Less is more: density influences the development of behavioural life skills in trout

Abstract

Theory suggests that habitat structure and population density profoundly influence the phenotypic development of animals. Here, we predicted that reduced rearing density and increased structural complexity promote food search ability, anti-predator response and the ability to forage on novel prey, all behavioural skills important for surviving in the wild. Brown trout were reared at three densities (conventional hatchery density, a fourth of conventional hatchery density and natural density) in tanks with or without structure. Treatment effects on behaviour were studied on trout fry and parr, whereupon 20 trout from each of the six treatment groups were released in an enclosed natural stream and recaptured after 36 days. Fry reared at natural density were faster to find prey in a maze. Moreover, parr reared at natural density were faster to eat novel prey, and showed more efficient anti-predator behaviour than fish reared at higher densities. Furthermore, parr reared at reduced densities were twice as likely to survive in the stream as trout reared at high density. In contrast, we found no clear treatment effects of structure. These novel results suggest that reduced rearing densities can facilitate the development of behavioural life skills in captive animals, thereby increasing their contribution to natural production.

Enriched rearing environment and wild genetic background can enhance survival and disease resistance of salmonid fishes during parasite epidemics

“…While some neutral or negative effects of enriched rearing have been reported (Brockmark et al . ; Brockmark, Adriaenssens & Johnsson ), the current evidence strongly highlights positive effects of environmental enrichment on fish physiology and behaviour. If enriched rearing had the potential to improve physical condition and disease resistance of fish, for instance through improved immune function or lowered stress levels, or decrease the level of exposure to infective stages of parasites, it could reduce the incidence of parasitic infections in aquaculture.…”

A Robotics-Based Behavioral Paradigm to Measure Anxiety-Related Responses in Zebrafish

“…This test has been used in several aquatic species, including sea bass and trout and has been demonstrated to be sensitive to treatments capable of modulating anxiety [47], [58]. This test does not feature an internal control whereby it does not involve an approach-avoidance conflict (that is, internal drive to explore the entire apparatus counterbalanced by the potential danger associated with the dark and with the robot containing compartments).…”

“…The behavioral measures were identical to those measured in the L/D test. Finally, for the shelter-seeking test, we scored the latency to enter the shelter area following the presentation of the threatening stimulus [47]. Data for the L/D test and for the robotics-based predator avoidance test were scored through the Observer 2.0 (Noldus, Wageningen, the Netherlands).…”

“…We then compared experimental data obtained in this test with data obtained in two traditional anxiety- and fear-evoking experimental paradigms [13], [25], [31]–[35]: a light/dark (L/D) preference test [14], [33] and a shelter-seeking test in response to the simulation of an attack performed by a heron (Fig. 1b) impacting the water surface [47]. With respect to the latter, we measured the latency of zebrafish to access a sheltered area.…”

Early Environmental Conditions Shape Personality Types in a Jumping Spider

“…Studies on animal intelligence have shown that increasing complexity in the social and/or in the physical environment induces behavioral and neural responses across different taxa (see e.g., Renner and Rosenzweig, 1987;Schrijver et al, 2004;Gonda et al, 2009;Brockmark et al, 2010;Kotrschal et al, 2012). This suggests that an increase in complexity directs animals to develop enhanced cognitive abilities allowing them to cope with increased information.…”