Hunger Induced Perceptional Shift Influence Decisive Behavior In Zebrafish

doi:10.21203/rs.3.rs-4925537/v1

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Hunger Induced Perceptional Shift Influence Decisive Behavior In Zebrafish

https://doi.org/10.21203/rs.3.rs-4925537/v1

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The plasticity of behavioral traits is shaped by a complex interplay of metabolic state and extrinsic factors. All organisms including human beings are subjected to behavioral choices and complex decision-making processes. The normal mechanism underlying the behavioral choice requires flexibility in potential cost and benefit for better survival. Decisive behavior is closely linked to perception, through which organisms evaluate and interpret the available options, consciously or subconsciously, and settle on the best possible choice as the final decision. Decisions to escape from threats and approaching the prey are crucial for the survival of organisms and perception of predatory and prey stimuli influence these decisions. The predatory-prey perception is influenced by feeding state and hunger induces increased aggression and may influence decisive choice. Here zebrafish perceive small black dots as their prey and decide to approach it. In a hungry state, the perception of small dots as prey and the frequency of visits are higher than in a normal well-fed state. The zebrafish was exposed to its sympatric predator (Anabas) and showed avoidance behavior to both dots and predator in a normal state. In a hungry state, zebrafish exposed to both dots and predator, take more risks to approach the dots by avoiding predatory stimuli presented on the same side. These modulations in decisive behavior is triggered by predatory-prey perceptional shifts due to induced feeding state and the decision to take a risk in between life and a nutritional benefit is achieved by a balance between costs and benefits. Our results support, how hunger shifts behavioral decisions from avoidance to approach and thereby influences decisive behavior in zebrafish.

Plasticity

behavioral choice

perception

prey-predator interaction

hunger

zebrafish

Behavior is the principal outcome of the nervous system and is intricate and multifaceted (Gomez-Marin et al., 2014; Anderson & Perona, 2014). To achieve goals, crucial for survival and reproduction, animals need to perform a wide range of behaviors and most importantly they must prioritize these behaviors in a way that caters to their most pertinent needs. The need for food is considered as one of the basic requirements in nature (Smith & Grueter, 2022). Controlled intake of food depending on caloric requirements is very vital for the health and survival of organism. The hypothalamus is regarded as the highly conserved central point for the neurological and biochemical processes responsible for this controlled mechanism (Anand & Brobeck, 1951). Hunger and satiety states are regulated by the opposing action of the caudal and lateral hypothalamus (Wee et al., 2019). In invertebrates, hunger can alter the processing of sensory stimuli and simple behavior like the taste and smell-dependent approaches of food sources (Bargmann, 2012; Inagaki et al., 2014; Longden et al., 2014; Marella et al., 2012). The interoceptive state, hunger is a universally recognized signal that can trigger an extensive shift in behavior, from promoting exploration and acquisition, to dampen competing motivation from pain to social behavior (Smith & Grueter, 2022).

Animals typically encounter food scarcity or even hunger due to seasonal shifts, environmental changes, and variations in the geographical distribution of food in nature (Bar, 2014; Méndez & Wieser, 1993). In the wild, animals are usually confronted with a conflict between hunger and predation risk. This exerts high selective forces on animals and their behavior should be adapted to make the decision (approach or escape) promptly (Burns & Rodd, 2008). Some previous studies are addressing the ecophysiological effects of hunger on fish (Jobling, 1981; Sheridan and Mommsen, 1991; Mehner and Wieser, 1994), and how hunger affects group selection, shoal related parameters, swimming speed (Reebs & Saulnier, 1997; Robinson & Pitcher, 1989), conflicting behavior of fish in response to food and predator (Uehara et al., 2015). A recent spike in the number of behavioral researches using zebrafish confirms its prestigious status as a model organism and the scientific benefits over other species (Kalueff, et al., 2014; Daggett et al., 2019). Zebrafish respond specifically to visual stimuli and respond to their sympatric predators. Even an animated moving image of a predator elicits significant behavioral responses (Gerlai et al., 2009). In spite of predatory prey perception, feeding state influences aggressive behavior in zebrafish. Six-day starved hungry zebrafish show increased aggressiveness and fighting behavior (Nakajo et al., 2020).

Here, we explored how metabolic state influence perceptual shifts in prey-predator interaction and decision-making behavior of zebrafish, using static dots mimicking prey and a natural predator as an aversive stimulus. The ability of hunger to enhance food intake by decreasing satiety and increasing food reward is a well-documented phenomenon (Sternson & Eiselt, 2017). However, the broader impact of hunger on a diverse array of behavior, extending beyond mere food consumption, remains less understood. Hunger can be conceptualized as the integrated neural representation of various stimuli that drive increased appetite, food reward and behavioral adjustments. Behavioral plasticity during energy deficits is therefore crucial, as it reveals how a hungry animal prioritizes its behavior across multiple domains beyond just feeding (Smith & Grueter, 2022). We demonstrate that this behavioral adaptation is significantly influenced by the feeding state. In the nematode C. elegans, food deprivation increases the willingness to cross aversive hyperosmotic barriers (Ghosh et al., 2016). Our findings reveal that hunger shifts zebrafish behavior from typical predator avoidance to approach-oriented strategy, highlighting how food deprivation alters perception and decision-making processes. This shift underscores the impact of hunger on behavioral priorities, where the drive for food can override instinctive threat response.

