One for All and All for One: The Importance of Shoaling on Behavioral and Stress Responses in Zebrafish

Abstract

Zebrafish has been increasingly used in behavioral studies, but data can present high variability. Most studies have been performed using isolated zebrafish, despite their interactive nature and shoaling behavior. We compared adult zebrafish behavior and cortisol levels after exposure to novelty as well as sensitivity to Pentylenetetrazole (PTZ)-induced seizures in animals tested individually or in groups of three (triplets). In the exploratory behavior task, data from single fish and triplets were not significantly different, but single fish data were more disperse in latency, to enter and time spent in the tank upper part, and crossings. In the light-dark task, time in the light zone and crossings were not different between groups, but latency to enter the dark zone and data variability were. We also observed that the latency to reach stage III seizures induced by PTZ was higher in triplets, but data dispersion was not different from single fish. Finally, cortisol levels of fish individually exposed to a novel environment were higher and more variable than triplets, while both groups had higher levels than unmanipulated animals. Thus, when tested individually, zebrafish are more stressed and present more variable behavior due to disruption of their natural shoal strategies. These features can be beneficial or detrimental depending on study aims and should be considered when designing, analyzing, and interpreting zebrafish behavioral data.

Chronic social isolation affects thigmotaxis and whole-brain serotonin levels in adult zebrafish

“…Isolated zebrafish in this study, however, did not show any locomotor hyperactivity in the open-tank. Nevertheless, our results are comparable to those of Pagnussat et al [1], who found no difference in zebrafish tested in isolation or in groups in an exploratory behavior task. In contrast, Kerr [17] reported hypoactivity in zebrafish isolated for 6-months, longer isolation period than what was employed in our current study.…”

“…Social interaction is an important and complex aspect of zebrafish behavior that has started to be analyzed [1,2]; however, neural mechanisms regulating zebrafish social behavior are not well-understood. Similarly, effects of social environment on behavior and physiological indices also remain largely unknown in this species.…”

“…In zebrafish, the behavior of isolated fish has been described as unpredictable and variable [1], with reduction in shoaling, locomotor activity, anxiety and stress reactivity [17,18]. Physiological indices showed that fish isolated prior to and/or during testing had reduced cortisol [4], decreased proliferating cells in sensory areas of the brain [19] and reduced serotonin in response to novelty [2,20].…”

The utility of zebrafish as a model for behavioural genetics

“…The absence of social interaction appears to be stressful; when tested individually fish show increased cortisol levels and behavioural variability compared to group-tested animals [9 ]. Zebrafish begin to shoal between 7 and 87 days post-fertilisation and show correlated strain-dependent changes in DA and 5-HT levels hinting at a neurochemical basis for this behaviour [36].…”

Benzodiazepines alter nucleotide and nucleoside hydrolysis in zebrafish (Danio rerio) brain

“…This species has a fast metabolism and a great sensitivity to drugs (Gebauer et al 2011;Pagnussat et al 2013). Zebrafish absorbs components directly from the water through their gills and accumulates them in different tissues, especially in CNS (Peterson and Macrae 2012), showing thus be an useful model for research in behavioral neuroscience (Rico et al 2011;Ng et al 2012).…”