A Behavioural Assay to Investigate Judgment Bias in Zebrafish

Optimistic and pessimistic cognitive judgement bias modulates the stress response and cancer progression in zebrafish

Cognitive judgement bias in decision-making under ambiguity occurs both in animals and humans, with some individuals interpreting ambiguous stimulus as positive (optimism) and others as negative (pessimism). We hypothesize that judgement bias is a personality trait and that individuals with a pessimistic bias would be more reactive to stressors and therefore more susceptible to stress-related diseases than optimistic ones. Here, we show that zebrafish judgment bias is a consistent behavioral trait over time, and that pessimistic and optimistic fish express phenotype-specific neurogenomic responses to stress. Furthermore, both phenotypes show differential activation of the hypothalamic-pituitary-interrenal axis in response to chronic stress, suggesting that optimists have a lower stress reactivity. Accordingly, optimists seem to be more resilient to disease than pessimists, as shown by a lower tumorigenesis in a zebrafish melanoma line [Tg(mtifa:HRAS-GFP)]. Together these results indicate that judgement bias is paralleled by differences in the stress response with implications for disease resilience.

Cognitive Bias in Adult Zebrafish (Danio rerio): A Systematic Review

OBJECTIVE

In recent years, the use of zebrafish (Danio rerio) as laboratory models has significantly increased. Ensuring their welfare is crucial, with the cognitive bias test emerging as a valuable tool to assess their emotional state. This systematic review examines the application of the cognitive bias test in zebrafish research.

DATA

The review adhered to PRISMA guidelines.

SOURCES

A systematic search was conducted in scientific databases, including PubMed and Scopus, yielding 30 articles. Additionally, one abstract identified through bibliographic screening of selected papers was included.

STUDY SELECTION

Six studies were selected for analysis, and their quality was assessed using SYRCLE's risk-of-bias tool.

RESULTS

Three experimental models were employed to conduct the cognitive bias test in zebrafish, focusing on the relationship between their affective state and environmental conditions, cognitive abilities, and life-history strategies but none of the studies adequately reported the techniques employed to reduce bias.

DISCUSSION

The cognitive bias test proved effective in assessing the emotional state of zebrafish; however, methodological biases may have influenced the results.

CONCLUSION

The cognitive bias test offers valuable insights into how emotional states affect cognitive abilities, responses to environmental changes (e.g., physical enrichment), and stress responses. Further research addressing methodological limitations is necessary to validate these findings and improve data reproducibility.

Stress produces negative judgement bias in cuttlefish

Judgement bias tasks (JBTs) are used to assess the emotional state and welfare of animals in zoos, farms and laboratories, based on the interpretation of an ambiguous or intermediate cue. Animals in positive affective states are more likely to interpret the ambiguous cue positively, whereas animals experiencing negative affect are more likely to interpret ambiguous cues pessimistically. Here, we developed a modified JBT assay for the stumpy-spined cuttlefish, Sepia bandensis, to determine whether cuttlefish exhibit negative affective states resulting from external stressors. Positive and neutral visual cues were presented twice daily until animals learned to associate food with the reinforced visual cue. After training, one treatment group was exposed to combined exposure and handling stress produced by 6 days of impoverished housing and simulated net capture. Our control group received no stress experience. In test trials performed after the stress experience, stressed animals showed higher latencies to approach ambiguous cues, spent significantly less time in rooms with ambiguous cues once they entered, and were less likely to enter first into the ambiguous cue-paired room compared with controls. These behaviours suggest that stress induces pessimistic judgement bias in cuttlefish, the first indication of this capacity in cephalopods.

"Why (Zebra)fish May Get Ulcers": Cognitive and Social Modulation of Stress in Fish

BACKGROUND

In the bestseller book "Why Zebras Don't Get Ulcers", Robert Sapolsky argues that animals do not suffer from stress-related diseases like humans because for them, stress is episodic, while humans in contrast suffer from chronic psychological stress. In particular, the idea that fish cannot experience psychological stress is still prevalent, partly due to the lack of a homologous brain area to the neocortex. However, emerging evidence suggests that teleosts can undergo psychological stress, defined as a subjective and perceptual experience of the stressor, and in recent years, the underlying mechanisms started to be unveiled.

SUMMARY

The occurrence of cognitive appraisal in the assessment of stressors has been demonstrated in fish, indicating that the subjective evaluation of stimulus valence and salience, rather than absolute intrinsic characteristics of the stimulus itself, play a key role in the activation of the stress response. Moreover, individual biases (i.e., cognitive bias) in the cognitive appraisal of stimuli have also been described in fish, with some individuals consistently evaluating ambiguous stimuli as positive (aka optimists) whereas other individuals (aka pessimists) appraise them as negative. As a result, optimists and pessimists show consistent differences in stress reactivity and susceptibility/resilience to disease. Finally, social context has also been shown to modulate the response to aversive stimuli with the behavior of conspecifics either buffering or enhancing the response (i.e., social buffering vs. social contagion).

