Fish Behavior Research Articles

Andean Lakes: endangered by natural and anthropogenic threats

The Andes mountains extend North-South in a latitudinal gradient of 8,500 km. Due to the great climatic variety and the peculiar north-south orographic distribution, lakes are very diverse, including different lake origins and very contrasting morphometries. Here, we reviewed more than 700 ecological studies on Andean lakes to identify the main threats to these freshwater systems. The most important threats are UV radiation, changes in water balance, eutrophication, all three interacting with climate change, alien species introduction, and mining. Ultraviolet radiation is an important factor in Andean lakes not only because of the altitude but also because many lakes are included in the Antarctic ozone hole. The introduction of alien species, particularly exotic salmonids, also had detrimental effects, affecting native fish populations and behaviour, and endemic species by disrupting the indigenous food web. Eutrophication and browning caused by human activities, including land use interacting with climate change, are increasing in Andean lakes causing a decrease in water quality. Finally, mining can cause water contamination (both groundwater and surface water) by chemicals emitted from mining processes thus, producing a loss of biodiversity. Although an important number of Andean lakes have been declared as RAMSAR sites because of their uniqueness and their extreme conditions, they are subject to significant human impacts. Here, for the first time, we identify these impacts all along the Andes, however, further studies at different scales are mandatory if we pretend to understand, conserve, and manage Andean lakes.

Imazalil and prochloraz toxicokinetics in fish probed by a physiologically based kinetic (PBK) model.

Azole fungicides are highly suspected endocrine disruptors (EDs) and are frequently detected in surface water. Among them, there are prochloraz (PCZ), a commonly used moleculefor ED studies, and imazalil (IMZ), a highly suspected ED. Little is known about their toxicokinetic (TK) behavior in fish. Hence, research suggested that an improved risk assessment could be achieved by gaining insight into their TK behavior. The aim of this study is to understand and model the TK of both substances in different fish species, irrespective of the scheme of exposure. TK data from the literature were retrieved including different modes of exposure (per os and waterborne). In addition, two experiments on zebrafish exposed to either IMZ or PCZ were performed to address the lack of in vivo TK data. A physiologically based kinetic (PBK) model applied to IMZ and PCZ was developed, capable of modeling different exposure scenarios. The parameters of the PBK model were simultaneously calibrated on datasets reporting internal concentration in several organs in three fish species (original and literature datasets) by Bayesian methods (Monte Carlo Markov Chain). Model predictions were then compared to other experimental data (i.e., excluded from the calibration step) to assess the predictive performance of the model. The results strongly suggest that PCZ and IMZ are actively transported across the gills, resulting in a small fraction being effectively absorbed by the fish. The model's results also confirm that both molecules are extensively metabolized by the liver into mainly glucuronate conjugates. Overall, the model performances were satisfying, predicting internal concentrations in several key organs. On average, 90% of experimental data were predicted within a two-fold range. The PBK model allows the understanding of IMZ and PCZ kinetics profiles by accurately predicting internal concentrations in three different fish species regardless of the exposure scenario. This enables a proper understanding of the mechanism of action of EDs at the molecular initiating event (MIE) by predicting bioaccumulation in target organs, thus linking this MIE to a possible adverse outcome.

Behavioral dysregulation in Nile tilapia (Oreochromis niloticus, GIFT) post-Streptococcus agalactia infection: Role of the microbiota-gut-brain axis

