Quiz 24: Fishes
The characters that distinguish fishes from other animals are: Fishes are aquatic vertebrates with limbs in the form of fins. They are poikilotherms and mostly gill breathing animals. They are different from other animals mainly in having a body design that allows them to live effortlessly in any water body. They are present in fresh water as well as brackish water of seas and oceans. They can adjust the buoyant force that should act on their body by filling or removing the air from their swim bladder. This feature allows them to have variable speeds (from stationary to fast moving) in water as per their need. They have excellent organs for salt and water regulation. Countercurrent flow between water and blood in gill lamellae saturate the blood with oxygen even though water contains 1/20 times less oxygen as compared to quantity of oxygen in air. They have well developed sense organs and unique lateral line system which makes them sensitive to water currents and vibrations.
• Both hagfishes and lampreys are jawless fishes while other fishes have jaws. • The skin of all fishes is usually covered with scales while scales are absent in both hagfishes and lampreys. • The hagfishes and lampreys do not have paired fins which are seen in all other fishes. • Internal ossification is also lacking in these two groups of fishes. The morphological differences between a hagfish and a lamprey are:
Hagfishes are predators of annelids, molluscs, crustaceans and dead or dying fishes. They can also be referred as scavengers as they feed on dead or dying fishes. They have strong sense of smell which attracts them to food. They enter the body of the dead or dying animal through an orifice or by digging in to the body. Inside the dead body they rip off the flesh using two toothed, keratinized plates on their tongue. Lampreys are parasitic fish. They suck the body fluids of other fish by attaching themselves to the surface of the prey with the help of sucker like mouth and teeth. They rasp through the flesh of their host with their sharp and keratinized teeth. Lampreys inject an anticoagulant in the flesh of the host to promote the flow of blood. When the lamprey has had its fill, it leaves its host with a gaping wound. This wound can be fatal to the host. Certain lampreys are non parasitic and they do not feed after emerging as adults. The larvae of such fishes are filter feeders.