| There are a wide variety of
fish -- from the goby which is less than one half an inch
long, to the whale shark which can be over 60 feet long.
Fishes
are vertebrates that have a skeleton made of either bone
or cartilage. About 95% of fishes have skeletons made of
bone. These bony fishes have a swim bladder, a gas-filled
sac, that they can inflate or deflate allowing them to
float in the water even when not swimming. Fishes with a
cartilage skeleton tend to be heavier than water and
sink. They must swim to keep afloat. Cartilage fish
include the ray and the shark.
Most fish swim using a tail fin. Muscles in the tail
fin move it from side to side, forcing water backward,
and propeling the fish forward. Other fins help the fish
change direction and stop. Pectoral fins on their side
help them swim up and down. Dorsal and anal fins on the
top and bottom keep the fish upright. Pelvic fins on the
underside help steer left and right. |
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