In the aquatic farming industry, understanding the factors affecting fish behavior is crucial, particularly in response to infections that compromise welfare and productivity. Swimming performance is a key life history trait critical to their ecology. This study explores the swimming behavior imbalance in Nile tilapia (Oreochromis niloticus, GIFT) post-infection with Streptococcus agalactiae (GBS), a common pathogen responsible for significant losses in aquaculture. We focused on how the microbiota-gut-brain axis influences the behavioral response of tilapia to GBS infection. Behavioral changes were quantified by measuring collision times and swimming speeds, which decreased significantly following infection. This behavioral downturn is mediated by alterations in the microbiota-gut-brain axis, evidenced by increased levels of monoamine neurotransmitters (serotonin, norepinephrine, and dopamine) in the brain and intestinal tissues. The study utilized pharmacological agents, the 5-HT1A receptor agonist (8-OH-DPAT) and antagonist (WAY-100635), to investigate their efficacy in mitigating these behavioral and biochemical changes. Both agents partially restored normal behavior by adjusting neurotransmitter concentrations disrupted by GBS infection. Additionally, a notable increase in the relative abundance of Streptococcus within the gut microbiota of infected fish highlights the potential role of specific bacterial populations in influencing host behavior. This research provides novel insights into the complex interactions between pathogen-induced gut microbiota changes and Nile tilapia's behavioral outcomes, highlighting potential avenues for improving fish health management through microbiota-targeted interventions.

Mortality events associated with microsporidian, Spraguea sp., in White Trevally culture in Japan.

In 2021, White Trevally or Striped Jack cultured in the western part of Japan exhibited mild, but chronic mortalities from late September through early October. The cumulative mortality rate was approximately 0.02% per a net pen containing approximately 50,000 fish. Although the cumulative mortality rate was not high, most of the fish in net pens showed characteristic gross signs and an abnormal swimming behaviour. The body of diseased fish became pale and the yellow lines on the lateral sides of fish body became darken. In addition, silver lines along the dorsal fin became apparent. Loss of schooling behaviour was noted during the mortality event. In addition, affected fish became lethargic and failed to swim against current, or frequently stopped swimming and sank to the bottom of net pens after feeding. The goal of this study was to identify the cause of the mortality event. To achieve the goal, we used histopathology and metatranscriptome analysis. Histopathological examination revealed that xenoma of microsporidian were frequently observed in the nerve axon in the brain and spinal cord. Spores observed in the sections were stained with a fluorescent dye, Uvitex 2B, indicating those spores are microsporidian. The data from metatranscriptome analysis indicated that the microsporidian is Spraguea sp. The microsporidian was frequently detected from diseased fish with similar symptoms collected in the same region, suggesting that the microsporidian was highly associated with abnormal swimming behaviour of fish.

Histological investigation of the liver of freshwater fish Cyprinus carpio after intoxication with Ibuprofen

Water contamination has a detrimental impact on streams and rivers, leading to a reduction in the diversity of terrestrial, aquatic, and aerial species. Furthermore, it disrupts the intricate equilibrium of existence. Pharmaceuticals are artificial compounds that belong to several chemical families and exhibit a diverse array of environmental biochemical responses, rendering them the most recent group of pollutants in all aquatic environments. The present study investigated the impact of Ibuprofen on freshwater fish Cyprinus carpio by determining the LC50 value of Ibuprofen during exposure to various concentrations for 24, 48, 72, and 96 hours in sets of aquariums at a concentration of 0.23ml/L. To investigate the impact of Ibuprofen on fish C. carpio, the study evaluates the effects of a sublethal concentration of 1/10th (0.023ml/L) of Ibuprofen LC50 on fish liver histology over a period of 7, 14, 21, and 28 days in both control and treatment aquarium cultures. Following exposure to a sublethal dose of Ibuprofen, significant changes in the behavior of fish and disruption of normal physiology were observed. These changes were clearly displayed through nuclear degeneration, cellular edema, cytoplasmic degeneration, altered hepatocytes, formation of vacuole, increased sinusoidal space, altered central vein, and degeneration of sinusoid. These results indicated that the release of pharmaceuticals had a significant negative impact on fish health and highlighted deterioration in water quality and the ecology of water resources .

