A NOTE ON THE COLLECTION OF OSTEOBRAMA BAKERI ( DAY ) AND LABEO DUSSUMIERI ( VALOENCIENNES ) , TWO RARE CYPRINID FISHES FROM THE PAMBA-MANIMALA RIVER SYSTEMS OF KERALA , SOUTH INDIA

Ichthyofaunal investigation in the Alappuzha district, Kerala State, conducted along with the faunistic survey of the district by the Zoological Survey of India, Calicut Station, revealed the continued occurrence of the two rare fishes namely Osteobrdma bakeri (Day) and Labeo dussumieri (Valenciennes) (family: Cyprinidae) in the westflowing rivers in southern Kerala, South India. The status of these two fISh species are known to be very rare or vulnerable (Menon 1997). The specimens of both these fish species (0. bakeri-l ex., L dussumieri-3 exs.) were obtained from the confluence of the Manimala and Pamba rivers at a locality near Mannar, Alappuzha district.


INTRODUCTION
Ichthyofaunal investigation in the Alappuzha district, Kerala State, conducted along with the faunistic survey of the district by the Zoological Survey of India, Calicut Station, revealed the continued occurrence of the two rare fishes namely Osteobrdma bakeri (Day) and Labeo dussumieri (Valenciennes) (family: Cyprinidae) in the westflowing rivers in southern Kerala, South India.The status of these two fISh species are known to be very rare or vulnerable (Menon 1997).The specimens of both these fish species (0. bakeri-l ex., L dussumieri-3 exs.) were obtained from the confluence of the Manimala and Pamba rivers at a locality near Mannar, Alappuzha district.Day (1878) described O. bakeri (formerly referred to the genus Rohtee i.e., Rohtee bakeri Day) based on the specimens obtained from the type locality 'Kottayam' in Kerala, South India It is so far reported only from the westflowing rivers in Kerala and, therefore, endemic to this geographic area.Its salient features are elongately trapezoid and laterally compressed body with abdominal edge sharp and trenchant between bases of pelvic and anal fins but rounded in front of pelvic fins; two pairs of small barbels; dorsal fin with a weak and serrated spine, anal fin with 11-14 branched rays and caudal fm deeply forked; lateral line with about 44 scales etc.
The distribution of O. bakeri being within a restricted geographical area or habitat, and that too in thin population, its specimens are hardly available in the ichthyofaunal explorations.After Day (op.cit.), John (1936) had reported its occurrence in the Manimala river and, much later, by Jayaram et. ale (1976) from Cardomom Hills in Southern Kerala.Raghunatban (1995), followed by Easaand Sbaji (1997) reported its occurrence in the westflowing river Chaliyar in northern Kerala revealing its extended range of distribution.More recently, it has also been recorded from the westflowing ChaJakkudy river in Central Kerala by Ajit Kumar et. ale (1999).The collection of O. bakeri (fig. 1) from the confluence of the Manimala and the Pamba rivers in the AJappuzha district, is the next authentic record of this species from southern Kerala after John (op.cit.).Day (op. cit.) has mentioned 11 branched anal (total 14 including 3 unbranched) rays for the species.Jayaram (op.cit.) has observed a range of 12-14 branched anal rays while discussing the biometric variations.The specimen collected by us is having 12 branched (total 15 including 3 unbranched) rays.Thus, O. bakeri is having a variable count (11-14) of branched anal rays, a feature (range in counts of branched anal rays) generally found among species of the genus (Talwar and Jingran, 1991).The colour of fish in live condition has not been recorded by Day or other workers.The fish in life is pale greenish on the back and silvery on the flanks and belly.The dorsal spine and the principal rays of caudal fin are deep red which become decolourised in preserved specimen, then tallying with the colour as mentioned in the original description.The live specimen of this fish species is easily distinguishable by its characteristic colouration.
Labeo dussumieri is considered a vulnerable species whose very sporadic populations or numbers in its geographic habitats are decreasing, though not reduced to a critical level, as evidenced in the sample-netting-catches during periodic ichthyofaunal explorations over the years.It is at present known from the westflowing rivers of Kerala and Sri Lanka, though it has been recorded as far north as Bombay and Gujarat (Menon, Ope cit.).Its occurrence in Sri Lanka is reported to be common (Pethiyagoda 1991).
Labeo dussumieri (Fig. 2) is distinguishable from all other species of the genus lAJbeo by having two pairs of barbels; body with small scales, 53-60 along the lateral line and 5-5 1 / 2 rows between lateral line and pelvic fin base; scales with dark edges forming distinct longitudinal stripes on body, etc.
The collection of specimens of these two species, obtained through random sampling ~fforts, from the confluence of the rivers Pamba and Manimala indicates the continued occurrence of these two fish species, possibly in good numbers, in both these westflowing rivers.It can be smmised beyond doubt that the populations of O. bakeri and L. dussumieri are still thriving in their threshold capacity ensuring the perpetuity of these two fish species in their known geographic habitats in KeraIa.