Hemigrammus Erythrozonus Research Articles

Mitochondrial Genome Structures and Phylogenetic Analyses of Two Tropical Characidae Fishes.

The Characidae family contains the largest number of tropical fish species. Morphological similarities make species identification difficult within this family. Here, the complete mitogenomes of two Characidae fish were determined and comparatively analyzed with those of nine other Characidae fish species. The two newly sequenced complete mitogenomes are circular DNA molecules with sizes of 16,701 bp (Hyphessobrycon amandae; MT484069) and 16,710 bp (Hemigrammus erythrozonus; MT484070); both have a highly conserved structure typical of Characidae, with the start codon ATN (ATG/ATT) and stop codon TAR (TAA/TAG) or an incomplete T−−/TA−. Most protein-coding genes of the 11 Characidae mitogenomes showed significant codon usage bias, and the protein-coding gene cox1 was found to be a comparatively slow-evolving gene. Phylogenetic analyses via the maximum likelihood and Bayesian inference methods confirmed that H. amandae and H. erythrozonus belong to the family Characidae. In all Characidae species studied, one genus was well supported; whereas other two genera showed marked differentiation. These findings provide a phylogenetic basis for improved classification of the family Characidae. Determining the mitogenomes of H. erythrozonus and H. amandae improves our understanding of the phylogeny and evolution of fish species.

Ultrastructure of the fertilized egg envelopes in Hemigrammus erythrozonus, Characidae, Teleostei

We examined the morphology and ultrastructures of fertilized egg envelopes of glowlight tetra (Hemigrammus erythrozonus) belong to Characidae using light and electron microscopes.The fertilized eggs were spherical, transparent, demersal, adhesive, and have no oil droplet. The perivitelline space was well-developed and the micropyle was surrounded by 15–20 uplifted lines of egg envelope in a spoke like pattern. The outer surface of egg envelope was rough side with grooves. Also, the total thickness of the fertilized egg envelope was about 2.1–2.3 μm, and the fertilized egg envelope consisted of two layers, an outer adhesive electron-dense layer with grooves and three feather-like lamellae layers. Collectively, these morphological characteristics of fertilized egg and micropyle with spoke-like structure showed family Characidae specificity, and ultrastructures of outer surface and section of fertilized egg envelope showed species specificity.

Acute toxicity of trichlorophon on two ornamental fish: tiger barb (Systomus tetrazona) and glowlight tetra (Hemigrammus erythrozonus)

Objective: To determine the acute toxicity of trichlorophon (an organ phosphorus compound used in agricultural fields and a common disinfectant used for fish diseases) towards two ornamental fish Systomus tetrazona and Hemigrammus erythrozonus. Methods: In this research, two aquarium fish were exposed to different concentrations of trichlorophon (5, 10, 20 and 40 mg/L) for 96 h and physicochemical properties of water used for these experiments were stable and every mortality was recorded daily for 96 h. LC50 of 24 h, 48 h, 72 h and 96 h were attained by probit analysis software SPSS version 16. Results: The 96-h LC50 of trichlorophon for Systomus tetrazona and Hemigrammus erythrozonus were 8.74 and 8.88 mg/L, respectively. Conclusions: Eventually, toxicity values indicated that trichlorophon has the same toxicity towards the studied species and the lower value of LC50 for studied species in comparison with that of most species can be stated. journal homepage: www.jclmm.com

Fin‐flicking behaviour as a means of cryptic olfactory sampling under threat of predation