Modulation of the internal wave regime over a tropical seamount ecosystem by basin-scale oceanographic processes

Shallow seamounts are becoming increasingly recognised as key habitats for conservation due to their role as biological refuges, particularly throughout oligotrophic oceans. Traditionally, Taylor caps have been invoked as the mechanism driving biomass aggregation over seamounts but emerging evidence based on higher resolution measurements highlights the importance of internal waves (IW) to the local ecosystem. These waves can flush the benthic habitat with cool water from depth and impact on nutrient supply over short time scales through turbulent mixing that may also influence fish behaviour. They are dependent on the regional stratification, however, and thus influenced by planetary-scale variability in oceanographic conditions. We present here detailed observations of the internal wave regime over a shallow seamount, called Sandes, in the central Indian Ocean throughout different phases of the Indian Ocean Dipole (IOD) that modulated the regional stratification. A deep thermocline, caused by the 2019 IOD event precluded internal wave activity over the summit, whereas a thermocline collocated with the summit during 2020 when the IOD reversed polarity resulted in a 30 m amplitude internal tide signal (t ∼ 12.5 h). A shallow thermocline, observed during 2022, resulted in propagation of IWs over the summit with less visible internal tide. Harmonic analysis shows the presence of high frequency waves (t ∼ 15 min) on both flanks of the seamount during 2020 & 2022, which are likely a result of local shear instability, whereas 2019 shows an asymmetric response, potentially due to the strong background current and suppression of the thermocline beneath the depth of the summit. The potential importance of the waves over the summit to the local ecosystem may be attributed to the elevated turbulence measured at the thermocline during internal wave propagation, with ε > 10-5 W kg-1 routinely observed. Our results highlight the ability of thermocline depth to act as a gating condition for internal wave evolution over the summit. These results show that, whilst the water column exhibits variability at short spatiotemporal scales compared to the frequently cited Taylor cap dynamics, it is also regulated by the wider basin scale processes. Thus, a more integrated approach is needed when assessing these dynamic and environmentally critical habitats to include the effects of physical oceanographic controls across multiple spatiotemporal scales.

In-depth histological, lectin-histochemical, immunohistochemical and ultrastructural description of the olfactory rosettes and olfactory bulbs of turbot (Scophthalmus maximus).

Chemical communication through olfaction is crucial for fish behaviours, mediating in socio-sexual behaviours as reproduction. Turbot, a flatfish with significant aquaculture production, possesses a well-developed olfactory system from early developmental stages. After metamorphosis, flatfish acquire their characteristic bilateral asymmetry with an ocular side facing the open water column, housing the dorsal olfactory rosette, and a blind side in contact with the sea bottom where the ventral rosette is located. This study aimed to address the existing gap in specific histological, ultrastructural, lectin-histochemical and immunohistochemical studies of the turbot olfactory rosettes and olfactory bulbs. We examined microdissected olfactory organs of adult turbots and premetamorphic larvae by using routine histological staining techniques, and a wide array of lectins and primary antibodies against G-proteins and calcium-binding proteins. We observed no discernible structural variations in the olfactory epithelium between rosettes, except for the dorsal rosette being larger in size compared to the ventral rosette. Additionally, the use of transmission electron microscopy significantly improved the characterization of the adult olfactory epithelium, exhibiting high cell density, small cell size, and a wide diversity of cell types. Moreover, specific immunopositivity in sensory and non-sensory cells provided us of essential information regarding their olfactory roles. The results obtained significantly enriched the scarce morphological and neurochemical information available on the turbot olfactory system, revealing a highly complex olfactory epithelium with distinct features compared to other teleost species, especially with regard to olfactory cell distribution and immunolabelling patterns.

Influence of humic acids on growth performance, bravery, stress resistance, antioxidant activity, and immune gene expression in male Siamese fighting fish (Betta splendens)

