning and reproduction happening in the spring after the first “crop” of phytoplankton bloom
- If an area becomes polluted or disturbed, these fish can move elsewhere
“City Fish”: Coral reef residents
Tropical waters are crystal clear, because almost nothing is suspended in the water to block one’s view. In other words, they are empty of life, except for coral reef communities. A coral reef is like a city in the desert—an oasis—which may provide the only food and shelter for many miles around. Tropical waters appear turquoise blue from above. The animals on the reef have evolved complex strategies to compete for food and dwelling places. Advantage: Many hiding places
The fishes of warm waters:
- Live in tight quarters at well-defined levels on the coral reef, like apartment dwellers in a high rise complex
- Even the smallest fish can be very territorial to protect their precious piece of real estate
- They are colorful, even flamboyant, to attract a mate or to defend their place on the reef
- There are specialists in
- Jobs—the cleaner wrasse
- Defense—the spines of the triggerfish
- Diet—the bird-like beak of the parrotfish, the long snout of the butterflyfish
- They have developed complex partnerships, such as symbiosis and parasitism
- Shaped to fit: Some are disc-shaped or eel-like to slip inside the coral reef/most are not build for long-distance travel because they rarely venture far from the security of the reef
- Coral reef is active both day and night. The rhythm of life here is diurnal. There are even predators that prey on weary commuters at dawn and dusk.
- If conditions on the reef deteriorate, there are few options for the residents. Most will die as adjoining reefs, is there are any, are already at capacity.
– Outline of a fish
– Paper and crayons/markers
– Globe or balloon
– Small flashlight
- What makes a fish a fish? Explain that no matter where they live, fishes share common characteristics that make them FISH. They also make us much better adapted for living in the sea than humans are. Here are some questions that students could research, with helpful hints below:
- How do fish breathe?
Fish have gills for extracting oxygen from the water. A lot of water has to be pumped over gills in order to get enough oxygen for a fish to breathe.Water contains less than five percent oxygen, whereas air has five times more oxygen, making it easier to breathe on land.
- How do fish find food? (senses)
Their senses are well designed for navigating underwater. In addition to the senses of smell, sight, hearing, taste, and a lateral line, some fish, like salmon, can sense the magnetic field of the Earth, which helps them find their way back to the very place they were born years before.
- How do fish use their fins?
Different fins are designed for swimming, turning, or staying upright in the water. Watch a fish in an aquarium some time to see how it uses its fins. Normally, it uses its tail fin for propulsion, top and bottom fins for balance, and the side fins for turning and stopping. Some fishes, such as marlins and tuna, are such good swimmers that they can sprint through the water at speeds approaching 80 kilometers an hour (50 mph).
- How do fish stay afloat?
Most fishes also have an organ called a swimbladder, which can inflate or deflate like a balloon to keep them at a certain level in the ocean.
- Are sharks fish?
Sharks are fish, too, but they lack a swimbladder. Sharks’ skeletons of cartilage are lighter than bone and help sharks to remain neutrally buoyant–able to float without sinking or rising. Sharks do have something other fishes don’t: ampullae of Lorenzini, tiny sense organs embedded in their jaws and snouts that can pick up the faint electric pulses given off by all living things. This sense enables a shark to detect the beating heart of a flounder hiding under the sand.
- How are fish different from mammals, like us?
Unless you have a fever, your body temperature remains the same—around 98.6oF (37oC) —whether it’s hot or cold outside. Fishes, with the notable exception of great white sharks and tuna, are cold-blooded, which means their internal body temperature takes on the temperature of the water around them.Humans, dogs, dolphins, whales, and other mammals are warm-blooded, so their body temperature stays the same wherever they are. Coats, fur, and blubber help mammals stay warm in cold temperatures.
Fish generally have scales instead of fur or hair.
Fish have bulbous eyes, almost like the goggles a swimmer wears, and they lack eyelids.
- Have students use the answers above to diagram the characteristics of a typical fish.
- Discuss the different climates around the globe. What determines climate? It is LIGHT, both the angle of the sun on the surface or inclination and the length of sunlight during the day.
- Why is the Equator warmer than the Poles?
Shine a flashlight on a globe (or a round balloon). First shine the beam at the equator, the line around the center of the earth, then move the light so it shines near a pole. Compare how concentrated the light beam is at the two different locations. Note that the light is more concentrated at the equator and more diffuse — spread out over a larger area– as it points toward the pole. Where is the light more intense? Where would the sunlight be more intense? (Equator)
Light spreads out over a larger area when it hits the North and South Poles. The light beam is concentrated when light (“the sun”) hits the equator. Because the sun provides not only light but heat to the earth, the equator heats up more than the poles. (Adapted from Stop Faking It! Air, Water, and Weather, by William C. Robertson, NSTA Press)
- Have students define latitude and longitude. The bioregions of the world are defined by their distance from the imaginary line around the center of the earth, the Equator:
0o-20o: Tropical region
20 o – 45 o: Semi tropical
45o -60o: Temperate
60 o -90 o: Polar
Maine is at 45o latitude, so what climate bioregion are we in?
