Record of an Abnormal Schizothoraichthys esocinus (Heckel) from the Himalayan River Chenab Draining Jammu Region of the J&K State, India

An important food fish Schizothoraichthys esocinus is widely distributed in cold water streams in the Himalayas. In the river Chenab, an important Himalayan river draining Jammu region, this fish is widely distributed from Doda to Pargwal wetland. During its hydrobiological study, over a period of three years, two adult deformed specimens of S. esocinus were noticed among the collections made by fishermen in Akhnoor area and is the first record of this deformed fish from any Himalayan stream in India and its neighbouring countries.


Introduction
An important food fish Schizothoraichthys esocinus is widely distributed in cold water streams in the Himalayas. In the river Chenab, an important Himalayan river draining Jammu region, this fish is widely distributed from Doda to Pargwal wetland. During its hydrobiological study, over a period of three years, two adult deformed specimens of S. esocinus were noticed among the collections made by fishermen in Akhnoor area and is the first record of this deformed fish from any Himalayan stream in India and its neighbouring countries.

Materials and Methodology
Two deformed specimens of S. esocinus were purchased from fishermen in Akhnoor area and studied for morphological aberrations. For detailed skeletal deformities, these fishes along with normal specimens were exposed to X-rays (Rays, India, Digital X-ray machine).

Observation
Deformed specimens of Schizothoraichthys esocinus seen in the collections made by the fishermen in the river Chenab are described as below (Figures 1-4).

Schizothoraichthys esocinus showing flat caudal peduncle and widely spaced caudal fin lobes
This aberrant specimen of Schizothoraichthys esocinus, measuring 25.9 cm and weighing 198 gm, was recognised by its flat caudal fin base and widely spaced caudal fin lobes. General body shape and placement of fins and number of fin rays in various fins viz. dorsal, pectoral, pelvic anal and caudal in this aberrant fish is like a normal fish (Figures 1 and 3). There is no deviation in various body ratios of normal and abnormal fish.
X-ray analysis has revealed normal shape of vertebral column, vertebrae, urostyle and caudal fin bones. However, caudal fin lobes are widely spaced in this abnormal fish (Figures 2 and 4).

Schizothoraichthys esocinus showing post dorsal truncated body with a trough, ventral anal bulge and a dome in the caudal peduncle region
In a normal streamlined fish placement of dorsal fin is more towards the snout than the caudal fin base ( Figure 1). In this aberrant fish, measuring 18 cm and weighing 85 g, placement of dorsal fin is   more towards the caudal fin base than the snout. Like a normal fish there is a wide space between the extension of the longest pectoral fin ray and pelvic fin origin and extension of the longest pelvic fin ray and anal fin origin. In a normal fish, there is a wide gap between longest anal fin ray extension and caudal fin base and caudal fin is bilobed. On the contrary, in this deformed specimen of Schizothrichthys esocinus caudal peduncle is short, caudal fin lobes overlap and is not well demarcated and longest anal fin ray extends beyond the caudal fin base ( Figure 5). There are some deviations in various body ratios of the normal and abnormal fish.
In normal and abnormal fish there are 46 and 42vertebrae, respectively, after complex vertebrae, as revealed by X-ray analysis (Figures 2, 6a and 6b). Vertebral column in normal fish following the body shape is streamlined and has normal vertebral thickness, intervertebral spaces, ribs, neural and haemal spines and caudal bones. Vertebral column in this aberrant fish is normal upto 27 th vertebrae. Posteriorly, vertebral column is directed upwards and forms a hook From the X-ray analysis it is clear that post dorsal truncated body with a dorsal trough, ventral anal bulge and dorsal dome in caudal peduncle is due to hook shaped structure of the vertebral column (scoliosis) and aberrations in vertebrae viz. reduced vertebral thickness and intervertebral spaces.

Discussion
Records of only two deformed specimens of S. esocinus observed over a period of three years suggests that fish anomalies in this clean water river are rare. The other possibility is that deformed fishes are unable to survive in torrential waters. Collection of these two adult deformed fishes suggests that these aberrations are non fatal, feeding is normal and they are able to avoid predators.

Conclusion
Among physical factors, truncated shape of one specimen of Schizothoraichthys esocinus is mostly probably due to fast currents in breeding grounds. This fish for breeding migrates into cold water torrential tributaries of the River Chenab. Aberrations in other specimen of S. esocinus with flat caudal fin base and widely spaced caudal fin lobes is due to some mechanical injury in fast flowing waters. Fish anomalies due to currents have also earlier been reported by Backiel et al. [12], Chaitan [13], Divanach et al. [14] and Dutta [15].