LOCOMOTIN OF FISHES

 LOCOMOTION IN FISHES 

     the locomotion or swimming of fishes mainly perfermed  by fateral movement tail .tail fin the other fin mainly used balancing swimming as steering devices and rudder 

when body is at rest the lateral fin maintain equilibrium position fin in long fishes act as leg and help for walking  

  in flying fishes exoceatus pectoral fin help for gliding .in male cortilagenous fishes pelvic fin are modified as external copulatory organs called claspers.in some fishes the enterior  dorsal fin formed as adhesive disc 

SCALES :

 the scales of fishes covering the body sed as exoskeleton is one the charaterstic feature of the fishes the scales are dermal electrivative , mesodermal in origin the scales are small thin conified clearance or horny plate the body of all fishes except some cloring have no scales

they have mainly 5 diffarent sacles are present in fishes 

   

1. COSMOID 

2.PLACOID 

3.GANOID 

4.CYCLOID 

5.TENOID 

1. COSMOID 

comoid these scales are not found in living fishes these scales are characteristic of fishes under placodermi which were extinct 

cosmoid scales consist of 4 distinect layers 

 1 outer most thin enamale like genoine 

2 Thick dentine like cosmine 

3 spongy bone 

4 inermost compact bone 

2.PLACOID :

      these scales are characteristic features of cartilagenous fishes .these are microscopic and each scale consist of backwaedly direated spine arising form rounded basal plate and basal plate dentine like bony material .there is acavity called pulp cavity in basal plate giving the skin as and paper like quality 

3.GANOID:     

    Ganoid or rhomoid scales are thick usally  rhomid or dimond shape claslly fulled site by site like tiles in some cases they may be overlaped these scales are found in polypterus and they are called ganoid fishes 

each scale consist of 3 layers outer ename like ganone middle dentine like cosmine inner bony is opedine 

4.CYCLOID :

    

      clycoid scales are characterstic feature of bony fishes also found in some lug fishes 

these are thin flexible ,translucent circular in outline these scales have several concentric ring the line of growth which are used to determine the age of fishes 

each scale is composed of thin upper layer which is bony and lower layer which is fibruea connective tissue 

the cycloid scales are overlaping to each other and embeded in dermis but directed backwardly 

5.TENOID :   

    

        tenoid scales are characteristic features of bony fishes found and some fish.

these are similar to cyloid but outer magin bear namerus small spine 

hence called tenoid scales because tenoid means comb.

 some scales are found intermidiate type in between cycloid and tenoid which bear both types  of character dorsal tenoid and ventral cycloid