Have students find these latitudes on globe and delineate them with a black marker.
- The world’s oceans also have different climates/regions.
Discuss how different areas of the ocean offer different advantage and disadvantages. Tropical coral reefs offer a wide variety of hiding places, but cold seas provide abundant food, more than enough to nourish huge schools of tuna, cod, and mackerel. Nutrients from land are carried by rivers into the sea where they fertilize the cold waters and promote the growth of tiny plants, phytoplankton, the base of the ocean food chain. Cold water also holds more oxygen, which both animals and plants need to live.
Review some of the characteristics and adaptations of the fishes in each habitat: color patterns, shapes, and adaptations for protection, feeding, and finding a mate.
- Draw one fish that is a characteristic animal of each ecosystem, such as
- Cold Marine: cod (large, mottled color, submarine shaped, easily identifiable lateral line for schooling, barbel or chin whisker for feeling/tasting clams and other bottom food)
- Tropical Coral Reef: four–eyed butterflyfish (disc-shaped, bright color, eyespot to confuse predators, specialized mouth with elongated snout for poking into coral reefs).
Alternatively, students could design their own fishes, which have the characteristics of fish in that region. Consider these questions: How might it protect itself? How does it capture prey—by luring it, chasing it, or surprising it? Once they have answered these questions, and others they might come up with, students can design their own fish.
- What’s in a Name?
Have students refer to field guides of birds, fishes, etc. to see that each organism has both a scientific name and a common name. They also can go online to Fishes of the Gulf of Maine at http://gma.org/fogm. Explain that the purpose of a scientific name is so that naturalists around the world will instantly recognize the plant or animal, whatever language they speak.
The system of scientific naming was created in the 1750s by a Swedish naturalist, Carl van Linne (which is usually Latinized to Carolus Linneas). Each organism is assigned a genus name, which is capitalized, and a species name in lower case. For example, the cod is Gadus callarias. When it is written, the scientific name is usually underlined or italicized.An organism’s scientific name often describes some aspect of its appearance or behavior. The discoverers of new species sometimes include their own name in the scientific name. Invite the students to give their fish both a common name and a scientific name.
- City Fish & the Country Fish
Read or ask student to paraphrase the story of The City Mouse and the Country Mouse. Now that students understand the difference between cold marine fishes and tropical fishes, perhaps they could re-write the classic fairy tale with a marine twist.
- Extension: Food Fish
Cod and their relatives, pollock and haddock, have firm, tasty flesh. This white fish is sought after by diners, and so the fish are sought after by fishermen. Many cold-water fish travel in giant schools, which makes it possible—and profitable—for fishermen to capture thousands of fish at a time. They drag huge nets along the ocean floor. As the fleeing fish tire, they are swept into a smaller net at the back, appropriately called the “cod end.”
Look at a map of the world and try to locate these prime fishing grounds listed below. How far are they from the Equator?
- Georges Bank, off Massachusetts
- Grand Banks, off Newfoundland
- Southern Africa
- North Sea
- Barents Sea
- Bering Sea in the North Pacific
- Gulf of Alaska
- Coastal areas around Japan
- Northeast Pacific
Many of the most popular food fish have declined by 80% or more from overfishing and habitat destruction. Find out more about the Sustainable Seafood movement. How could students promote eating varieties of seafood that aren’t endangered?
http://www.marine-ed.org/The Bridge, an extensive web-based marine education center
http://www.montereybayaquarium.org/education/classroom-resources/curriculum Monterey Bay Aquarium teacher resources (Note: Most aquariums have resources for educators)
http://www.fishbase.org/search.php Scientific data on fish species
www.seafoodwatch.org Seafood Watch, Sustainable Seafood
The Cod’s Tale, Mark Kurlansky, 2001, NY:G.P. Putnam’s Sons. The history of the fish that changed the world
Hello, Fish! Visiting the Coral Reef, Sylvia Earle, 2001, Washington, DC: National Geographic Society An introduction to some of the fishes that live on a coral reef for ages 4-8.
The Truth about Dangerous Marine Animals, Mary M. Cerullo, 2003, San Francisco: Chronicle
As children read about notorious sea creatures, they learn that many of the most dangerous creatures in the ocean live in tropical waters.