Fins and locomotion in fishes by Iram Bee M.Sc. II Year.pptx

locomotory organs of fishes are discussed.

1. F INS AND LOCOMOTION IN F ISHES 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.

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