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Superclass Pisces

Superclass Pisces
 

Introduction:

  • This superclass includes true fishes.
  • Fishes were dominant during ‘Devonian period’ . Thus ‘Devonian period’ is known as “Golden period of fishes”
  • The study of fishes is known as Ichthyology.

Topics covered

  • Placodermi
  • Chondrichthyes
  • Osteichthyes

Detailed explanation:
 

General characteristics of subphylum Pisces
 

Habit and habitat

  • They are aquatic i.e found in freshwater or marine water.
  • They are Poikilotherms (cold blooded animals) i.e. they can’t regulate their body temperature rather adjust their temperature as per the external temperature.

Body

  • Their body is long, boat shaped and streamlined.
  • It is divided into head, trunk and tail.
  • Acrodont teeths are present.
  • Their bodies are covered by dermal scales.
  • But some fishes like Catfish, Torpedo & Wallagonia fishes do not have scales on their body.
  • For swimming, paired fins are present e.g. Pectoral and pelvic fins.
  • Unpaired fins are also found on the body e.g. mid dorsal fin and caudal fin.
  • Dirhynous condition i.e paired nostrils are present.
  • Internal ear is present that works as a statoreceptor for balancing.
  • External and middle ears are absent.

Respiration

  • Respiration takes place by gills
  • Gills are naked or covered by an operculum.

Circulatory system

  • Two chambered hearts are present which is known as “Venous heart” as it contains only impure blood.
  • This impure blood moves to the gills for purification and then transported to all parts of the body directly from the gills i.e single circulation of blood.
  • Sinus venosus and truncus arteriosus present.
  • Renal and hepatic portal systems are found.
  • RBCs are nucleated and filled with haemoglobin.

Excretion

  • Kidneys in fishes are mesonephric type, Urinary bladder is absent.
  • Cartilaginous fishes excrete Urea.
  • Marine bony fishes excrete Trimethylamine oxide and freshwater.
  • Bony fishes excrete Ammonia.

Nervous system

  • Monochondylar type skull is present i.e the skull of fishes only one occipital condyle.
  • 10-pairs of cranial nerves are present.
  • Lateral line sensory system is present in the body of all fishes.
  • Few members have receptor organs which can detect vibrations (Rheoreceptor) and Electric field.

Reproductive System

  • Reproduction is sexual.
  • They are mostly unisexual i.e., sexes are separate in them.
  • Fertilization is internal or external.

Development

  • Development is mostly direct i.e larval stages are not formed.
  • Baby fishes are called Fry or Hatchling.

Classification of pisces :

Super-class pisces is divided into three classes -
1. Placodermi
2. Chondrichthyes
3. Osteichthyes

Placodermi
 

Detailed explanation:

  • Extinct fishes (Fossil fish) are included under this class.
  • They lived from the Devonian period to the Permian period. Thus, these were the first freshwater true fishes.
  • Their body has an external protective armour of bony scales or plates. So, these fishes are known as "Armoured fishes".
  • Example - Climatius (first jawed fish).

Chondrichthyes or Elasmobranchi
 

Introduction

  • This class includes all cartilaginous fishes.
  • There are about 600 species of cartilaginous fishes.

Detailed explanation:
 

General characteristics of class Chondrichthyes
 

Habit and habitat

  • These are marine fishes.
  • Predaceous in nature.

Body

  • Their endoskeleton is made up of cartilage while the exoskeleton over the skin is made up of placoid scales.

Notochord

  • Notochord is persistent throughout life.

Digestive system

  • Complete digestive system.
  • Placoid scales are modified into teeth which are backwardly directed.
  • Their mouth is present at the ventral surface of the head.
  • Their jaws are very powerful.
  • A spiral valve or scroll valve is found in the intestine to increase absorptive surface area.
  • Cloacal aperture is present and their genital ducts open into cloacal aperture.
  • Bilobed liver is present

Respiratory system

  • 5 - 7 pairs of gills are present.
  • The gills are directly open outside the body through gill slits.
  • Operculum (gill cover) are generally absent in these fishes (exception- Chimaera or "Rat fish" or "King of herrings" or Ghost fish).
  • They swim constantly due to the absence of air bladder to avoid sinking.

Circulatory system

  • Two-chambered heart in present.

Excretory system

  • Kidneys are mesonephric.
  • Nitrogenous waste is urea.

Nervous system

  • 10 pairs of cranial nerves.

Sense organs

  • Lateral line sensory system is present in the body of all fishes.
  • Paired lateral eyes
  • Dirhynous nose
  • Ampulla of lorenzini present which can detect vibrations (Rheoreceptor) and Electric field.

Reproductive system

  • Sexes are separate.
  • In males, pelvic fins bear claspers which helps in copulation.
  • Internal fertilisation present.
  • They are oviparous or ovoviviparous.

Common examples :
 

1. Scoliodon

  • Commonly known as “Dog fish'' or “common Indian shark”.
  • It is viviparous.

    scoliodon
     

2. Pristis

  • commonly known as “Saw - fish”.

    pristis
     

3. Trygon

  • Commonly known as “Sting ray”.
  • Its dorsal fin has poisonous spines.

