Tactile stimulation reduces fear in fish

Oogenesis and in vitro reproduction of the twospot astyanax Astyanax bimaculatus (Linnaeus, 1758) exposed to conspecific alarm substance

Stress situations can be essential to trigger reproduction in fish; however, it may also inhibit it. One of those situations involves the release of the conspecific alarm substance (CAS), a natural stressor, into the water by specific fish epidermal cells after a predator attack. Little is known about the effects of that substance on fish reproduction. This study aimed to evaluate the effects of CAS exposure on the oogenesis and reproduction of the twospot astyanax Astyanax bimaculatus before the hormonal induction for artificial reproduction. No macroscopic or cellular changes in the ovaries were observed for the females exposed to CAS, and the oocyte stages show all females in the same phase of maturation (Spawning Capable). Females exposed to CAS spawned 20 min before the females without exposure. On the other hand, they ovulated only once, whereas the females from the control group ovulated multiple times for approximately two hours after hormonal induction. Moreover, the precocious ovulation of the females submitted to CAS did not generate offspring, since all generated zygotes did not develop. In contrast, the control group females produced more than 11 thousand healthy larvae. Exposing the female fish to CAS during their reproductive management in captivity may reduce breeding success.

Short daylight photoperiod alleviated alarm substance-stimulated fear response of zebrafish

Photoperiod has been well-documented to be involved in regulating many activities of animals. However, whether photoperiod takes part in mood control, such as fear response in fish and the underlying mode(s) of action remain unclear. In this study, adult zebrafish males and females (Danio rerio) were exposed to different photoperiods, Blank (12 h light: 12 h dark), Control (12 h light: 12 h dark), Short daylight (SD, 6 h light: 18 h dark) and Long daylight (LD, 18 h light: 6 h dark) for 28 days. After exposure, fear response of the fish was investigated using a novel tank diving test. After alarm substance administration, the onset to higher half, total duration in lower half and duration of freezing in SD-fish were significantly decreased, suggesting that short daylight photoperiod is capable of alleviating fear response in zebrafish. In contrast, comparing with the Control, LD didn't show significant effect on fear response of the fish. Further investigation revealed that SD increased the levels of melatonin (MT), serotonin (5-HT) and dopamine (DA) in the brain while decreased the plasma level of cortisol comparing to the Control. Moreover, the expressions of genes in MT, 5-HT and DA pathways and HPI axis were also altered consistently. Our data indicated that short daylight photoperiod might alleviate fear response of zebrafish probably through interfering with MT/5-HT/DA pathways and HPI axis.

Long-term body tactile stimulation reduces aggression and improves productive performance in Nile tilapia groups

One concern of the Anthropocene is the effects of human activities on animal welfare, revealing the urgency to mitigate impacts of rearing environments. Body tactile stimulation (TS), like massage therapy, has emerged as an enrichment method to counteract stress and anxiety in vertebrates. In the current study, we evaluated the effects of long-term TS on four-member groups of male Nile tilapia, a worldwide reared species whose socially aggressive behavior is an essential source of stress. We placed a rectangular PVC frame fitted with vertical plastic sticks sided with silicone bristles in the center of aquarium to enable the fish to receive body TS when passing through the bristles. A similar apparatus without bristles was used as the control. Fish subjected to TS for 21 days showed a gradual lowering of overt fights over time, but with no reduction in cortisol or androgen levels. Nevertheless, TS improved the specific growth rate, maintained balanced length/weight gain, and increased feed efficiency, probably owing to the lowered energy expenditure during fights. Thus, we show for the first time that long-term TS provided by a simple device can be used as a tool to improve the welfare and productive performance of territorial fish.

