Conspecific Chemical Alarm Cues Research Articles

Social learning and acquired recognition of a predator by a marine fish

Predation is known to influence the distribution of behavioural traits among prey individuals, populations and communities over both evolutionary and ecological time scales. Prey have evolved mechanisms of rapidly learning the identity of predators. Chemical cues are often used by prey to assess predation risk especially in aquatic systems where visual cues are unreliable. Social learning is a method of threat assessment common among a variety of freshwater fish taxa, which incorporates chemosensory information. Learning predator identities through social learning is beneficial to naïve individuals as it eliminates the need for direct interaction with a potential threat. Although social learning is widespread throughout the animal kingdom, no research on the use of this mechanism exists for marine species. In this study, we examined the role of social learning in predator recognition for a tropical damselfish, Acanthochromis polyacanthus. This species was found to not only possess and respond to conspecific chemical alarm cues, but naïve individuals were able to learn a predators' identity from experienced individuals, the process of social learning. Fish that learned to associate risk with the olfactory cue of a predator responded with the same intensity as conspecifics that were exposed to a chemical alarm cue from a conspecific skin extract.

Response across a gradient: behavioural reactions of newly settled fish to predation cues

How individuals respond to predation threats will have a large influence on which individuals survive within a population. The magnitude and timing of these responses will be particularly important during periods of high predation susceptibility, such as that experienced by coral reef fishes immediately following settlement to the reef environment. Although reef fish are known to adopt certain antipredator behaviours when exposed to chemical alarm scents during this early period, the role of visual cues, and how the response varies with different levels of predation threat (both olfactory and visual), remains unknown. This study examined the behavioural response of a newly settled coral reef fish (Pomacentrus amboinensis) to different levels of an olfactory and visual predation threat. The concentration of a conspecific chemical alarm cue and the visual proximity to a potential predator (Pseudochromis fuscus) were manipulated in separate aquarium experiments. Behavioural responses were found to be threat sensitive in nature, with higher-level threat cues eliciting a more intense response. Although significant changes were observed, responses to visual cues were more inconsistent, while responses to extremely low chemical cue concentrations were marginal, indicating a possible threshold lower limit. These findings demonstrate the ability of newly settled fish to assess the level of predation risk using both visual and chemical cues, and respond appropriately.

Cross-population responses to conspecific chemical alarm cues in wild Trinidadian guppies, Poecilia reticulata: evidence for local conservation of cue production

Within freshwater fishes, closely related species produce alarm cues that are chemically similar, leading to conserved antipredator responses. Similar conservation trends are predicted for species with geographically isolated populations. Here, we tested this hypothesis with the guppy ( Poecilia reticulata Peters, 1859) from two populations within the Aripo River, Trinidad. Free-ranging guppies in the Lower Aripo (high-predation population) exhibited more risk-aversive inspection behaviour towards a fish predator model paired with the alarm cues of guppies collected from the same population versus a river water control. In comparison, when paired with the alarm cues of guppies from the Upper Aripo (low-predation population), the response was intermediate. In the laboratory, we tested Upper and Lower Aripo guppies to the alarm cues of the same or different Aripo River donors, Quaré River guppies (a high-predation population from a different drainage), or a water control. Both Upper and Lower Aripo River guppies exhibited the highest intensity response to donors from the same population and the lowest intensity response to Quaré River donors, with the response to different Aripo donors being intermediate. Collectively, these results demonstrate a trend of intraspecific conservation of chemical alarm cue production, leading to population-specific responses to conspecific cues.