The current study investigated the effects of a humic acid supplement on the growth performance, antioxidant enzyme activity, immune-related genes, behavior and endocrinology of male Betta splendens fish. Fish species that are naturally exposed to high levels of humic substances in their environment are likely to perform better under captive conditions when given these substances. In this study, fish were fed a diet containing 0, 0.5 %, 1 %, and 1.5 % humic acid for six weeks. The results showed no significant differences in growth and feeding parameters between treatments (p > 0.05). The fish with a diet of 1.5 % humic acid showed more aggressive behavior in the mirror test than the control group (p < 0.05). In contrast, the fish fed a diet containing 1 % and 1.5 % humic acid showed a higher level of activity in the test with new objects than the control group (p < 0.05). The testosterone levels after aggression were significantly higher in the fish fed diets containing 1 % and 1.5 % humic acid than in the control group (p < 0.05). In addition, the humic acid-treated fish showed lower oxidative stress and cortisol production in common aquaculture stressors than the control (p < 0.05). Gene expression analysis showed upregulation of immune-related genes, including β-defensin 1, c-type lysozyme, interleukin-1β, and tumor necrosis factor-α, in response to humic acid supplementation compared to control (p < 0.05). Overall, the results of this study indicate that a diet containing 1 % humic acid has a positive effect on the physiology, immunology, and behavior of male B. splendens.

Learning obstacle avoidance and predation in complex reef environments with deep reinforcement learning

The reef ecosystem plays a vital role as a habitat for fish species with limited swimming capabilities, serving not only as a sanctuary and food source but also influencing their behavioral tendencies. Understanding the intricate mechanism through which fish adeptly navigate the moving targets within reef environments within complex water flow, all while evading obstacles and maintaining stable postures, has remained a challenging and prominent subject in the realms of fish behavior, ecology, and biomimetics alike. An integrated simulation framework is used to investigate fish predation problems within intricate environments, combining deep reinforcement learning algorithms (DRL) with high-precision fluid-structure interaction numerical methods-immersed boundary lattice Boltzmann method (lB-LBM). The Soft Actor-Critic (SAC) algorithm is used to improve the intelligent fish's capacity for random exploration, tackling the multi-objective sparse reward challenge inherent in real-world scenarios. Additionally, a reward shaping method tailored to its action purposes has been developed, capable of capturing outcomes and trend characteristics effectively. The convergence and robustness advantages of the method elucidated in this paper are showcased through two case studies: one addressing fish capturing randomly moving targets in hydrostatic flow field, and the other focusing on fish counter-current foraging in reef environments to capture drifting food. A comprehensive analysis was conducted of the influence and significance of various reward types on the decision-making processes of intelligent fish within intricate environments.

Baseline polycyclic aromatic hydrocarbon maternal transfer data in Lesser Numbfish Narcine brasiliensis (Elasmobranchii: Batoidea) from an impacted estuary in Southeastern Brazil

Maternal offloading of polycyclic aromatic hydrocarbons (PAHs) poses a significant exposure route for developing embryos, with implications for subsequent generations. Despite known developmental effects regarding fish physiology and behavior, maternal PAH transfer assessments in elasmobranchii are still lacking. This study investigated PAH contamination and maternal transfer in one female Lesser Numbfish (Narcine brasiliensis) electric ray and seven embryos for the first time. Naphthalene was identified as the predominant low molecular weight PAH, and dibenzo[a,h]anthracene was the most abundant high molecular weight compound. Most embryos exhibited some level of PAH exposure, with varying accumulation patterns potentially influenced by size, developmental stage, and yolk absorption rates. Further investigation is warranted to understand the impacts of PAH maternal offloading on elasmobranchii uterine contents and embryos.

Dining in danger: Resolving adaptive fish behavior increases realism of modeled ecosystem dynamics.