The brain-body disconnect: A somatic sensory basis for trauma-related disorders

Although the manifestation of trauma in the body is a phenomenon well-endorsed by clinicians and traumatized individuals, the neurobiological underpinnings of this manifestation remain unclear. The notion of somatic sensory processing, which encompasses vestibular and somatosensory processing and relates to the sensory systems concerned with how the physical body exists in and relates to physical space, is introduced as a major contributor to overall regulatory, social-emotional, and self-referential functioning. From a phylogenetically and ontogenetically informed perspective, trauma-related symptomology is conceptualized to be grounded in brainstem-level somatic sensory processing dysfunction and its cascading influences on physiological arousal modulation, affect regulation, and higher-order capacities. Lastly, we introduce a novel hierarchical model bridging somatic sensory processes with limbic and neocortical mechanisms regulating an individual's emotional experience and sense of a relational, agentive self. This model provides a working framework for the neurobiologically informed assessment and treatment of trauma-related conditions from a somatic sensory processing perspective.

Looking beyond the Shoal: Fish Welfare as an Individual Attribute

Simple Summary

The fish farming industry is characterized by settings where large numbers of fishes are raised together at high stocking densities, effectively obliterating the individual. Given that animal welfare is an individual attribute that refers to how an animal experiences her world, it follows that ensuring good welfare for the different individuals is difficult in fish farms. In this paper we review evidence supporting the notion that fishes are individuals and fish welfare should thus also be considered at the individual level, examine the ways that animal welfare is assessed in fish farms, evaluate these practices in light of individualized terrestrial animal welfare assessment methods, and make recommendations regarding research that could lead to a better understanding of how to provide each individual fish with good welfare in captivity.

Abstract

Welfare is an individual attribute. In general, providing captive nonhuman animals with conditions conducive to good welfare is an idea more easily applied when dealing with few individuals. However, this becomes much harder—if not impossible—under farming conditions that may imply high numbers of animals living in large group sizes. Although this is a problem inherent to intensive animal farming, it is possibly best exemplified in fish farming, for these practices often rely on extremely high numbers. In this paper we review evidence supporting the notion that fishes are individuals and fish welfare should thus also be considered at the individual level, examine the current state of welfare assessment in the aquaculture industry, evaluate these practices in light of individualized terrestrial animal welfare assessment methods, and make recommendations regarding research that could lead to a better understanding of how to provide each individual fish with good welfare in captivity.

HOX epimutations driven by maternal SMCHD1/LRIF1 haploinsufficiency trigger homeotic transformations in genetically wildtype offspring

The body plan of animals is laid out by an evolutionary-conserved HOX code which is colinearly transcribed after zygotic genome activation (ZGA). Here we report that SMCHD1, a chromatin-modifying enzyme needed for X-inactivation in mammals, is maternally required for timely HOX expression. Using zebrafish and mouse Smchd1 knockout animals, we demonstrate that Smchd1 haplo-insufficiency brings about precocious and ectopic HOX transcription during oogenesis and embryogenesis. Unexpectedly, wild-type offspring born to heterozygous knockout zebrafish smchd1 mothers exhibited patent vertebrate patterning defects. The loss of maternal Smchd1 was accompanied by HOX epi-mutations driven by aberrant DNA methylation. We further show that this regulation is mediated by Lrif1, a direct interacting partner of Smchd1, whose knockout in zebrafish phenocopies that of Smchd1. Rather than being a short-lived maternal effect, HOX mis-regulation is stably inherited through cell divisions and persists in cultured fibroblasts derived from FSHD2 patients haploinsufficient for SMCHD1. We conclude that maternal SMCHD1/LRIF1 sets up an epigenetic state in the HOX loci that can only be reset in the germline. Such an unusual inter-generational inheritance, whereby a phenotype can be one generation removed from its genotype, casts a new light on how unresolved Mendelian diseases may be interpreted.

Hox genes are known to control anteroposterior patterning, including the vertebrate spine. Here Xue et al. show that maternal Smchd1 regulates Hox expression in an epigenetic manner, and that wild type offspring from heterozygous mothers show skeletal homeotic transformations as a result of this dysregulation.

Resilience to stress and social touch

Modern lifestyle and adversities such as the COVID-19 pandemic pose challenges for our physical and mental health. Hence, it is of the utmost importance to identify mechanisms by which we can improve resilience to stress and quickly adapt to adversity. While there are several factors that improve stress resilience, social behavior—primarily in the form of social touch—is especially vital. This article provides an overview of how the somatosensory system plays a key role in translating the socio-emotional information of social touch into active coping with stress. Important future directions include evaluating in humans whether stress resilience can be modulated through the stimulation of low-threshold C-fiber mechanoreceptors and using this technology in the prevention of stress-related neuropsychiatric disorders such as major depressive disorder.

