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Hello! This video is about fish and we will start speaking about cartilaginous fish.

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Cartilaginous fish are those fish that do not have bones but their skeleton is composed of cartilage.

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As you can see the fish that are cartilaginous are rays or skates and sharks.

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Here we have an example of a skate, which is actually a ray, that is the scientific name, and this is how we call it in Spanish.

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These are the eggs laid by this animal, so this animal is an example of an oviparous animal, because it lays eggs.

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This animal, like all cartilaginous fish, has internal fertilization.

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It means the male and the female must come together,

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and the male must introduce sperm cells inside the female.

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That's why it is called internal fertilization.

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So, this ray is an example of an oviparous animal.

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Now, some sharks are also oviparous,

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But some sharks are viviparous, the same as most mammals.

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Here you can see an example of a viviparous shark.

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The big one is the mother and the small one is one of its offspring.

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So this little shark is a baby shark and is coming out from the mother.

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And as you can see it has this tube, which is the equivalent of our umbilical cord.

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This means it is the tube through which the baby got the nutrients and the oxygen when it was inside the mother.

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So some cartilaginous fish are oviparous and some are viviparous, because they do not lay eggs,

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but the offspring develop inside the mother, getting nutrients through an umbilical cord.

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But there is one more option for cartilaginous fish.

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Here we have an example of another species of shark.

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This is the sand tiger shark, which has this name in Spanish.

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And this shark also has internal fertilization.

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So the male introduces the sperm cells inside the female.

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But this shark is not oviparous and it is not viviparous.

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It is ovoviviparous.

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Ovoviviparous means the female produces eggs,

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but then she keeps the eggs inside, okay?

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So the eggs are inside the female.

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Then the embryos develop inside the eggs,

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and finally, when they are ready, they hatch, okay?

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So the eggs hatch inside the female.

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Then the mother is going to release the little sharks,

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But the little sharks did not have an umbilical cord.

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They just were inside an egg, inside the mother.

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Okay, this is all for cartilaginous fish.

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And now we're going to speak about bony fish.

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Bony fish are the most numerous type of fish.

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Most fish species are bony fish.

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This means their skeleton is composed of bones.

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one special trait of bony fish is that most of them have a swim bladder swim bladder this is

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the name in spanish a swim bladder is like a balloon full of gas inside the fish because of

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this balloon if the fish stops swimming it is not going to sink to sink okay so it will stay

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where it is. This means if a fish gets tired and it does not want to swim for a while it can stop

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swimming and there is no problem it will not sink. Okay so this is an advantage of bony fish having

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the swim bladder. The cartilaginous fish we have studied before the sharks do not have that balloon

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they do not have a swim bladder this means if they stop swimming they will start sinking going down

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So, if they don't want to sink, they have to swim, but bony fish do not need to swim all the time, if they stop, they stay where they are because of the swim bladder.

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Now, the reproduction of bony fish is mostly with external fertilization.

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This means the male is not going to introduce sperm cells inside the female, but the female is going to lay the eggs and then the male is going to release the sperm cells to the water.

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So the eggs and the sperm cells are going to meet in water.

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this is external fertilization and this means these animals like for instance the salmon are

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oviparous because the female is laying the eggs okay so they are oviparous with external fertilization

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a very strange case of reproduction is this bony fish here okay this bony fish as you probably know

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lives very deep under water and it is called the anglerfish the anglerfish as probably you know

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has this special appendage here which produces light okay and it uses this light to attract

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other fish when those other fish are attracted then it can eat them because this is the way

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it gets its prey okay so it is a carnivore and it attracts other fish with this light to then

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eat them. This fish is very special because it has what we may call sexual parasitism

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and it consists of the following. What you see here is the female and what you see here

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is the male. The male cannot get food on its own. It is not able to feed.

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What it needs to do is the male needs to find a female, then it bites the female and it gets attached to the female permanently.

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It will stay attached to the female the rest of his life.

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So it gets attached to the female to get blood from the female.

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So the male is like a parasite of the female, it is getting blood.

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A female may have up to four males.

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So scientists have discovered cases of one female that had four males attached to her, to different body parts.

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So the males are permanently attached to the female.

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When the female spawns, this means when the female releases the eggs,

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then the males will be ready to release the sperm cells to the water

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water so that there is external fertilization and the eggs released by

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the female are fertilized by the sperm cells released by the males. So this is

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all about fish.