Length-weight relationship and condition factor of armored catfish (Pterygoplichthys sp.) in the Grijalva and Usumacinta rivers, Mexico

Length-weight relationship and condition factor (K) are descriptors of the biology of fish populations, providing fundamental information on growth strategies, nutritional status, and reproduction. These parameters are used to compare the condition of fish populations in aquatic systems with different degrees of anthropogenic intervention. This study aimed to explore the length-weight relationship of Pterygoplichthys sp., to observe whether the physiological condition factor reveals variation from a dammed river (Grijalva) to a free-flowing river (Usumacinta). Given the physiological characteristics of armored catfish (benthic consumer, tolerance to hydrological disturbance and aquatic pollution, and wide reproductive range), we predict that this fish will have a better welfare condition in the Grijalva River than in the Usumacinta. Highest abundance of armored catfish was obtained in the Grijalva River (282 specimens). However, the largest and heaviest fish were caught in the Usumacinta River (34.4 ± 5.31 cm and 389 ± 138 g, respectively). Length-weight ratio of armored catfish showed a negative allometric growth rate in both rivers (b>3), i.e., the fish grew more in length than in weight. However, the condition factor revealed that armored catfish have better physiological conditions in the Usumacinta River. Food availability, species population density, intra- and interspecific competition probably played an important role in fish welfare. Information generated in this study can be used as a guide to analyze more detailed the populations of armored catfish, taking into consideration sex and different bodies of water, to adequately monitor the populations of Pterygoplichthys sp., in the Mexican southeast.