Enrichment for Laboratory Zebrafish-A Review of the Evidence and the Challenges

Simple Summary

The zebrafish is one of the most commonly used animals in scientific research, but there remains a lack of consensus over good practice for zebrafish housing and care. One such area which lacks agreement is whether laboratory zebrafish should be provided with environmental enrichment—additions or modifications to the basic laboratory environment which aim to improve welfare, such as plastic plants in tanks. The need for the provision of appropriate environmental enrichment has been recognised in other laboratory animal species, but some scientists and animal care staff are hesitant to provide enrichment for zebrafish, arguing that there is little or no evidence that enrichment can benefit zebrafish welfare. This review aims to summarise the current literature on the effects of enrichment on zebrafish physiology, behaviour and welfare, and identifies some forms of enrichment which are likely to benefit zebrafish. It also considers the possible challenges that might be associated with introducing more enrichment, and how these might be addressed.

Abstract

Good practice for the housing and care of laboratory zebrafish Danio rerio is an increasingly discussed topic, with focus on appropriate water quality parameters, stocking densities, feeding regimes, anaesthesia and analgesia practices, methods of humane killing, and more. One area of current attention is around the provision of environmental enrichment. Enrichment is accepted as an essential requirement for meeting the behavioural needs and improving the welfare of many laboratory animal species, but in general, provision for zebrafish is minimal. Some of those involved in the care and use of zebrafish suggest there is a ‘lack of evidence’ that enrichment has welfare benefits for this species, or cite a belief that zebrafish do not ‘need’ enrichment. Concerns are also sometimes raised around the practical challenges of providing enrichments, or that they may impact on the science being undertaken. However, there is a growing body of evidence suggesting that various forms of enrichment are preferred by zebrafish over a barren tank, and that enriched conditions can improve welfare by reducing stress and anxiety. This review explores the effects that enrichment can have on zebrafish behaviour, physiology and welfare, and considers the challenges to facilities of providing more enrichment for the zebrafish they house.

Recording Channelrhodopsin-Evoked Field Potentials and Startle Responses from Larval Zebrafish

Zebrafish are an excellent model organism to study many aspects of vertebrate sensory encoding and behavior. Their escape responses begin with a C-shaped body bend followed by several swimming bouts away from the potentially threatening stimulus. This highly stereotyped motor behavior provides a model for studying startle reflexes and the neural circuitry underlying multisensory encoding and locomotion. Channelrhodopsin (ChR2) can be expressed in the lateral line and ear hair cells of zebrafish and can be excited in vivo to elicit these rapid forms of escape. Here we review our methods for studying transgenic ChR2-expressing zebrafish larvae, including screening for positive expression of ChR2 and recording field potentials and high-speed videos of optically evoked escape responses. We also highlight important features of the acquired data and provide a brief review of other zebrafish research that utilizes or has the potential to benefit from ChR2 and optogenetics.

Development of New Food-Sharing Relationships in Vampire Bats

Some nonhuman animals form adaptive long-term cooperative relationships with nonkin that seem analogous in form and function to human friendship [1-4]. However, it remains unclear how these bonds initially form, especially when they entail investments of time and energy. Theory suggests individuals can reduce the risk of exploitation by initially spreading out smaller cooperative investments across time [e.g., 5] or partners [6], then gradually escalating investments in more cooperative partnerships [7]. Despite its intuitive appeal, this raising-the-stakes model [7] has gained surprisingly scarce empirical support. Although human strangers do "raise the stakes" when making bids in cooperation games [8], there has been no clear evidence for raising the stakes during formation of social bonds in nature. Existing studies are limited to cooperative interactions with severe power asymmetries (e.g., the cleaner-client fish mutualism [9]) or snapshots of a single behavior within established relationships (grooming in primates [10-13]). Raising the stakes during relationship formation might involve escalating to more costly behaviors. For example, individuals could "test the waters" by first clustering for warmth (no cost), then conditionally grooming (low cost), and eventually providing coalitionary support (high cost). Detecting such a pattern requires introducing random strangers and measuring the emergence of natural helping behaviors that vary in costs. We performed this test by tracking the emergence of social grooming and regurgitated food donations among previously unfamiliar captive vampire bats (Desmodus rotundus) over 15 months. We found compelling evidence that vampire bats selectively escalate low-cost grooming before developing higher-cost food-sharing relationships.

