Record of Semi-operculum Deformity in Sahyadria denisonii (Teleostei: Cyprinidae)

Morphological deformities are not infrequent in fish, having been recorded in both freshwater and marine fish species. Deformities in fishes are known to be caused as a result of environmental pollutants, scarcity of nutrients, sudden changes in temperature, water current, gene mutation, inbreeding, parasitic infestation and attack from predators [1,2]. Fin anomalies in general are extremely well documented in both wild and reared fish, but not operculum anomalies. Sahyadria denisonii (Day 1865) an ornamental fish, popularly known as the Redline Torpedo Barb or ‘Miss Kerala’ is endemic to the rivers flowing through the Western Ghats of southern India [3,4]. Due to over exploitation from wild for the global ornamental fish trade, this species has been listed as Endangered [4].  We document for the first time, a case of semi-operculum deformity in S.denisonii from the rivers of Western Ghats in India.

Deformed S.denisonii was caught in drag net operation from Palappuzha region of River Valapattanam (11.9499 latitude and 75.7338 longitudes) in May 2013. Morphological abnormality was photographed with a digital camera (Sony DSC-H20). For the comparison with deformed specimen, a normal fish (Figure 1a-1e) from the same catch (Standard Length=30 mm) was also collected.

 Figure 1: a. Deformed specimen of Sahyadria denisonii; b. Normal specimen; c-e. Deformed specimen with semi-operculum

A deformed specimen of S.denisonii collected from River Valapattanam was recorded with standard length of 29 mm, total weight of 79 mg with an age 0⁺. Age of the deformed fish was estimated from length frequency studies of S.denisonii by Sajan et al., [5]. Generally, operculum related deformities are related to inside or outside folding, shortening or abnormal positioning of the opercular and sub-opercular bones, both bilaterally or unilaterally [6]. In present records compared to a healthy normal fish (Figure 1b), the deformed wild caught specimen of S.denisonii possessed unilateral semi-operculum on the left side (Figure 1a,c-e). Similar types of operculum deformity have been reported in Oreochromis niloticus and O.mossambicus [7]. Although operculum abnormality is known to be generally unilateral, some species also show bilateral semi-operculum [8]. 

The streams and rivers in India, especially in the Western Ghats are facing number of environmental problems as a result of anthropogenic activities [9]. Record of malformed fish from polluted area are used as indicators of water pollution [8]. KSCSTE [10], reported that the River valapattanam has been polluted by the extensive usage of pesticides in adjacent land for agriculture and also by destructive fishing using dynamite and chemicals. Harikumar [9], also reported, upstream part of River valapattanam was found to be slightly polluted in both monsoon and post monsoon season. Subha [10], also specified pollutants have been a factor responsible for deformity in fishes. 

Parasitic infestations, oxygen deficiency, water current, salinity, sudden change in temperature, toxic chemicals, hereditary may also accountable for deformity in fishes [11,12]. Environmental stress related deformities were also recorded in Cirrhinus mrigala and Hypothalmichthys molitrix from Bhavani River in Kerala [13]. Developmental errors such as embryonic, larval or early post larval development are also responsible for deformation in fishes [14]. Vitamin-C deficiency related operculum deformity has also been reported in hatchery reared Cyprinus carpio [15], O.niloticus and O.mossambicus [16]. Inbreeding [17], as well as genetic factors [18,19], can also elicit such abnormalities in fish species, although operculum deformity was found to be non-inheritable [18-22].

From the above discussion, it is clear that the fish deformities are very complex and are caused by multiple factors. Even though the exact cause for deformity in S.denisonii was not determined; combination of pollutants, pesticides, or genetic factors could be responsible. However, the present record is nevertheless significant owing to the evidence of the occurrence of semi-operculum in wild population of S.denisonii.