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Plasticity of gastrointestinal tract structure and function in the invasive fish Pterygoplichthys disjunctivus (Teleostei: Loricariidae)

Pterygoplichthys disjunctivus, which is native to tropical South America, is an invasive fish species found in at least nine countries outside of the neotropics, including the United States. We tested the hypothesis that P. disjunctivus has a broad diet and exhibits plasticity of gastrointestinal (GI) tract structure and function in relation to food quality and intake, thereby contributing to its success. Stable isotope analyses (δ13C and δ15N) of several tissues of wild‐caught fish confirmed that P. disjunctivus has a variable diet over time. Individuals of this species were raised in the laboratory on a high‐quality algal diet, a low‐quality wood diet, or no food at all (starvation) for 150 days and the effects of diet, intake, and starvation on GI tract structure and function were examined. Individuals that were starved or consumed large amounts of a low‐quality diet showed little mortality but reduced their intestinal surface areas by 70 and 78%, respectively, and reduced the microvilli surface area by 52 and 27%, respectively, in comparison to wild‐caught fish. Intake and dietary quality did not affect the patterns of 10 digestive enzymes active along the fish's intestine, but the algae‐fed fish had higher activities of most enzymes and higher levels of GI fermentation. Overall, our results support our hypothesis and may provide insight into the success of P. disjunctivus as an invasive species across the globe.