Ambient pH and the Response to Chemical Alarm Cues in Juvenile Atlantic Salmon: Mechanisms of Reduced Behavioral Responses

AbstractEven at sublethal concentrations, various anthropogenic pollutants may disrupt the transfer of chemosensory information, often inducing maladaptive behavioral responses. Recent studies of freshwater prey fishes have shown impaired abilities to respond to damage‐released chemical alarm cues from conspecifics under weakly acidic conditions (pH ∼ 6.0). Several factors acting individually or collectively may account for such chemosensory impairment. By itself, acidification may chemically disrupt the alarm cues and affect fish olfactory functions. Alternatively, differences in local environmental conditions may affect biochemical composition, quantity of chemical alarm cues produced by epidermal tissue, or both, leading to variations in alarm response. Our goal was to assess whether the ability to produce and detect conspecific chemical alarm cues is similar in individuals reared under neutral versus acidic conditions. We conducted two experiments in which we measured the behavioral response of wild juvenile Atlantic salmon Salmo salar exposed to chemical alarm cues. In particular, we looked for differences in the ability of individual fish to (1) produce alarm cues capable of eliciting consistent antipredator behavior in conspecifics and (2) detect alarm cues upon the fish's introduction into a stream with a pH differing from that of the stream of origin; the latter experiment involved reciprocal transplant of fish between neutral (pH range ∼ 7.0–7.3) and acidic (pH range ∼ 5.9–6.3) sites. Our results demonstrate that the ability to produce and respond to chemical alarm cues is maintained in Atlantic salmon reared under acidic conditions and did not differ from that of fish reared under neutral conditions. Overall, these data suggest that no permanent olfactory damage occurred under reduced pH and, likewise, no significant difference in functional alarm cue production existed between Atlantic salmon reared under neutral and acidic conditions. Short‐term reduction in olfactory sensitivity and degradation of the chemical alarm cues under acidic conditions are the likely mechanisms affecting detection of these important chemicals by prey fish.

Effects of acid rainfall on juvenile Atlantic salmon (Salmo salar) antipredator behaviour: loss of chemical alarm function and potential survival consequences during predation

Many organisms rely on chemosensory cues to mediate predation risks. Recent studies have demonstrated impaired chemosensory detection ability under weak acidification. Because rainfall may lead to episodic acidification of surface water, we assessed the effects of acid rain on chemosensory alarm functions. Under natural conditions, we quantified alarm behaviour of juvenile Atlantic salmon (Salmo salar) exposed to conspecific chemical alarm cues before and following rainfall. Before rainfall, salmon were capable of an alarm response in the study streams. After rainfall, salmon from Devil’s Brook did not respond to the alarm cues whereas the detection of salmon from Catamaran Brook (a comparable stream having higher acid neutralising capacity) was maintained. To relate these findings to predator–prey encounters, we performed a second experiment where we staged encounters between prey (rainbow trout, Oncorhynchus mykiss) and predator (largemouth bass, Micropterus salmoides) exposed to acidified and unacidified rainbow trout chemical alarm cues. Trout exposed to acidified alarm cues survived for a significantly shorter amount of time than trout exposed to unacidified alarm cues, whereas no difference in overall predator behaviour was observed. Our results suggest that episodic acidification in small nursery streams may disrupt the chemical information mediated by the chemical alarm cues that can translate into higher survival costs for prey.

Do you smell what I smell? Olfactory impairment in wild yellow perch from metal-contaminated waters

In this study, we sampled yellow perch from three lakes along a metal-contamination gradient and examined their olfactory ability in response to conspecific chemical alarm cues and metal-binding characteristics of their olfactory epithelium (OE). We measured the electrophysiological response at the OE, tested their antipredator behaviour and measured neuronal density at the olfactory rosette and bulb. Yellow perch from contaminated lakes exhibited significantly larger electrophysiological responses to alarm cues than clean lake fish, but showed no antipredator behaviour contrary to clean lake fish. Neuron density did not differ at either the olfactory rosette or bulb between clean and contaminated fish. Unlike fishes raised under laboratory or aquaculture settings, fish from contaminated lakes possessed a functional OE after metal exposure, but similar to laboratory/aquaculture fishes, yellow perch did not exhibit olfactory-mediated behaviours. Thus, wild fish from contaminated lakes can detect chemical stimuli but olfactory signal processing is disrupted which could alter ecological functioning.

