Trophic ecology of <i>Plagioscion magdalenae</i> (Pisces, Sciaenidae) in a neotropical reservoir in the lower Magdalena River Basin, Colombia

Plagioscion magdalenae is an endemic species of the Magdalena River basin in Colombia. It is classified within the near-threatened category. The species supports the artisanal fishery in the Lower Magdalena Basin. As little is known about its role and trophic relationships in aquatic ecosystems we studied aspects of its trophic ecology such as diet, trophic niche, feeding period, and degree of robustness in the El Guájaro reservoir, Department of Atlántico, Colombia. Monthly fish capture sampling was carried out over 10 months, from April 2018 to January 2019 so as to cover the flood pulse of the area. We collected and studied a total of 211 individuals. Sample analysis included the numerical method, volumetrics, frequency of occurrence, vacancy coefficient, food importance index, condition factor, trophic niche breadth, and trophic overlap analysis between sizes. Our results indicate that P. magdalenae is a specialist carnivore with piscivorous tendencies. Similarity of the trophic overlap between small and large sized fish was below 70 %, with the diet consisting of invertebrates such as Chironomidae, Campsurus sp. and Macrobrachium sp. for juveniles (14.5–21.8 cm LE) and fish such as Caquetaia kraussii, Andinoacara latifrons and fish remains for adults (29.2–36.5 cm LE). The supply of prey in the system was lower in the dry season than in the rainy season. However, condition factor K showed that the species has a high degree of robustness in dry periods, associated with preparation for reproduction when the water level rises due to increased flow. Plagioscion magdalenae is the primary predator in the reservoir, using multiple trophic resources that vary depending on body size differences. Plagioscion magdalenae showed adaptive strategies to decrease intraspecific competition for food and a relationship with the variation of the reservoir water level, reaching robustness in dry periods so as to be fit for reproduction in rainy periods. Key words: Diet, Diversity, Endemic fish, Predator