Skeletal Deformities in Farmed Rainbow Trout, Oncorhynchus mykiss, at an Early Stage of Development: A Case Study of Indian Himalayan States

The rainbow trout, Oncorhynchus mykiss, is the most extensively cultured coldwater fish species in India. However, skeletal deformities remain a significant concern and are frequently reported in rainbow trout farming operations. The incidence of skeletal deformities can serve as an indicator of the quality of rearing conditions and environmental factors. The present study was conducted to assess the skeletal deformities of rainbow trout, from selected farms in Himachal Pradesh, and Uttarakhand, India. During the study, physicochemical parameters such as water temperature, pH, dissolved oxygen (DO), nitrogen and phosphorus compounds, and chlorides were recorded. The brain, gill, and muscle tissues were examined under optical microscope to inspect myxozoan parasite infections. Nevertheless, myxozoan parasites were not detected in the microscopic examination. For histopathological analysis, tissue samples from the internal organs were processed. The degree of acinar cell necrosis, fibrosis, and macrophage aggregation were determined through histopathological examination. The skeletal deformities, whirling behavior, and mortality were directly associated with the major pancreatic anomalies but no signs of parasite presence.