Honestly, where do we start? Fish are as general as it gets. However, they are separated from the rest of the animal kingdom because of their fins, gills, and knack for the waters. Fish are a group of aquatic animals separated into four groups: cartilaginous fish, bony fish, jawless fish, and hagfish. For these fellows, it isn’t really that easy to live underwater. Living in water opens up a new dimension of problems. A fish must be able to maintain salt concentration and neutral buoyancy––two skills refined by millions of years of evolution.
You heard that right! Fish were the first vertebrate animals to evolve. They are the reason why vertebrate animals are found both in water and on land. Fascinating, isn’t it? It’s been said that fossils of fish have dated back 530 million years ago! In that many years, fish have evolved into more than 30,000 species all around the world. If you think this is interesting, stick around and let’s have a chat!
Description and Appearance
Fish are cold-blooded. Unlike mammals, fish cannot maintain a constant internal body temperature. Instead, they just rely on the temperature of their environment. Physically, true fish have fins, a backbone, gills, and scales.
Their fins are mainly used for their movement––how they propel and steer underwater. There are many kinds of fins. The caudal fin (or tail fin) is the main fin that helps the fish move forward underwater. The dorsal and anal fins (found on top and bottom, respectively), on the other hand, maintains the fish’s balance and prevent it from rolling over. Paired fins are mainly used for steering and hovering. Fish don’t have it easy, you know?
On their skin, most fish have scales that overlap in rows. These scales are actually there to safeguard the fish from injuries. Some scales are sharper than others while some are smoother. The most interesting part is that fish cover these scales with another layer of protection: their mucus. This helps immobilize viruses to keep fish away from infection while also reducing friction underwater. Pufferfish, on the other hand, don’t have any scales. In their case, they have spines that you’ll be able to see when they puff up. Either way, pufferfish are cute animals––cute enough to maybe stay on your bed, even. Thanks to Gage Beasley’s Lifelike Pufferfish Boxfish Stuffed Plush Toy, you can have one of your own! Don’t worry, it won’t be popping at the sight of you and your beautiful face. It’ll just look straight into your eyes, put you in a trance, and magically put you to sleep.
Gage Beasley’s Lifelike Pufferfish Boxfish Stuffed Plush Toy
Fish also have gills––a massive roleplayer in a fish’s underwater life. The gills are found on the side of the fish and just behind the head. It contains capillaries or most notably known as blood vessels. The gills filter the oxygen out of the water and directly into the fish’s blood. Not only that but gills are also used for the excretion of waste––usually ammonia from the bloodstream.
Fish have another unique internal organ to land animals––their swim bladders. Usually, their swim or air bladder is found in the abdomen of the fish. It helps the fish move up or down underwater just by adjusting the air inside of the bladder. Elasmobranchs (sharks and rays), however, do not have swim bladders. Some fish don’t have swim bladders, just like our friendly old oarfish––but it does have something more important: a plush toy equivalent. Normally, oarfishes are long, serpent-like animals drifting through the waters while enjoying all the planktons they can eat. Gage Beasley’s Oarfish Soft Stuff Plush Toy is just happy to be by your side. It doesn’t need any more planktons as it does get full just by watching you sleep. How sweet is that?
Gage Beasley’s Oarfish Soft Stuff Plush Toy
Fish have excellent senses, too! In fact, they can even see color. Their nostrils are made to detect odors even in the water. Fish have something that’s called a lateral line and its main function is to sense underwater vibrations and determine where it’s coming from––helping the fish even when they’re in murky or low-light environments. Their teeth also depend from species to species.
What do fish eat? That is the question, mostly because the fish diet is a very diverse one. In the ocean, fish are divided into three types: herbivores, carnivores, and omnivores. Herbivores, like the Parrotfish, play an important role in the ocean’s ecosystem––especially the coral reefs. Herbivores are responsible for removing the algae that rob the corals of the light and space they need to grow further. Carnivorous fish, by definition, can eat from the likes of small fish and crustaceans to fellow sharks––depending on the species, of course. Some fish are omnivores––ones that enjoy a diverse set of food underwater. Then can enjoy sponges and shrimps, or krill and seaweed. Either way, they’ll have tons of choices and can easily feed themselves with what’s around them.
