Technical contribution Length-weight relationships of 29 fish species from the Tucuru  ı Reservoir (Tocantins/Araguaia Basin, Brazil) By J. R. Garcia-Ayala 1,2 , E. M. Brambilla 2 , F. A. Travassos 1 , E. D. Carvalho 1,2,† and G. S. David 3 1 CAUNESP, Centro de Aquicultura da UNESP, Campus de Jaboticabal, Jaboticabal, SP, Brasil; 2 Laborato ´rio de Biologia e Ecologia de Peixes, Instituto de Biocieˆncias, UNESP, Botucatu, SP, Brasil; 3 Age ˆncia Paulista de Tecnologia do Agronego ´cio (APTA/SAA), Jau ´, SP, Brasil Summary The length-weight relationships (LWRs) are described for 29 fish species in the region of the Tucuru  ı Reservoir, located in the Tocantins/Araguaia Basin, northern Brazil. Fishes in fourteen sites were sampled seasonally for 10 years, from 2001 to 2010. Significant differences between sexes were found for two species, while 27 species had similar LWRs for males and females. The relationship of standard length and total length is presented for all species as well as the minimum and average size of reproductive females and sea- sonality of occurrence. No information on LWRs of these 29 species was heretofore available in FishBase. Introduction This study was performed in the Tocantins/Araguaia Basin, located in the tropical, northern Brazilian region, where the ichthyofauna is neotropical and very similar to that of the Amazon, with a great richness and abundance of fishes. Characiforms and siluriforms are the main fish taxa (Agost- inho et al., 2007; M erona et al., 2010), represented by Serrasalmidae and Curimatidae as the most abundant fami- lies. Among the 260 species found in the Tucuru  ı Reservoir area of influence, 29 of the studied species had no LWR records according to Fishbase data (http://www.fishbase.org) version (04/2013). In the present study, the parameters of the length-weight relationship (LWR) are given for these 29 species. Materials and methods The study area comprises the region influenced by the Tucurui Reservoir, located in the state of Par a, Brazil (lat. 03°45 0 03″S; long. 49°40 0 03″W). This large, dammed reservoir has an area of 2430 km 2 and mean depth of 18.9 m. Samples were collected seasonally in eight reservoir sites and at six sites downstream the dam from 2001 to 2010, as part of the environmental monitoring program of the hydro- electric power generation company, Eletronorte, which pro- vided data for scientific purposes. Fish collections used standardized monofilament nylon multi-mesh (40–200 mm) gillnets; fish species were identified based on reference guides (Britski, 1972; Britski et al., 1988, 1999) and checked against FishBase; each specimen was measured for standard length (SL), weighed (WT), and dissected for macroscopic gonad analysis for sexual recognition. Study data from 21 096 fish included 29 species. The LWRs were determined by linear regression: log WT = log a + b log SL (Froese, 2006). Evaluation of possible differ- ences between males and females was performed by compar- ing the 95% confidence limits of a and b; when no significant differences were found, the LWR was calculated for males and females together; outliers were removed using a logSL- logWT plot (Froese, 2006). Results This is the first assessment for the Tocantins River Basin, of LWRs covering 29 fish species from 14 families and four orders. Significant differences in male and female LWRs were found for two species and are presented separately. LWRs are summarized in Table 1, showing that all values estimated for b were between 2.453 and 3.248. According to FishBase data (http://www.fishbase.org) version (04/2013), we report new maximum total lengths for 17 species and new LWR records for all 29 species. Parameters of the linear equation with SL and TL for all species studied are given in Table 2, which also shows data of minimum and average size of ripe or spent females, and the season when these were more frequent than what was expected by chance. Discussion According to Froese (2006), b should normally fall between 2.5 and 3.5. Only Pterygoplichthys joselimaianus had esti- mated values for b outside of this range, probably because of its peculiar, elongated shape. † Deceased J. Appl. Ichthyol. (2014), 1–4 © 2014 Blackwell Verlag GmbH ISSN 0175–8659 Received: August 2, 2013 Accepted: January 8, 2014 doi: 10.1111/jai.12449 Applied Ichthyology Journal of