105 © Department of Aquatic Biology & Fisheries, University of Kerala Journal of Aquatic Biology & Fisheries | Vol. 3 | 2015 | pp. 105-110 ISSN 2321–340X LENGTH-WEIGHT RELATIONSHIP AND CONDITION FACTOR OF A LARGE PREDATORY CATFISH, WALLAGO ATTU (SCHNEIDER, 1801) FROM THE RIVERS OF CENTRAL KERALA, INDIA Rufus, T., 1 Eldho, P.S., 1 Anvar Ali 1 , Neelesh Dahanukar 2 and Rajeev Raghavan 1* 1 Department of Fisheries Resource Management, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi, India 2 Indian Institute of Science Education and Research (IISER), Pune, India *Email: rajeevraq@hotmail.com Abstract: Length-weight relationship and condition factor of a large predatory catfish, Wallago attu from three small westward-flowing rivers of Peninsular India revealed b values in the ranges of 2.7 to 3.5 and condition factor (K) lower than unity with significant differences in these values across populations. Key words: Asian Sheat Catfish, conservation, Pampa River, Siluridae INTRODUCTION The Asian silurid catfish, Wallago attu (Schneider, 1801) also known as the ‘Asian sheat catfish’ or the ‘freshwater shark’ is one of the twenty megafishes on Earth (Stone, 2007), and a high-value species targeted in rivers and their associated flood plains, lakes and reservoirs across south and south east Asia (Poulsen et al., 2004; Montana, 2011; Renjithkumar et al., 2011). Although overfishing is known to have resulted in large-scale population declines (Patra et al ., 2005; Montana, 2011) and the species is currently assessed as ‘Near Threatened’ in the IUCN Red List (Ng, 2010), exploitation, continues unabated with thousands of kilograms of W. attu caught from many rivers in which they occur (Renjithkumar et al., 2011). The confluent rivers of Lake Vembanad (i.e. Pampa, Achankovil, Manimala, Meenachil and Muvattupuzha) in Central Kerala support significant fisheries of commercially important fin-fishes and shell fishes including Horabagrus brachysoma, Labeo dussumieri, Channa diplogramma, W. attu and Macrobrachium rosenbergii (Kurup, 1998; Harikrishnan and Kurup, 2001; Raghavan et al., 2016; Benzgier et al., 2011; Renjithkumar et al., 2011). For example, the average annual exploited fishery of the Pampa River was estimated close to 400 tons with two species, L. dussumieri and W. attu contributing to 30% of the catches (Renjithkumar et al., 2011). However, except for H. brachysoma (see Raghavan et al ., 2016 for a review) and L. dussumieri (Kurup, 1997; 1998), none of the other commercially important species including W. attu have been the focus of any organized studies pertaining to age, growth, population status and/or dynamics. As a first step towards understanding the demographic aspects and need for management of species of conservation-concern, we determined the length-weight relationship and condition factor of W. attu from three rivers in this region viz. Pampa, Achankovil and Manimala. MATERIALS AND METHODS Samples for our study originated from six important landing centres, Edathua, Parumala, Prayikkara, Payippad, Changanassery and Tiruvalla, located on the banks of three major rivers draining into the Vembanad Lake (Table 1; Fig. 1). Study was carried out during two phases (January to May 2013 and October to December 2015) when each of the landing centre was visited on random days (twice a month),