Class: Placodermi
• The placoderms dominated the waters of the late Devonian period and died out completely in the late Carboniferous period (about 350 million years ago).
• Body was typically fish-like with bony armour.
• Jaws were present, but not properly formed.
• Paired and unpaired fins were present.
• Cranium was partially ossified.
• Vertebral column had neural and haemal arches.
• Notochord persisted throughout life.
• Example: Dunkleosteus spp. (Figure 2.2).
• Mostly marine and includes largest fishes that ever lived.
• Endoskeleton is cartilaginous which is partially calcified.
• There are 5-7 pairs of gills without operculum.
• There is no air bladder and lungs.
• Spiracle is generally present.
• Skin is naked or covered by small placoid scales, composing toothlike denticles that give the skin an abrasive texture.
• Mouth is generally ventral.
• Dorsal fins are rigid.
• Fins are without rays. Tail is heterocercal.
• The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm (Figure 2.3).
• Intestine has a characteristic spiral valve.
• A cloaca is present.
• Fertilization is generally internal.
• Examples: Carcharodon carcharias (White shark) (Figure 2.4), Rhincodon typus (Whale shark), Scoliodon laticaudus (Spadenose shark), Manta birostris (Ray) (Figure 2.5), Raja erinacea (Skate).
Figure 2.3. Male and female sharks, (A) Male with claspers, (B) female without claspers.
Figure 2.4. Carcharodon carcharias
Figure 2.5. Manta birostris
Class: Holocephali
• This class includes deep sea and carnivorous fishes.
• Endoskeleton is cartilaginous.
• There are 4 pairs of gills with operculum.
• Spiracle is absent.
• There is no air bladder.
• Skin is naked or covered by small placoid scales.
• Mouth is generally ventral.
• There is no cloaca.
• In male, a pair of claspers is present posterior to the pelvic fins as in Elasmobranchii. Besides these, a frontal clasper is present on the dorsal surface of the head of some species known as tenaculum.
• Examples: Chimaera spp. (Ratfish), Harriotta spp. (Spookfish) (Figure 2.6).
Figure 2.6. A. Chimaera spp., B. Harriotta haeckeli
Class: Dipnoi
• Mostly found in freshwater and commonly known as lungfish.
• The air bladder is modified into lung which serves for aerial respiration. Gills are also present.
• Notochord is persistent and unconstricted. Skeleton is largely cartilaginous.
• Skin is covered by cycloid scales.
• Operculum is present and there is only one external branchial aperture.
• Paired fins are lobate, cylindrical, with joined median axis.
• Internal nostrils are present.
• Intestine has a spiral valve.
• A cloaca is present.
• Examples: Protopterus spp. (African lungfish) (Figure 2.7), Lepidosiren spp. (American lungfish).
Figure 2.7. Protopterus spp.
Class: Teleostomi
• The endoskeleton is bony, and are known as bony fishes.
• There are 4 pairs of gills; the 5th pair of gill arch is modified into tooth bearing lower pharyngeal.
• Operculum is present.
• Spiracle is absent.
• Air bladder is usually present.
• Skin is generally covered by cycloid or ctenoid scales.
• Branchial lamellae are supported by a double row of branchial rays.
• Fins are with fin rays. Tail is homocercal or diphycercal.
• No spiral valve in the intestine.
• There is no cloaca.
• Fertilization is generally external.
• Examples: All fishes found in Nepal.
The class Teleostomi is divided into two sub-classes, Crossopterygii and Actinopterygii.
Sub-class: Crossopterygii
• This is the rare (almost extinct) sub-class, which is characterized by the presence of lobed paired fins covered with scales, and are known as lobed-fin fishes.
• There are two dorsal fins.
• The inner nostrils are present.
• The air bladder is modified into lung.• The scales are cosmoid type.
• This sub-class is not represented in Nepal, and includes some rare marine fishes.
• Examples: Latimeria (Figure 2.8), Coelocanthus.
Figure 2.8. Latimeria
Sub-class: Actinopterygii
• This sub-class contains most of the bony fish species that exist today.
• The paired fins are unlobed and without scales.
• There are generally single dorsal fin.
• The inner nostrils are completely absent.
• The external nostrils are present.
• The scales are cycloid or ctenoid type.
• This sub-class is represented by all fish species in Nepal.
• Examples: Labeo rohita, Tor putitora, Catla catla (Figure 2.9), Oreochromis niloticus (Figure 2.10) and all other fish species found in Nepal.