2.1. Ethical statement

All the experiments involving animals were undertaken with the approval of the Ethics committee of the University of Calicut (426/GO/Re/S/01/CCSEA) and as per the Committee for Control and Supervision of Experiments on Animals (CPCSEA) regulation 2021. All efforts were made to minimize the number of animals used and their suffering.

2.2. Experimental animals

A total of 160 experimentally naive wild-type adult zebrafish (Danio rerio) belonging to AB strain of both sexes were used in this experiment. Fish were acclimated to laboratory conditions for 30 days in continuously aerated dechlorinated tap water. They were maintained in a re-circulating, three-rack standalone zebrafish system at 27 ± 1 °C with a pH of 6.5-7, under a 14-hour light/10-hour dark cycle. The fish were fed once daily with commercial pellet and live cultures of brine shrimp (Artemia salina) and were maintained in these conditions prior to the start of behavioral trials. All fishes were raised under standard conditions (Westerfield, 2000).

2.3. Food Deprivation

All control experiments were done with normal well-fed zebrafish and tests fishes were starved according to previous reports (Nakajo et al., 2020). For the non-starved group, fish were fed twice daily with brine shrimp in the morning and commercial pellet in the evening. The starved group was completely deprived of food for 6 days, during which no fish mortality was observed. Both the non-starved and starved group were kept in individual preholding tanks 16 L (which could hold 20-25 fishes at a time) separated from the original group housed tanks for 6 days before the experiments.

2.4. Behavioural assays

All recording session were conducted between 10 am to 4:30 pm in a temperature-controlled room (28°C) with limited experimenter intervention. The current study involves a battery of different behavioral assays, including exploratory behavior, dot biting paradigm, predatory exposure, and its combination. Experiments were conducted in three chambered glass tank (60 cm L X 15 cm W X 20 cm H) filled with system water up to two-thirds and the experimental zebrafish was introduced into the middle chamber. In all experimental conditions, two side walls of the middle chamber were covered with visual barriers during the habituation period. Following the habituation, the behavioral responses of zebrafish exposed to specific stimuli were recorded. In all cases, a 3-minute habituation time was given and a 6-minute video recording was done using Logitech webcam 720p C270. A sample size of 20 fish was used in each control and test experiment and after each test, the water was removed and refilled to avoid any cues released by the experimental zebrafish which may influence the behavior of the succeeding individuals. Behavioral analysis was performed using Smart 3.0 video tracking software (Harvard Apparatus) and the middle chamber of the three-chambered tank was divided into two equal areas, the stimulus zone (Blue) and the non-stimulus zone (Red).

2.4.1. Exploratory Behavior

The exploratory behavior of the zebrafish was monitored to assess their natural tendencies to explore and interact with an environment devoid of stimulus. The fish were allowed to explore the middle chamber of the tank for a predefined period, typically ranging from 3 to 10 minutes. During this period, the tank is completely free of any external stimuli, such as visual cues or interactive objects, ensuring that the observed behavior is solely indicative of exploratory tendencies. Once the test was over, the experimental fish was carefully taken out and put back into the holding tanks until the beginning of the next recording session. Important behavioral metrics such as total distance traveled, total speed, resting time in stimulus zones, and zone transitions were recorded.

2.4.2. Dot-biting paradigm

Zebrafish were exposed to visual stimuli consisting of small black dots, mimicking prey to evoke natural hunting behavior. Twenty dots, each with an average diameter of 1.5 mm, were randomly distributed across the wall of the tank's middle chamber. The black dots were created using a non-toxic, high-contrast ink to ensure visibility against the tank’s background. This artificial visual cue was designed to simulate innate predatory response in the adult zebrafish. The random distribution of dots was carefully arranged, ensuring that the stimuli were spread evenly to avoid any spatial bias. Control groups with no visual stimuli were also included to distinguish between spontaneous behavior and responses induced by the stimuli. Post-experiment analysis focused on key behavioral parameters, including latency to enter the stimulus zone, frequency of hunting attempts (such as bites at the dots), zone transitions between the stimulus and non-stimulus areas, entries into the stimulus zone, and total time spent near the visual stimuli. This methodological framework was adapted from Filosa et al., (2016) and Bianco et al., (2011) with modifications made to meet the specific needs of this study.

