Length and weight data are useful in fisheries management and standard results of fish monitoring programs. Length-weight relationship (LWR) is used for estimating the weight corresponding to a given length, and the condition factor is used to compare the body condition, fatness or health of fish populations. This study aimed to estimate the LWR and the condition factor for 12 freshwater fish species from the Igarapé Fortaleza basin, a tributary of the Amazonas River system in the State of Amapá, eastern Amazon (Brazil). The coefficient of determination, the allometric condition factor and the allometric coefficient varied among species, and were compared with populations elsewhere. In 83.3% of the species, the allometric coefficient remained within the expected range. This was the first record of LWR parameters for Acestrorhynchus falcirostris.

O presente estudo teve como objetivo avaliar a atividade pesqueira no alto e médio rio Araguari, Estado do Amapá.  Aplicou-se 20 questionários aos pescadores associados à Colônia Z-16, com a finalidade de identificar os apetrechos de pesca, principais espécies capturadas, locais de pesca da atividade pesqueira no período de cheia e seca. A  captura por unidade de esforço (CPUE) foi estimada através de dados de 1695 mapas de pesca do ano de 2003 a 2010. As embarcações foram caracterizadas por batelão e canoa, os principais petrechos descritos pelos pescadores foram o trapo/trapão, tiradeira, a rede de emalhar, bóia, linha de mão, caniço, trapinho, zagaia e tarrafa. As principais espécies explotadas são o H. aimara T.trilobatus, A. inermis M. asterias – Myloplus sp, H. malabaricus, S. rhombeus, Cichla, Pimelodus maculatus, L. trifasciatus, C. inornata, Prosomyleus rhomboidalis, Triportheus brachipomus e C. inornata. Os ambientes de pesca foram caracterizados por remansos, varjão, baixão, poços, corredeiras e igarapés. Os maiores picos de CPUE foi no período da seca, no mês de outubro de 2005 com 105 kg/pescador-1dia. A atividade é caracterizada como pesca artesanal comercial de pequena escala praticada por pescadores interioranos, multiespecífica e multiapetrecho.

The present study estimated parameters of the length-weight relationship (LWR) and allometric condition factor for eight fish species from the upper Araguari River, in the State of Amapá, Brazil. A total of 615 fish of eight species were analyzed: Acestrorhynchus falcatus, A. falcirostris, Ageneiosus inermis, Hemiodus unimaculatus, Hoplias aimara, Myloplus asterias, M. ternetzi and Tometes trilobatus. The allometric condition factor varied from 0.742 to 1.435. The coefficient of allometry ranged from 2.723 to 3.225. The coefficient of determination (R2) of the LWR ranged from 0.742 to 0.985. This is the first estimate of the length-weight relationship for fish from the Araguari River and the first record of these parameters for Myloplus ternetzi and Tometes trilobatus.

Summary The present study investigated the length‐weight relationship (LWR) and allometric condition factor for 11 freshwater fish species of the Igarapé Fortaleza basin (00°02037.5″N; 51°06019.2″W), a tributary from the Amazon River system in the State of Amapá, northern Brazil. The fish were collected in the period from 2012 to 2014 using gillnets with different mesh sizes (10–40 mm between opposite knots). LWR parameters were estimated had angular coefficient (b) varying from 2.055 to 3.158. The allometric condition factor presented interspecific variation. These data complement the efforts to understand the biology of these Amazonian fish species.