Do cannibalistic fish possess an intrinsic higher growth capacity than others? A case study in the Asian redtail catfishHemibagrus nemurus(Valenciennes, 1840)

Abstract

This study relied on the day‐by‐day analysis of bioenergetics and prey size preference in larvae and juveniles of Hemibagrus nemurus selected at random, held in isolation (28.5°C, 12L:12D) and feeding ad libitum on conspecifics [21 fish, 12–46 mm total length (TL), dry mass (DM) of 1–145 mg]. Several traits concur to make young H. nemurus highly cannibalistic: (1) high predation capacities (largest prey = 88% and 70% TL in fish of 8 and >40 mm TL, respectively), (2) opportunistic feeding behaviours with no marked size preference and (3) an unusual combination of high food intake (>100% DM at 1 mg DM) and very high gross conversion efficiency (>0.70). A growth model was constructed from the top performances of fish feeding maximally (16 of 21 fish) and indicated that the risk of cannibalism would be high and permanent except for meal frequencies over five daily meals. Cannibals emerging spontaneously under communal rearing (6 fish L−1, three daily meals) grew more slowly or just at the same rate as predicted by the growth model constructed from siblings selected at random. This indicates that the individuals that become cannibals do not possess higher intrinsic capacities for growth than others.

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

“…Likewise, the question of whether optimal foraging is driven by the capacity of growing as fast as possible, or by the optimization of food conversion efficiency is of limited interest in the particular context of cannibalism, because GCE increases with food intake (and thus with growth). This trend was observed here, but also in every study where the bioenergetics of cannibalistic fishes was investigated (e.g., Baras et al , 2011Baras et al , 2013.…”

“…This observation suggests that the fastgrowing capacities documented here are shared by a substantial proportion of a progeny, and not by just a "happy few" that would be predestined to become cannibals because of their exceptionally high capacities for growth. This trend is not unique among fish species with strong cannibalistic habits (for further discussion on this topic, see Baras and Lucas 2010;Baras 2013;Baras et al 2013). …”

“…Variables and calculations were as in Baras et al ( , 2011Baras et al ( , 2013. All calculations were made on the basis of DM preferentially to WM, as the energy contents of small fish vary substantially with increasing fish size, essentially because of decreasing hydration (Kamler 1992), and estimations of growth or energy transformation on the basis of wet body mass frequently produce biases (Canale and Breck 2013).…”

“…The design of predation experiments was as in Baras et al ( , 2011Baras et al ( , 2013. Briefly in each experiment, a large fish (putative cannibal) was placed for 24 h together with smaller siblings (prey fish) of known wet body mass (WM) in a predation cage (2.0 L, 15 × 15 × 9 [h] cm) that was immersed in a tank of the water recirculation system.…”

“…Information on the allometric variations of mouth and body dimensions has been used often to predict the occurrence or risk of cannibalism (Hecht and Appelbaum 1988;Brabrand 1995;Hseu et al 2003Hseu et al , 2004Hseu et al , 2007Hseu and Huang 2014). In some cases, cannibalistic fishes have been found to ingest siblings near the maximal possible size (e.g., largemouth bass Micropterus salmoides, Johnson and Post 1996; redtail catfish Hemibagrus nemurus, Baras et al 2013), whereas this "maximalistic" behaviour is infrequent with other types of piscivory (Juanes 1994(Juanes , 2003Juanes et al 2002). However, cannibals generally prefer small over large conspecifics (Atlantic cod Gadus morhua, Folkvord and Otterå 1993; walleye pollock Theragra chalcogramma, Sogard and Olla 1994; Arctic charr Salvelinus alpinus, Amundsen et al 1995;snakehead Channa striata, Qin and Fast 1996;dorada Brycon moorei, Baras et al 2000).…”