Animals occupying higher trophic levels can have disproportionately large influence on ecosystem structure and functioning, owning to intricate behavioral responses to their environment, but the effects of behavioral adaptations on aquatic ecosystem dynamics are underrepresented, especially in model studies. Here, we explore how adaptive behavior of fish can affect the dynamics of aquatics ecosystems. We frame fish behavior in the context of the central trade-off between feeding and predation, calculating the optimal level of feeding determined by ambient food availability and predation risk. To explore whole-ecosystem consequences of fish behavior, we embed our behavioral model within the Water Ecosystems Tool (WET), a contemporary end-to-end aquatic ecosystem model. The principle of optimality provides a robust and mechanistic framework for representing animal behavior that is relevant for complex models, and can provide a stabilizing effect on model dynamics. The model predicts an emergent functional response similar to Holling type III, but with richer dynamics and a more rigorous theoretical foundation. We show how adaptive fish behavior works to stabilize food web dynamics compared to a control model with no optimal behavior, and how changing the strength of the underlying trade-off has profound effects on trophic control and food web structure. Furthermore, we demonstrate how including fish behavior allows for an overall more realistic response of the model system to environmental perturbation in the form of nutrient enhancement. We discuss the structuring effects of behavioral adaptations in real ecosystems, and how approaches like this one may benefit aquatic ecological modeling. Our study further highlights how a mechanistic approach based on concepts from theoretical ecology can be successfully implemented in complex operational models resulting in improved dynamics and descriptive power.

Hypothalamic integration of nutrient sensing in fish.

The hypothalamus plays a crucial role in regulating feeding behavior in fish. In this Review, we aim to summarise current knowledge on specific mechanisms for sensing glucose, fatty acids and amino acids in fish, and to consider how this information is integrated in the hypothalamus to modulate feed intake. In fish, specific neuronal populations in the nucleus lateralis tuberalis (NLTv) of the hypothalamus are equipped with nutrient sensors and hormone receptors, allowing them to respond to changes in metabolite levels and hormonal signals. These neurons produce orexigenic (Npy and Agrp) and anorexigenic (Pomc and Cart) neuropeptides, which stimulate and suppress appetite, respectively. The modulation of feeding behavior involves adjusting the expression of these neuropeptides based on physiological conditions, ultimately influencing feeding through reciprocal inhibition of anorexigenic and orexigenic neurons and signalling to higher-order neurons. The activation of nutrient sensors in fish leads to an enhanced anorexigenic effect, with downregulation of agrp and npy, and upregulation of cart and pomc. Connections between hypothalamic neurons and other populations in various brain regions contribute to the intricate regulation of feeding behaviour in fish. Understanding how feed intake is regulated in fish through these processes is relevant to understanding fish evolution and is also important in the context of aquaculture.

The water content, apoptosis, and proliferation of the brain in marine medaka affected by seawater acidification.

A possible explanation for ocean acidification-induced changes in fish behavior is a systemic effect on the nervous system. Three biological barriers at the blood-brain interface effectively separate the brain from the body fluids. It is not known whether fish brain regions in contact with these barriers are affected by acidification. Here, we studied structural changes in medaka (Oryzias melastigma) brain regions contacting cerebrospinal fluid (CSF) after short-term (7 days) CO2 exposure. The brain water content decreased significantly and the superficial structure of the pia mater was changed, but there was no obvious damage to the internal structures of the brain after seawater acidification. Seawater acidification also led to an increase in apoptosis and a decrease in the number of proliferative cells in brain areas contacting CSF. These results indicate that the structure of CSF-contacting brain regions in medaka was affected by seawater acidification, and the brain responded to seawater acidification stress by increasing apoptosis and reducing proliferation.

Exposure to neonicotinoid pesticides induces physiological disorders and affects color performance and foraging behavior in goldfish.

We investigated the effects of neonicotinoid pesticides (NEOs) on the spontaneous swimming and foraging behavior, as well as the morphological and physiological changes of goldfish. Most fish reared in thiamethoxam (THM)-sprayed rice fields showed the scales easily peeled off, and increased ascites. Some individuals showed decreased bio-defense activity and low plasma Ca2+. Similar changes were found in the exposure test to THM (1.0 and 20.0 μg/L) and dinotefuran (1.2 and 23.5 μg/L). Next, the effects of a low concentration of THM (1.0 μg/L) on the spontaneous swimming and foraging behavior of fish were examined. Fish exposed to THM for 1 week became restless and had increased the swimming performance, especially under natural light, white LED lighting and blue LED lighting. Goldfish exposed to THM had also increased intake of shiny white beads under green LED illumination. These results indicate that the exposure to NEO, even for a short period and at low levels, not only suppressed bio-defense activities and metabolic abnormalities, but also stress response, the swimming and foraging behavior of the fish are likely to be significantly suffered.

