Fishes are classified into two main classes: Sarcopterygii and Actinopterygii. Sarcopterygii have lobe-like paired fins while Actinopterygii have ray-like fins. Actinopterygii are further divided into subclasses including Selachii (cartilaginous fishes), Branchyodonti, and Actinopterygii (ray-finned fishes). Ray-finned fishes are then categorized into superorders such as Chondrostei, Holostei, and Teleostei based on characteristics of their scales, fins, mouths and other physical attributes. Numerous examples of characteristic fishes from different orders are provided

1. CLASSIFICATION OF FISHES

3.  Exclusively Aquatic.
 Poikilotherms (coldblooded animals).
 Body divided into head, trunk and tail.
 Paired appendages present as fins.
 Fin rays are present in fins.
 Skin with dermal scales and mucous glands.
 Lateral line system well developed.
 Endoskeleton cartilaginous or bony.
 Heart two-chambered.
 Respiration through gills. Lungs are present
in dipnoi.

4.  RBC nucleated.
 Digestive System Complete.
 Kidney mesonephric.
 External ear absent.
 Sexual dimorphism seen.
 Fertilisation generally external.
 Oviparous.

5.  Extinct.
 Primitive fishes.
 External bony armour present.
 Powerful jaws.
 Fast and efficient swimmers.
 Order Arthordiformes: Dinichthyes.
 Order Antiarchiformes: Bothriolepis.

6. DINICHTHYES

7.  Also known as elasmobranchi.
 Endoskeleton Cartilaginous.
 Mouth ventral.
 Placoid scales present.
 Teeth modified placoid scale.
 Gill slits uncovered.
 Brain withlarge olfactory lobes.

8. SubClass Selachii
 Multiple gills on either side protected by
individual skin flaps.
 Spiracles behind each eye.
 Order Pleurotremata: Scoliodon,Stegostoma,Zygaena
 Order Hypotremata: Torpedo,Myiobatius.

9. SCOLIODON
STEGOSTOMA
ZYGANEA

10. MYLIOBATIUS
TORPEDO

11. SubClass Branchyodonti
 Include both extinct and modern fishes.
 No spiracles present.
 Order Eubrachydonti: extinct.
 Order holocephali:Chimaera.

12. CHIMAERA

13.  Bony endoskeleton, therefore also known as
bony fishes.
 Mouth terminal.
 Gills covered with operculum.
 Ctenoid or cycloid scales present.
 Airbladder often present.
 Brain with small olfactory lobes.

14. SubClass Actinopterygii
 Paired fins broad without fleshy lobes,
supported by fin rays. Therefore, commonly
known as ray finned fishes.
 One dorsal fin.
 Caudal fin without epichordal lobe.
 Olfactory sacs not connected to mouth( few
exceptions maybe seen).

15. SuperOrder Chondrostei
 Primitive ray-finned fish.
 Mouth large.
 Ganoid Scale.
 Tail fin heterocercal.
 Order Polypteriformes: Polypterus(Bichir).
 OrderAcipenseriformes: Acipensor(Sturgeon).

16. ACIPENSOR

17. SuperOrder Holostei
 Transition between chondrostei and telostei.
 Mouth opening small.
 Ganoid or cycloid scale.
 Tail fin heterocercal.
 Order Amiiformes: Amia(Bowfish).
 Order Semiontiformes: Lepidopsteus.

18. LEPIDOSTEUS

19. SuperOrder Teleostei
 Modeern ray-finned fishes.
 Mouth terminaland small.
 Cycloid or ctenoid scale.
 Tail fin homocercal.
 Order Clupeiformes: Clupea(herring)
 Order Scopeliformes: Harpodon(Mumbaiduck)
 Order Cypriniformes: Cyprinus(carp)
 Order Anguiliformes: Anguilla(freshwatereel)

20.  Order Beloniformes: Belone(garfish)
 Order Syngnathiformes: Hippocampus(Sea horse)
 Order Ophiocephaliformes: Channa(Snake head)
 Order Symbranchiformes: Symbranchus(Eels)
 Order Mastacembeliformes: Mastocembelus
 Order Perciformes: Anabus(Climbing perch)
 Order Scorpaeiformes: Pterois (Scorpion fish)
 Order Pleuronectiformes: Pleuronectus( Flatfish)
 Order Echeneiformes: Echeneis(Suckerfish)
 Order Tetradontiformes: Tetradon(Globe fish)
 Order Lophiiformes: Antennarius (Anglerfish)

21. HIPPOCAMPUS (MALE) ANABUS

22. PLEURONECTUSECHENEIS

23. LABEO TETRADON DIODON

24. SubClass Sarcopterygii
 Paired fins lobe like. Thus, commonly known
as Lobed finned fishes.
 2 dorsal fins.
 Caudal fin present with epichordal lobe.
 Olfactory Sacs connected to mouth.
 Order Crosspterygii: Latimeria.
 Order Dipnoi: Protopterus,Lepidosiren.

25. PROTOPTERUS