locomotory organs of fishes are discussed.

1. FINS AND LOCOMOTION IN
FISHES
IRAM BEE
M.Sc. Final
DEPARTMENT OF ZOOLOGY
BAREILLY COLLEGE BAREILLY

2. INTRODUCTION
• Fins are generally the most distinctive anatomical features of a fish.
• Composed of bony spines or rays protruding from the body with
skin covering fins and joining together, either in a webbed fashion (bony
fish), or similar to a flipper (sharks).
• Apart from the caudal fin, fish fins have no direct connection with the
spine and supported by muscles only. Their main function is to help the fish
in swimming.
• Fins located in different places on the fish serve different purposes such as
moving forward, turning, keeping an upright position or stopping.
• Most fish use fins when swimming, flying fish use pectoral fins for gliding,
and frogfish use them for crawling.

3. • Fins can also be used for other purposes -
- male sharks and mosquitofish use a modified fin to deliver sperm,
- thresher sharks use their caudal fin to stun prey,
- reef stonefish have spines in their dorsal fins that inject venom,
- anglerfish use the first spine of dorsal fin like a fishing rod to lure prey,
- triggerfish avoid predators by squeezing into coral crevices and using
spines in their fins to lock themselves in place.

4. Types of Fins
1. Paired Fins
- Pectoral Fins
- Pelvic or Ventral Fins
2. Unpaired Fins
- Dorsal Fin
- Anal/Cloacal Fin
- Adipose Fin
- Caudal or Tail Fin
- Caudal Keel/Finlets

5. PECTORAL FINS
• The paired pectoral fins are located on each
side, just behind the operculum, and are
homologous to the forelimbs of tetrapods.
• A peculiar function of pectoral fins is the
creation of the dynamic lifting force that
assists some fish, such as sharks, in
maintaining depth and also enables the
"flight" for flying fish.
• The pectoral fins aid in walking, especially
in the lobe-like fins of some anglerfish and
in the mudskipper.

6. PELVIC OR VENTRAL FIN
• The paired pelvic or ventral fins are
typically located ventrally below and
behind the pectoral fins, although in many
fish families they may be positioned in
front of the pectoral fins (e.g. cods).
• They are homologous to the hindlimbs of
tetrapod.
• The pelvic fin assists the fish in going up
or down through the water, turning sharply,
and stopping quickly.

7. DORSAL FIN
• Dorsal fins are located on the back. A fish can have up to three
dorsal fins. The dorsal fins serve to protect the fish against
rolling, and assist it in sudden turns and stops.
• In anglerfish, the anterior of the dorsal fin is modified into
an illicium and esca, a biological equivalent to a
fishing rod and lure.

8. ANAL/CLOACAL FIN
• The anal/cloacal fin is located on the ventral surface behind
the anus/cloaca. This fin is used to stabilize the fish while swimming.

9. ADIPOSE FIN
• The adipose fin is a soft, fleshy fin found on
the back behind the dorsal fin and just forward
to the caudal fin.
• It is absent in many fish families, but found in
nine of the 31 euteleostean orders. Famous
representatives of these orders are Salmon,
characids and catfish.
• The function of the adipose fin was a mystery.
Researches in 2011 has suggested that the fin
may be vital for the detection and response to
stimuli such as touch, sound and changes in
pressure.

10. CAUDAL/TAIL FIN
The caudal fin (L. cauda=tail) is located at the end of the caudal peduncle and is
used for propulsion.
(A) Heterocercal means the vertebrae extend into the upper lobe of the tail,
making it longer (sharks).
Hypocercal (reversed heterocercal) means that the vertebrae extend into the
lower lobe of the tail, making it longer (Anaspida).
(B) Protocercal means the vertebrae extend to the tip of the tail and the tail is
symmetrical but not expanded (fist fishes, cyclostomes and lancelets).

11. (C) Homocercal where the fin appears superficially symmetric but in fact the
vertebrae extend for a very short distance into the upper lobe of the fin.
(D) Diphycercal means the vertebrae extend to the tip of the tail and the tail is
symmetrical and expanded (bichir, lungfish, lamprey and coelacanth). Most
Palaeozoic fishes had a diphycercal tail.
Most modern fishes (teleosts) have a homocercal tail. These appear in a variety
of shapes, and can appear:
• rounded
• truncated
• forked
• emarginate
• lunate

12. Generating Thrust and controlled motion
• Foil shaped fins generate thrust when
moved, the lift of the fin sets water or air in
motion and pushes the fin in the opposite
direction.
• Aquatic animals get significant thrust by
moving fins back and forth in water.
• Often the tail fin is used, but some aquatic
animals generate thrust from pectoral fins.
• Once motion has been established, the
motion itself can be controlled with the use
of other fins.