Sex, drugs, and zebrafish: Acute exposure to anxiety-modulating compounds in a modified novel tank dive test

This study investigated the effects of anxiogenic and anxiolytic drugs on zebrafish (Danio rerio) behaviour using a modified novel tank dive test with higher walls and a narrower depth. Zebrafish were administered chondroitin sulfate, beta-carboline, delta-9-tetrahydrocannabinol (THC), ethanol, and beta-caryophyllene, and their behaviours were evaluated for geotaxis, swimming velocity, and immobility. Both anxiogenic and anxiolytic compounds generally increased bottom-dwelling behaviour, suggesting that the tank's modified dimensions significantly influence zebrafish responses. EC50 values for ethanol showed a lower threshold for velocity reduction compared to zone preference. Chondroitin sulfate uniquely caused a sex-specific increase in male swimming velocity, whereas no other sex-differences were observed with any compound. Interestingly, the presence of drug-treated fish did not alter the behaviour of observer fish, suggesting limited social buffering effects. The findings underscore the complexity of zebrafish behavioural phenotypes and highlight the need for considering tank dimensions and multiple behavioural parameters to accurately assess the effects of anxiety-modulating drugs. This study demonstrates the utility of the modified novel tank dive test in providing nuanced insights into the behavioural effects of different pharmacological agents in zebrafish.

Advancements in Research on Cichlid: Reproductive Biology, Social Structure, and Communication

The social behavior of cichlid fish emerged as a captivating subject within the realm of ichthyological research. The sociality of these aquatic organisms often encompasses a wealth of intricate elements. Within this complexity, the reproductive biology of cichlids was observed to mirror the characteristics pivotal for progeny propagation and population development. Their social structures were characterized by stringent hierarchies and occupational specialization among individuals. Communication mechanisms were found to be instrumental in ensuring the timely exchange of information across members of the species. Furthermore, population behaviors served as vital conduits, maintaining the cohesion of the aforementioned elements and securing the seamless operation of this organic system. Given these aspects, this study chose these topics as entry points for inquiry, synthesizing recent scholarly work on cichlid sociality to retrace the trajectory of research in this field. This retrospective analysis was conducted to distill clear future directions based on the examined data. The research undertaken provided a scientific reference poised to enhance further inquiry into the enigmatic subject of cichlid sociality, laying a robust foundation for both advancing the study of these fishes and fostering their conservation.

Efficacy of clove oil and rosewood oil as anesthetics on goldfish (Carassius auratus)

Anesthetics have an essential role in aquaculture operations because they minimize physical injury during various handling practices such as sampling, weighing, length measurement and tagging, which decreases stress on fish. Many fish farmers are involved in using alternative fish anesthetic agents with minimal side effects to life such as herbal essential oils. This study aims at investigating the efficacy of clove oil and rosewood oil as anesthetics on goldfish Carassius auratus. Anesthesia effect of both oils was tested in six different concentrations (i.e., 100, 150, 200, 250, 300 and 350 mg/l of water) on ten fish between 6–25 g weight and 9–14 cm length. The efficacy of both oils was assessed on the basis of the fish behavior. The induction time (min) was assessed by loss of swimming (LS), partial loss of equilibrium (PLE), final loss of equilibrium (FLE), and medullar collapse (Mc). The fish were observed for balance and response to a tactile stimulus in each treatment. Both clove oil and rosewood oil contributed well as anesthetics as they caused loss of equilibrium and swimming ability in the goldfish. In contrast, clove oil generated more rapid induction, prolonged recovery, and a narrow margin of safety. Fish farmers should use natural and environment friendly anesthetic agents instead of chemical ones, as they may alter negatively the growth and health of fish.