Figure 2.9. Catla catla
Figure 2.10. Oreochromis niloticus
• The placoderms dominated the waters of the late Devonian period and died out completely in the late Carboniferous period (about 350 million years ago).
• Body was typically fish-like with bony armour.
• Jaws were present, but not properly formed.
• Paired and unpaired fins were present.
• Cranium was partially ossified.
• Vertebral column had neural and haemal arches.
• Notochord persisted throughout life.
• Example: Dunkleosteus spp. (Figure 2.2).
Figure 2.2. A. Dunkleosteus skull present at Sam Noble Museum, Oklahoma, USA.
B. An imaginary drawing of Dunkleosteus.
Class: Elasmobranchii
B. An imaginary drawing of Dunkleosteus.
• Mostly marine and includes largest fishes that ever lived.
• Endoskeleton is cartilaginous which is partially calcified.
• There are 5-7 pairs of gills without operculum.
• There is no air bladder and lungs.
• Spiracle is generally present.
• Skin is naked or covered by small placoid scales, composing toothlike denticles that give the skin an abrasive texture.
• Mouth is generally ventral.
• Dorsal fins are rigid.
• Fins are without rays. Tail is heterocercal.
• The inner margin of each pelvic fin in the male fish is grooved to constitute a clasper for the transmission of sperm (Figure 2.3).
• Intestine has a characteristic spiral valve.
• A cloaca is present.
• Fertilization is generally internal.
• Examples: Carcharodon carcharias (White shark) (Figure 2.4), Rhincodon typus (Whale shark), Scoliodon laticaudus (Spadenose shark), Manta birostris (Ray) (Figure 2.5), Raja erinacea (Skate).
Class: Holocephali
• This class includes deep sea and carnivorous fishes.
• Endoskeleton is cartilaginous.
• There are 4 pairs of gills with operculum.
• Spiracle is absent.
• There is no air bladder.
• Skin is naked or covered by small placoid scales.
• Mouth is generally ventral.
• There is no cloaca.
• In male, a pair of claspers is present posterior to the pelvic fins as in Elasmobranchii. Besides these, a frontal clasper is present on the dorsal surface of the head of some species known as tenaculum.
• Examples: Chimaera spp. (Ratfish), Harriotta spp. (Spookfish) (Figure 2.6).
Class: Dipnoi
• Mostly found in freshwater and commonly known as lungfish.
• The air bladder is modified into lung which serves for aerial respiration. Gills are also present.
• Notochord is persistent and unconstricted. Skeleton is largely cartilaginous.
• Skin is covered by cycloid scales.
• Operculum is present and there is only one external branchial aperture.
• Paired fins are lobate, cylindrical, with joined median axis.
• Internal nostrils are present.
• Intestine has a spiral valve.
• A cloaca is present.
• Examples: Protopterus spp. (African lungfish) (Figure 2.7), Lepidosiren spp. (American lungfish).
Class: Teleostomi
• The endoskeleton is bony, and are known as bony fishes.
• There are 4 pairs of gills; the 5th pair of gill arch is modified into tooth bearing lower pharyngeal.
• Operculum is present.
• Spiracle is absent.
• Air bladder is usually present.
• Skin is generally covered by cycloid or ctenoid scales.
• Branchial lamellae are supported by a double row of branchial rays.
• Fins are with fin rays. Tail is homocercal or diphycercal.
• No spiral valve in the intestine.
• There is no cloaca.
• Fertilization is generally external.
• Examples: All fishes found in Nepal.
The class Teleostomi is divided into two sub-classes, Crossopterygii and Actinopterygii.
Sub-class: Crossopterygii
• This is the rare (almost extinct) sub-class, which is characterized by the presence of lobed paired fins covered with scales, and are known as lobed-fin fishes.
• There are two dorsal fins.
• The inner nostrils are present.
• The air bladder is modified into lung.• The scales are cosmoid type.
• This sub-class is not represented in Nepal, and includes some rare marine fishes.
• Examples: Latimeria (Figure 2.8), Coelocanthus.
Figure 2.8. Latimeria
Sub-class: Actinopterygii
• This sub-class contains most of the bony fish species that exist today.
• The paired fins are unlobed and without scales.
• There are generally single dorsal fin.
• The inner nostrils are completely absent.
• The external nostrils are present.
• The scales are cycloid or ctenoid type.
• This sub-class is represented by all fish species in Nepal.
• Examples: Labeo rohita, Tor putitora, Catla catla (Figure 2.9), Oreochromis niloticus (Figure 2.10) and all other fish species found in Nepal.
Figure 2.9. Catla catla
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