Question

A fish taken out of water cannot survive for a long time. Why?

Answer 1

Hint: Fishes are a member of the superclass Pisces. They belong to the phylum Chordata or Vertebrata. This is because they have a notochord that develops into the vertebral column. They belong to the group Gnathostoma that consists of the members with jaws.

Complete answer:
Fishes are aquatic creatures. They live exclusively in water, either freshwater or marine. Fishes have various kinds of fins that help them to swim. Moreover, they have different kinds of scales present on their bodies. The bodies of fishes are streamlined to cut the water so that they can swim easily inside it.
A fish taken out of water cannot survive for a long time and it dies eventually. This is because fishes respire with the help of gills. They do not have lungs for respiration, unlike other vertebrates. The water enters the mouth of the fishes. This water has fair amounts of dissolved oxygen in it. It then passes through the feathery filaments of the gills. These gills are rich in blood capillaries. The filaments of the gills absorb oxygen from the water which then moves into their bloodstream. The carbon dioxide is exhaled out through the gills of the fishes. In the absence of water, the gills of the fishes collapse as their gill filaments stick together. Due to this reason, the fishes are not able to respire as they do not get oxygen, so they ultimately die within a short span of time.

Note: Some fishes have lungs also along with the gills. These fishes are an exception and are kept under the category of Lung fishes. There are three types of lungfishes. The first one is the African lungfish also known as Protopterus, which has two well-developed lungs and poorly developed gills. The second one is the American lungfish also known as Lepidosiren, which has two less developed lungs and more developed gills. The third one is the Australian lungfish also known as Neoceratodus, which has poorly developed lungs and highly developed gills.