2.4.3. Predator Exposure

In the predatory test fishes were exposed to Anabas, which is a sympatric predator. (Modified from Amar & Ramachandran 2023). The experimental tank is a three-chambered glass tank (60cm length x 20cm height x 20cm width) equally divided and filled two-third with system water. The middle compartment is for the zebrafish, while the other two compartments contained stimulus fish (anabas) and the system water. The control fish were treated similarly, with the left and right compartments remaining unstimulated. Following the removal of the visual barrier, the zebrafish were given three minutes of habituation. The middle compartment was virtually divided into two zones: A non-stimulus zone, which is close to the empty tank and a stimulus zone which is close to the stimulus tank. Behavioral metrics like time spent in stimulus zone (s), latency to enter stimulus zone (s), mean speed (cm/s), resting time in stimulus zone (s), and zone transition (in number) were measured. The presentation of stimuli in each experimental condition was counterbalanced (Ladu et al., 2015).

2.4.4. Dot-biting and predatory Assay

To evaluate both prey capture and predator avoidance behavior, fishes were subjected to two distinct but complementary assays. A combined assay integrating the dot-biting paradigm and predatory exposure was developed. In this novel approach, zebrafish were exposed to visual cue consisting of small black dots-mimicking prey-and simultaneously confronted with predator. The black dots were adhered to the wall of the middle chamber, while the adjacent chamber housed the predator to simulate a realistic predatory threat. The behavioral testing aimed to provide a deeper understanding of zebrafish behavior in the complex setting of predatory threat and prey stimulation.

2.5 Data analysis and statistics

All data analysis was conducted using Graphpad prism 9.5 alongside Python 3.12. Python libraries utilized for scientific computing included NumPy (Harris et al., 2020), SciPy (Virtanen et al., 2020), Scikit-learn (Pedregosa, 2011)and dabest (Ho et al., 2019). All figures were produced using Matplotlib (Hunter, 2007). All statistical tests were conducted using nonparametric, Mann–Whitney U tests for unpaired comparisons (mannwhitneyu from scipy.stats) and two-sided permutation t-test. Heat maps were used to summarize the differences in the time spent in the stimulus zone across various groups. Spearman’s rank correlation analysis was conducted to assess the association between the number of dot bites among the different groups, independent of the testing order. A p-value < 0.05 was considered statistically significant.

3.1. Hunger Induction Affects Exploratory Behavior in Zebrafish

To investigate the effects of hunger on zebrafish exploratory behavior, we used wild-type zebrafish deprived of food for 6 days. We adapted a protocol used to induce starvation from (Nakajo et al., 2020). Figure. 1 represents the effect of food deprivation on the exploratory behavior of control (CNTRL) and hungry (HGRY) zebrafish. The result revealed that the motor activity parameters like, total distance travelled (Fig. 1A, cohen’s d = -1.84 [95.0%CI -2.56, -1.01], two-sided permutation t-test p = 0.0001) and total speed (Fig. 1C; cohen’s d = -1.84 [95.0%CI -2.55, -1.13], two-sided permutation t-test p = 0.0001) were decreased in the starved fish when compared to control, potentially due to the depletion of energy reserves, and reduced motivation to explore or engage in movement. Which limit the fish capacity to sustain normal locomotor activity, reflecting an adaptive strategy to conserve energy during periods of food scarcity (Wang et al., 2006).

While total resting time (Fig. 1B, cohen’s d = 1.29 [95.0%CI 0.897, 1.7], two-sided permutation t-test p = 0.0001) was higher in the HGRY group, the number of zone transitions (Fig. 1D, cohen’s d = -0.457 [95.0%CI -1.24, 0.22], two-sided permutation t-test p = 0.1990) was non-significant, though the test group made fewer transitions compared to the control group. This suggests that food deprivation may significantly increase the amount of resting time, it does not significantly impact the frequency of transitions between zones. This could indicate that although the HGRY group is more sedentary overall, their exploratory behavior remains relatively stable, possibly due to the prioritization of energy conservation over increased activity. Together, these energy state-dependent behavioral adaptations enhance the probability of finding food while reducing the energy expenditure (Smith & Grueter, 2022).

3.2. Visual Stimuli Trigger Prey Capture-related Responses in Hungry fish.

Hungry zebrafish exhibit a pronounced increase in object orientation and prey capture-related behavior, specifically dot biting when exposed to artificial visual stimuli (as black dots) mimicking prey, reflecting their heightened predatory drive. Hunger, as shown by earlier studies (Semmelhack et al., 2014; Bianco & Engert, 2015), alters brain circuits linked to prey detection, increasing an organism's sensitivity to visual cues that resemble prey.

The behavior of the CNTRL+D group exhibited a significant increase in the time spent within the stimulus zone (Fig. 2A&B p = 0.0181) and a markedly higher frequency of bites on black dots compared to controls (Fig. 4B, p = 0.0001). Figure 4.A displays the variability in pairwise relationships of dot bite frequencies highlights the differential impact of the experimental conditions on prey capture behavior across different groups. This suggests that the normal-fed zebrafish also perceive small black dots as prey and show hunting behavior in the form of bites. However, no significant difference was observed in latency to enter the stimulus zone (Fig. 2C&D, p = 0.08175), the number of zone transitions (Fig. 3B, p = 0.4407), or entries into the stimulus zone (Fig. 2E&F, p = 0.4250).