Risk of predation is a ubiquitous component of behavioural decision-making (Lima & Dill 1990). For small littoral fishes, chemical cues released from predators and/or injured conspecifics, comprise important sources of information about the presence and nature of predation risk (see Kelley 2008; Ferrari et al. 2010 for recent reviews). Behavioural responses to these chemical cues include area avoidance, increased shoal cohesion, reduction in activity, movement out of the water column, use of shelter and finflicking (Lawrence & Smith 1989; Ferrari et al. 2010). Collectively, these behavioural responses reduce the probability of predation (Mathis & Smith 1993). Fin-flicking is a behaviour in which fish quickly sweep their pectoral fins anteriorly, matched with concomitant counterbalancing forward thrusts of the anal and caudal fin, resulting in no net movement. The function of fin-flicking has not received much attention in the context of antipredator behaviour. Fin-flicking by glowlight tetras (Hemigrammus erythrozonus, Durbin 1909) in response to conspecific chemical alarm cues induced greater shoal cohesion in conspecifics and also deterred attack behaviour by a potential predator, the Jack Dempsey cichlid (Rocio octofasciata, Regan 1903; Brown et al. 1999). Be that as it may, the precursor function of fin-flicking signals may be more utilitarian in nature and only later became co-opted into a visual signalling system. This brief communication presents a test of the hypothesis that fin-flicking by alarmed fish serves the selfish benefit of allowing individuals to sample chemical cues in the surrounding waters whilst remaining motionless to avoid attracting attention from predators. Receptors that detect chemical alarm cues and predator odours are arranged in rosettes in the nares, which are blind pouches in the rostrum (Doving & Lastein 2009). Advection (mass water movement) of water to the nares is generated by ram ventilation as fish move through the water column. When risk is detected, fish are faced with a trade-off because the physical swimming movements needed to assess predation risk are conspicuous to predators. Fin-flicking behaviour may be a solution to this trade-off if it allows individuals to discreetly create microcurrents of water past the nares resulting in continuous sampling of chemical information of the surrounding water without the accompanying movements that would compromise crypsis. Java moss (Taxiphyllum barbieri) was chopped into 2-mm pieces to create small neutrally buoyant particles that would allow us to visualise water currents generated by fin-flicking. In one recording session, an adult fathead minnow (Pimephales promelas, Rafinesque 1820) was placed in a shallow white plastic trough that afforded good visual contrast with the moss fragments. In a second recording session, an adult fathead minnow was placed into a narrow aquarium with a small amount of clay to visualise water currents. Skin extract was prepared by killing an adult fathead minnow by cervical dislocation and then lightly scoring its flanks with a clean razor blade. One minnow was killed for each session of filming. The minnow carcasses were then soaked in 100 ml of deionised water for 10 min. The test dose of alarm cue was 10 ml of minnow skin extract administered to the side of the container to induce fin-flicking behaviour. All procedures were approved by the Minnesota State University Moorhead Institutional Animal Care

A latitudinal cline in the efficacy of endogenous signals: evidence derived from retinal cone contraction in fish

Like many physiological systems synchronised to the light:dark cycle, retinomotor movements in 'lower' vertebrates are controlled by both the ambient illumination and input from endogenous circadian oscillators. In the present study, we examine the relative influence of these two signals in various species of teleost fish with different latitudes of origin. We find equatorial species show very strong endogenous control. The cones of the glowlight tetra, for example, continue to go through undiminished cycles of contraction and relaxation that mirror the previous light:dark cycle for at least two weeks in continual darkness. To quantify the relative effectiveness of the ambient light compared with endogenous signals in causing cone contraction, the degree to which seven teleost species responded to light during the dark phase of their light:dark cycle was examined. In this situation the retina receives conflicting instructions; while the light is acting directly to cause light adaptation, any endogenous signal tends to keep the retinal elements dark adapted. The further from the equator a species originated, the more its cones contracted in response to such illumination, suggesting animals from higher latitudes make little use of endogenous oscillators and rely more on ambient illumination to control behaviours. Equatorial species, however, rely on internal pacemakers to a much greater degree and are relatively insensitive to exogenous light signals. Because these data are consistent with published observations in systems as diverse as melatonin synthesis in Arctic reindeer and the behaviour of regional populations of Drosophila, latitudinal clines in the efficacy of circadian oscillators may be a common feature among animals.

Comparison of spermiogenesis in the externally fertilizing Hemigrammus erythrozonus and the inseminating Corynopoma riisei (Teleostei: Characiformes: Characidae)

