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Aquatic Animal Adaptations

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Instructor: Amanda Robb

Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

Explore the adaptations that enable aquatic animals to survive in their ecosystems. Discover the adaptations different animals develop to cope with the salinity of the water and a range of water temperatures, perform respiration, and enable locomotion. Updated: 01/04/2022

Adaptations

Think about the most extreme environments on Earth. You might be thinking of hot environments like the Sahara Desert, or cold environments like Antarctica. However, water can also be pretty extreme. The open ocean gets deep, dark, and cold as you descend, and rivers rush, tumbling over boulders and cliffs. When you think about, it might feel surprising that anything could live there. Animals, however, have evolved special traits that help them survive in an environment, called adaptations.

Today, we're going to look at some specific adaptations for aquatic animals that allow them to survive in both freshwater, like rivers and lakes, and saltwater, like the ocean.

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  • 0:04 Adaptations
  • 0:43 Salinity
  • 2:02 Temperature
  • 2:48 Respiration
  • 3:19 Locomotion
  • 4:52 Lesson Summary
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Salinity

All living things need to be in balance, which is a fancy word known as homeostasis. Organisms need to have the right amount of water, salt, and exactly the right temperature to survive. Adaptations help maintain this balance. A major problem in any aquatic environment is salinity, or the salt concentration of a solution. If the environment has too much salt, the animal will lose water and get dehydrated. If there's too little salt, the animal will take up lots of water, and their cells can explode.

Animals in freshwater have an environment with too little salt. They have developed adaptations to get rid of extra water and hold onto salt using an organ called the kidney. The kidney is responsible for water balance in the body, or osmoregulation. In freshwater fish, their kidneys are specially designed to produce lots of dilute urine. Special structures in the kidney absorb lots of salt to maintain homeostasis. In addition, their gills have proteins that actively take salt from the water and bring it into the body.

Animals in saltwater have the opposite problem. A high salt concentration in the environment drives water out of the animal. Saltwater fish have kidneys that produce very little urine and keep most of their water inside their body. They also do the opposite process in their gills; instead of bringing in extra salt, the gills in saltwater fish pump the salt out.

Temperature

What happens when you're too cold? You shiver to generate heat and keep warm. Your body takes action to keep you in homeostasis without you even thinking about it. Aquatic animals have a pretty big problem when it comes to keeping warm. Water transfers heat about 25 times faster than air does, which means an animal is going to lose heat a lot faster in an aquatic environment than a terrestrial one.

Sea otters have evolved thick fur to keep them warm in cold waters. The fur isn't just thick, though. Their fur is designed to interlock and create pockets of air between their skin and the water. Sea otters also secrete an oily layer on their skin to further prevent water from coming in contact with them. So, sea otters actually try to avoid getting their skin wet at all, even though they are aquatic animals.

Sea otters have fur to minimize heat loss
sea otters

Respiration

On land, air is plentiful, and we simply breathe it in from the atmosphere. However, if you were submerged in water, you would quickly drown as your lungs became flooded with water. Fish and sharks have ways to get around this problem. These animals have gills, which are respiratory organs that filter air from water. Fish gills are designed for filtering oxygen, not simply filling the lungs like ours do. Fish forcibly push water over their feathery gills to extract oxygen and transfer it into their blood, allowing them to breathe underwater.

Gills of a rainbow trout
gills

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