In the comparison between HGRY and HGRY+D groups, the HGRY+D cohort demonstrated significant increase in time spent in the stimulus zone (Fig. 2B, p = 0.0001) and a higher number of dot bites (Fig. 4B, p = 0.0001). This indicates that hungry zebrafish not only recognized the black dots as prey but also spent more time in the stimulus area and displayed heightened biting behavior. Despite these observations, the HGRY+D group showed reduced zone transitions (Fig. 3B) and fewer entries into the stimulus zone (Fig. 2E&F, p = 0.0001), suggesting that while the fish focused their interaction more with the stimulus (prey), their overall exploratory behavior was less dynamic. Figure 2D represents individual density plots that visualize the distribution of latency for zebrafish to enter the stimulus zone, showing the variation in response across different experimental conditions. Additionally, the latency to enter the stimulus zone was not significantly different (Fig. 2D, p = 0.0585), indicating that while the HGRY+D fish showed a stronger predatory response, their initial reaction time to the stimulus was comparable to that of the HGRY group. These results highlight, the addition of prey (black dots) enhances prey-directed behavior in food deprived zebrafish and alters their exploratory behavior pattern.

CNTRL+D and HGRY+D groups revealed that hungry zebrafish (HGRY+D) spent significantly more time in the stimulus zone (Fig. 2B, p = 0.0001) and exhibited a higher number of bites on the black dots (Fig. 4B, p = 0.0001) compared to their well-fed counterparts. This suggests a notable shift in the activity pattern by nutritional status, with hungry fish demonstrating a stronger predatory response to the black dots, interpreting them as prey and increased their engagement. In contrast, HGRY+D fish showed significantly fewer zone transitions (Fig. 3B, cohen’s d = -2.62 [95.0%CI -3.44, -1.61]) and reduced entries to the stimulus zone (Fig. 4E&F, p = 0.0001) relative to CNTRL+D fish. This decrease in exploratory behavior may indicate that, the hungry fish has increased time spent in the stimulus zone, which is associated with a more focused, albeit less exploratory, intense predatory strategy. Our results reveal that the orientation towards these artificial stimuli is closely linked to the motivational state of hunger, which modulates the zebrafish to exhibit predator-like behavior, including increased attention and engagement with prey-like stimuli. This finding also indicates that hunger not only enhances the fish focus on potential food sources but also influences their behavioral patterns to mimic those observed in natural predatory state. This pattern highlights a distinct shift in behavior, transform their normal behavior to a goal-oriented approach, typical of predator-prey interactions.

3.3. Intrinsic Metabolic Demand Prime the Individuals in a Challenging Environment for Risk Taking Behavior

The physiological state of food deprivation has been observed to prime zebrafish for risk-taking behavior in challenging environment, as evidenced by their altered responses to predator cues. Food-deprived zebrafish exhibit increased boldness, spending more time in proximity to predator zone, reflecting a heightened willingness to take risks compared to their control fishes. Animals receiving limited dietary treatments are more likely to exhibit high-risk behavior in a variety of situations involving predation (Moran et al., 2021).

The comparison between CNTRL and CNTRL+PDTR groups, the CNTRL+PDTR fishes exhibited a significantly longer latency to enter the stimulus zone (Fig. 2C&D, p = 0.0004). Additionally, the time spent in the stimulus zone (Fig. 2B, p = 0.0001), the number of zone transitions (Fig. 3B, p = 0.0001), and the resting time within the stimulus zone (Fig. 3A, p = 0.0151) were all significantly reduced compared to the CNTRL group. These findings suggest that the presence of a predator stimulus in the CNTRL+PDTR group induced an aversive response, leading to decreased exploratory behavior and reduced engagement with the stimulus zone. This indicates that the predator stimulus effectively altered the zebrafish behavior, making them more cautious or fear in the presence of a potential threat.

Similar to the above findings, zebrafish in the HGRY+PDTR group displayed a significantly longer latency to enter the stimulus zone (Fig. 2D, p = 0.0221). Also, the zebrafish spent less time in the stimulus zone (Fig. 2B, p = 0.0001), exhibited fewer zone transitions (Fig. 3B, p = 0.0069), and had reduced resting time within the stimulus zone (Fig. 3A, p = 0.0240) compared to the HGRY group. The observed changes reflect an avoidance behavior consistent with heightened threat perception in the presence of a predator.

