This document discusses the external morphology of fish. It describes features such as the lateral line system for sensing movement and vibration, different types of scales like ctenoid and cycloid, tail types including heterocercal, protocercal, diphycercal and homocercal, mouth positions like ventral, and tooth types including incisors, canines and molariform. Internal anatomy of fish is also briefly mentioned.

1. External Morphology of Fish
BY
MAHABUBUR RAHMAN
LECTURER, FIMS, NSTU

2. External Morphology of fish

4. External features of a catfish

5. External Morphology of Shark

6. Lateral line
• The lateral line is a system of sense organs found in
aquatic vertebrates, mainly fish, used to detect
movement and vibration in the surrounding water.

7. Lateral line

8. Fish scale types

9. Ctenoid Scale

10. Cycloid Scale

14. Scutes/
finlets

16. (A) - Heterocercal, (B) - Protocercal,
(C) - Homocercal, (D) - Diphycercal

17. Fish tail
• Heterocercal if the vertebrae extend into the upper lobe of
the tail, making it longer (as in sharks)
• Protocercal if the vertebrae extend to the tip of the tail and
the tail is symmetrical but not expanded (as in amphioxus)
• Diphycercal if the vertebrae extend to the tip of the tail and
the tail is symmetrical and expanded (as in the bichir,
lungfish, lamprey and coelacanth. Most Palaeozoic fishes
had a diphycercal heterocercal tail.
• Most fish have a homocercal tail, where the fin appears
superficially symmetric but the vertebrae extend for a very
short distance into the upper lobe of the fin. This can be
expressed in a variety of shapes.

19. Mouth Position of Fish

21. Ventral Mouth position

22. Types and shape of dorsal fin
1. Fin margin straight
2. Concave
3. Rounded
4. Filamentous

23. Teeth of fish
1. Incisors
2. Canines
3. Molariform
4. Villiform
5. Grasping pharyngeal teeth
6. Tearing pharyngeal teeth
7. Grinding pharyngeal teeth
8. Comb-like pharyngeal teeth

24. Incisors

25. Canines

26. Molariform

28. Shark Teeth

32. Internal Anatomy of Fish