Premature birth stunts early growth and is a possible driver of stress-induced maternal effects in the guppy Poecilia reticulata

We tested the effects of gestational stress, principally in the form of alarm cue extracted from the skin of conspecifics, on reproduction in female guppies (Poecilia reticulata) and the growth and behaviour of their offspring. Offspring from mothers exposed to alarm cue exhibited stunted growth in the first few days post-partum, which appeared to be mediated by shortening of the gestation period, the length of which directly correlated with growth rate within the first 6 days post-partum. Mature offspring did not differ in behaviour or stress responses compared with controls and so the effects of maternal predation stress did not appear to persist into adulthood. A different form of gestational stress, dietary restriction, did not significantly affect offspring growth, though brood size was reduced, suggesting that the effects of predation stress were not mediated by differences in resource demand or consumption.

Do vampire bats groom others based on need?

Allogrooming provides a window into the social lives of many group-living mammals and birds. The fitness benefits of allogrooming are encouraged by proximate mechanisms that make it physiologically rewarding for both actors and receivers. However, receivers might not always benefit from allogrooming. Some allogrooming decisions might be the actor’s response to cues of the recipient’s need. Other decisions might only be caused by the actor’s motivational state. To test these ideas, we studied what triggers allogrooming in common vampire bats. In test 1, subjects that had experimentally disturbed and wetted fur were more likely to be allogroomed, even when controlling for increased self-grooming. In test 2, allogrooming rates were elevated not only by receiver self-grooming (a cue for receiver need) but also by the actor’s previous self-grooming. Both effects were significantly greater than the effect of self-grooming by third parties. Interestingly, we detected a negative interaction: the positive effect of receiver need on allogrooming was smaller when the actor was previously self-grooming. This is consistent with the hypothesis that there are “receiver-driven” allogrooming decisions, which are responses to recipient need, and “actor-driven” decisions, which are not. We predict that receiver-driven allogrooming will bestow greater benefits to recipients compared with actor-driven allogrooming.

An Automated Assay System to Study Novel Tank Induced Anxiety

New environments are known to be anxiogenic initially for many animals including the zebrafish. In the zebrafish, a novel tank diving (NTD) assay for solitary fish has been used extensively to model anxiety and the effect of anxiolytics. However, studies can differ in the conditions used to perform this assay. Here, we report the development of an efficient, automated toolset and optimal conditions for effective use of this assay. Applying these tools, we found that two important variables in previous studies, the direction of illumination of the novel tank and the age of the subject fish, both influence endpoints commonly measured to assess anxiety. When tanks are illuminated from underneath, several parameters such as the time spent at the bottom of the tank, or the transitions to the top half of the tank become poor measures of acclimation to the novel environment. Older fish acclimate faster to the same settings. The size of the novel tank and the intensity of the illuminating light can also influence acclimation. Among the parameters measured, reduction in the frequency of erratic swimming (darting) is the most reliable indicator of anxiolysis. Open source pipeline for automated data acquisition and systematic analysis generated here and available to other researchers will improve accessibility and uniformity in measurements. They can also be directly applied to study other fish. As this assay is commonly used to model anxiety phenotype of neuropsychiatric ailments in zebrafish, we expect our tools will further aid comparative and meta-analyses.

