Home › Biology › Q
BiologyAnimal Kingdom
Select the set of fishes belonging to class Osteichthyes:
Options
1
Devil fish, Cuttlefish and Hagfish
2
Starfish, Hagfish and Cuttlefish
3
Flying fish, Angel fish and Fighting fish
4
Sawfish, Fighting fish and Dogfish
Correct Answer
Flying fish, Angel fish and Fighting fish
Solution
1

Osteichthyes = bony fish: bony skeleton, operculum, scales, swim bladder, lateral line.

Option 3: Flying fish (Exocoetus) + Angel fish (Pterophyllum) + Fighting fish (Betta) = ALL bony fish ✅

2

Option 1: Devil fish (ray=Chondrichthyes), Cuttlefish (Mollusca), Hagfish (Agnatha) ❌

Option 2: Starfish (Echinodermata), Hagfish (Agnatha), Cuttlefish (Mollusca) ❌

Option 4: Sawfish (Chondrichthyes), Fighting fish (Osteichthyes), Dogfish (Chondrichthyes) ❌

Flying fish + Angel fish + Fighting fish = Osteichthyes (bony fish)
Exocoetus + Pterophyllum + Betta splendens
Theory: Animal Kingdom
1. Class Osteichthyes — Bony Fish

Osteichthyes are the largest class of vertebrates with ~30,000 species. Key features: bony (ossified) endoskeleton. Scales: cycloid (smooth, rounded — Catla) or ctenoid (toothed/spiny edge — Labeo). Operculum: bony flap covering gills (4 pairs). Swim bladder (gas bladder): controls buoyancy — fish adjusts gas content to float at different depths. Air-breathing fish lack functional swim bladder or use it as accessory air organ. Lateral line system: detects water vibrations and pressure changes. Mouth: terminal (at front of head). Heart: 2-chambered (1 auricle + 1 ventricle). Cold-blooded (ectothermic). Fertilisation: usually external. Examples: Labeo rohita (rohu), Catla catla (catla), Clarias batrachus (climbing perch/magur), Hippocampus (seahorse), Exocoetus (flying fish), Pterophyllum (angel fish), Betta splendens (Siamese fighting fish). Commercial importance: food (rohu, catla, tuna), aquarium (angel fish, fighting fish, goldfish).

2. Class Chondrichthyes — Cartilaginous Fish

Chondrichthyes have cartilaginous (not bony) endoskeleton. Features: cartilaginous skeleton throughout life. Scales: placoid (dermal denticles — toothlike, tough). NO operculum — 5-7 exposed gill slits. NO swim bladder. Asymmetric (heterocercal) tail fin. Mostly marine. Oviparous or ovoviviparous. Copulatory organ (claspers) in males — internal fertilisation. Examples: Scoliodon (dogfish shark), Carcharadon (great white shark), Trygon (stingray), Torpedo (electric ray), Pristis (sawfish), Rhinobatus (guitarfish), Chimaera (ratfish). Electric ray Torpedo: generates electrical discharge from modified muscle cells (electrocytes) — up to 200 volts to stun prey. Sharks: apex predators, crucial for marine ecosystem health.

3. Class Agnatha — Jawless Vertebrates

Agnatha = most primitive living vertebrates. NO jaws (agnatha = without jaws). NO paired appendages (no pectoral/pelvic fins). Cartilaginous skeleton. Elongated eel-like body. Notochord persists in adults. Examples: Petromyzon (lamprey): ectoparasite of other fish. Attaches to host fish with sucker mouth, rasps flesh with teeth-like structures. Anadromous (lives in sea, spawns in freshwater). Myxine (hagfish): marine scavengers. Produce large amounts of slime (defence). Skull present but no vertebrae (considered craniates, not true vertebrates by some). Historical significance: first jawless fish dominated Palaeozoic era (ostracoderms). Jaws evolved from modified gill arches (~450 mya) — major evolutionary innovation enabling gnathostomes (jawed vertebrates) to dominate.

4. Non-Fish Animals With Fish in Their Name

Many common names include fish but the organisms are NOT fish (not chordates): Starfish (sea star): Phylum Echinodermata, class Asteroidea. Radially symmetrical, tube feet, water vascular system. Brittle star (Ophiura), Sea cucumber, Sea urchin = also echinoderms. Cuttlefish (Sepia): Phylum Mollusca, class Cephalopoda. 8 arms + 2 tentacles. Ink sac. Internal cuttlebone (shell). Squid (Loligo), Octopus = also cephalopod molluscs. Jellyfish: Phylum Cnidaria (coelenterate). Aurelia (moon jellyfish). Radially symmetrical, nematocysts. Silverfish: Class Insecta (not fish at all) — Lepisma. Crayfish: Class Crustacea (arthropod, not fish). Shellfish: common name for molluscs and crustaceans. For NEET: remember these organisms belong to their proper phyla, not to fish classes.