Spermiogenesis and sperm ultrastructure were analyzed in two species of characids with different modes of fertilization: externally fertilizing Hemigrammus erythrozonus and inseminating Corynopoma riisei. Spermiogenesis in H. erythrozonus is characterized by lateral development of the flagellum, nuclear rotation, formation of a shallow nuclear fossa, condensation of the chromatin by elimination of the electron-lucent area from the peripheral region of the nucleus, and renewal of the nuclear membrane. Multilammelated membrane and multivesicular bodies were also observed during elimination of the excess cytoplasm. The spermatozoon exhibits characters typical of "aquasperm," i.e. a spherical head containing a spherical nucleus with highly condensed chromatin, several small mitochondria located at the base of the nucleus within a cytoplasmic collar that extends into a long cytoplasmic sleeve surrounding the anterior part of the single flagellum, which is contained within a cytoplasmic canal. The flagellum lacks fins. The proximal and distal centrioles are nearly parallel to one another, with the anterior tips of both located within shallow nuclear fossae. Spermiogenesis in C. riisei is characterized by nuclear elongation alongside the forming flagellum, formation of an elongate cytoplasmic canal, displacement and elongation of the mitochondria, and uniform condensation of chromatin throughout the nucleus through enlargement of the diameter of the chromatin granules. The spermatozoon has an elongate nucleus with two elongate mitochondria localized to one side. Mitochondria are also located posterior to the nucleus forming a mitochondrial region. The single flagellum, which lacks fins, is lateral to the nucleus and initially contained within the greatly elongate cytoplasmic canal before exiting the canal at its posterior terminus. The spermatozoon of C. riisei exhibits several characters typical of "introsperm," such as an elongate nucleus and midpiece (mitochondrial region). The nuclear chromatin in the spermatozoon remains "flocculent" and is never as condensed as that seen in many characid sperm. Differences in spermiogenesis between externally fertilizing and inseminating characids are discussed.

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.

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.

Acquired recognition of novel predator odour cocktails by juvenile glowlight tetras

Prey can learn to recognize novel predators through the association of aversive stimuli (visual or chemical) paired with a predator cue (i.e. acquired predator recognition). Previous studies have demonstrated that a variety of prey can readily learn the identity of a single predator. In this study, we examined whether predator-naive glowlight tetras, Hemigrammus erythrozonus, could simultaneously acquire recognition of three novel heterospecific odours as predation threats, and whether this simultaneous learning confers a survival benefit. Tetras were conditioned to the odours of largemouth bass, Micropterus salmoides, convict cichlids, Archocentrus nigrofasciatus, and comet goldfish, Carassius auratus, simultaneously, then subsequently tested 48 h later for learned recognition of each odour individually. Tetras were also tested for the recognition of yellow perch, Perca flavescens, a novel predator, to assess whether learned recognition is generalized. Tetras significantly increased antipredator behaviour when exposed to each of the conditioned predator odours and the nonpredator goldfish odour, but not to perch odour (i.e. not different from the distilled water control). These results demonstrate acquired recognition and not a generalization to novel predator odours. Subsequent staged encounters with live pumpkinseed sunfish, Lepomis gibbosus, predators showed that tetras conditioned to either sunfish odour alone or multiple odours increased survival over unconditioned tetras. These results are the first indication that prey possess the ability to learn the cues of multiple predators simultaneously, and that this multiple learning provides a survival benefit.

Assessment of local predation risk: the role of subthreshold concentrations of chemical alarm cues

The ability to accurately assess local predation risk is critical to prey individuals, as it allows them to maximize threat-sensitive trade-offs between predator avoidance and other fitness related activities. A wide range of taxonomically diverse prey (including many freshwater fishes) relies on chemical alarm cues (alarm pheromones) as their primary information source for local risk assessment. However, the value of chemical alarm cues has been questioned due to the availability of additional sensory inputs (i.e., visual cues) and the lack of an overt antipredator response under conditions of low perceived risk. In this paper, we test the hypothesis that chemical alarm cues at concentrations below the point at which they elicit an overt behavioral response function to increase vigilance towards other sensory modalities (i.e., visual alarm cues). Shoals of glowlight tetras (Hemigrammus erythrozonus) exposed to the subthreshold concentration of hypoxanthine-3-N-oxide (the putative Ostariophysan alarm pheromone) did not exhibit an overt antipredator response in the absence of secondary visual cues (not different than the distilled water control). However, when exposed to the sight of a visually alarmed conspecific, they significantly increased the intensity of their antipredator response (not different from shoals exposed to the suprathreshold alarm cue). This study demonstrates that prey may benefit from responding to low concentration alarm cues by increasing vigilance towards secondary cues during local risk assessment, even in the absence of an overt behavioral response. By increasing vigilance towards secondary risk assessment cues in the presence of a low risk chemical cue, individuals are likely able to maximize the threat-sensitive trade-offs between predator avoidance and other fitness related activities.