The zebrafish subcortical social brain as a model for studying social behavior disorders

Social behaviors are essential for the survival and reproduction of social species. Many, if not most, neuropsychiatric disorders in humans are either associated with underlying social deficits or are accompanied by social dysfunctions. Traditionally, rodent models have been used to model these behavioral impairments. However, rodent assays are often difficult to scale up and adapt to high-throughput formats, which severely limits their use for systems-level science. In recent years, an increasing number of studies have used zebrafish (Danio rerio) as a model system to study social behavior. These studies have demonstrated clear potential in overcoming some of the limitations of rodent models. In this Review, we explore the evolutionary conservation of a subcortical social brain between teleosts and mammals as the biological basis for using zebrafish to model human social behavior disorders, while summarizing relevant experimental tools and assays. We then discuss the recent advances gleaned from zebrafish social behavior assays, the applications of these assays to studying related disorders, and the opportunities and challenges that lie ahead.

Sensory ecology of ostariophysan alarm substances

Chemical communication of predation risk has evolved multiple times in fish species, with conspecific alarm substance (CAS) being the most well understood mechanism. CAS is released after epithelial damage, usually when prey fish are captured by a predator and elicits neurobehavioural adjustments in conspecifics which increase the probability of avoiding predation. As such, CAS is a partial predator stimulus, eliciting risk assessment-like and avoidance behaviours and disrupting the predation sequence. The present paper reviews the distribution and putative composition of CAS in fish and presents a model for the neural processing of these structures by the olfactory and the brain aversive systems. Applications of CAS in the behavioural neurosciences and neuropharmacology are also presented, exploiting the potential of model fish [e.g., zebrafish Danio rerio, guppies Poecilia reticulata, minnows Phoxinus phoxinus) in neurobehavioural research.

Tactile stimulation reduces aggressiveness but does not lower stress in a territorial fish

Body tactile stimulation has a positive effect upon highly social animals, such as mammals and cleaner-client coral-reef fish, by relieving stress and improving health. Conversely, some tactile contacts are naturally detrimental, such as those resulted from aggressive interactions. To study whether positive responses from tactile stimulation are generalized among vertebrates, we tested its effect on stress response and aggressive behavior in a territorial fish species, Nile tilapia. We developed an apparatus made of a row of sticks bordered by silicone bristles that was positioned in the middle of the aquarium, and through which fish had to pass to access food, thus receiving tactile stimulation. Isolated fish experienced tactile stimulation for 7 days, and  were assigned to 2 types of stressors: non-social (confinement) or social (aggressive interaction). Each of them had a corresponding control treatment without tactile stimulation. Although fish spontaneously crossed the apparatus, we did not observe a decrease in plasma cortisol levels immediately after stressor application as a response to the use of the apparatus, either for social or non-social treatment. However, tactile stimulation reduced aggressive interaction in the social treatment, showing a positive effect on a territorial fish species, and pointing to a way to improve welfare.

The right touch: Stroking of CT-innervated skin promotes vocal emotion processing

Research has revealed a special mechanoreceptor, called C-tactile (CT) afferent, that is situated in hairy skin and that seems relevant for the processing of social touch. We pursued a possible role of this receptor in the perception of other social signals such as a person’s voice. Participants completed three sessions in which they heard surprised and neutral vocal and nonvocal sounds and detected rare sound repetitions. In a given session, participants received no touch or soft brushstrokes to the arm (CT innervated) or palm (CT free). Event-related potentials elicited to sounds revealed that stroking to the arm facilitated the integration of vocal and emotional information. The late positive potential was greater for surprised vocal relative to neutral vocal and nonvocal sounds, and this effect was greater for arm touch relative to both palm touch and no touch. Together, these results indicate that stroking to the arm facilitates the allocation of processing resources to emotional voices, thus supporting the possibility that CT stimulation benefits social perception cross-modally.