13. Reproduction • Gonopodia are found on the males of
some species in the Anablepidae and
Poeciliidae families. They are modified
anal fins functioning as movable
intromittent organs, used to impregnate
females with milt during mating.
• Claspers are found in the males
of cartilaginous fishes. They are the
posterior part of the pelvic fins, modified
to function as intromittent organs, and are
used to channel semen into the
female's cloaca during copulation.

14. Other uses of Fins
Frogfish use their
pectoral and pelvic fins
to walk along the ocean
bottom
Flying fish achieve
sufficient lift to glide above
the surface of the water
due to their enlarged
pectoral fins
Large retractable dorsal fin of
the Indo-Pacific sailfish
The thresher shark uses
its caudal fin to stun prey
The Oriental flying gurnard has
large pectoral fins with eye
spots which it displays to scare
predators
During courtship, the
female cichlid, Pelvicachromis
taeniatus, displays her visually
arresting purple pelvic fin

15. SWIMMING IN FISHES
• Based on energy costs, swimming can be classified into 3 groups (Hoar &
Randall, 1978), namely, sustained, prolonged and burst swimming.
1.Sustained swimming
• Swimming speed is slow (6-7 body lengths/second) and maintained for long
periods. Energy required by muscles is provided by aerobic respiration and
since the speed is slow, oxygen debt is not built up as fatigue comes very
slowly. This is used for foraging over large areas or long distance migrations.
2. Burst swimming
• This type of locomotion is used for escaping predators, chasing a prey or for
swimming against currents of water. High speeds (up to 20 body
lengths/second) are achieved but can be sustained only for short periods.
Power is generated by anaerobic respiration, fatigue comes very rapidly and
therefore burst swimming can be sustained for short periods.

16. 3. Prolonged swimming
• This type of swimming is intermediate between the above two
types in speed and energy. Energy is supplied by both aerobic
and anaerobic respiration. Prolonged swimming can last up to 3
hours and longer bouts can end up in fatigue. This type of
locomotion is used occasionally as the situation demands.

17. Types of Locomotion
Anguilliform locomotion
• Eels (Anguilla) and cyclostomes having serpentine
body swim by lateral undulation of the entire body,
caused by rhythmic contraction of myotomes. This
swimming is quite efficient, but consumes more
energy, since the whole body is involved.
Carangiform locomotion
• In most fishes, lateral undulation of body is restricted
to the posterior one-third of body. Tail is lashed from
side to side in such a way that it always has a
backwardly facing component of push.
Ostraciform locomotion
• In box fishes and trunk fishes (family Ostraciidae),
the body is not flexible and only tail fin propels the
body forward.

18. Special modes of Locomotion
1. Jumping:
• Some fishes jump to escape from enemy, for food or for purely joy sake.
Generally by the fish swimming rapidly upwards through the surface of water
into the air, giving a sharp flick with its tail as it leaves the water medium.
Example – Mullets, Marine gar etc.
2. Flying:
• Flying fishes when projected from the water by a stroke of powerful tail,
expands its large pectoral fins and using them after the fashion of parachuits,
floats or glide through the air with fins stretched and rigid like an aeroplane.
Example – Exocoetus and Dachylopterus.
3. Walking:
• In Cephalocanthus, the lower portion of their pectoral fins are divided into 3
or 4 finger like rays which they use for walking as an insect uses its legs.

19. 4. Crawling:
Lophius (Angler fish) habitually uses the pectoral fins for crawling above the
sea bottom.
5. Skipping:
Mudskipper uses its pectoral fins which are bent at an angle like elbow joint,
for hopping over sandy flats left bare by the repeating tides.
6. Climbing:
Indian climbing perch, Anabas uses its opercular spines for ascending over
trees.
7. Tetrapod like Walking:
Lung fishes raise themselves on their peculiar pectoral appendages and pose for
a while and then they move their head region sideways.
8. Burrowing:
Eels burrow into mud by their snouts forcibly resting into the mud unless a best
grip is achieved.

20. THANK
YOU