Lipid spray beads for delivery of riboflavin to first-feeding fish larvae

High nutrient loss due to leakage from microparticulate diets is an important problem in the development of artificial diets for marine fish larvae. Lipid spray beads (LSB) are promising as they can be used to deliver low-molecular weight, water-soluble nutrients. Here, we describe a simple method for the production of LSB composed of methyl palmitate (MP), a low melting point wax, for delivering riboflavin to first-feeding freshwater fish larvae of zebra fish, Brachydanio rerio, and glowlight tetra, Hemigrammus erythrozonus. Characteristics of LSB, such as inclusion, retention and delivery efficiencies as well as overall leaching patterns over time, were used to compare the performances of LSB prepared with different materials. The mean inclusion efficiency (IE) of riboflavin within LSB was 96.70% and it was improved by addition of emulsifiers to the lipid matrix. Addition of the solid (at room temperature) emulsifier, sorbitan monopalmitate (SMP) resulted in higher retention efficiencies compared to the additions of liquid emulsifier sorbitan sesquioleate (SSO). Additions of SMP were found to have a positive effect on retention and delivery efficiencies of LSB at concentrations of 10% and 25% (w/w) of lipid. LSB composed of a mixture of MP+10% SMP+10% ethyl cellulose (EC, w/w) were shown to retain riboflavin with the highest retention efficiencies over a period of 6 h of aqueous suspension. Use of MP facilitated digestive breakdown of LSB by larvae of zebrafish and glowlight tetra as indicated by release of free riboflavin from ingested LSB. There is a need to balance the wall stability of LSB with the digestion requirements of target species. The results suggest that it is possible to formulate a carrier lipid matrix that both retains riboflavin and is digested by fish larvae. Besides riboflavin delivery, LSB may also be useful as a carrier for other water-soluble nutrients, such as dietary amino acids and peptides.

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.

Predator Inspection Behaviour in a Characin Fish: an Interaction between Chemical and Visual Information?

AbstractRecent evidence suggests that predator inspection behaviour by Ostariophysan prey fishes is regulated by both the chemical and visual cues of potential predators. In laboratory trials, we assessed the relative importance of chemical and visual information during inspection visits by varying both ambient light (visual cues) and predator odour (chemical cues) in a 2 × 2 experimental design. Shoals of glowlight tetras (Hemigrammus erythrozonus) were exposed to a live convict cichlid (Archocentrus nigrofasciatus) predator under low (3 lux) or high (50 lux) light levels and in the presence of the odour of a cichild fed tetras (with an alarm cue) or swordtails (Xiphophorus helleri, with an alarm cue not recognized by tetras). Tetras exhibited threat‐sensitive inspection behaviour (increased latency to inspect, reduced frequency of inspection, smaller inspecting group sizes and increased minimum approach distance) towards a predator paired with a tetra‐fed diet cue, regardless of light levels. Similar threat‐sensitive inspection patterns were observed towards cichlids paired with a swordtail‐fed diet cue only under high light conditions. Our data suggest that chemical cues in the form of prey alarm cues in the diet of the predator, are the primary source of information regarding local predation risk during inspection behaviour, and that visual cues are used when chemical information is unavailable or ambiguous.

Predator inspection behaviour and attack cone avoidance in a characin fish: the effects of predator diet and prey experience

Individuals that dare approach predators (predator inspection behaviour) can reduce their overall risk of predation by engaging in attack cone avoidance. Under laboratory conditions, we investigated the interaction between predator diet and prey experience with predators in attack cone avoidance during predator inspection visits by glowlight tetras,Hemigrammus erythrozonus (Characidae, Ostariophysi). Shoals of predator-experienced versus predator-naı̈ve glowlight tetras were exposed to live Jack Dempsey cichlids, Cichlasoma octofaciatum, that had been fed a diet of tetras (possessing an alarm pheromone) or swordtails, Xiphophorus helleri (lacking a recognizable alarm pheromone). Naı̈ve tetras exposed to tetra-fed predators significantly increased their antipredator response (increased shoaling, dashing and freezing) and altered their predator inspection behaviour (increased latency to respond, decreased rate of inspection and decreased inspecting group size) compared with naı̈ve tetras exposed to swordtail-fed predators. In addition, naı̈ve tetras exposed to tetra-fed predators directed significantly greater proportions of their inspection visits towards the tail versus the head of the predator (attack cone avoidance) versus naı̈ve tetras exposed to swordtail-fed predators. Experienced tetras, regardless of predator diet, also significantly increased antipredator responses and altered their inspection behaviour. Experienced tetras also displayed significant attack cone avoidance. These data suggest that both predator diet and prey experience play a significant role in the threat-sensitive mediation of predator inspection behaviour in prey fish. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Chemical Predator Inspection in a Characin Fish (Hemigrammus erythrozonus,Characidae, Ostariophysi): The Effects of Mixed Predator Diets