The fish diet is a very diverse one, as has been said. Even the biggest fish in the ocean, the whale shark, only eats planktons and other small animals. They’re not apex predators unlike killer whales and white sharks.
There are two main types of fish pregnancies: ovoviviparity and viviparous. Both types are considered live-bearing. Ovoviviparity develops and hatches the eggs internally. It can be either ovuliparity (eggs are fertilized externally and zygote development), oviparity (eggs are fertilized and developed internally as eggs with yolks), or ovoviviparity (eggs are fertilized and developed internally as embryos with yolks). The likes of stingrays, seahorses, guppies, and numerous shark species are ovoviviparous. Coelacanths are also ovoviviparous fish. They have been known to gestate for as long as a year to three years before giving birth to live young. Once they grow up, though, they’re beautiful open-mouthed creatures of the sea. They don’t look as majestic as the other ovoviviparous fish, but they are pretty fluffy in plushie form! Gage Beasley’s Coelacanth Fish Soft Stuffed Plush Toy is the truest evidence for that.
Gage Beasley’s Coelacanth Fish Soft Stuffed Plush Toy
Viviparity, on the other hand, develops embryos internally before being born. Viviparity can come in two forms: histotrophic viviparity or hemotrophic viviparity. The former lets the mother provide no nutrition and embryos are left to eat their unborn siblings or their mother’s unfertilized eggs. The latter lets the mother provide nutrition through a placenta. The majority of sharks are viviparous.
Distribution and Conservation Status
Where there is water, there are fish. Almost all bodies of water have fish life––except for hot pongs or salty lakes (the extremely salty ones) like the Dead Sea or the Great Salt Lake. The distribution of fish has the history of the Earth to thank. The development of Earth helped, and is still helping, fish to evolve and adapt to certain habitats. Fish are distributed according to their habitat and preference of geographical areas. Habitats like freshwater and marine differ from each other and so, fish that stay in one or the other differ too. Salmons, however, migrate from one to the other.
Thankfully, information about the present geographical distribution of fish is abundant. Fish found in temperate streams, tropical lakes, and arctic lakes, for example, will certainly have differences from one another––both in how they survive and physical attributes. The deep oceanic habitat is the same all over the world, but the differences in species will always be there.
The conservation status of fish is concerning, though. According to the Internation Union for Conservation of Nature (IUCN), there are over 400 critically endangered species and almost 100 tagged as “possibly extinct” in the fish population in 2017. Additionally, over 3,000 fish species are listed as data deficient––meaning there is little to no information to implement a full assessment of their conservation status. Since these species are more likely to be in small distributions, the chances of them being threatened are very high. “Date deficient” fish, according to the IUCN, should be treated with the same degree of attention as threatened fish––until their status is known.
The fish is what lives under the water. Some can be scary and some can be pleasing, but they are all beautiful in their own little fishy ways. The fish you were drawing when you were a kid makes up for only a mere percent of the fish population. Not all fish look like what you imagine. Some have weirdly shaped heads, some have spears on their heads, some hide behind rocks, and some glow in the dark. Once you step into the water, you’re sharing it with over 30,000 species of fish––and that’s an idea both alluring and horrifying.
Unfortunately, though the fish population could be abundant on its own, there are species out there that are facing difficulties and are on the brink of extinction. It isn’t too farfetched to think that maybe there are external factors that are affecting their population––most likely humans. However, if left alone, the fish population can be as abundant as ever. They’re key pieces to what makes up 70% of Earth. Their ecosystem and how herbivorous fish can clean reefs are important to the people’s way of living.
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