“Active complete cannibalism” is described for the first time among adult individuals of the non-piscivorous gobioid fish Knipowitschia panizzae. Although the data represent preliminary observations, they demonstrate that female aggressiveness with respect to conspecifics is enhanced during pre-spawning courtship and male choice for nest construction, particularly in times of food shortage. In fact, the number of attacks and instances of cannibalism increased a few days before egg deposition. The role of starvation, energy requests, and intrinsic aggressiveness during captivity rearing is discussed with respect to the different phases which characterize the behavioural sequence of cannibalism: motivation, prey detection, approach, capture, ingestion. In addition, the possibility that intraspecific predation would occur in natural populations of K. panizzae is also hypothesized in relation to the particular ecological conditions that influence the goby densities in the Po delta coastal lagoons. Survival of a limited number of adults during benthos shortage due to summer dystrophic events could be correlated to the induction of intraspecific piscivory.