In the case of CNTRL+PDTR and HGRY+PDTR groups, the HGRY+PDTR demonstrated significantly higher time spent in the stimulus zone (Fig. 2B, p = 0.0001), more zone transitions (Fig. 3B, cohen’s d = 1.27 [95.0%CI 0.405, 2.04]), and increased resting time in the stimulus zone (Fig. 3A, cohen’s d = 0.861 [95.0%CI 0.51, 1.26]). These findings suggest that hunger may drive a more aggressive or bold behavior, potentially mitigating the intensity of fear responses triggered by the predator stimulus. Despite both the CNTRL+PDTR and HGRY+PDTR groups shows aversive behavior to their sympatric predator (anabas), the HGRY+PDTR condition exhibited a significantly heightened approach behavior compared to CNTRL+PDTR, as evidenced by increased time spent in the stimulus zone, more zone transitions, and longer resting time in the stimulus zone. This behavior reflects an adaptive response where the fish weighs the immediate need for food against the potential cost of predation, demonstrating the complex interplay between internal state (like hunger) and external environmental factors (like predatory threats) in decision-making processes. The nutritional state plays a crucial role in contexts involving both direct and indirect predation risk. Similarly, in risk-taking scenarios where physical condition offers a clearer benefit, such as intraspecific contest, the nutritional state becomes a significant factor (Moran et al., 2021). This hunger-driven behavioral shift highlights a complex interaction between motivational states and risk assessment, where the need for food may override the cautionary behavior, typically seen in the presence of a predator.

3.4. Food Deprivation Reverse Aversive Behavior to an Approach Strategy

This study confirms, food deprivation can reverse typical predator avoidance to a more exploratory and approach-oriented strategy. In a predatory environment, food-deprived zebrafish were observed to approach the black dots (prey) rather than the expected fear-driven aversive response seen in well-fed individuals. Similar findings have been reported in earlier studies, where a risk-taking behavior was displayed by fishes following food deprivation (Gotceitas & Godin 1991; Pettersson & Brönmark 1993; Damsgird & Dill 1998; Krause et al., 1998).

The CNTRL+D+PDTR group exhibited a significantly longer latency to enter the stimulus zone (Fig. 2D, p = 0.0001). In addition, there was a notable decrease in the time spent in the stimulus zone (Fig. 2B, p = 0.0001), the number of entries into the stimulus zone (Fig. 2F, p = 0.0001), and the number of bites on the dots (Fig. 4B, p = 0.0001) when compared to CNTRL+D group. These results indicate that the presence of the predator stimulus induces a fear response even in satiated zebrafish, leading to reduced exploration and engagement with the stimulus. In the HGRY+D+PDTR group, both the time spent in the stimulus zone (Fig. 2B, p = 0.0001) and the number of bites on the dots (Fig. 4B, p = 0.0001) were significantly reduced when compared to the HGRY+D group. This reduction reflects an aversive response to the predator stimulus in hungry fish. Despite this, HGRY+D+PDTR zebrafish exhibited a higher number of entries to the stimulus zone (Fig. 2F, p = 0.0002), indicating a risk-taking behavior.

Comparing the CNTRL+PDTR and CNTRL+D+PDTR condition, the CNTRL+D+PDTR group showed a significant reduction in time spent in the stimulus zone (Fig. 2B, p = 0.0483), indicating an increased fear response induced by the predator stimulus. However, other parameters including latency to enter the stimulus zone (Fig. 2D, p = 0.4987), entries to the stimulus zone (Fig. 2F, p = 0.1093), resting time (Fig. 3A), and mean speed (Fig. 3C, p = 0.5968) were not statistically significant. While the HGRY+PDTR and HGRY+D+PDTR, the HGRY+D+PDTR group exhibited a significantly reduced time spent in the stimulus zone (Fig. 2B, p = 0.0001) and resting time in the stimulus zone (Fig. 3A, p = 0.0027). Conversely, the latency to enter the stimulus zone was significantly decreased in the HGRY+D+PDTR group (Fig. 2D, p = 0.0002). This indicates a perceptual shift in hungry fish exposed to both predator and prey stimuli, where prey perception and approach behavior appeared to dominate over predator-induced avoidance behavior, reflecting an increased risk-taking tendency in the hunger state.

In CNTRL+D+PDTR and HGRY+D+PDTR groups, zebrafish in the HGRY+D+PDTR group exhibited a significant increase in time spent in the stimulus zone (Fig. 2B, p = 0.0001), entries to the stimulus zone (Fig. 2F, p = 0.0001), resting time in the stimulus zone (Fig. 3A, cohen’s d = 1.08 [95.0%CI 0.821, 1.49]), and number of dot bites (Fig. 4B, p = 0.0001). Additionally, the latency to enter the stimulus zone was significantly reduced in the HGRY+D+PDTR group (Fig. 2D, p = 0.0001). These findings suggest that hunger drives zebrafish to focus more actively to the stimulus (prey), indicating a shift in the risk-taking behavior even in the presence of predator cues. To determine the frequency of prey capture behavior among the various conditions (CNTRL, HGRY, CNTRL+D, HGRY+D, HGRY+D+PDTR, and CNTRL+D+PDTR), we calculated the average pairwise correlation of the number of dot bites. The analysis revealed that the number of dot bites was negatively correlated between the HGRY+D and CNTRL+D conditions, as well as between the HGRY+D+PDTR and CNTRL+D+PDTR conditions (Fig. 4C). This indicates that as the frequency of prey capture behavior increased in one group, it decreased in the other. With the exception of CNTRL and HGRY, where the approach behavior showed a strong correlation, most paired groups exhibited relatively weak correlations. The prey capture behavior among different conditions are not uniformly consistent, reflecting variability in the extent to which hunger and predator presence influence prey capture.

