Why are fish fish-shaped?

Fish have a streamlined body elongated with fins and a tail. This shape helps them to flow easily with little resistance. Thousands of fish species have these features with variations to survive in unique habitats.

According to the type of motion, fish can be categorized into two types:

  1. Body – Caudal Fin
  2. Median-paired Fin


Body – Caudal Fin

About 85% of fish species fall into this group. In this type of motion, the body and tail are the primary forces that help the fish move. This type of motion is well suited for species in open water that need speed, thrust, and control for swimming efficiently.

This type of motion is divided into five groups of fish:

  1. Anguilliform group: These are long lean fish such as eels. Their entire body moves in a wave-like motion.
  2. Sub-carangiform group: These types of fishes move by their rear half.
  3. Carangiform group: These types are stiffer and faster moving than the previous groups, they have rapid oscillating tails at the very rear of the body.
  4. Thunniform group: These types of fish have a large and crescent-shaped tail which helps them to move fast and chase, and catch their prey easily.
  5. Ostraciiform group: These types of fish are inflexible and only their tail oscillates rapidly.

Median paired Fin

These types of fish create force through their fins and move. This type of motion is found in fishes that have to navigate complex habitats. This type of motion helps fishes that don’t have a streamlined body. Like a Seahorse, doesn’t appear fish-shaped in any conventional way yet they use their fins to move. A pufferfish looks like a balloon, but if it needs to swim rapidly then it will retract its spines and swim rapidly using its fin.

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