Why Whales are Not Grouped in Fishes

Whales are not grouped in fishes due to four main reasons. Whales are warm-blooded animals while fishes are cold-blooded. Whales give birth to live young while fishes lay eggs. Whales have mammary glands to feed their young while fishes do not have. Whales have four chambers in their heart while fishes have two. Therefore, whales are classified under a separate class called mammals.

 

Key Areas Covered

1. What are the Characteristics of Fish
     – Definition, Characteristics, Classification
2. Why Whales are not Grouped in Fishes
    – Similarities and Major Difference Between Whales and Fish

Key Terms: Bony Fish, Cartilaginous Fish, Heart, Mammary Glands, Reproductive Method, Whales

Why Whales are Not Grouped in Fishes - Infographic

What are the Characteristics of Fish 

A fish is a limbless, cold-blooded vertebrate that lives in water. It uses gills to breathe and fins to swim. Fish is classified under two classes known as bony fish (Osteichthyes) and cartilaginous fish (Chondrichthyes). The major difference between bony fish and cartilaginous fish is the endoskeleton. The difference between bony fish and cartilaginous fish are described in table 1.

Difference Between Bony Fish and Cartilaginous Fish

 Bony Fish

Cartilaginous Fish

Habitat

Both fresh and marine water

Mainly marine water

Endoskeleton

Made up of bones

Made up of cartilages

Exoskeleton

Made up of thin bony plates known as cycloids

Made up of very small denticles coated with sharp enamel known as placoid.

Position of the Mouth

Mouth at the anterior of the body

Mouth is ventrically-positioned

Oral Jaw Sets

Two sets

Single set

Gill Pairs

Four pairs

Five to seven pairs

Bladder for Swimming

Bladder filled with air

Bladder filled with oil

Tail Fin

Homocercal tail fin

Heterocercal tail fin

Fertilization

Internal fertilization

External fertilization

Excretion

Ammonia

Urea

Examples

Salmon fish, rohu, trout, seahorse, etc

Shark, skates, rays, etc

Why Whales are not Grouped in Fishes_Figure 1

Figure 1: Fish

Similarities Between Whales and Fish

There are many similarities between whales and fish. Some of them are listed below.

  1. Habitat – Both whales and fishes live in water. Whales are exclusively marine.
  2. Both whales and fishes are vertebrates.
  3. Endoskeleton – Endoskeleton of whales is made up of bones.
  4. Both whales and fishes have fins and tails.
  5. Their mouth is in the anterior part of the body.
  6. Both whales and fishes have a scaly skin.
  7. Both have similar body shapes.
Why Whales are not Grouped in Fishes

Figure 2: Sperm Whales

Why Whales are not Grouped in Fishes

Though there are many similarities, there are some differences between whales and fishes as listed below.

  1. Whales are warm-blooded animals while fishes are cold-blooded.
  2. Whales give birth to live young while fishes lay eggs.
  3. Whales have mammary glands to feed their young while fishes lack mammary glands.
  4. Whales nurse their young while fishes are not.
  5. Whales have four chambers in their heart while fishes have two.
  6. Whales breathe through lungs while fishes breathe through gills.
  7. Whales have sweat glands and hair on their skin.
  8. Whales have a horizontal tail, which flaps up and down. Fishes have vertical tails, which moves side-to-side.

Due to these differences, whales are not considered as a type of fish. Instead, they are grouped under mammals that live in water.

Conclusion

Both whales and fish are aquatic animals with similar body shapes and behavior. Whales are not considered as fishes due to several key factors. Whales have mammary glands, give birth to young and are warm-blooded animals. Hence, Whales are classified under mammals.

Reference:

1.“Basic Facts About Whales.” Defenders of Wildlife, 19 Sept. 2016, Available here.

Image Courtesy:

1. “213399” (CC0) via Pexels
2. “Mother and baby sperm whale” By Gabriel Barathieu(CC BY-SA 2.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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