The increased number of dot bites, higher entries into the stimulus zone, reduced latency, and extended resting time within the stimulus zone illustrate that food-deprived zebrafish are willing to take the risk of encountering a predator by abandoning defensive behavior in favor of securing food. The tendency of risk taking decision during foraging seems to be regulated by the feeding state (Filosa et al., 2016). This shift in behavior, characterized by an increased approach towards prey despite the potential threat, underscores how hunger can alter perception and influence decision-making process in zebrafish. Previous research by Killen et al. (2011) also revealed how intrinsic metabolic demand can affect risk-taking behavior. The observed reversal from aversion to approach in food-deprived zebrafish highlights the profound impact of physiological state on decision-making process, particularly in balancing the trade-off between avoidance and approach.

The reward is one of the most prominent areas in which adult zebrafish has contributed to behavioral genetics. This reward behavior provides animals with an instinctive drive to search for food (Norton & Bally-Cuif 2010). The current study attempted to unveil how the hunger-induced perceptional shift influence the decisive behavior in zebrafish. Hunger can influence behavior through a wide range of processes (Skrynka & Vincent, 2019), including food preferences (Lozano et al., 1999), social decision making (Aarøe & Petersen, 2013; Strang et al., 2017), the general goal-oriented focus on food (Russell, 2006), the risk preferences (Rad & Ginges, 2017), the subjective time perception (Fung et al., 2017), behavior in virtual foraging tasks (Korn & Bach, 2015).

In the normal exploratory test, the starved fish group showed a decline in locomotory activity than well-fed fish i.e., the hungry fish limited their distance travelled and speed. It may be due to the loss of energy through starvation. A previous study reported a compromise in swimming endurance (time or distance) of starved cod Gadus morhua and it was approximately 30% of satiated one (Martinez et al., 2003). In three cyprinids, herring and plaice hunger decreases routine locomotor activity. Such a decline in locomotor activity could be an energy-saving strategy (Blaxter and Ehrlich, 1974; Wieser et al., 1992; Martinez et al., 2003). Contrary to our results, starved gold fish and tetra larvae exhibited a four times faster swimming rate than satiated when tested in a familiar environment (Mikheev et al., 1992). A study carried out in juvenile qingbo, a cyprinid fish species also revealed that fish in feed deprived group presented faster swimming speed, acceleration, and longer inter-individual distances than well-fed cohorts (Zheng & Fu, 2021).

From the dot biting behavioural assays, the normal fed zebrafish perceive small black dots as prey and try to spent time in the stimulus zone and start biting the dots (CNTRL and CNTRL+D). Small spots having a diameter of 5-8⁰are typically interpreted as prey and larger spots as predator and evoke approach and avoidance behavior respectively (Bianco et al., 2015). Dot-biting tendency is also high in hungry zebrafish exposed to dots and the results confirm that feed-deprived fish perceived the small black dots as prey, and decided to approach the dots (HGRY and HGRY+D). In the case of CNTRL+D and HGRY+D, the dot-biting tendency of hungry zebrafish exposed to dots is much higher when compared to normal controls. Here a perceptional shift in which hungry zebrafish exposed to dots perceive small black dots as their prey than a normal well-fed zebrafish exposed to dots, indicates the hungry fish showed an increased tendency to explore in the vicinity of dots and more dot biting frequency. Here the zebrafish approach the prey stimulus (small dots) which is a strategy for fulfilling food requirements for survival. This corroborates with idea of previous reports, where small black circles drifting beneath the visual field of fish predominantly evoke prey capture swims, whereas the large black circles produced escapes. Starved fish chase small objects rather than satiated fish (Filosa et al., 2016). In general food items are smaller than predators so that the animal can effectively employ size categorization to decide whether to access an unknown object or not (Ewert, 1970). Zebrafish larvae make use of information related to the size and speed of the stimulus to differentiate between prey and predator during hunting behavior towards a visual stimulus that resemble prey features (Bianco & Engert, 2015; Semmelhack et al., 2014). A previous study in larval zebrafish based on fluorescent ingestion and hunting bouts reported that food-deprived animals exhibit elevated hunting behavior and prey intake up to 15 minutes after prey presentation (voracious feeding) than normally fed (Wee et al., 2019). Under starving state, larvae are more likely to approach prey-like visual stimuli rather than avoidance. Hunger modulates tectal processing of prey and predator like visual stimuli in zebrafish larvae and increases the tendency to approach small moving dots (Filosa et al., 2016; Barker & Baier, 2015).

