welcome! :]

Lake Trout, Retail Catfish, and a Arrowana! 💕

Royal Whiptails

With their upturned long snoot and armor plating, and being a bottom feeding fish, they have real sturgeon energy.

I have one and he's a lovely docile thing

What is this thjing

Pike trinket tray, for placing smaller fish inside.

Water is ~800 times more dense than air. This density provides buoyancy, which means fish don't have to counteract the forces of gravity. This leads to something called indeterminate growth, which means as long as you're living and eating, you keep growing. This is why we have a lot of species of fish that can grow to quite literal monstrous lengths and sizes.

Water is in-compressible, which means it must be completely displaced to move through it. Due to something called the Reynold's Number [R] (which is a ratio of inertial forces to frictional forces as they relate to solids and water movement) your size in the ocean determines how well you can travel. If you are small, water is very hard to move through (R<1, frictional forces dominate, water basically feels like molasses); if you are large, water is easier to move through (R>200, inertial forces dominate, water basically feels like alcohol). This is why large species have very wide ranges of habitat.

Water being very dense and in-compressible has other passive properties. Sound travels through water better than air; so well in fact that there is a magic-like depth called the sofar channel where sound can literally go on forever. Whales uses this to communicate and find each other. These properties also helped fish develop suction feeding/vacuum effect, which is one of the primary forces driving the diversity of fish.

Water is a universal solvent, and sea water is one of the most corrosive things on the planet. Being a solvent means it can hold dissolved gases like oxygen, carbon dioxide, and ammonium (the ionized, nontoxic form of ammonia, which is very toxic). This means fish can safely eliminate waste products across their gills. PS this is also how our blood works with the help of hemoglobin. So thanks water.

Light is heavily absorbed by water, which is known as electromagnetic absorption. Because light is made up of differing wave lengths (with red being the least energetic and violet being the most energetic), you lose colors the deeper you go in the ocean. This means that most deep sea fishes are "color blind" and only sea in shades of green/blue. This provides one species of fish in particular the ultimate evolutionary cheat code: the Red Dragon fish not only kept the ability to see the color red, it also emits red light using an organ under their eyes like a spot light. This means they can use the light to hunt fish without being seen by predators themselves. Hollywood wishes it could make shit like this up.

Because water is so heavy, water pressure increases rapidly with depth. Every ~10 meters (or 33 feet) of depth you have the equivalent of 1 additional weight of Earth's atmosphere (atm) exerted on your body. This has an effect on dissolved gases such as Boyle's law (the volume of a gas is inversely proportional to the pressure; in layman's terms, the volume of a gas increases as pressure decreases), which in turn has a effect on the amount of dissolved gases can be available in water. Increased pressure also effects the structure of proteins, which is why most deep sea fish that are brought to the surface look vastly different when they are at depth. This also contributed to the evolution of something called chaperone proteins/molecules, which are proteins that help normal proteins keep there shape in vertical migratory fishes like lantern fish.

They do! I’d say most species of animals sloughs off “old” parts of their bodies at some point of their lives in some capacity. The word “molting” is used as a catch-all term for this process, although exactly what body part they shed and how they do it varies from animal to animal. Arthropods grow an entire new exoskeleton and shed the old one, but for most other animals, this process only involves shedding the outermost layer of their bodies, the pelage and/or their first layer of skin. Reptiles are quite famous for this because they sometimes manage to come out of their old skins and leave them almost fully intact as if they were kigurumi pajamas:

Mammals tend to mostly only shed fur or hair, growing thicker fur during colder months and losing it in favor of shorter fur during warmer months. How obvious this is depends on the climate, though. It’s quite perceptible in mammals that live in the arctic whose fur changes color depending on the season:

But even the difference between the summer coats and winter coats of domestic dogs can be palpable if you live in places with colder climates!

(I’m quite fascinated by this because I was born and raised in a tropical country and my dogs look the same all year round heh)

But back to the seals. Pinnipeds don’t really use their fur to keep warm like other mammals do, but they still have it, and they have to shed their old coats and grow new ones accordingly, which they do once a year!

In elephant seals, this process is so sudden and so extreme it’s called catastrophic molting. They don’t only lose their fur, but also a layer of dead skin all at once and this forces them to stay on land for a full month without swimming (and therefore, without hunting and eating) until the process is fully done. Because molting requires redirecting blood flow towards the skin instead of to their vital organs as usual, if they swam in the cold waters they’re usually accustomed to while molting, they’d freeze!

Bonus fun fact: despite having lost their fur during the evolution process, cetaceans like whales and dolphins also go through a molting process where they lose a layer of dead skin, which they scrape off by rubbing against rocks and rolling on sand banks.

Blotched upside-down catfish!