Welfare Challenges Influence the Complexity of Movement: Fractal Analysis of Behaviour in Zebrafish

Abstract

The ability to assess welfare is an important refinement that will ensure the good condition of animals used in experimentation. The present study investigated the impact of invasive procedures on the patterns of movement of zebrafish (Danio rerio). Recordings were made before and after fin clipping, PIT tagging and a standard pain test and these were compared with control and sham handled zebrafish. The fractal dimension (FD) from the 3D trajectories was calculated to determine the effect of these treatments on the complexity of movement patterns. While the FD of zebrafish trajectories did not differ over time in either the control or sham group, the FDs of the treatment groups reduced in complexity. The FD of fish injected with different strengths of acetic acid declined in a dose-dependent manner allowing us to develop an arbitrary scale of severity of the treatments. The 3D trajectory plots from some groups indicated the presence of repetitive swimming patterns akin to stereotypical movements. When administered with lidocaine, which has analgesic properties, the movement complexity of fin clipped fish reverted to a pattern that resembled that of control fish. Fractal analysis of zebrafish locomotion could potentially be adopted as a tool for fish welfare assessment.

Acute and chronic stress prevents responses to pain in zebrafish: evidence for stress-induced analgesia

“…This effect of naloxone was seen to a lesser extent in time spent at the bottom, with intermediate values between SF-control and SF-FC. Fractal dimension reduces the 3D complex swimming trajectories of zebrafish to one value and has been applied to a variety of painful treatments in zebrafish to produce an arbitrary scale of pain intensity (Deakin et al, 2019b). Any fractal dimension values above 1.08 are reflective of normal healthy zebrafish; below this value, individuals can be classified as acutely stressed (1.03-1.08), or experiencing pain (mild, 0.97-1.03; moderate, 0.94-0.97; and severe (<0.94).…”

“…Using this software, it was also possible to divide the tank in half horizontally and calculate what percentage of each 25 min video recording zebrafish spent in the bottom half of the tank (% bottom time). Fractal dimension analysis was also applied to each video as described in Deakin et al (2019b). The fractal dimension is a measure of complexity (Mandelbrot, 1967), derived from the 3D movement and swimming coordinates of the focal fish, that produces a single value, the fractal dimension; a more complex swimming pattern was identified by higher fractal dimension values and a more repetitive, less complex pattern was identified by lower fractal dimension values, which has been shown to reflect poor welfare (Deakin et al, 2019b).…”

Ethical considerations in fish research

“…Lidocaine effectively prevents behavioural and physiological alterations in O. mykiss during subcutaneous injection of acetic acid (Mettam et al ., ). Exposure to lidocaine by emersion also ameliorates substantial changes in the behaviour of adult D. rerio subject to caudal‐fin clipping (Schroeder & Sneddon, ; Deakin et al ., ) and was also effective when used with larval D. rerio exposed to noxious chemical and thermal stimuli (Lopez‐Luna et al ., ,b,c,d). Infiltration of rainbow trout with lidocaine appears to damage skeletal muscle and connective tissue with higher concentrations of (10 mg kg −1 ) but not to cause adverse behavioural side‐effects (20 mg kg −1 ), compared with saline infiltration (Chatigny et al ., 2018a,b).…”

“…Examples of studies which have considered the efficacy of three classes of analgesic drugs in fishes, documenting the range of doses investigated, the species employed in the study, side effects including whether the analgesic prevented changes related to noxious stimuli and a comment on analgesic efficacy (based on data fromCurtright et al, 2015;Davis et al, 2006;Deakin et al, 2019;Harms et al, 2005;Lopez-Luna et al, 2017a; …”

Welfare of Fish—No Longer the Elephant in the Room

“…The number of cultured individuals arguably rivals any other commercially farmed species, yet even when the subject of welfare in aquaculture started to be addressed, zebrafish were apparently left behind. Say no more because two studies by Woodward et al [8] and Deakin et al [9] focus on two important topics that impact zebrafish welfare: the first shows that environmental enrichment in zebrafish housing promotes aggression and risk-taking behaviours in zebrafish [8], and the authors explain this with the social and territorial behaviour of the species, in which the enrichment structures provide resources to monopolise; the second suggests a novel method to analyse pain responses to standard experimental procedures in this species. Using fractal analysis of behaviour, the authors create (and validate) a pain intensity scale for zebrafish, and propose that variations in complexity of movement should be a good indicator of welfare in this species [9].…”