Fish!
Everyone knows that there are fish in the ocean! I mean, fish is the first thing that you think about when you think of animals or creatures in the oceans. At least, it is for me. Fish are the main creatures that fill the oceans, since they are best adapted to the underwater life. When you say the word "fish", you could mean any type of fish. Butterflyfish, clownfish, parrotfish, cod, trout, even sharks, eels, seahorses, and stingrays could be counted as fish. When I say fish are the best adapted, I mean that they have all the equipment needed for life underwater. Fish, unlike mammals, don't need to breathe air from the surface. Instead, they have gills, and here's how they work. While a fish is moving, water passes through the gills as it opens and closes, and the fish's body takes what it needs from the water. Then, the water passes out of the fish's body (through the gills). So, it is important that the fish keeps moving so that the water keeps flowing through their gills. Fish move their tails back and forth to propel them through the water, instead of up and down like dolphins and whales. They use their other fins to navigate and direct themselves in the water.
Fish are cold-blooded creatures. This means that their body temperature is regulated by their surroundings. If it were very cold, say 2°C in the water, then a fish's body would be 2°C. So, fish would rely on where they go to regulate their body temperature. If they were too cold, they would have to swim somewhere warm. If they were too hot, they would have to swim somewhere cooler. Mammals are warm-blooded, which mean that their body temperatures stay pretty much the same, within a couple of degrees. If we get too warm or too cold, we sweat or shiver, which is our body's way of regulating our body temperatures.
Many kinds of fish swim in groups called schools. In many cases, the fish in these schools swim and turn in unison, so that it looks very organized. These schools have many purposes and benefits. Fish in schools have more of a chance of spotting a predator than one fish alone. Many fish can confuse a predator and make it think that the school is one big creature, so that if it goes for the "creature", it is more likely to misjudge and miss all of the fish. Also, if you're in a group with a lot of other fish, there's less of a chance that a predator will pick you for a target, out of all of the fish there.
Fish could be anywhere on the food chain. Plankton, a microscopic type of "fish", is usually on the very bottom. Then, you just increase by size. Small fish eat the plankton. Bigger fish eat the small fish. Even bigger fish eat the bigger fish, and even bigger fish eat those bigger fish. And it goes on and on, until you get to a really big creature, like a shark or a dolphin, that's usually on the top of the food chain.
There is a "process" that happens every year when the seasons change. It is common with most fish, but the most noted journeys are by salmon. When winter comes, there is no more food in the ocean, so the fish must move, or they will die. Millions of fish gather together with their "families" to begin a long migration that is traveled every year. When they have finished with their journey, or maybe along the way, a safe place is found for the females to lay their eggs. This is called spawning. After the eggs hatch, the fish continue their trip. It is at this time of year that there is the most fish at our bays and shores. Salmon are born in rivers, mostly freshwater, then trek to the oceans. When they migrate, they must make a journey all the way back to the river where they "hatched" or were born, even if it includes jumping waterfalls, swimming upstream against the currents, and facing hungry predators. It is the journey each salmon must make in its lifetime.
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