Disrupted-in-Schizophrenia-1 is essential for normal hypothalamic-pituitary-interrenal (HPI) axis function

Psychiatric disorders arise due to an interplay of genetic and environmental factors, including stress. Studies in rodents have shown that mutants for Disrupted-In-Schizophrenia-1 (DISC1), a well-accepted genetic risk factor for mental illness, display abnormal behaviours in response to stress, but the mechanisms through which DISC1 affects stress responses remain poorly understood. Using two lines of zebrafish homozygous mutant for disc1, we investigated behaviour and functioning of the hypothalamic-pituitary-interrenal (HPI) axis, the fish equivalent of the hypothalamic-pituitary-adrenal (HPA) axis. Here, we show that the role of DISC1 in stress responses is evolutionarily conserved and that DISC1 is essential for normal functioning of the HPI axis. Adult zebrafish homozygous mutant for disc1 show aberrant behavioural responses to stress. Our studies reveal that in the embryo, disc1 is expressed in neural progenitor cells of the hypothalamus, a conserved region of the vertebrate brain that centrally controls responses to environmental stressors. In disc1 mutant embryos, proliferating rx3+ hypothalamic progenitors are not maintained normally and neuronal differentiation is compromised: rx3-derived ff1b+ neurons, implicated in anxiety-related behaviours, and corticotrophin releasing hormone (crh) neurons, key regulators of the stress axis, develop abnormally, and rx3-derived pomc+ neurons are disorganised. Abnormal hypothalamic development is associated with dysfunctional behavioural and neuroendocrine stress responses. In contrast to wild type siblings, disc1 mutant larvae show altered crh levels, fail to upregulate cortisol levels when under stress and do not modulate shoal cohesion, indicative of abnormal social behaviour. These data indicate that disc1 is essential for normal development of the hypothalamus and for the correct functioning of the HPA/HPI axis.

Mechanisms of social buffering of fear in zebrafish

Some humans thrive whereas others resign when exposed to threatening situations throughout life. Social support has been identified as an important modulator of these discrepancies in human behaviour, and other social animals also exhibit phenomena in which individuals recover better from aversive events when conspecifics are present - aka social buffering. Here we studied social buffering in zebrafish, by exposing focal fish to an aversive stimulus (alarm substance - AS) either in the absence or presence of conspecific cues. When exposed to AS in the presence of both olfactory (shoal water) and visual (sight of shoal) conspecific cues, focal fish exhibited a lower fear response than when tested alone, demonstrating social buffering in zebrafish. When separately testing each cue's effectiveness, we verified that the visual cue was more effective than the olfactory in reducing freezing in a persistent threat scenario. Finally, we verified that social buffering was independent of shoal size and coincided with a distinct pattern of co-activation of brain regions known to be involved in mammalian social buffering. Thus, this study suggests a shared evolutionary origin for social buffering in vertebrates, bringing new evidence on the behavioural, sensory and neural mechanisms underlying this phenomenon.

Emotion Perception from Face, Voice, and Touch: Comparisons and Convergence

Historically, research on emotion perception has focused on facial expressions, and findings from this modality have come to dominate our thinking about other modalities. Here we examine emotion perception through a wider lens by comparing facial with vocal and tactile processing. We review stimulus characteristics and ensuing behavioral and brain responses and show that audition and touch do not simply duplicate visual mechanisms. Each modality provides a distinct input channel and engages partly nonoverlapping neuroanatomical systems with different processing specializations (e.g., specific emotions versus affect). Moreover, processing of signals across the different modalities converges, first into multi- and later into amodal representations that enable holistic emotion judgments.

Conspecific injury raises an alarm in medaka

In the late 1930s, Karl von Frisch reported that semiochemicals released upon injury, act as alarm substances (Schreckstoff) in fish. In Ostariophysi species, club cells in the epidermis are believed to contain cues related to alarm substance; however, the function of club cells, primarily as reservoirs of alarm substance has been debated. Here, I describe an alarm response in the Japanese rice fish Oryzias latipes (medaka), a member of the order Beloniformes. The response to alarm substance (Schreckreaction) in medaka is characterized by bouts of immobility and an increase in cortisol levels within minutes of exposure to conspecific skin extract. Histological analysis, however, suggests that club cells are either rare or absent in the medaka epidermis. In addition to describing an uncharacterized behavior in a vertebrate popular for genetic and developmental studies, these results support the hypothesis that the primary function of epidermal club cells may be unrelated to a role as alarm substance cells. The existence of similar behavioral responses in two evolutionarily distant but well established laboratory models, the zebrafish and the medaka, offers the possibility of comparative analyses of neural circuits encoding innate fear.