KEY MESSAGES

Cognitive appraisal of stressors occurs in fish, implying that the stress response is modulated by a subjective and perceptual experience of the stressor. Moreover, interindividual consistent cognitive biases in the appraisal of stressors are also present in fish making some individuals more susceptible to stress-related diseases. Therefore, psychological stress has a health toll in fish, and psychologically stressed fish can potentially have ulcers.

Unexpected appetitive events promote positive affective state in juvenile European sea bass

Some animal species exhibit considerable physiological and behavioural alterations in response to captivity. It has been hypothesized, but rarely tested, that such changes reflect a negative affective state that is associated to this specific context. In the last years, judgement bias measures have emerged as reliable indicators of animal affective state, under the assumption that individuals in a negative affective state are more likely to evaluate ambiguous stimuli as negative and display therefore pessimistic behaviours. Here, we have developed a judgement bias task for juvenile European sea bass (Dicentrarchus labrax) aiming to measure optimism/pessimism in this marine species, which have previously been reported to show important dysregulations in captive settings. Our results show that juvenile sea bass exhibit a considerable bias towards pessimistic behaviours in laboratory settings. Furthermore, juveniles that received an unexpected positive event during the judgement bias test displayed more optimistic responses toward ambiguous stimuli as compared to control fish, indicating a positive change in their affective state induced by the appetitive experience. These results reveal a direct interaction of the internal affective state with decision-making processing under ambiguity in juvenile European sea bass, highlighting therefore the potential of judgement bias tests as a tool for the advancement and improvement of our understanding of welfare in finfish aquaculture.

Smart sharks: a review of chondrichthyan cognition

450 million years of evolution have given chondrichthyans (sharks, rays and allies) ample time to adapt perfectly to their respective everyday life challenges and cognitive abilities have played an important part in that process. The diversity of niches that sharks and rays occupy corresponds to matching diversity in brains and behaviour, but we have only scratched the surface in terms of investigating cognition in this important group of animals. The handful of species that have been cognitively assessed in some detail over the last decade have provided enough data to safely conclude that sharks and rays are cognitively on par with most other vertebrates, including mammals and birds. Experiments in the lab as well as in the wild pose their own unique challenges, mainly due to the handling and maintenance of these animals as well as controlling environmental conditions and elimination of confounding factors. Nonetheless, significant advancements have been obtained in the fields of spatial and social cognition, discrimination learning, memory retention as well as several others. Most studies have focused on behaviour and the underlying neural substrates involved in cognitive information processing are still largely unknown. Our understanding of shark cognition has multiple practical benefits for welfare and conservation management but there are obvious gaps in our knowledge. Like most marine animals, sharks and rays face multiple threats. The effects of climate change, pollution and resulting ecosystem changes on the cognitive abilities of sharks and stingrays remain poorly investigated and we can only speculate what the likely impacts might be based on research on bony fishes. Lastly, sharks still suffer from their bad reputation as mindless killers and are heavily targeted by commercial fishing operations for their fins. This public relations issue clouds people's expectations of shark intelligence and is a serious impediment to their conservation. In the light of the fascinating results presented here, it seems obvious that the general perception of sharks and rays as well as their status as sentient, cognitive animals, needs to be urgently revisited.

Pessimistic cognitive bias is associated with enhanced reproductive investment in female zebrafish

Optimistic and pessimistic cognitive biases have been described in many animals and are related to the perceived valence of the environment. We, therefore, hypothesize that such cognitive bias can be adaptive depending on environmental conditions. In reward-rich environments, an optimistic bias would be favoured, whereas in harsh environments, a pessimistic one would thrive. Here, we empirically investigated the potential adaptive value of such bias using zebrafish as a model. We first phenotyped female zebrafish in an optimistic/pessimistic axis using a previously validated judgement bias assay. Optimistic and pessimistic females were then exposed to an unpredictable chronic stress protocol for 17 days, after which fish were euthanized and the sectional area of the different ovarian structures was quantified in both undisturbed and stressed groups. Our results show that zebrafish ovarian development responded to chronic stress, and that judgement bias impacted the relative area of the vitellogenic developmental stage, with pessimists showing higher vitellogenic areas as compared with optimists. These results suggest that pessimism maximizes reproductive investment, through increased vitellogenesis, indicating a relationship between cognitive bias and life-history organismal decisions.