Length-weight relationships and condition factor of five ornamental fish species of the middle of the Negro River basin, Amazon, Brazil.

Length-weight relationships (LWR) were calculated for five freshwater ornamental fish species from the middle Negro River basin in the Brazilian Amazon. Samplings were carried out from October 2011 to February 2012, and the specimens were found close to stream margins and submersed tree trunks and captured with hand nets. This study provides the LWR and condition factor (Kn) parameters for <italic>Carnegiella strigata </italic>butterfly fish, <italic>Dekeyseria brachyura </italic>jaguar fish, <italic>Dicrossus maculatus </italic>chess fish, <italic>Paracheirodon axelrodi</italic> cardinal and <italic>Petitella georgiae </italic>drunk's nose. Descriptive statistics and estimated LWR parameters, including coefficient of determination (r2) and 95% confidence limits for a and b. Values of a ranged from 0.005 to 0.014, b ranged from 2.555 to 3.418, and r2 ranged from 0.931 to 0.996. Every species of fish displayed allometric growth (b ≠ 3). No difference was observed between the Kn of the five fish species, indicating good body condition. The information gathered here could be helpful for population dynamics research as well as for developing conservation and sustainable management plans for ornamental fish populations in the middle Negro River basin, Amazonas, Brazil.