Occurrence of Malabar Snakehead , Channa diplogramma ( Perciformes : Channidae ) from River Valapattanam , Western Ghats of Kerala , India

Freshwater snakehead fishes of the family Channidae have widespread distribution in the tropics [1], represented by 38 species, of which 35 are of the Asian genus Channa [2] and three of the African genus Parachanna [1, 3, 4]. The Western Ghats biodiversity of India extends along the west coast and is crisscrossed with many streams, which form the major rivers draining water to the plains of Peninsular India [5]. The freshwater fish diversity in the Western Ghats hotspots is very high [6], with 320 species belonging to 212 endemic species 47% being under Threatened or Near Threatened categories and 23% being under Data Deficient or Not Evaluated categories [7]. The Valapattanam River is one of the west-flowing Rivers in the Western Ghats region of India and the main tributaries are Srikandapurampuzha, Bavalipuzha, Venipuzha, and Aralampuzha. In this paper, we report the occurrence and biometric characteristics of C. diplogramma (Day 1865) [8] from the river Valapattanam, Western Ghats of Kerala, India.


Introduction
Freshwater snakehead fishes of the family Channidae have widespread distribution in the tropics [1], represented by 38 species, of which 35 are of the Asian genus Channa [2] and three of the African genus Parachanna [1,3,4].The Western Ghats biodiversity of India extends along the west coast and is crisscrossed with many streams, which form the major rivers draining water to the plains of Peninsular India [5].The freshwater fish diversity in the Western Ghats hotspots is very high [6], with 320 species belonging to 212 endemic species 47% being under Threatened or Near Threatened categories and 23% being under Data Deficient or Not Evaluated categories [7].The Valapattanam River is one of the west-flowing Rivers in the Western Ghats region of India and the main tributaries are Srikandapurampuzha, Bavalipuzha, Venipuzha, and Aralampuzha.In this paper, we report the occurrence and biometric characteristics of C. diplogramma (Day 1865) [8] from the river Valapattanam, Western Ghats of Kerala, India.

Materials and Methods
A specimen of C. diplogramma (Figure 1) was caught with an encircling net (length 50 meter; height 1.5 meter; mesh size 0.8 mm) from the River Valapattanam, northern Kerala (11.93 ∘ N, 75.30 ∘ E) on 15 March 2013.The morphometric measurements of the formalin-preserved specimen were measured with a Vernier calliper to the nearest 0.1 millimetres and weighed to the nearest 0.01 gram using an electric balance (Sartorius-GD-603).The morphometric measurements and meristic counts were made by following Ng et al. [9].Measurements of body parts are reported as percentage of standard length (%SL) and measurements of subunits of head are reported as percentage of head length (%HL).The specimen was preserved in 4% formaldehyde solution and deposited in the Museum of the Faculty of Fisheries, College of Fisheries, Kerala University of Fisheries and Ocean Studies, Panangad, Kerala, India (FRM-CH-DIP/2013-1).

Results and Discussion
Channa diplogramma was first described as Ophiocephalus diplogramma (Day 1865) based on one juvenile specimen (42 mm in length) collected near the mouth of the Cochin estuary in the port city of Cochin (Kerala, India).The close similarity of this juvenile specimen with C. micropeltes, originally described by Cuvier and Valenciennes [10] from Indonesia, may have misled author to synonymise C. diplogramma with C. micropeltes [11].Recently researchers suggested that C. diplogramma is distinct from C. micropeltes and should be considered as a valid species [12,13].After 134 years of it being synonymised, C. diplogramma is known to be a valid endemic species of Peninsular India [11].Channa diplogramma is endemic to southern Western Ghats region of India, where it has been reported from the River Meenachil, Manimala, Pampa, Achankovil, and Kallada in Kerala state, as well as the River Chittar and Tambraparni in Tamil Nadu state [11,14,15].Benziger et al. [11] reported that they used comparative specimens of C. diplogramma from Canara and Mangalore region of south India, but there is no specific record from River Valapattanam [11].This species has not been reported from the Valapattanam River in earlier works [16,17].Hence, this current record adds to the recorded ichthyodiversity of River Valapattanam in Kerala (Figure 2).
The morphometric and meristic characters of the collected C. diplogramma are presented in Tables 1 and 2. All the morphometric measurements and meristic counts of the current specimen were in the prescribed range for C. diplogramma as described by Benziger et al. [11].Some researchers have used molecular analysis methods for the taxonomic identification of a species [2,12,18,19]; however, we could not follow the molecular analysis in the current study.Benziger et al. [11] reported that C. diplogramma, collected from the riverine system of Kerala, had 103-105 lateral line scales, which was more than all other species in this genus.Similarly, the current specimen also had 104 lateral line scales and has a relatively long broad body with a laterally compressed head.
Snakeheads are very hardy animals due to the presence of several biological features that they share among their family [18].In the present study C. diplogramma was collected from middle stream part of the river, pool type of habitat with riparian shade and bottom with rock, gravel, and sand.Banks of the site was supported with shrubs and trees giving strong shade into the water.In nature, snakeheads are carnivorous which feed only on live animals including small fishes, insects, crustaceans, frogs, and even baby turtles [20].Mohsin and Ambak [21] and Roberts [22] noted that C. micropeltes kills more individual fish than it actually eats (i.e., not all prey is consumed); likewise, C. diplogramma may possibly be a biological threat to the small indigenous freshwater fishes in these rivers [18].To understand its effects over indigenous freshwater fish diversity, more studies are to be conducted.
Due to the attractive colour pattern of juveniles of C. diplogramma, they have been overexploited from the wild for the international aquarium pet trade [23].However, this profitable business sometimes poses a threat to the environment especially in places where snakehead is not a native fish since some of the fish find their way into dams, rivers, and other water bodies, either by accident or otherwise by being released by traders or by hobbyists when they mature into less attractive colours [18].Channa diplogramma shows a similar pattern of body colouration as in C. micropeltes [11]; the current specimen showed to be dark blue with white spots along the whole of its profile down to its white underside.According to Benziger et al. [11], C. diplogramma shows multiple colour stages during its life history, which makes local fishermen believe that they are different species.Because of this colour differentiation, C. diplogramma is locally known by different vernacular names  The population of C. diplogramma is declining due to the overexploitation for consumption and aquarium trading [1,11].A recent study revealed that C. diplogramma contributed 0.79 tonnes in the exploited fishery from River Pampa [24].Kurup and Ranjeeth [25] reported that the population of C. diplogramma has declined significantly over the last two decades in the rivers of Kerala (>90%).Kurup [26] noticed that this species was subjected to alarming decline in its population due to destructive type of fishing activities including dynamiting and poisoning, EUS, habitat alteration, and pollution.Consulting the local fishermen and fish collectors in the River Valapattanam, it is known that C. diplogramma is caught occasionally by artisanal fishing, namely, seine netting, gill netting, or long lining.Our personal observations and discussions with local fishermen reveal that most of the extensive fishing of C. diplogramma was carried out during the monsoon season.Habitat destruction and sand mining in the river basin of Valapattanam have posed serious problems to the freshwater fish population by affecting their breeding and spawning grounds.Due to its restricted distribution, small population size, illegal fishing, and anthropogenic pressure to its natural habitats, the species is classified under Vulnerable by the IUCN [27].However, the present record is nevertheless significant in extending recorded distribution of C. diplogramma in the Western Ghats of India.

Figure 2 :
Figure 2: Distribution of Channa diplogramma in the rivers of Kerala.