So not all fish are designed the same, there are some built for holding on to deep oceanic shelves, and there are others that are made for running quickly through shallow water. Whatever it may be, the main feature that helps determine this on species is their tail. The design of the tail of a fish determines not only how they live, but where they live and what they eat for food. It is evolutions major statements, and it is truly noticeable by examining so many different species of fish. The different types of tails serve different purposes, and the best way to think about this is to think about cooking. So different cooking utensils serve different purposes, so you wouldn’t use a strainer to collect water to boil, or you wouldn’t use a knife to scoop ice cream. So evolution has allowed certain species to adapt to their environments and better suite their living style by using the most crucial part of a fishes propulsion.

https://www.igfa.org/species/67-sailfish-atlantic.aspx?CommonName=67-sailfish-atlantic.aspx

The sailfish (pictured above) is the fastest recorded fish in the ocean, that tops out at a speed of 70 mph, but much like a cheetah, only for quick/short bursts. The tail type has been found to move large amounts of water without creating too much drag, thus allowing for rapid propulsion of the fish. This is true for smaller fish such as the bonefish which also sports the forked tail and is known for its blistering speed in shallow water.

The tail types vary greatly from that of species such as grouper which sport large, flat tails to serve the purpose of holding them in place in heavy currents or underwater structure.

http://forshorefishing.blogs.theledger.com/10025/big-fish-photo-of-the-week-82409/

This species of grouper, the Goliath Grouper, which rightfully is a great demonstration of the large paddle like tail and how it serves its purpose. The fish is commonly found around areas with heavy currents and structure, such as bridges or man made shipwrecks offshore. By having this tail, they are able to hold themselves in place amidst the heavy current which brings the food to them. This allows for minimal exertion of energy, while still being efficient predators (hence why they are so big).

In conclusion, there are different applications for the types of tails that fish have. So next time you go to the beach or lake and see fish, think about the habitat that they are living in and look at how their bodies have evolved to suit their needs in that body of water.