Extension of range of the Marine Puffer Fish Chelonodon patoca ( Tetraodontiformes : Tetraodontidae ) to freshwater habitat of Kerala , India

Chelonodon patoca is a marine puffer fish common along the Coromandal Coast of India. It has also been reported in the Aghnashini River in Karnataka state, a freshwater habitat. During a recent ichthyological survey five specimens of Chelonodon patoca were collected in another freshwater habitat, the Payaswani River in Kerala state. These specimens document an extension in the distributional range from Karnataka to Kerala state in peninsular India.

Tetraodon travancoria and Chelonodon patoca, both belonging to the family Tetraodontidae, are the two puffer fish species reported in the freshwater habitats of the Western Ghats, India.Hora & Nair (1941) described Tetraodon travancoria from the Pamba River, Kerala.Later Easa & Shaji (1997) recorded the same species from the Nilgiri Biosphere Reserve in Kerala, Western Ghats, and Remadevi et al. (2000) reported it in Mavincar in South Canara, Karnataka.Tetraodon travancoria was the only known freshwater puffer fish from Western Ghats until Chelonodon patoca was reported (Arunachalam et al. 1999) from the Aghnashini River in Kritikada, Karnataka.The present study reports the occurrence of Chelonodon patoca collected from the Payaswani River at Eranchipuzha in the Chandragiri River basin documenting the extension of the distribution of this species into Kerala.

Materials and Methods
Fish were collected using cast nets.Meristic counts and morphometric characters were measured and proportions were calculated following Hubbs & Lagler (1958).
The measurements that have been modified slightly are provided here in detail.Head length was measured from tip of snout to insertion point of pectoral fin.Eye diameter is the distance between anterior and posterior rim of eye through pupil.Inter orbital space is the distance between bony margins of eyes in

Diagnosis
Body heavy and fairly elongate, gill opening not reaching below middle of pectoral fin base.Nasal organ in the form of a depression with slightly raised margin expanded before and behind into a pair of elongate flaps.Two lateral lines.Pectoral fin round and caudal fin truncate, with curved edges.Back and side of body with round fluorescent olive green to yellowish spots, variable in number and size.

Colour
Upper surface of body deep grey, becoming white below.Abdomen silvery white.Back and sides with numerous small round olive fluorescent green spots extending up to caudal fin.Spots on caudal fin in vertical rows, the interspaces form two to three distinct dark bands, the posteriormost the broadest (Fig. 1b).Spots variable in size and form.Three black cross bands descend from back to middle of lateral surface of body, one passes over the head with a V shaped light interorbital band posterior to it.Also is seen another band that extends backward in the median line towards an irregular band formed by congregation of spots of same colour.The second band, in the form of a saddle, is seen in the space between the pectoral fins on either side, the posterior one spreads from slightly ahead of the dorsal origin.Olive green spots encircle a part of the third band.
Colour in formalin: Fluorescent yellow colour turned to dirty white in preservation.Body pale grey on the dorsal surface, and the spots along the body are dull white but are prominent.

Discussion
Most of the meristic and morphometric characters studied for the five specimens are similar to the comparative material from the Aghnashini River in Karnataka except for the variation in number of branched rays and the shape of the distal margin of both the dorsal and anal fins.The branched rays of the dorsal fins in the specimen from Aghnashini were 10 versus 9, the anal fins were 8 versus 7 and the shape of the margin of the dorsal and anal fins of the Aghnashini specimen tend to be more truncate versus round in the Payaswani specimens.
Chelonodon patoca (Hamilton-Buchanan 1822) was described from the estuary of the Ganges, West Bengal and is very common along the Coromandal Coast of India (Day 1875-78).It has also been reported from tropical Indo-West Pacific waters (Talwar & Jhingran 1991).Its distribution in freshwater habitats of the Western Ghats was established when it was reported in the Aghnashini River in Karnataka.Now the specimens collected from the Payaswani River in Kerala represents a new record from the Kerala area of the Western Ghats.
. Mouth terminal, jaws with median suture.Eyes large, in dorsolateral position situated slightly anterior to half the distance of head length.Eye diameter 22.72-30.36(25.35)%HL and inter orbital space 56.30-64.71(61.43)%HL.Nostril immediately near eye, nasal organ cuplike produced into two rounded flaps, gill opening narrow, ending before middle of pectoral fin base, predorsal distance 74.83-77.56(76.22)%SL covered by laminae, vent positioned very close to anal fin.Two lateral lines, upper one joins lower one behind anal fin, and reaches caudal fin base.Inconspicuous line around eyes, the circles thus formed are connected by an inter link at the nape.Dorsal fin round, inserted slightly behind the vent above anal fin.Its height less than length of head excluding snout 21.50-23.74(22.28)%SL.Anal fin round 15.22-20.34(17.58)%SL, its origin from first branched ray of dorsal fin above.Caudal fin truncate 34.53-37.05(35.21)%SL.Pectoral fins small and round, placed at middle of body, vertically in regard to height, its length roughly equal to snout length and 15.58-18.49(16.86)%SL.

Figure 1 .
Figure 1.Lateral view of Chelonodon patoca and shape of fourrooted spine a -Four-rooted spine; b -Lateral view of Chelonodon patoca OPEN ACCESS | FREE DOWNLOAD dorsal position.Caudal fin length was measured from posterior end of urocentrum to tip of fin.Standard length was measured from snout tip to base of caudal fin.All measurements were made to the nearest 0.1m using digital calipers.The specimens are housed in the registered collection of the Manonmaniam Sundaranar University Museum of Natural History (MSUMNH), Alwarkurichi.Tamil Nadu.Chandragiri River basin at Eranchipuzha, Kasaragod District, Kerala, coll.M. Arunachalam, M. Muralidharan & P. Sivakumar, MSUMNH 46.Chelonodon patoca (Hamilton-Buchanan) Tetraodon patoca Hamilton-Buchanan 1822, by original designation; estuaries of the Ganges, (West Bengal, India) 7, 362, Pl. 18, fig.2