Validating gut flushing as a non‐lethal sampling technique for diet monitoring in agastric fish

Abstract

Non‐lethal diet sampling is essential where individual‐level monitoring and welfare matter, yet evidence on season‐long outcomes in agastric fishes is scarce. We tested syringe‐based gut flushing in pond‐reared common carp Cyprinus carpio over one growing season (April–September) using PIT‐tagged fish assigned a priori to three handling histories: flushed (sedated, measured, flushed), handled‐only (sedated, measured), and unhandled controls. At harvest, recapture (survival proxy) remained high and statistically similar among handled groups and growth to harvest did not differ across treatments (end‐point mass: flushed 1857.3 ± 367.4 g; handled‐only 1769.7 ± 311.8 g; unhandled 1731.9 ± 392.6 g). A mid‐season divergence in July (handled‐only > flushed in weight gain) was transient and absent at harvest. Operational performance scaled predictably: total water required to clear effluent increased with fish size (~20 mL in small carp to >90 mL in large individuals; occasional ~120 mL) and varied seasonally, rising from May to August and easing in September. Practical safeguards (rounded catheters guided between pharyngeal teeth; conservative advancement ≤2 cm beyond the teeth; controlled bolus infusions; standardised recovery) supported complete evacuations with low injury risk. Collectively, these results validate gut flushing as a field‐ready, non‐lethal method that can be integrated into routine dietary monitoring of agastric cyprinids without compromising survival or harvest growth, while providing simple, size‐ and season‐based parameters to standardise protocols across studies.

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