The first thing I am going to blog about is how fish are classified and what something needs to have to be a fish.First a fish needs to have fins.Fins help fish move or swim around.The next thing is that it needs to be cold blooded.That means that a fish can change its temperature to the temperature that is around it.The last thing a fish needs to be called a fish is gills.Gills help fish breathe under water. Fish take in water through their mouth and go through their circulatory system then out of their gills.Their membranes protect their gills.Fish are streamlined which helps them move around easily and fast.
Fish are the oldest living vertebra's.That means they are the oldest organism that has a backbone.There are three groups of fish bony,jaw less,and cartilaginous.Bony fish is the largest group.Bony fish have bones.Bony fish use swim bladders to be bouyant like to go up and down in the water.
The cartilaginous group is in the middle.In this group there are sharks,rays,skates and more.Those animals all have something in common,it's that they do not have bones.Their bones are made of cartilage.
The last group is the jaw less fish.You probably know that they do not have jaws.There are two types of jaw less fish hag fish and lamprey.They both suck on their food.There use to be more than sixty species of jaw less fish,but now there is only two species left.The fishes that are extinct are now fossils.
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