The ontogeny of chemically mediated antipredator responses of fathead minnows Pimephales promelas

The antipredator responses of adult and larval fathead minnows Pimephales promelas to chemical alarm cues prepared throughout ontogeny were tested using various behavioural assays. Larval epidermis was also examined during ontogeny using standard haematoxylin and eosin staining techniques. Adults elicited an antipredator response to chemical alarm cue made from larvae as young as 8–17 days post‐hatch. Interestingly, larvae did not possess visible club cells until 28–37 days post‐hatch and did not respond to conspecific chemical alarm cue until 48–57 days post‐hatch. These results suggest that chemical alarm cue may not be contained within club cells and that the components of larval and adult chemical alarm cue may be similar throughout ontogeny.

Effects of Single and Combined Embryonic Exposures to Herbicide and Conspecific Chemical Alarm Cues on Hatching and Larval Traits in the Common Frog (Rana temporaria)

Recent studies indicate that amphibian embryos can exhibit hatching plasticity in response to chemical cues indicative of a predation risk. However, data are lacking concerning the possible impacts of waterborne contaminants on such a process. To investigate this impact, we raised eggs of the common frog (Rana temporaria) until hatching in water contaminated with sublethal concentrations (0.01, 0.1, and 1 mg/L) of amitrole, a widely used triazole herbicide, either with or without the presence of chemical alarm cues from crushed conspecific tadpoles. Embryonic exposure to conspecific alarm cues resulted in a delay in hatching, reduced growth, and decreased larval activity, regardless of the amitrole concentration present during the incubation. Conspecific cues also induced morphological changes, but only in individuals incubated in water contaminated with the highest amitrole concentration. The herbicide impacts on hatching time were restricted to embryos incubated in the presence of conspecific cues, with individuals exposed to 0.1 and 1 mg/L showing an extended embryonic period compared to controls in uncontaminated water. Whether tested alone or in combination with conspecific cues, amitrole also induced slight morphological changes but did not affect larval growth or behavioral activity. Thus, depending on the trait considered, both chemical stressors exhibited either single or interactive effects. Furthermore, our data indicate that a stressing factor without apparent impact when tested alone could exert effects when combined with another stressor. Such results highlight the importance of considering multiple environmental factors and biological traits when examining stress-induced phenotypic variability.

Response to Chemical Alarm Cues under Weakly Acidic Conditions: A Graded Loss of Antipredator Behaviour in Juvenile Rainbow Trout

A wide variety of aquatic organisms, including juvenile salmonids, assess local predation risks using chemosensory cues. Such chemical cues are typically released from injured conspecifics and their detection may lead to species-typical antipredator behaviour, increasing the probability of prey to survive during predator encounters. Studies have demonstrated however, that under weak acidification (pH ~6.0), the response towards these chemical alarm cues is impaired. However, it remains unknown if the loss of response is graded (i.e., the behavioural response decreases with a reduction in pH) or if there is a threshold pH at which prey can no longer detect the alarm cues. We conducted two laboratory experiments to examine the effects of a graded reduction in pH on the behavioural response of juvenile rainbow trout to conspecific chemical alarm cues. The results of our first experiment suggest that at pH 6.6 and above, the alarm cues elicited a strong antipredator response, while alarm cues buffered to pH 6.2 did not (i.e. not different from distilled water). However, alarm cues buffered to pH 6.4 elicited a weak response, suggesting a graded response. We directly tested this in our second experiment using a repeated measures design. The response to alarm cues at varying pH levels did indeed follow a graded loss of function. Together, our results suggest that juvenile rainbow trout exhibit a reduction in the response to conspecific alarm cues proportional to ambient acidity and that the response to these critically important cues is lost at pH below 6.4. As the detection and response to these chemical alarm cues have been shown to confer direct survival benefit to individuals, these results are therefore presented in relation to possible sub-lethal effects of anthropogenic acidification to freshwater fish.

