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
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 |
Figure 1: Fish
Similarities Between Whales and Fish
There are many similarities between whales and fish. Some of them are listed below.
- Habitat – Both whales and fishes live in water. Whales are exclusively marine.
- Both whales and fishes are vertebrates.
- Endoskeleton – Endoskeleton of whales is made up of bones.
- Both whales and fishes have fins and tails.
- Their mouth is in the anterior part of the body.
- Both whales and fishes have a scaly skin.
- Both have similar body shapes.
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.
- 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 lack mammary glands.
- Whales nurse their young while fishes are not.
- Whales have four chambers in their heart while fishes have two.
- Whales breathe through lungs while fishes breathe through gills.
- Whales have sweat glands and hair on their skin.
- 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
Leave a Reply