Quote:
Originally Posted by jamesqf
Err... So why aren't all fish the same shape?
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Because different species of fish occupy different nitches in the environment which can place an emphasis on factors other than most efficient shape. The lowest drag shapes are found on pelagic fish such as marlin, swordfish, tuna, and mackeral which need to travel great distances quickly in the most efficient manner. But in nitches, especially in reefs where there are plenty of hiding places and where pure speed isn't quite so important, other shapes can develop depending on whether the greatest need is for flexibility (eel), armored crush resistance (boxfish, seahorse), or if a distinctive shape (angel fish, moorish idol) is needed for quick species recognition for territorial defense, school formation, or for wowing potential mates.
You could also ask the same question for birds (why aren't all birds the same shape?) and the answer is similar to the one for fish above.