Do cannibalistic fish forage optimally? An experimental study of prey size preference, bioenergetics of cannibalism and their ontogenetic variations in the African catfishHeterobranchus longifilis

Abstract

-This study relied on the day-by-day analysis of bioenergetics and prey size preference in isolated cannibals of the African catfish Heterobranchus longifilis (13-57 mm standard length, 3-500 mg dry body mass, n = 153) that were offered ad libitum conspecific prey of adequate sizes in small-sized (2-L) environments under controlled conditions (12L:12D, 30• C). In these conditions, cannibals of increasing body size selected preferentially prey of decreasing size relative to their own, and increasingly closer to the optimal prey size (producing the highest gross conversion efficiency). The role of experience in cannibalism was found of secondary importance relative to body size, both as regards food intake and prey size selectivity. These results indicate that in environments that minimize the escape capacities of their potential victims, as applies to most aquacultural contexts, fish exercising cannibalism tend to forage optimally, which has rarely been evidenced for piscivorous behaviour. The present study further highlights that H. longifilis possesses a very high capacity for growth, which originates from the combination of high food intake and very high conversion efficiency, and makes this species of utmost interest for aquaculturists wherever fast growth is desirable, but also extremely prone to cannibalism wherever feeding schedules are inadequate.

Identifying conversion efficiency as a key mechanism underlying food webs evolution: A step forward, or backward?

“…Indeed, we showed that simply considering a non-constant biomass conversion efficiency can solve most problems encountered with previous models. In addition, empirical data suggest that there is indeed an optimal size of prey size where predation is the most efficient (Baras et al, 2014;Norin and Clark, 2017). Our model is, in a sense, closer to data and observations and one might argue that such adaptive dynamics models really tell us how food webs emerge from eco-evolutionary processes.…”

“…Conversely, if preys are very small, a predator has to feed on a large number of preys and then the handling time (per unit of biomass) becomes critical. This suggests that λ 0 should depend on z − y as a function ξ(z −y), accordingly to empirical results (Baras et al, 2014;Norin and Clark, 2017), where ξ(z − y) should converge to zero when z − y converges to ±∞.…”

Intracohort cannibalism and methods for its mitigation in cultured freshwater fish

“…In contrast, the emergence of cannibalism was dependent strictly on the development of oral teeth at the embryonic stage (Baras et al 2000a, b), suggesting that fish hatching slightly later, or developing at a slightly slower rate than others, incur a major penalty for this very short delay. In particular, this is likely to apply to fish species with oral teeth that facilitate the exercise of incomplete cannibalism (which does not require that the cannibal be larger than its victim), as individuals with a slightly faster growth than others during the first days of exogenous feeding would not be safe from cannibalism (Baras et al 2014). The size advantage gained through the exercise of type I cannibalism at the embryonic and larval stages, later enables cannibals to exert type II cannibalism over smaller siblings, resulting in high mortality throughout the larval and early juvenile stages (Hecht and Appelbaum 1988;Baras 1999b).…”

“…Due to species-dependent morphological differences, the variability of dimensions during ontogeny and behaviour typical of a given species, diverse mathematical models are applied. The most commonly used models include those based on direct measurements of total length (TL) of cannibals and their prey or models based on such parameters as mouth width (MW), mouth gape (MG), body depth (BD) of a prey, head depth (HD) of a prey and head width (HW) of a prey (Folkvord and Otterå 1993;Baras and Dalmeida 2001;Hseu 2002;Kailasam et al 2002;Kestemont et al 2003;Hseu et al 2003b;Fessehaye et al 2005;Wallat et al 2005;Hseu et al 2007;Policar et al 2013;Baras et al 2014;Hseu and Huang 2014;Ribeiro and Qin 2015).…”

“…family is beneficial, as this reduces mortality and incidence of cannibalistic behaviour and is favourable from an economic standpoint (Piotrowska et al 2013). However, in some cases, mixed feeding may also cause different individuals to feed on different types of food with different nutritional values, which may result in growing size heterogeneity (Baras et al 2014).…”