Anti-predator behaviour in response to conspecific chemical alarm cues in an esociform fish, Umbra limi (Kirtland 1840)

When a predators attack prey, damaged prey tissue releases chemical information that reli- ably indicates an actively foraging predator. Prey use these semiochemicals to cue anti-predator behaviour and reduce their probability of predation. Here, we test central mudminnows, Umbra limi (Kirtland 1840), for anti-predator behavioural responses to chemical cues in conspecific skin extract. In a field experiment, traps scented with mudminnow skin extract (alarm cue) caught fewer mudminnows than traps scented with water (control). Under controlled laboratory conditions, mudminnows showed a signif- icant reduction in activity and movement to the bottom in response to alarm cues relative to water controls. Reduced activity and increased time on the bottom of the tank are both known components of an anti-predator response. Thus, based on field and lab data, mudminnows exhibited anti-predator behavio- ural responses to chemical alarm cues released by damaged epidermal tissue. Histological preparations of epidermal tissue did not reveal the presence of specialised ''alarm substance'' cells for the produc- tion of chemical alarm cues. This is the first report of an alarm reaction in an esociform, an order with a long evolutionary history of piscivory.

Effects of ambient acidity on chemosensory learning: an example of an environmental constraint on acquired predator recognition in wild juvenile Atlantic salmon (Salmo salar)

Abstract – In many prey fish species, learning the identity of novel predators may be facilitated when novel predator cues and an aversive stimulus are presented together. Damage‐released chemical alarm cues are typically released from the skin of prey individuals following mechanical damage and are known to mediate the learned recognition of novel predators. While such chemically mediated acquired predator recognition can provide increased survival benefits to prey, environmental constraints impeding learning may exist. For example, in several fish species the ability to detect chemical alarm cues is impaired in under acidic conditions and as such, inhibits this chemically mediated learning. In this experiment, we studied in two streams of different mean acidity level (pH c. 6.0 and 7.0), to assess if wild juvenile Atlantic salmon (Salmo salar) had the ability to acquire the recognition of a novel lemon essence odour when paired with conspecific chemical alarm cues. Our results demonstrate that under acidic conditions, no learned recognition of the novel odour occurred. In neutral conditions, however, salmon recognised the novel odour as a predation threat. This result suggests that ambient acidity creates an environmental constraint on chemically mediated learned recognition of a novel cue.

Sound the alarm: learned association of predation risk with novel auditory stimuli by fathead minnows (Pimephales promelas) and glowlight tetras (Hemigrammus erythrozonus) after single simultaneous pairings with conspecific chemical alarm cues

Fathead minnows, Pimephales promelas, and glowlight tetras, Hemigrammus erythrozonus, were tested for their ability to associate predation risk with novel auditory stimuli after auditory stimuli were presented simultaneously with chemical alarm cues. Minnows and tetras gave a fright response when exposed to skin extract (alarm cue) and an artificial auditory sound stimulus, but no response to water (control) and sound, indicating that they did not have a pre-existing aversion to the auditory stimulus. When retested with sound stimuli alone, minnows and glowlight tetras that had previously been conditioned with water and sound showed no response, but those that had been conditioned with alarm cues and sound exhibited antipredator behaviour (reduced activity) in response to the auditory cue. This is the first known demonstration of learned association of an auditory cue with predation risk, and raises questions about the role of sound in mediating predator-prey interactions in fishes.

