Fish move in the water using special fins on their bodies. In general, fish have two sets of fins—the pectoral fins and the tail fin. The pectoral fins are located near the front of a fish’s body, behind its head.
These specialized fins work like paddles to push water backwards and propel the fish forward. In most fish, a separate set of fins—the pelvic fins—are located near the belly area, behind the pectoral fins. The two sets of fins work together to give fish excellent control over their movements in water.
As they swim, fish push water backwards with their pectoral fins. This pushes them forward and keeps them from sinking to the bottom of lakes and oceans where they would have difficulty finding food. But how do fish keep from moving sideways? The answer lies in their tail fin or caudal fin.
A long muscle called an internal accelerator , which runs along most of the length of the body, controls movement of this tail fin (see diagram). When a fish wants to move left, the accelerator muscle contracts , pulling the tail to the left.
When a fish wants to move right, it contracts the left side of its accelerator muscle and moves its tail fin to the right. Sometimes larger fish have two sets of fins on their tails or caudals.
The tail is continuously moving very fast in order for fish to swim forward at varying speeds. The faster the tail goes, the more water gets pushed backwards (in comparison with slower movements where less water is moved). Also, because there are more muscles involved in moving faster, there is greater force applied onto the water relative to slow movements.
The faster the tail moves, the more efficiently a fish can move through water. The size of the tail fin depends on how much it is needed for that particular species or type of fish. Fast-moving fish like tuna have large caudal fins, while slower ones like eels have smaller ones.
Fish swimming in groups often work together to get one of their kind moving forward faster. They do this by using what scientists call a “wake” as they swim behind each other. This is done because the water that was traveling forwards from the fish’s pectoral fins has now been pushed backwards (creating a wake), which then creates greater resistance against which it can move forward.
This happens when a group of fish swims in a closely-packed formation and individuals take turns leading the way. The follower, or those closest to the leader, use their caudal fins to push against water coming from behind—this propels them forward and keeps them closer to leader, all while reducing drag .
The lead fish will also be pushed forward from the wake created by those swimming behind it. This type of group movement also reduces drag, which means that less energy is used to swim .
These types of different fish are called ‘ schooling ‘ and they help each other in their natural environment because it increases their chances for survival. It’s a win-win situation.
Scientists have found that there are even more methods some fish use to move about in water—some species can even glide on top of the surface without using fins at all! However, these are not common in most freshwater or saltwater fish, although some species do occasionally practice this method.
While there isn’t a single answer as to how exactly fish swim, we hope that what we shared today will help shed some light on the subject.