The predatory test ensures that the normal well-fed zebrafish show avoidance behavior to the predatory stimulus (CNTRL and CNTRL+PDTR). Zebrafish perceived Anabas as a predator, the predatory perception is due to either genetic predispositions (Bass & Gerlai, 2008) or the large size of Anabas. Here the zebrafish showed an avoidance or escape behavior from the predatory stimulus which is a key element in survival. Satiety state affects additional circuits that further enhance safety against predators during exploration. The fed fish exhibit longer interbout intervals, lower energy exploring bouts, and wider eye divergence. Less movement and widened observation make them less visible to predators (Johnson et al., 2020). Studies have established that zebrafish respond well to fear-inducing predatory stimuli like Indian leaf fish or even an animated moving image of a predator and show behavior like freezing, jumping, and erratic movements (Gerlai et al., 2009; Ahmed et al., 2011). Here HGRY+PDTR group spent considerably less amount of time in the stimulus zone, revealing its avoidance behavior to the predatory stimulus. The zebrafish perceived Anabas as a potential threat and decided to stay away or escape from the predator (HGRY and HGRY+PDTR). The HGRY+PDTR group explored more in the predator zone than CNTRL+PDTR. Time spent in the stimulus zone and freezing (resting time) is higher for starved fish exposed to predator. This indicates that even though fear is induced in hungry zebrafish due to predatory perception, the hunger-induced aggression reduced the intensity of fear and they made more transitions than the control (CNTRL+PDTR and HGRY+ PDTR). Previous studies have proven that starvation and induced hunger will lead to increased aggression and fighting behavior in zebrafish (Nakajo et al., 2020).

From dot biting and predatory test, CNTRL+D+PDTR showed reduced entries, time in the stimulus zone, longer latency to enter the stimulus zone and presented a decreased number of bites. Even though dot is present in both experiments, prey perception of dots and approach behavior is negligible in CNTRL+D+PDTR than in CNTRL+D group. In this case, fear-inducing predatory perception is dominating which is indicated by avoidance behavior (CNTRL+D and CNTRL+D+PDTR). Comparison of HGRY+D with HGRY+D+PDTR showed almost the same trend of behavior pointing to avoidance, increased entries to stimulus zone showing a mild tendency of risk-taking behavior. Previously it has been demonstrated that food-deprived mice tested in elevated plus maze and open field behavioral tests showed reduced basal anxiety level (Li et al., 2019). Starved animals with reduced anxiety-like behavior showed readiness to enter challenging surroundings. This will increase the food foraging behavior, likewise food-deprived mice spent more than 40% of time in the area with a foot shock than mice showing avoidance in normal condition (Padilla et al., 2016). In CNTRL+PDTR and CNTRL+D+PDTR group, it is evident that the predator perception is dominant and prey perception is negligible. In HGRY+PDTR and HGRY+D+PDTR comparison a perceptional shift occurred when hungry zebrafish were exposed to both dots and predator. HGRY+D+PDTR presented reduced latency to enter the stimulus zone and an increased amount of time spent. So here the prey perception and approach behavior dominated over the predatory perception and avoidance behavior. An increase in prey perception induced by hunger elicit an increased tendency to take more risk. The HGRY+D+PDTR group decided to approach the dots (perceived as food) by masking the predatory stimulus. Interestingly there exists a correlation between an individual’s nutritional state and inclination to take risks. Hungry individuals are more likely to take risks, explore their surroundings, and exhibit aggressive behavior (Mikheev et al., 1992; Godin & Crossman, 1994; Chapman et al., 2010). An upsurge in energy demand makes the individual take adverse challenges to optimize foraging and replenish the energy needed for survival (Ariyomo & Watt, 2015). In CNTRL+D+PDTR and HGRY+D+PDTR, a perceptional shift is visible here. Time spent in the stimulus zone, and entries to the stimulus zone are higher, whereas latency was found to be reduced in HGRY+D+PDTR. This supports the notion that the prey perception dominates over the predatory perception and takes risk to approach the dots (which is perceived as prey) even though a predatory stimulus is present. The ability to precisely evaluate sensory inputs and decide the appropriate behavioral response is crucial for one’s survival. When presented with ambiguous stimuli brain needs to perform the task of choosing one action and blocking others (Barker & Baier, 2015). Earlier studies describe, unfed zebrafish larvae executed reduced escapes and more pursuits under the presence of small circles at 7dpf and they were less inclined to flee from circles of intermediate size than fed larvae and this finding confirms the hunger-mediated reduction of aversive behavior. starved larvae exhibited reduced avoidance in response to medium-sized circles (10⁰) (Filosa et al., 2016). These circles are too large to be regarded as food (Semmelhack et al., 2014) and are more likely to be considered as a potential threat. So, this difference in behavior highlights the perceptional shift in decision making by the feeding state. Hunger diminishes predator vigilance since escapes are energy demanding (Matassa & Trussell 2014).

In nature, animals are constantly confronted with choices that affect their survival and well-being (Kristan, 2008). Approach and escape decisions need to be flexible and consider potential risks and benefits. A trade-off between acquiring resources and becoming a resource for others is faced by the animals in a complex, real-time environment. So, an unfed or hungry animal may increase its risk of predation to stop starvation (Lima & Dill 1990; Filosa et al., 2016; Roy et al., 2017). The nervous system has developed to select and produce adaptive behavioral responses by combining information from the surroundings with the internal state (Johnson et al., 2020).