5. Flying Fish and Other Unusual Osteichthyes

Flying fish (Exocoetus): tropical/subtropical marine fish. Elongated pectoral fins act as wings — can glide 50-400 m above water surface. Speed: up to 70 km/h. Used to escape predators. NOT true flight — powered gliding using momentum gained underwater. Seahorse (Hippocampus): unusual bony fish — males carry eggs in brood pouch. Monogamous. Swim upright. No stomach (continuously eat). Protected species. Angel fish (Pterophyllum): South American freshwater cichlid. Popular aquarium fish. Disc-shaped body, long fins. Fighting fish/Siamese fighting fish (Betta splendens): Southeast Asian freshwater fish. Males are extremely aggressive to each other. Brilliant colours (selective breeding for aquarium). Build bubble nests. Puffer fish (Tetraodon): inflate when threatened. Contain tetrodotoxin (TTX) — deadly neurotoxin. Some species edible (fugu in Japan) if prepared by licensed chef.

6. Vertebrate Comparative Anatomy — Heart Chambers

Heart evolution in vertebrates: Fish (Osteichthyes, Chondrichthyes): 2-chambered heart (1 auricle + 1 ventricle). Single circulation — blood goes: heart → gills → body → heart. Amphibia: 3-chambered heart (2 auricles + 1 ventricle). Some mixing of oxygenated and deoxygenated blood in single ventricle. Double (incomplete) circulation. Reptilia (except crocodiles): 3-chambered (2 auricles + 1 ventricle with partial septum). Less mixing than amphibia. Crocodilia: 4-chambered heart (2 auricles + 2 ventricles). Complete double circulation like birds and mammals. Aves (birds): 4-chambered heart (2 auricles + 2 ventricles). Complete double circulation. Warm-blooded — need efficient O2 supply. Right aortic arch. Mammalia: 4-chambered. Left aortic arch. Most efficient. Memory: 2(fish) → 3(amphibia, reptiles) → 4(crocodile, birds, mammals).

7. Aquaculture — Fish Farming

Aquaculture: controlled cultivation of aquatic organisms (fish, shellfish, seaweed) for food. India: second largest aquaculture producer globally (after China). Freshwater aquaculture: Indian Major Carps (IMC): Catla catla, Labeo rohita (rohu), Cirrhinus mrigala (mrigal). Composite fish culture: grow multiple species together using different food niches. Also: Tilapia, Common carp, Grass carp, Silver carp. Marine aquaculture: Penaeus (shrimp/prawn) — most valuable. Chanos (milkfish). Salmon (Atlantic/Pacific). Seaweed cultivation. Pearl culture: Pinctada pearl oyster. National Fisheries Development Board (NFDB): promotes fisheries in India. Blue Revolution: rapid increase in fish production through aquaculture. Related to Green Revolution (agriculture) and White Revolution (milk). Fish meal: ground dried fish used as protein-rich animal feed. Omega-3 fatty acids (EPA, DHA) from fatty fish (sardine, salmon, tuna) — important for cardiovascular health.

8. Important Vertebrate Examples for NEET

Key examples per class: Osteichthyes: Labeo (rohu), Catla, Clarias (walking catfish), Hippocampus (seahorse), Exocoetus (flying fish), Pterophyllum (angel fish), Betta (fighting fish), Salmopetrus (climbing perch). Chondrichthyes: Scoliodon (dogfish), Carcharadon (white shark), Trygon (sting ray), Torpedo (electric ray), Pristis (sawfish). Agnatha: Petromyzon (lamprey), Myxine (hagfish). Amphibia: Rana (frog), Bufo (toad), Hyla (tree frog), Salamandra (salamander), Ichthyophis (caecilian — legless). Reptilia: Calotes (garden lizard), Chameleon, Chelone (turtle), Testudo (tortoise), Naja (cobra), Vipera (viper), Crocodylus (crocodile), Alligator. Aves: Corvus (crow), Pavo (peacock), Psittacula (parakeet), Struthio (ostrich), Aptenodytes (penguin). Mammalia: Oryctolagus (rabbit), Macaca (monkey), Rattus (rat), Canis (dog), Felis (cat), Bos (cattle), Balaenoptera (blue whale), Pteropus (flying fox/fruit bat), Ornithorhynchus (platypus), Macropus (kangaroo).

