Unit IV — Fishes Study Guide

Unit IV — Fishes Study Guide

Part A — 2-mark answers (keywords + 1 line)

  1. Two differences between Petromyzon and Myxine:
    • Petromyzon: ectoparasitic, sucker mouth with horny teeth, well-developed eyes.
    • Myxine: scavenger, slit-like mouth with barbels, slime glands, reduced eyes.
  2. Why are cyclostomes called “jawless fishes”?
    • They lack true jaws; mouth is circular or slit-like, no hinged jaws.
  3. Type of scales in cartilaginous fishes:
    • Placoid scales (dermal denticles) — tooth-like structure of enamel & dentine.
  4. Examples:
    • Cartilaginous: Scoliodon (shark), Bony: Labeo rohita (Rohu)
  5. Define “homocercal tail”:
    • Symmetrical upper & lower lobes around vertebral axis; e.g., Rohu.
  6. Two accessory respiratory organs:
    • Lungs (lungfish) & Labyrinth organ (Anabas).
  7. Function of swim bladder:
    • Buoyancy regulation; may aid in sound production/resonance.
  8. Two lung fishes:
    • Protopterus, Lepidosiren.
  9. Economic importance of fishes:
    • Major source of animal protein; important for fisheries economy.
  10. Retrogressive metamorphosis:
    • Primarily in tunicates; lamprey adults degenerate after spawning.

Part B — 5-mark answers (short/medium)

  1. General characteristics of Cyclostomata:
    • Jawless, eel-like, no paired fins; cartilaginous endoskeleton, persistent notochord.
    • Circular/slit mouth; horny teeth; multiple gill openings.
    • Two-chambered heart; external fertilization; larval stage present.
    • Examples: Petromyzon, Myxine.
  2. External features of Petromyzon vs Myxine:
    • Petromyzon: round sucker mouth, well-developed eyes, 7 gill openings, low slime.
    • Myxine: slit mouth with barbels, degenerate eyes, many slime glands, 6–15 gill openings.
  3. Accessory respiratory organs:
    • Lungfish: paired lungs, gulp air, aestivate in mud.
    • Climbing perch: labyrinth organ, survive hypoxic water.
  4. Differentiation: Chondrichthyes vs Osteichthyes:
    • Skeleton: cartilage vs bone; Scales: placoid vs cycloid/ctenoid/ganoid.
    • Gill cover: absent vs operculum; Buoyancy: oily liver vs swim bladder.
    • Fertilization: mostly internal vs mostly external. Examples: shark vs rohu.
  5. Economic importance:
    • Food, employment, raw materials, recreation, ecological services.

Part C — 12-mark answers (detailed)

For Part C, include introduction, clear headings, numbered points, diagrams, and conclusion.

[Diagram placeholder — Petromyzon, Myxine, Shark, Rohu]