Technical contribution Length-weight and length-length relationships and form factor of three threatened fishes from the Ganges River (NW Bangladesh) By M. Y. Hossain 1,2 , M. Mosaddequr Rahman 2 , F. Ahamed 1 , Z. F. Ahmed 3 and J. Ohtomi 1 1 Faculty of Fisheries, Kagoshima University, Kagoshima, Japan; 2 Department of Fisheries, Faculty of Agriculture, University of Rajshahi, Rajshahi, Bangladesh; 3 Department of Fisheries Management, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh, Bangladesh Summary Data and information are needed to avert the alarming decline and initiate conservation measures for three threa- tened fishes, Labeo boga (Hamilton, 1822), Nandus nandus (Hamilton, 1822) and Puntius ticto (Hamilton, 1822), from the Ganges River and surrounding ecosystems. These fishes are decreasing rapidly due to high fishing pressures as well as environmental degradation. This study furnishes the length– weight relationships (LWRs), length–length relationships (LLRs) and form factor (a 3.0 ) of these three threatened species from the Ganges River, northwestern Bangladesh. A total of 773 specimens from the three species and two fam- ilies used for this study were caught by traditional fishing gear between April 2011 and March 2012. The analysis of covariance (ANCOVA) revealed significant differences between the sexes in LWRs for L. boga (P < 0.001), but not with the remaining species (P > 0.05). Furthermore, the LLRs were highly correlated (r 2 > 0.983; P < 0.001), and ANCOVA analyses additionally indicated that LLRs did not differ between sexes (P > 0.05). The calculated form factor (a 3.0 ) was 0.0111, 0.0159 and 0.0129 for L. boga, N. nandus and P. ticto, respectively. This study presents the first references on LWRs, LLRs and form factor for these three threatened species in Bangladesh. The results would be useful for further studies on the population assessment and sustainable conser- vation of the limited stocks in the Ganges River ecosystem. Introduction Labeo boga (Cyprinidae), Nandus nandus (Nandidae), and Puntius ticto (Cyprinidae) are three of 54 threatened freshwa- ter fish species in Bangladesh (IUCN Bangladesh, 2000). These fishes are widely distributed in rivers, streams, canals, beels, ponds, pools, etc. of Bangladesh, Bhutan, India, Myanmar, Nepal and Pakistan (Petr, 1999; IUCN Bangla- desh, 2000; Froese and Pauly, 2012). All of these indigenous fishes are integral components of fish diversity in Bangladesh and play an important role in the elimination of problems associated with malnutrition (Roos et al., 2007). In addition, Puntius ticto can also be used as an aquarium fish (Froese and Pauly, 2012). However, due to habitat degradation, overexploitation and other ecological changes, the popula- tions of these fish species are declining in Bangladeshi waters (Hossain et al., 2012a); subsequently, N. nandus and P. ticto are categorized as vulnerable, and L. boga as critically endangered by the IUCN Bangladesh (2000). Length–weight relationships (LWRs), length–length rela- tionships (LLRs) and the form factor of threatened fishes are the most important biological parameters for management and conservation of natural populations (Sarkar et al., 2009; Muchlisin et al., 2010; Hossain et al., 2012b). A number of studies in Bangladesh have been conducted on various aspects of these species including the fecundity and sex ratio of L. boga in Rajshahi (Parvin et al., 2011), LWRs of N. nandus using combined sexes in the Mathabhanga River, (Hossain et al., 2006a), growth parameters of P. ticto in the Dikshi beel of Pabna and the Shapla beel of B. Baria District (Mustafa and de Graaf, 2008), and LWRs and LLRs using combined sexes of P. ticto in the Padma River (Hossain et al., 2009; Hossain, 2010). However, no information is available in the literature on LWRs, LLRs and form factor of these threatened fishes in Bangladesh or elsewhere with consideration of sexes (Hossain et al., 2006a,b, 2009, 2012a,b). Therefore, this study presents the first reference on LWRs, LLRs and form factor of L. boga, N. nandus and P. ticto with consideration of sexes from the Ganges River (NW Bangladesh). Materials and methods This study was conducted in the lower part of the Ganges (Lat. 24°22′N; Long. 88°35′E), known as the Padma River in northwestern Bangladesh. Samples were collected during daytime on a seasonal basis from fishing catches landed at Rajshahi city (Jahaj ghat, Binodpur), and Godagari, Raj- shahi (Padma River: 24°46′N; 88°32′E) Bangladesh, April 2011 to March 2012. The main gear used by the commercial fishers included traditional fishing gear, namely, the jhaki jal (cast net), tar jal (square lift net), and dughair (conical trap). The fresh samples were immediately chilled in ice onsite and fixed with 10% buffered formalin upon arrival in the labora- tory. Morphometric measurements were conducted according to Froese and Pauly (2012). All specimens were sexed by morphometric characteristics and gonad observation under a binocular microscope. The fixed specimens were individually measured and weighed. Total length (TL), fork length (FL), and standard length (SL) were measured to the nearest 0.01 cm using digital slide calipers (Mitutoyo, CD-15PS; Mitutoyo Corporation, Tokyo, Japan), and total body weight (BW) was measured using an electronic balance (Shimadzu, EB-430DW; Shimadzu Seisakusho, Tokyo, Japan) with 0.01 g accuracy. J. Appl. Ichthyol. (2013), 1–4 © 2013 Blackwell Verlag GmbH ISSN 0175–8659 Received: September 11, 2012 Accepted: April 15, 2013 doi: 10.1111/jai.12251 Applied Ichthyology Journal of