The dynamic nature of antipredator behavior: prey fish integrate threat-sensitive antipredator responses within background levels of predation risk

Prey animals often have to face a dynamic tradeoff between the costs of antipredator behavior and the benefits of other fitness-related activities such as foraging and reproduction. According to the threat-sensitive predator avoidance hypothesis, prey animals should match the intensity of their antipredator behavior to the degree of immediate threat posed by the predator. Moreover, longer-term temporal variability in predation risk (over days to weeks) can shape the intensity of antipredator behavior. According to the risk allocation hypothesis, changing the background level of risk for several days is often enough to change the response intensity of the prey to a given stimulus. As the background level of risk increases, the response intensity of the prey decreases. In this study, we tested for possible interactions between immediate threat-sensitive responses to varying levels of current perceived risk and temporal variability in background risk experienced over the past 3 days. Juvenile convict cichlids were preexposed to either low or high frequencies of predation risk (using conspecific chemical alarm cues) for 3 days and were then tested for a response to one of five concentrations (100, 50, 25, 12.5%, or a distilled water control). According to the threat-sensitive predator avoidance hypothesis, we found greater intensity responses to greater concentrations of alarm cues. Moreover, in accordance with the risk allocation hypothesis, we found that cichlids previously exposed to the high background level of risk exhibited a lower overall intensity response to each alarm cue concentration than those exposed to the low background level of risk. It is interesting to note that we found that the background level of risk over the past 3 days influenced the threshold level of response to varying concentrations of alarm cues. Indeed, the minimum stimulus concentration that evoked a behavioral response was lower for fish exposed to high background levels of predation than those exposed to low background levels of predation. These results illustrate a remarkable interplay between immediate (current) risk and background risk in shaping the intensity of antipredator responses.

Can the ratio of aromatic skeletons explain cross-species responses within evolutionarily conserved Ostariophysan alarm cues?: testing the purine-ratio hypothesis

While the response to damage-released chemical alarm cues within the superorder Ostariophysi appears to be highly conserved across species, it is generally observed that the intensity of response to heterospecific alarm cues decreases with increasing phylogenetic distance. Recent studies have demonstrated that purine-N-oxides function as chemical alarm cues within Ostariophyian fishes and that the nitrogen-oxide functional group is conserved as the chief molecular trigger. According to the purine-ratio hypothesis, these cross-species differences may be due to the relative proportion of different carrier compounds associated with the nitrogen-oxide molecular trigger. To test this hypothesis, we exposed glowlight tetras (Hemigrammus erythrozonus, Characidae, Ostariophysi) to one of five synthetic stimuli (hypoxanthine-3-N-oxide (H3NO), pyridine-N-oxide (PNO) or mixed stimuli of 75 % H3NO-25 % PNO, 50 % H3NO-50 % PNO, or 25 % H3NO-75 % PNO), natural conspecific chemical alarm cue or a distilled water control. We quantified changes in shoal cohesion and vertical area use as species typical indicators of an antipredator response. As predicted, response intensity decreased as the ratio of hypoxanthine-3-N-oxide to pyridine-N-oxide decreased and the strongest response was to natural alarm cue. These results suggest that species-specific carrier compounds may account for the well-documented cross-species differences in the response to heterospecific alarm cues within phylogenetically related taxa.

Effects of group size on the threat-sensitive response to varying concentrations of chemical alarm cues by juvenile convict cichlids

The threat-sensitive predator avoidance model predicts that prey should balance the intensity of antipredator responses against perceived predation risk, resulting in a graded response pattern. Recent studies have demonstrated considerable interspecific variation in the intensity of threat-sensitive response patterns, ranging from strongly graded to relatively nongraded or "hypersensitive" threat-sensitive response patterns. Here, we test for intraspecific plasticity in threat-sensitive responses by varying group size. We exposed juvenile convict cichlids, Archocentrus nigrofasciatus (Günther, 1867), as individuals or in small (groups of three) or large (groups of six) shoals to a series of dilutions of conspecific chemical alarm cues and a distilled water control. Singleton cichlids exhibited significant reductions in time spent moving and in frequency of foraging attempts (relative to distilled water controls) when exposed to a 12.5% dilution of conspecific alarm cue, with no difference in response intensity at higher stimulus concentrations, suggesting a nongraded (hypersensitive) response pattern. Small shoals exhibited a similar response pattern, but at a higher response threshold (25% dilution of stock alarm cue solution). Large shoals, however, exhibited a graded response pattern. These results suggest that group size influences the trade-off between predator avoidance and other fitness related activities, resulting in flexible threat-sensitive response patterns.

