Intracohort cannibalism in Dourado (Salminus brasiliensis): Ontogeny, behavior and morphological limitation
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The present study assessed the ontogeny and delimitated the morphological boundaries of intracohort cannibalism in dourado (Salminus brasiliensis), a native fish species with potential for aquaculture diversification in South America, but presenting high incidence of cannibalism during the early life stages. Replicated larvicultures of dourado were performed in 30 L aquaria aiming to assess the ontogeny of cannibalism based on a behavioral approach. In parallel, medium-scale larvicultures were carried out in 100 L tanks from where periodic fish samples were collected. Samples were then measured for morphological traits in order to develop predictive models of the boundaries of size-limited cannibalism. Two models were developed assuming (alternative model, Modelalt) or not (standard model, Modelstd) inter-individual variability in the morphological traits. Finally, these models were cross-validated with empirical data collected from a predation experiments where cannibals were challenged with progressively increment of prey sizes. Cannibalism was extremely intense in the first days of life, removing 85.7 ± 3.8% of the original population by 05 days after hatching (DAH). The vast majority of predation acts within this period was tail-first orientated. However, its effectiveness reduced down as fish grew larger, becoming fully inefficient for fish older than 07 DAH. From this moment onwards, cannibalism turned exclusively head-orientated, but less intense. By 10 DAH, cannibalism removed 97.7 ± 0.5% of the original population. While the standard model based on the average values of the body depth and mouth width underestimate the morphological boundaries of cannibalism, the model built on the interindividual variability of the respective body parts precisely predicted the maximum prey size that dourado cannibals are able to ingest, when compared with the empirical data. The large mouth size and relative shallow head/body depth during the very early life stages of dourado makes cannibalism not size-limited among individuals smaller than 20 mm total length (TL). However, as cannibals grow larger, cannibalism become size-limited and the maximum ingestible prey size reduces from 100 to 80% TLcannibal for cannibals sizing 20 to 54 mm TL, respectively. The outcomes of this study provide fundamental knowledge to understand the ontogeny of cannibalism and to develop novel techniques of cannibalism reduction for the species.