Feeding Morphology Supports Carnivorous Habits in Algansea lacustris: A Multitrait Approach

Accurate classification of fish trophic strategies based solely on gut contents can be misleading, especially when plant material is ingested incidentally during predatory benthic foraging. The Pátzcuaro chub (Algansea lacustris) is a critically endangered cyprinid endemic to Central Mexico. It has historically been described as omnivorous with a tendency toward algivory, despite limited anatomical evidence. In this study, integrated anatomical, morphometric, and functional approaches were used to reassess the feeding strategy of A. lacustris and inform conservation-oriented aquaculture. Double-staining techniques revealed a specialised filtering and crushing branchial–pharyngeal system adapted to capture and process animal prey. Relative intestinal length (RIL) was measured from freshly dissected intestines. Intestinal transit time was experimentally evaluated using a formulated diet and live Artemia. Algansea lacustris exhibited a short intestine (RIL = 0.86 ± 0.10) and rapid intestinal transit (