UTTAR PRADESH JOURNAL OF ZOOLOGY

The study uses Scanning Electron Microscopy (SEM) to analyze the lower jaw and gills of Oncorhynchus mykiss collected from Kashmir's clear mountain streams. A total of eight specimens were analyzed. The high-resolution images provide detailed information about these parts, helping researchers understand their functional adaptations. SEM work on the rainbow trout showed that the lower jaw and gills are finely adapted for feeding and breathing. The lower jaw displays a dense arrangement of teeth: strong forward points grip prey while softer, finer teeth process food. SEM examinations revealed the occurrence of canine teeth, ranging from 11-13 (designated as CT). The mean diameter of a tooth in Oncorhynchus mykiss was relatively small, measuring between about 1 and 2 millimeters. The jaw is divided into a smooth front half and a folded, ridged back half with a central bump or tubercle. The gills (arches, rakers, and filaments) work together to move oxygen into the blood and remove carbon dioxide. Long, thin filaments arranged in two rows along the arch, forming anterior and posterior hemibranches. Gill rakers (comb-like structures) filter debris to protect the gill filaments. Primary lamellae branch out into many secondary lamellae, increasing the respiratory surface area available to the fish. The study highlights the structural features that facilitate feeding, respiration, and environmental interactions, providing useful knowledge for fish farmers and conservation biologists.