Heads up: juvenile convict cichlids switch to threat-sensitive foraging tactics based on chemosensory information

The ability to accurately assess local predation risk is crucial, as it allows prey individuals to maximize trade-offs between predator avoidance and foraging behaviour. Here, we test the hypothesis that juvenile convict cichlids, Archocentrus nigrofasciatus, rely on ambient chemosensory information to make threat-sensitive foraging decisions. In experiment 1, juvenile cichlids were exposed to conspecific chemical alarm cues above or below the threshold required to elicit an overt antipredator response and were allowed to forage on a choice of horizontal (on the substrate) or vertical (perpendicular to the substrate) food patches. Although cichlids exposed to a subthreshold alarm cue did not show an overt antipredator response, they significantly increased their use of the vertical food patch (head-up foraging posture). Cichlids exposed to a suprathreshold alarm cue significantly reduced foraging and aggressive behaviour and shifted to the head-up foraging position. In experiment 2, juvenile cichlids were exposed to the odour of an adult conspecific fed a vegetable diet, or one of two prey fish diets (juvenile cichlids or swordtails, Xiphophorus hellerii), or a distilled water control. Although we found no evidence of an overt antipredator response towards any of the stimuli, cichlids exposed to the odour of predators fed a prey fish diet significantly increased their use of the head-up foraging posture. Our results clearly show that juvenile cichlids are able to adjust their foraging patterns in a threat-sensitive fashion in response to ambient chemosensory information.

Learning to recognize novel predators under weakly acidic conditions: the effects of reduced pH on acquired predator recognition by juvenile rainbow trout

Recent studies have demonstrated that under weakly acidic conditions (pH 6.0), many prey fishes, including juvenile rainbow trout (Onchorhynchus mykiss), do not exhibit overt antipredator responses to conspecific chemical alarm cues. In laboratory trials, we investigated the potential effects of reduced pH on the ability of hatchery reared, predator naive juvenile rainbow trout to acquire the recognition of a novel predator (yellow perch, Perca flavenscens). Initially, we exposed trout to the odour of a predatory yellow perch, buffered to pH 6.0 (weakly acidic) or pH 7.0 (neutral) paired with conspecific skin extracts (also buffered to pH 6.0 or 7.0) or a distilled water control. Juvenile trout exhibited significant increase in antipredator behaviour when exposed to neutral skin extract (pH 7.0). When retested 48 hours later to perch odour alone (pH 7.0), only trout initially conditioned with neutral skin extracts (pairs with either neutral or acidic perch odour) exhibited a learned recognition of perch odour as a predator risk. Those initially exposed to weakly acidic skin extract or the distilled water control did not show a learned response to predator odour. These results demonstrate that the ability to acquire the recognition of novel predators is impaired under weakly acidic conditions, as would occur in natural waterways affected by acidic precipitation.

Detection of conspecific alarm cues by juvenile salmonids under neutral and weakly acidic conditions: laboratory and field tests.