In teleost fish, Hypothalamic-pituitary-interrenal (HPI) axis is responsible for the regulation of defensive behavior to the threat. In hungry fish, the decline in aversive behavior could be related to a decrease in HPI axis activity, evidenced by a reduced level of cortisol in starved larvae compared to satiated ones. This reports the role of the HPI axis and serotonergic system in mediating the effects of hunger on behavior and tectal activity in zebrafish larvae. Starvation changes the visual-motor transformations in the tectum by blocking the HPI axis and enhancing the serotonergic system via stimulation of a particular neuronal population capable of biasing behavioral choice (Filosa et al., 2016). The optic tectum of the zebrafish brain is responsible for the processing of visual objects (Barker & Baier, 2015).

Future research is essential to elucidate the framework underlying risk-taking and decision-making processes that enable organisms to switch between various survival actions, such as prey-predator and predator-prey interactions. Understanding the mechanistic basis of this feedback loop-how organisms balance risk-taking and desire suppression based on survival instincts and internal states-is crucial. A recent study by Kim et al. (2024) highlighted that the hypothalamus interacts with cognitive task-switching regions to facilitate transitions between hunting and escape behavior. Specifically, investigations are needed to mark the network loop and the molecular mechanism involved in prioritizing the representation of two distinct visual stimuli for survival and avoidance.

This behavioral study unfolds how, the hunger-induced perceptional shift influences decisive behavior in zebrafish. The normal exploratory behavior of control and hungry zebrafish exhibited almost uniform exploration but the locomotory activities of hungry zebrafish were compromised due to energy loss by starvation. Even though, normal well-fed zebrafish exhibited dot-biting (prey capture) tendency, it was comparatively high in starved fish due to increased prey perception. Both control and hungry zebrafish perceived the Anabas as a potential threat and exhibited escape behavior but hunger-mediated aggression slightly masked the predatory fear in unfed fish. When the control and hungry zebrafish were exposed to both dots and predator, the prey perception dominated predatory perception and the hungry zebrafish exhibited approach behavior to dots which is perceived as its prey (hunger reduces aversive behaviour). Hunger-induced aggression masks the fear induced by the predatory stimulus to take more risk for a nutritional benefit. In all cases, the decision to approach the prey stimulus and to escape from the predatory stimulus is taken in the light of the prey-predatory perceptions which were influenced by hunger and induced aggression. Intellectual decision-making is essential for survival and hunger induced aggression may cause perceptional shift and biased decision in human beings.

Ethical statement

The University of Calicut's Ethics Committee and the Committee for the Control and Supervision of Experiments on Animals (CCSEA) regulation 2021 were followed for all animal-related research projects. Every effort was made to reduce the number of animals utilised and their suffering.

Consent for publication

Not applicable

Competing interests

The authors have no competing interests or other interests that might be perceived to influence the results and discussion reported in this article.

Authorship contribution statement:

Binu Ramachandran: Conceptualization, Investigation, Writing - original draft, Supervision, Project administration, Funding acquisition. Nimisha C, Atheena Amar, Ashil AK, Dhanusha Sivarajan, Methodology, Formal analysis, Writing - original draft, Investigation. All authors have read and agreed to the published version of the manuscript.

Funding

The Department of Science and Technology, Science Engineering and Research Board (DST-SERB), Government of India is gratefully acknowledged for awarding research funding under the Early Career Research Scheme (ECR/2018/002479) and Seed grant from (U.O. No.16249/2022/Admn) University of Calicut to Dr Binu Ramachandran.

Availability of data and materials

The availability of datasets and materials used in this article can be accessed upon request.

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No competing interests reported.

GA.png
Graphical abstract A schematic representation of different behavioral experiments conducted and their corresponding behavioral outputs. A) Experimental design of normal exploration by control fish, A1) Representative track path & A2) Heat map of normal exploration by control fish. B) Experimental design of normal exploration by hungry fish, B1) Representative track path & B2) Heat map of normal exploration by hungry fish. C) Experimental design of dot biting test by control fish, C1) Representative track path & C2) Heat map of dot biting by control fish. D) Experimental design of dot biting test by hungry fish, D1) Representative track path & D2) Heat map of dot biting by hungry fish. E) Experimental design of predatory test by control fish, E1) Representative track path & E2) Heat map of predatory test by control fish. F) Experimental design of predatory test by hungry fish, F1) Representative track path & F2) Heat map of predatory test by hungry fish. G) Experimental design of dot biting & predatory test by control fish, G1) Representative track path & G2) Heat map of dot biting & predatory test by control fish. H) Experimental design of dot biting & Predatory test by hungry fish, H1) Representative track path & H2) Heat map of dot biting & predatory test by hungry fish.

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Hunger Induced Perceptional Shift Influence Decisive Behavior In Zebrafish

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