4. Torpedo

  • Commonly known as “Electric ray”.
  • In this fish an electric organ is found which is a modified muscle, it can give shock averaging 100–400 volts.

5. Carcharodon

  • Commonly known as “Great white shark”.

6. Chimaera

  • Commonly known as "Rat fish" or "King of herrings" or Ghost fish.
  • These are the connecting link between bony and cartilaginous fish.

Osteichthyes or Teleostomi
 

Introduction

  • This class includes all bony fishes.
  • There are about 25,000 species of bony fishes.

Detailed explanation:
 

General characteristics of class Osteichthyes
 

Habit and habitat

  • Both marine and freshwater animals.

Body

  • endoskeleton is made up of bones in adults.
  • Cartilaginous endoskeleton is found in larvae.
  • Their exoskeleton, if present, is made up of cycloid, ctenoid and ganoid scales. Placoid scales are absent.
  • They have streamlined body.
  • External nares are present on the dorsal surface of the snout.

Digestion

  • Digestive system is present and the digestive tract leads to anus.
  • Their mouth is mostly terminal.
  • Scroll valve in the intestine is absent.
  • Cloacal aperture is absent and in place of cloaca, anus is present.
  • Trilobed liver is present.

Respiration

  • 4 pairs of gills are present which are covered by an operculum on each side.
  • Air bladder is present which regulates buoyancy.

Excretory system

  • Kidneys are mesonephric.
  • Nitrogenous waste is ammonia.

Circulatory system

  • Two-chambered heart (one auricle and one ventricle) in present.

Nervous system

  • 10 pairs of cranial nerves

Sense organs

  • Lateral line sensory system is present in the body of all fishes.
  • Paired lateral eyes
  • Dirhynous nose

Reproductive system

  • Sexes are separate.
  • In male fishes, claspers are absent.
  • They have external fertilisation.
  • They are oviparous.

Common examples :
 

Marine water fishes -

1. Hippocampus

  • Commonly known as “Sea-horse”.
  • It swims in sea water in a vertical position.
  • A pouch-like structure is present at the abdomen of male fishes known as "Brood - pouch" in which the male collects the eggs.
  • Secondary vivipary and parental care is found.

    hippocampus
     

2. Exocoetus

  • Commonly known as “Flying fish”.

Fresh water fishes

3. Labeo rohita

  • Commonly known as "Rohu" or "Indian carp".

4. Clarias

  • Commonly known as "Cat fish" or Magur.

5. Catla catla

  • Commonly known as Katla.

    catla-catla
     

Aquarium fishes

6. Betta

  • Commonly known as “Fighting Fish”

7. Pterophyllum

  • Commonly known as “Angel Fish”

Other fishes

8. Latimeria or coelacanth

  • Living fossil or oldest living vertebrate known till now.

9. Gambusia

  • Larvivorous fish.

LUNG FISHSES (GROUP - DIPNOI)

  • They are commonly known as “Uncle of amphibia” as they have some amphibian-like characters.
  • Connecting link between fishes and amphibians.
  • Air bladder helps in respiration.
  • They can survive without water.
  • A three chambered heart is present.
  • External and internal both the nares are present.
  • Cycloid type scales are present.
  • Example -
  • Protopterus - African lung fish (living fossil)
  • Lepidosiren - South American lung fish
  • Neoceratodus - Australian lung fish

Frequently Asked Questions: FAQs
 

Q1. Which period is known as the “Golden age of fishes”?
Ans :
Devonian period

Q2. What is the study of fishes called ?
Ans :
Ichthyology

Q3. Define poikilotherms.
Ans :

  • Poikilotherms (cold blooded animals) are those animals which can’t regulate their body temperature.

Q4. Define the circulatory system of fishes ?
Ans :

  • Two chambered hearts are present which is known as “Venous heart” as it contains only impure blood.
  • This impure blood moves to the gills for purification and then transported to all parts of the body directly from the gills
  • Thus, fishes possess single circulation of blood.

Q5. Which type of kidney is present in fishes ?
Ans :
Mesonephric kidney

Q6. What is the common name of Scoliodon ?
Ans :

  • Scoliodon is commonly known as “Dog fish'' or “common Indian shark”.

Q7. Which is the connecting link between bony and cartilaginous fishes ?
Ans :

  • Chimaera commonly known as "Rat fish" or "King of herrings" or “Ghost fish” is the connecting link between bony and cartilaginous fish.

Q8. Why are lung fishes known as “Uncle of Amphibia ''?
Ans :

  • Lung fishes are known as “Uncle of amphibia” as they have some amphibian-like characters.
    - Air bladder helps in respiration.
    - They can survive without water.
    - A three chambered heart is present.
    - External and internal both the nares are present.
    - Cycloid type scales are present.

Q9. Name any two aquarium fishes.
Ans :

  • Betta (Fighting Fish) and Pterophyllum (Angel Fish).
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