Frequently Asked Questions
1. What are the key differences between Osteichthyes and Chondrichthyes? ⌄
Osteichthyes (bony fish): bony endoskeleton, cycloid/ctenoid scales, operculum covers gills, swim bladder for buoyancy, mostly external fertilisation. Examples: rohu, catla, flying fish, angel fish. Chondrichthyes (cartilaginous fish): cartilaginous skeleton, placoid scales (like tiny teeth), no operculum (5-7 exposed gill slits), no swim bladder (must swim to breathe), internal fertilisation (claspers in male), mostly marine. Examples: shark (Scoliodon), ray (Trygon), electric ray (Torpedo). Memory: Chondrichthyes = Cartilaginous = No operculum, No swim bladder, Cartilage skeleton.
2. Name some examples of each class of fish for NEET? ⌄
Agnatha (jawless): Petromyzon (lamprey), Myxine (hagfish). Chondrichthyes (cartilaginous): Scoliodon (dogfish shark), Trygon (stingray), Torpedo (electric ray), Pristis (sawfish), Carcharadon (great white shark). Osteichthyes (bony): Labeo rohita (rohu), Catla catla, Clarias (catfish), Hippocampus (seahorse), Exocoetus (flying fish), Pterophyllum (angel fish), Betta (fighting fish), Salmopetrus, Anabas (climbing perch). Memory technique: Sharks and rays = Chondrichthyes (both have cartilage). Common food fish (rohu, catla) = Osteichthyes. Lamprey and hagfish = Agnatha (primitive, jawless).
3. Why does dogfish belong to Chondrichthyes not Osteichthyes? ⌄
Despite the name "dogfish," Squalus (spiny dogfish) and Scoliodon (spadenose shark) are sharks — cartilaginous fish (Chondrichthyes). Features: cartilaginous skeleton (NOT bony). Placoid scales (dermal denticles). No operculum — 5 exposed gill slits visible on sides. No swim bladder. Internal fertilisation via claspers. Ovoviviparous. These are all Chondrichthyes features. The name "dogfish" is misleading — it refers to their pack-hunting behaviour, not their fish class. Similarly, "sawfish" (Pristis) is a cartilaginous fish despite sawfish appearing to resemble bony fish superficially.
4. What is the significance of swim bladder in Osteichthyes? ⌄
Swim bladder (gas bladder) is a gas-filled sac derived from the gut (lung-homolog) in bony fish. Functions: Primary: buoyancy control — fish can adjust the amount of gas (mainly oxygen, nitrogen, CO2) to maintain neutral buoyancy at different depths without constant swimming. In physoclistous fish (closed bladder): gas added/removed via gas gland and oval (resorption gland). In physostomous fish (open bladder): connected to gut, fish gulp air. Evolutionary significance: swim bladder is homologous to the tetrapod lung. The sequence: ancestral bony fish (swim bladder as accessory breathing organ) → land vertebrates (lung as primary breathing organ). Some fish (lungfish — Protopterus) use swim bladder as lung to breathe air directly during droughts.
5. What are the features of electric ray Torpedo? ⌄
Torpedo (electric ray): class Chondrichthyes. Found in Mediterranean Sea, Atlantic Ocean, and Indian Ocean. Flattened disc-shaped body (like all rays). Generates electricity from paired electric organs (modified branchiomeric muscles on each side of disc). Electric organs: stacks of electrocytes (disc-shaped cells). Nerve impulse → simultaneous discharge → potential difference → electric shock. Voltage: 8-220 volts depending on species. Used to: stun prey (fish, invertebrates), deter predators, possibly navigation. Torpedo gave its name to the torpedo weapon (naval mine/underwater missile) because of its stunning ability. Other bioelectric fish: Electrophorus electricus (electric eel, actually a knifefish — NOT a true eel, Osteichthyes) — up to 860 volts. Gymnarchus (African knifefish), Apteronotus — use weak electric fields for navigation/communication (electroreception).
Previous Questions
Q.
Correct statements about cell organelles endomembrane system ER DNA
Cell Biology · Answer: B, C and D only
Q.
Match bioactive molecules Streptokinase Statins Lipases Cyclosporin A
Biotechnology · Answer: A-II, B-III, C-IV, D-I
Q.
Flightless bird with paddle-like forelimbs Aptenodytes penguin
Animal Kingdom · Answer: Aptenodytes
Q.
Ecological pyramids generally inverted for pyramid of biomass sea
Ecosystem · Answer: Pyramid of biomass in sea
Q.
Non-membrane bound organelles both prokaryotes eukaryotes
Cell Biology · Answer: Ribosomes