Many prey organisms will approach (inspect) potential predators, primarily to assess local risk of predation. It has been demonstrated that Ostariphysan prey fishes can detect conspecific alarm pheromones in the diet of potential predators and use this chemical information to reduce their risk of predation while still gaining significant benefits associated with predator inspection. We conducted the current study to examine the possible effects of mixed diets on the use of these chemical predator diet cues during inspection visits. Shoals of four glowlight tetras (Hemigrammus erythrozonus) were exposed to Jack Dempsey cichlids (Cichlasoma octofaciatum) which had been fed diets consisting of: 100% tetras (with alarm pheromone); 75% tetra, 25% swordtail (Xiphophorus helleri, which lack a recognizable alarm pheromone); 25% tetra, 75% swordtail; or 100% swordtails. Tetras significantly increased their anti‐predator behaviour in response to predators fed 100% tetra or the two mixed predator diets, but not when exposed to predators fed a 100% swordtail diet. Likewise, we observed significant differences in inspection behaviour. Tetras took longer to initiate an inspection, inspected in smaller groups and directed a greater proportion of inspection visits towards the tail region of the predator when it had been fed 100% tetra or either of the two mixed prey diets. We found no significant differences in either anti‐predator or inspection behaviour among the three diet treatments containing tetras. These data strongly suggest that glowlight tetras are capable of detecting relatively small amounts of conspecific alarm pheromone in the diet of potential predators and that they modify their behaviour based on the presence or absence of these cues.

CHEMICAL PREDATOR INSPECTION AND ATTACK CONE AVOIDANCE IN A CHARACIN FISH: THE EFFECTS OF PREDATOR DIET

AbstractMany prey organisms will approach (inspect) a potential predator, primarily to assess local risk of predation. It has been argued that by avoiding the head region of predators during inspections, prey can reduce the risks associated with such behaviour (attack cone avoidance). Prior experiments, however, have not incorporated the combined chemical and visual predator cues. We conducted laboratory experiments to determine the effects of combined predator dietary (chemical) and visual cues on the form and location of predator inspection visits by glowlight tetras (Hemigrammus erythrozonus). Tetras were exposed to a live cichlid predator (Cichlasoma octofasciatum) which had been fed tetras (with alarm pheromone), swordtails (Xiphophorus helleri; lacking Ostariophysan alarm pheromones) or food deprived. There was no significant difference in the overall rate of predator inspection by tetras to tetra-fed, swordtail-fed or food deprived cichlids. There was, however, a significant effect of predator diet on the size of inspection shoals and the location of inspections. Tetras inspected a tetrafed predator in significantly smaller groups, more often as singletons and directed a greater proportion of their inspections towards the tail of the predator. Tetras exposed to swordtail-fed or food deprived cichlids inspected in larger groups and directed more inspections towards the head of the predator. When the predator dietary cue contained tetra alarm pheromone, there was a significant increase in the attack latency by predators. Taken together, these data suggest that tetras use both chemical and visual predator cues during inspection visits and will modify their behaviour based on the presence or absence of conspecific alarm pheromone in the diet of a potential predator.

Chemically mediated predator inspection behaviour in the absence of predator visual cues by a characin fish

Animals commonly approach (i.e. ‘inspect’) potential predators. Glowlight tetras,Hemigrammus erythrozonus , have previously been shown to inspect the combined chemical and visual cues originating from novel predators and to modify their inspection (approach) behaviour depending upon the predator's diet. We conducted two experiments to determine whether tetras would inspect the chemical cues of injured prey or the dietary cues of a novel predator in the absence of any visual cues. Shoals of glowlight tetras were exposed to either distilled water (control) or the skin extract of swordtail (lacking ostariophysan alarm pheromones) or the skin extract of tetra (with alarm pheromones). There was no significant difference in the frequency of predator inspection behaviour towards swordtail or tetra skin extract compared to the distilled water controls. In the second experiment, we exposed shoals of tetras to either distilled water or the odour of Jack Dempsey cichlids, Cichlasoma octofasciatum, which had been food deprived, or fed a diet of swordtails or tetras. There was no significant difference in the frequency of predator inspection behaviour towards the odour of the starved cichlids and the odour of the fed cichlids in either of the two diet treatments. However, when tetras were exposed to the odour of cichlids fed tetras, they took significantly longer to initiate an inspection visit, remained further from the source of the chemical cues and inspected in smaller groups, compared with the odour of a starved cichlid or a cichlid fed swordtails. These data strongly suggest that tetras will inspect chemical cues alone, but only if the cue contains information about the predator.

