Background:

The distribution and diet of fish, as well as the specific composition of their prey, have been affected by the magnification of the spatial variations in salinity due to hydraulic infrastructure and climate change. Cathorops aguadulce was selected based on previous records of its diet and its current dominance in the estuarine systems in the southern Gulf of Mexico.

Goals:

The feeding habits were evaluated in relation to the variation of size composition, day-night, and seasonality in a coastal lagoon in the southern Gulf of Mexico.

Methods:

Two hundred ten digestive tracts were analyzed in juveniles and adults captured in a sampling that included the day-night and seasonal variation in three sampling sites located in a salinity gradient. The size composition was correlated (Spearman coefficient) with the spatial and temporal variation of salinity and temperature. The temporal and spatial variations of the Repletion (IR) and Relative Importance (IIR) indexes were analyzed using Kruskal-Wallis test and hierarchical clustering.

Results:

The size composition was inde pendent of salinity variation and IR values (Kruskal-Wallis; p =0.649). Yet diet intensity in the dry season was significantly greater than in the transition and rainy seasons (Kruskal-Wallis; p =0.00001). Among the 11 food items defined, animal detritus and malacostracans, mainly tanaids, were the dominant feeding categories in the frequency of occurrence and according to the IIR. However, detritus predominated in juveniles, while tanaids were the preponderant item in the adults.

Conclusions:

Even though laguna Mecoacan recorded an ample salinity variation, C. aguadulce recorded a significant temporal variation in intensity of diet; the ontogenic shift of its diet was more relevant than the effects of the environmen tal variation of its feeding habits. This conclusion opens the possibility of testing whether the ontogenetic variation of their functional morphological traits is associated with the acquisition of food or movement.