A variety of fishes possess damage-released chemical alarm cues, which play a critical role in the detection and avoidance of potential predation threats. Recently, we have demonstrated that the ability of fathead minnows ( Pimephales promelas) and finescale dace ( Phoxinus neogaeus) to detect and respond to conspecific alarm cues is significantly reduced under weakly acidic conditions (pH 6.0). Rainbow trout ( Oncorhynchus mykiss) and brook charr ( Salvelinus fontinalis) possess an analogous alarm cue system. However, it is unknown if the trout alarm cue system is likewise affected by relatively small changes in pH. In addition, previous studies have not verified this phenomenon under natural conditions. We conducted laboratory and field trials to examine the potential effects of acute exposure to weakly acidic (pH 6.0) conditions on the detection and response of conspecific alarm cues by juvenile trout. Our laboratory results demonstrate that while juvenile rainbow trout exhibit significant increases in antipredator behaviour under normal pH conditions (pH 7.0-7.2), they do not respond to the presence of conspecific chemical alarm cues (i.e. response is not different from controls) under weakly acidic conditions. Similarly, a wild strain of brook charr in their natural streams near Sudbury, Ontario, failed to detect conspecific alarm cues in a weakly acidic stream (mean pH 6.11) while they responded to these cues in a neutral stream (mean pH of 6.88). This is the first demonstration that relatively small changes in ambient pH can influence alarm responses under natural conditions. These data suggest significant, sub-lethal effects of acid precipitation on natural waterways.

Quality or quantity? the role of donor condition in the production of chemical alarm cues in juvenile convict cichlids

AbstractMuch study has been devoted to the function of chemical alarm cues in predator-prey relationships in aquatic environments, but little is known about the production of these valuable sources of chemosensory information. Recent studies have demonstrated that donor (cue sender) condition may play an important role in the production of chemical alarm cues in juvenile convict cichlids (Archocentrus nigrofasciatus). In laboratory experiments, we conducted trials to test for the effect of donor body condition on the minimum behavioural response threshold and/or intensity of antipredator response to conspecific chemical alarm cues. Chemical alarm cue donors were sampled from high or low condition populations. Pairs of juvenile cichlids were exposed to the skin extracts of high condition versus low condition donors, across a range of relative concentrations (200, 100, 50, 25, and 12.5%), and a distilled water control. We found that cichlids exhibited overt antipredator behaviour beginning at a concentration of 25% for the high condition cue, while a minimum response threshold concentration of 50% was seen for low condition cue. The intensity of antipredator response was greater following exposure to the alarm cues of high condition stimulus versus low condition donors. Taken together, these findings suggest that the damage-released chemical alarm cues from high condition donors are qualitatively and quantitatively greater than those of low condition donors.

Is there a fish alarm cue? Affirming evidence from a wild study

Chemical alarm cues released from injured tissue are not released under any other context and therefore reliably inform nearby prey of the presence of a predator. Laboratory and field studies have demonstrated that most aquatic taxa show antipredator responses to chemical alarm cues. Ostariophysan fish (e.g. minnows) possess specialized skin cells that contain an alarm chemical. Magurran et al. (1996, Proceedings of the Royal Society of London, Series B, 263, 1551–1556) were the first to use underwater video to carefully document the behavioural response of free-ranging wild populations of minnows to minnow alarm cues. They found no evidence of an antipredator response, and challenged the assumption that the contents of these cells indicate risk in the field. They proposed that alarm responses are context dependent in that they are an artefact of enclosed environments such as laboratory aquaria and field traps. Here, we repeat their experiment on free-swimming field populations of littoral fish and report a significant decrease in the number of fish in areas where chemical alarm cues of blacknose shiners, Notropis heterolepis (Ostariophysi: Cyprinidae) were released. The effect of these chemical cues was equal in magnitude to the effect of the presentation of a model predator. The response to the approach of a model predator (visual cue) was intensified by pre-exposure to chemical alarm cues. We corroborated this interaction between chemical and visual indicators of predation risk in a laboratory study using glowlight tetras, Hemigrammus erythrozonus (Ostariophysi: Characidae). Response to the visual stimulus of a predator was significantly intensified by previous exposure to conspecific chemical alarm cues. We conclude that ostariophysan skin indeed contains an alarm cue that (1) informs nearby prey of imminent predation risk, (2) induces some form of antipredator behaviour in most contexts, and (3) affects subsequent behavioural responses to stimuli in other sensory modalities.