Objective : Study of morphological adaptation of fish in different habitat

Adaptation of Hill stream fishes:eg. Glyptothorax, Glyptosternum, Pseudochenies, L. dero, L. dyocheilus, Gara gotyla, Schizothorax, Barilius.Nemocheilus and Tor sp.External shape & form of body:Generally a dorsoventrally flattened body which becomes leaf like in highly specialized form. eg. Glyptothorax, Pseudocheneis and Gara gotyla. Head is small in size & semi-circular.ScalesMinute and embedded in skin, eg. Schizothorax & Nemacheilus. In some species small scales present on dorsal and lateral side of body and absent on ventral side due to presence of adhesive organ.

Position of mouth & lips:• Mouth is usually shifted to ventral side of snout and not transverse

opening at the anterior end.• Mouth is semicircular or crescent shaped having thick lips and strong

jaws for scrapping food from the bottom.Barbels:Size is reduced, short and stumpy in nature and they provide additional

surface for attachment to stones ad rocks.Fins:Outer edge of fins become thick, flat and develop ridges, while inner rays

increase in number and are directed upward.Position of fin also changed, shifted outward along the sides of the body.

Caudal fin and peduncle is long and narrow to become stable in fast flowing water. In everal species lower lobe of caudal fin longer than upper one.Eyes:Eyes are reduced in size and situated on upper surface of head close to each other, eg. Glyptothorax and Pseudocheneis sp.Gills:Gill slits are reduced in size and present along the sides of body. They are not extended beyond the base of pectoral.Adhesive apparatus:Adhesive apparatus is the modification of skin surrounding mouth. It is present in form of disc located posterior to mouth. It consists of a central callous plate. It works as an efficient organ of adhesion based on suction principle.

Adaptation in marine fishes:Epipelagic- Mackerrel, Sardine, Herrings etc.

These are found near surface of water, streamlined body which is laterally compressed with well developed fins to facilitate fast and easy movement in the vast horizontal extend and to the large distance of the ocean.Prominent eyes with well developed perforated gills.

Adaptation of Shoaling fishes:All of these are small sized fishes. They are uniformly spaced and

oriented in the common direction. When they are in shoal they seems to respire slowly, eat more and exhibit less nervous behaviour.

Adaptation to mesopelagic fisheseg. Myctophid, stomiatoid, Parclepis, Melamphes sp.

These fishes live in dim lighted zone and migrate to surface at night in searh of food. During day these fishes return to mesopelagic zone leading an active life. Well developed muscular body with scales. Eye are large and some species possess tubular eye directed upward and foreword. Some species possess photophores in their ventral region which shows bioluminescence. Small mouth with fine gill racker in plankton feeder, large mouth with teeth in carnivorous species. These fishes silvery grey or deep black in colour.

Deep sea fishesMalacosteus, Cyclothane (Bristle mouth), Saccopharynx (Gulpen

eel), Linophryne (Angler fish), Myctophium (lantern fish).Dark black or colourless or dirty white, bottom fishes. Very small eyes or they lack eyes, compensated by long fin rays. Well developed lateral line system.

Mouth of deep sea water fishes is large with long and pointed teeth. Body totally flattened.

Phenomenon of larger size with increasing depth is called as abysal gigentism. Bioluminescence organ are located in the head and along the ventral and lateral side of the body. Large luminescent organs are present below the eye in Photoblepharon. Large no. of photophores are present along the lateral line in Porichthys (toad fish). In the latern fish myctophium luminescent organs are located along the fin rays.