MORPHO-FUNCTIONAL AND DEVELOPMENTAL STUDY OF SWIM BLADDER IN PRE TO POST FLEXION STAGES LARVAE OF HIMALAYAN SNOW TROUT SCHIZOTHORAX PLAGIOSTOMUS (HECKEL) REARED IN ARTIFICIAL AND NATURAL CONDITIONS

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Present study deals with histology, gross morphology of the larvae and its behavioural aspects to describe the progression of the development of swim bladder in pre to post flexion stages larvae of the Himalayan Snow Trout Schizothorax plagiostomus (Heckel) reared in laboratory as well as in natural site. It reveals a very significant information in respect to derivation, tissue differentiation, initial inflation as well as factors responsible for noninflation of swim bladder especially among laboratory reared larvae. At hatching (108-110 and 124-130 hours after fertilization in laboratory and natural site respectively), larvae measured 9.00 mm and 10.5 mm in laboratory and natural site respectively, and their body cavity was mostly occupied with a huge amount of yolk. The mouth, pharynx and esophagus were impervious till 3rd day post hatching (dph). Primordial swim bladder appeared on 3rd.dph as a cluster of mesenchymal cells evaginating from the posterior dorsal surface of the differentiating esophagus. Later on it grows toward the caudal direction below the differentiating vertebral column and kidney. Initial swim bladder inflation occurred by 6-dph when larvae attained 12.50–13.50 mm length, with the onset of first exogenous feeding. During this phase a mucous like substance was also observed in the pneumatic duct as well as lumen of swim bladder of some laboratory reared larvae and later on they got mortality. By 8-dph well differentiated and inflated swim bladder becomes externally visible and pneumatic duct extended to join the dorsal wall of esophagus. A number of biotic and abiotic factors were found associated with preventing swim bladder inflation during Pre flexion to Post flexion stages.