Fin-flicking behaviour: a visual antipredator alarm signal in a characin fish, Hemigrammus erythrozonus

Glowlight tetras, Hemigrammus erythrozonus, show a conspicuous visual display (‘fin flicking’) upon detecting a conspecific chemical alarm signal (alarm pheromone). We conducted laboratory studies to test two, nonmutually exclusive hypotheses regarding the function of this behaviour. To test the hypothesis that fin flicking acts as a visual alarm signal to conspecifics, we paired shoals of tetras with a stimulus tetra in an adjacent tank (separated by a one-way mirror) and exposed the stimulus tetras to conspecific skin extract (with alarm pheromone) or swordtail skin extract (which lacks ostariophysan alarm pheromone). Stimulus tetras significantly increased their frequency of fin flicking when exposed to conspecific skin extract, but not to the swordtail skin extract control. The test shoals showed a significant increase in antipredator behaviour in response to fin-flicking stimulus tetras, but not to stimulus tetras that did not fin-flick. To test the hypothesis that fin flicking serves as a predator deterrent, we paired predatory Jack Dempsey cichlids, Cichlasoma octofaciatum, with tetras in adjacent tanks and exposed the tetras to either conspecific or swordtail skin extract. Predators remained further away from the stimulus tetra, took longer to initiate a bite and displayed fewer bites towards tetras that fin-flicked compared with tetras that did not fin-flick. These results support our hypothesis that fin flicking in tetras serves as both a visual alarm signal to conspecifics and a deterring signal to predators, and suggest that individual tetras may reduce their risk of predation by fin flicking upon detecting a predation threat.

Who dares, learns: chemical inspection behaviour and acquired predator recognition in a characin fish

Individuals that dare approach predators (predator inspection behaviour) may benefit by acquiring information regarding the potential threat of predation. Although information acquisition based on visual cues has been demonstrated for fish, it is unknown whether fish will inspect predators on the basis of chemical cues or whether such inspection behaviour results in information acquisition. Here, we first ascertained whether predator inspection behaviour can be mediated by chemical cues from predators by exposing groups of predator-naive glowlight tetras (Hemigrammus erythrozonus) to the chemical cues of a potential fish predator (convict cichlidCichlasoma nigrofasciatum) that had been fed either tetras (which possess an alarm pheromone) or swordtails (Xiphophorus helleri, which lack Ostariophysan alarm pheromones). Tetras showed a significant increase in antipredator behaviour when exposed to the tetra-diet cue, but not when exposed to the swordtail-diet cue. Chemically mediated predator inspection behaviour was also affected. Both the latency to inspect and the minimum approach distance to the predator significantly increased, and the mean number of inspectors per predator inspection visit significantly decreased when tetras were exposed to the tetra-diet versus the swordtail-diet chemical cues. We then examined a potential benefit associated with chemically mediated predator inspection behaviour. Only tetras that were initially exposed to the tetra-diet cue and that had inspected the predator acquired the visual recognition of a convict cichlid as a predation threat. Our results thus demonstrate that (1) predator inspection behaviour in the glowlight tetra can be initiated by chemical cues, (2) chemically mediated inspection behaviour is affected by the presence of alarm pheromone, and (3) inspectors benefit by acquiring the recognition of novel predators.

Group Vigilance and Shoal Size in a Small Characin Fish

The relationship between shoal size and group vigilance was investigated in the laboratory using a strongly schooling characin fish, the glowlight tetra (Hemigrammus erythrozonus). Group vigilance, as measured by the probability that at least one fish in the group detected (i.e. exhibited a startle response to) a brief, artificial alarm stimulus, increased curvilinearly at a decelerating rate with increasing shoal size. This would be predicted by the proposed early predator warning function of social groups. The observed relationship between corporate vigilance and shoal size was similar in form to one predicted by a simple signal detection model. However, observed detection probabilities for shoal sizes above 7 fish were lower than expected on the basis of this model, suggesting that an individual's probability of detection was not always independent of shoal size nor of the probabilities of detection of other shoal members. The numbers of tetras in a shoal exhibiting a startle response to an alarm stimulus increased non-linearly with increasing shoal size and exceeded the values predicted by the above mentioned model for the larger shoals, which implies social transmission of the alarm response among shoal members. The importance of the enhanced predator detection ability of fish shoals and the social transmission of alarms within them is discussed in relation to predator avoidance behaviour and other activities of fish in shoals.