How do fish float?

wikifishblutangThere are a few different answers – depending on what type of fish we are asking about.

The most sophisticated types of fishes – bony fishes – have a swim bladder. These fish can inflate their swim bladder with gas from a special gas gland. The gas is basically oxygen from the fish’s blood. Bony fishes that spend most of their lives on the bottom of the ocean floor (e.g., flounder) don’t have a strong swim bladder – therefore, don’t float.

Sharks, skates, and rays are all types of fish. However, these fishes are more primitive – lacking bones. They stay afloat with a liver filled with oil. They use long pectoral fins for balance in mid-waters while maintaining a light framework. The ‘light framework’ is made up of cartilage (the same material found in our nose and ears).

Image (c) wiki-fish.com. (Yellow Tang – a true bony fish)

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What is the biggest fish in the sea?

Picture taken at Georgia Aquarium, pictured is...

Image via Wikipedia

The whale shark is the biggest fish on the planet. The largest whale shark measures about 66 feet long and 74,957 pounds.

Not to be confused with the blue whale, a mammal, which is the largest animal on the planet. The largest blue whale measured about 110 feet and up to 400,000 pounds!

The whale shark got its name because the shark’s mouth is shaped just like baleen whales. Baleen whales and whale sharks both munch on krill. For being the largest fish in the sea the whale shark is surprisingly affable to divers and known as a relaxed fish.

How are ‘whale sharks’ and ‘whales’ different?

Whales are mammals, just like people, and must breathe air. Dolphins, seals, porpoises, otters (and some people say, polar bears) are mammals that live in the ocean (ie., marine mammals).

Another difference is that mammals raise their young. Whale sharks give live birth like mammals, but, move on right after and don’t raise them. Most other fish do lay eggs.

Fish also have gills to breathe underwater, unlike mammals that must come up to the surface of the ocean and breathe air.

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Are flounder born flat?

They hatch from the egg looking exactly like typical fish, swimming in the upper waters. After two weeks the bridge of the fish’s nose fades away and then one of the eyes, depending on the species, shifts to one side. The process of becoming a complete “flat” fish takes a bit of time, but, once complete the flounder is content to live the rest of its life on its side on the bottom of the ocean floor.

Winter flounder move their left eye to the right side. Summer flounder move their right eye to the left side. There are many more flounder species, but, this is just an example of where their eyes shift.

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What are those tiny black pods with tendrils near the ends?

They are egg cases from a juvenile thorny skate. skateThe skate is related to sharks and rays. Sharks, skates, and rays all have a skeleton made up of cartilage, the flexible material that is found in our noses and ears. One tiny skate will hatch from each egg after nine months – hatching under the surface of the water. Usually, what we see wrapped up in the seaweed “wrack line” is the discarded egg cases. Another nickname for these egg cases is the “mermaid’s purse.” Check out this BCS post to learn the difference between skates and rays.

Image (c) NOAA – Alaska Fisheries Science Center.

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Can you tell how old a fish is by looking at it?

fishscaleagerings1There is one possible way to tell how old a fish is while it’s still alive. And, at that, – it’s pretty invasive. You need to take some of its scales (see image).

The scales are similar to the rings of a tree. Depending on how many dark rings you may see (if you were to hold the scale up to a light source) it will determine the age of the fish. However, since scales can regenerate often, the rings could be cloudy and difficult to decipher.  You can get a more accurate age of a fish by other methods which require the fish to be dead. These include reading the rings on the cross-section of a fish ear bone (otolith) or fin ray.

Knowing the age of a fish is very important for understanding how to maintain populations and stocks for fisheries management.

Image (c) eralabs.com.

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