Contextual fear conditioning in zebrafish: Influence of different shock frequencies, context, and pharmacological modulation on behavior

Contextual fear conditioning is a protocol used to assess associative learning across species, including fish. Here, our goal was to expand the analysis of behavioral parameters that may reflect aversive behaviors in a contextual fear conditioning protocol using adult zebrafish (Danio rerio) and to verify how such parameters can be modulated. First, we analyzed the influence of an aversive stimulus (3 mild electric shocks for 5 s each at frequencies of 10, 100 or 1000 Hz) on fish behavior, and their ability to elicit fear responses in the absence of shock during a test session. To confirm whether the aversive responses are context-dependent, behaviors were also measured in a different experimental environment in a test session. Furthermore, we investigated the effects of dizocilpine (MK-801, 2 mg/kg, i.p.) on fear-related responses. Zebrafish showed significant changes in baseline activity immediately after shock exposure in the training session, in which 100 Hz induced robust contextual fear responses during the test session. Importantly, when introduced to a different environment, animals exposed to the aversive stimulus did not show any differences in locomotion and immobility-related parameters. MK-801 administered after the training session reduced fear responses during the test, indicating that glutamate NMDA-receptors play a key role in the consolidation of contextual fear-related memory in zebrafish. In conclusion, by further exploring fear-related behaviors in a contextual fear conditioning task, we show the effects of different shock frequencies and confirm the importance of context on aversive responses for associative learning in zebrafish. Additionally, our data support the use of zebrafish in contextual fear conditioning tasks, as well as for advancing pharmacological studies related to associative learning in translational neurobehavioral research.

Fish Behavior, Mortality, Diet, and Movement Following a Monsoonal Spate in the San Juan River, Utah, USA

Fish Behavior, Mortality, Diet, and Movement Following a Monsoonal Spate in the San Juan River, Utah, USA

Kiss1 kisspeptin of bony fish and mammalian kisspeptin analogs enhance the communicative behavior of &lt;i&gt;Danio rerio&lt;/i&gt; induced by social isolation

BACKGROUND: Rodents are often used as a social isolation model. This study investigated the effects of social isolation on Danio rerio. These animals form groups and social hierarchies and exhibit complex social interactions similar to rodents. The expression of some brain genes of fish reared in isolation was found to be different from individuals reared in a group. AIM: This study aimed to investigate the effect of kisspeptins on the social behavior of Danio rerio in social isolation. MATERIALS AND METHODS: Fish were placed in 200-mL measuring cups for 48 h. After the social isolation period, bony fish kisspeptins and mammalian kisspeptin analogs were administered, and their effects were tested. The animal was placed in 1-L individual tanks for 15 min and then in the tank with a glass partition, behind which are a group of congeners. Fish were allowed to approach or swim away from the partition. Two patterns were used to assess behavior: latency time and number of swims to the partition. RESULTS: Compared with the control group with fish kept in social isolation, reliable differences were observed: The number of swims to the partition after isolation was 1.3 times higher than that in the control group (p 0.05). After the administration of bony fish kisspeptins Kiss1 and Kiss2, no significant changes in the number of swims to the partition were observed. Moreover, after the administration of KS6 and KS10, the number of swims to the aquarium partition increased 1.6 times (p 0.01) and 1.8 times (p 0.001), respectively. After the administration of the comparison drug oxytocin, the number of swims to the aquarium partition increased 1.6 times (p 0.01) compared with that in the untreated isolated group. The latency time of swimming to the partition increased 2.4 times in the untreated isolated group compared with the control group (p 0.001). Latency time decreased 2.3 times in the group administered with oxytocin compared with the untreated isolated group (p 0.001). In the group administered with Kiss1, the latency time decreased 2 times (p 0.001) compared with that in the untreated isolated group. The latency time decreased 5 times (p 0.001) after KS10 administration and 3.4 times (p 0.001) after KS6 administration compared with that in the untreated isolated group. CONCLUSIONS: Thus, social isolation in Danio rerio reduces communicative behavior. Analogs of mammalian kisspeptin, such as Kiss1, of bony fish and oxytocin normalize the communicative behavior of fish after a period of social isolation to the level of the control group.