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The early social environment an animal experiences may have pervasive effects on its behaviour. The social decision‐making network (SDMN), consisting of interconnected brain nuclei from the forebrain and midbrain, is involved in the regulation of behaviours during social interactions. In species with advanced sociality such as cooperative breeders, offspring are exposed to a large number and a great diversity of social interactions every day of their early life. This diverse social environment may have life‐long consequences on the development of several neurophysiological systems within the SDMN, although these effects are largely unknown. We studied these life‐long effects in a cooperatively breeding fish, Neolamprologus pulcher, focusing on the expression of genes involved in the monoaminergic and stress response systems in the SDMN. N. pulcher fry were raised until an age of 2 months either with their parents, subordinate helpers and same‐clutch siblings (+F), or with same‐clutch siblings only (−F). Analysis of the expression of glucocorticoid receptor, mineralocorticoid receptor, corticotropin releasing factor, dopamine receptors 1 and 2, serotonin transporter and DNA methyltransferase 1 genes showed that early social experiences altered the neurogenomic profile of the preoptic area. Moreover, the dopamine receptor 1 gene was up‐regulated in the preoptic area of −F fish compared to +F fish. −F fish also showed up‐regulation of GR1 expression in the dorsal medial telencephalon (functional equivalent to the basolateral amygdala), and in the dorsolateral telencephalon (functional equivalent to the hippocampus). Our results suggest that early social environment has life‐long effects on the development of several neurophysiological systems within the SDMN. [ABSTRACT FROM AUTHOR]

Background: In the best-seller book "Why zebras don't get ulcers" [1] 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, inter-individual consistent cognitive biases in the appraisal of stressors is 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., (S. Karger AG, Basel.)

In this protocol, we describe for the first time a judgment bias paradigm to phenotype the way zebrafish assess ambiguous stimuli. We have developed and validated a protocol for a judgment bias test based on a Go/No-go task, and performed using a half radial maze. After a habituation phase, fish are trained to discriminate between two reference arms [positive (P) and negative (N)]. For this purpose, they experience a positive event (food reward in P), when presented with a specific location/color cue, and a negative event (chasing with net in N), when presented with a different location/color cue. Acquisition of the discrimination learning between P and N is revealed by the latencies to enter the experimental arms of the behavioral maze being significantly lower for the P arm than for the N arm. Once zebrafish are able to discriminate between P and N arms, their latency to enter other maze arms spatially located between P and N [(Near Positive (NP), Ambiguous (A) = half-way between P and N, and Near Negative (NN)] is analyzed. Latencies (L) to enter NP, A and NN maze arms are interpreted as indicating the individual expectancy to experience a reward/punishment on each of them. A judgment bias score (JBS) is calculated from the latencies to enter the P, N, and A arms for each fish [JBS = (L A -L P )*100/(L N -L P )], based on which fish can be classified into an optimistic/pessimistic axis. A JBS below 50 indicates that fish perceive the ambiguous stimulus as a positive one (optimistic bias), while JBS above 50 indicates that fish perceive the ambiguous stimulus as a negative one (pessimistic bias). However, for classification criteria, it could be advantageous to use the method of selecting extreme phenotypes ( e.g. , upper and lower quartiles of the JBS), since JBS in zebrafish falls into a bimodal distribution (unpublished data). Therefore, this protocol provides a unique, inexpensive, and effective alternative to other methods of measuring affective states in zebrafish that might be of great interest to a broad target audience and have a large number of applications. Graphic abstract: Flow chart of the judgment bias protocol in zebrafish., Competing Interests: Competing interestsThe authors declare they have no competing interests., (Copyright © 2022 The Authors; exclusive licensee Bio-protocol LLC.)