Pseudomugil Signifer Research Articles

Behavioural plasticity in a native species may be related to foraging resilience in the presence of an aggressive invader.

Competition between invasive and native species can result in the exploitation of resources by the invader, reducing foraging rates of natives. However, it is increasingly recognized that multiple factors can enhance the resilience of native species competing for limiting resources with invaders. Although extensively studied in terrestrial species, little research has focused on behavioural plasticity in aquatic ecosystems and how this influences native species resilience. Here, we examined the role of behavioural plasticity in interactions between a native Australian fish, Pseudomugil signifer, and a widespread invasive fish, Gambusia holbrooki. To determine whether P. signifer displays behavioural plasticity that may mitigate competition with G. holbrooki, we first quantified social behaviours (aggression, submission and affiliation) and shoal cohesion for each species in single- and mixed-species groups. Second, we compared the feeding rates of both species in these groups to ascertain if any modulation of social behaviours and cohesion related to foraging success. We found that aggressive and submissive behaviours of G. holbrooki and P. signifer showed plasticity in the presence of heterospecifics, but social affiliation, shoaling and, most importantly, foraging, remained inflexible. This variation in the degree of plasticity highlights the complexity of the behavioural response of a native species and suggests that both behavioural modulation and consistency may be related to sustaining foraging efficiency in the presence of an invader.

Quantifying the structure and dynamics of fish shoals under predation threat in three dimensions

Abstract Detailed quantifications of how predators and their grouping prey interact in three dimensions (3D) remain rare. Here we record the structure and dynamics of fish shoals (Pseudomugil signifer) in 3D both with and without live predators (Philypnodon grandiceps) under controlled laboratory conditions. Shoals adopted two distinct types of shoal structure: “sphere-like” geometries at depth and flat “carpet-like” structures at the water’s surface, with shoals becoming more compact in both horizontal and vertical planes in the presence of a predator. The predators actively stalked and attacked the prey, with attacks being initiated when the shoals were not in their usual configurations. These attacks caused the shoals to break apart, but shoal reformation was rapid and involved individuals adjusting their positions in both horizontal and vertical dimensions. Our analyses revealed that targeted prey were more isolated from other conspecifics, and were closer in terms of distance and direction to the predator compared to non-targeted prey. Moreover, which prey were targeted could largely be identified based on individuals’ positions from a single plane. This highlights that previously proposed 2D theoretical models and their assumptions appear valid when considering how predators target groups in 3D. Our work provides experimental, and not just anecdotal, support for classic theoretical predictions and also lends new insights into predatory–prey interactions in three-dimensional environments.

Body size affects the strength of social interactions and spatial organization of a schooling fish (Pseudomugil signifer).

While a rich variety of self-propelled particle models propose to explain the collective motion of fish and other animals, rigorous statistical comparison between models and data remains a challenge. Plausible models should be flexible enough to capture changes in the collective behaviour of animal groups at their different developmental stages and group sizes. Here, we analyse the statistical properties of schooling fish (Pseudomugil signifer) through a combination of experiments and simulations. We make novel use of a Boltzmann inversion method, usually applied in molecular dynamics, to identify the effective potential of the mean force of fish interactions. Specifically, we show that larger fish have a larger repulsion zone, but stronger attraction, resulting in greater alignment in their collective motion. We model the collective dynamics of schools using a self-propelled particle model, modified to include varying particle speed and a local repulsion rule. We demonstrate that the statistical properties of the fish schools are reproduced by our model, thereby capturing a number of features of the behaviour and development of schooling fish.

Escape path complexity and its context dependency in Pacific blue-eyes (Pseudomugil signifer).

The escape paths prey animals take following a predatory attack appear to be highly unpredictable - a property that has been described as 'protean behaviour'. Here, we present a method of quantifying the escape paths of individual animals using a path complexity approach. When individual fish (Pseudomugil signifer) were attacked, we found that a fish's movement path rapidly increased in complexity following the attack. This path complexity remained elevated (indicating a more unpredictable path) for a sustained period (at least 10 s) after the attack. The complexity of the path was context dependent: paths were more complex when attacks were made closer to the fish, suggesting that these responses are tailored to the perceived level of threat. We separated out the components of speed and turning rate changes to determine which of these components contributed to the overall increase in path complexity following an attack. We found that both speed and turning rate measures contributed similarly to an individual's path complexity in absolute terms. Overall, our work highlights the context-dependent escape responses that animals use to avoid predators, and also provides a method for quantifying the escape paths of animals.

Depth-related composition and structuring of tropical riverine fish assemblages revealed by baited video

The aim of the present study was to determine whether boat-based deployment of remote underwater video cameras is effective for surveying fish assemblages in the deepest reaches of two large tropical rivers in north-eastern Australia. In addition, we compared fish assemblages recorded on baited versus unbaited cameras, and evaluated the sampling effort (duration of recording) required to estimate fish assemblages using remote underwater videos. We found that fish assemblages differed according to the depth, with statistically significant differences largely attributable to the prevalence of small-bodied species (<10-cm total length, TL), such as Ambassis sp., Melanotaenia sp. and Pseudomugil signifer recorded in shallow (0.4–2.0m) and intermediate (2.1–4.9m) depths, and larger-bodied fish species (>10cm TL), such as Lutjanus argentimaculatus, Mesopristes argenteus and Caranx sexfasciatus, in deep water (>5.0m). Estimates of fish assemblage attributes generally stabilised after 60min recording duration, suggesting that interrogation of video footage beyond this duration may not be cost-effective. We conclude that depth is an important consideration when surveying large and deep river fish assemblages and that where water clarity is favourable, underwater video provides one of the means by which an assemblage can be investigated across the entire depth profile.

Corrigendum to: Depth-related composition and structuring of tropical riverine fish assemblages revealed by baited video

The aim of the present study was to determine whether boat-based deployment of remote underwater video cameras is effective for surveying fish assemblages in the deepest reaches of two large tropical rivers in north-eastern Australia. In addition, we compared fish assemblages recorded on baited versus unbaited cameras, and evaluated the sampling effort (duration of recording) required to estimate fish assemblages using remote underwater videos. We found that fish assemblages differed according to the depth, with statistically significant differences largely attributable to the prevalence of small-bodied species (Ambassis sp., Melanotaenia sp. and Pseudomugil signifer recorded in shallow (0.4–2.0m) and intermediate (2.1–4.9m) depths, and larger-bodied fish species (>10cm TL), such as Lutjanus argentimaculatus, Mesopristes argenteus and Caranx sexfasciatus, in deep water (>5.0m). Estimates of fish assemblage attributes generally stabilised after 60min recording duration, suggesting that interrogation of video footage beyond this duration may not be cost-effective. We conclude that depth is an important consideration when surveying large and deep river fish assemblages and that where water clarity is favourable, underwater video provides one of the means by which an assemblage can be investigated across the entire depth profile.

The efficacy of clove oil for anaesthesia of eight species of Australian tropical freshwater teleosts

AbstractThe efficacy of clove oil for anaesthesia was examined on eight species of Australian tropical freshwater fishes: the native Mulgrave goby (Glossogobius bellendenensis, Gobiidae), empire gudgeon (Hypseleotris compressa) and sleepy cod (Oxyeleotris lineolatus) (both Eleotrididae), Eastern rainbowfish (Melanotaenia splendida, Melanotaeniidae), Pacific blue‐eye (Pseudomugil signifer, Pseudomugilidae), and eel‐tailed catfish (Tandanus tandanus, Plotosidae), and the non‐native species spotted tilapia (Pelmatolapia mariae, Cichlidae) and guppy (Poecilia reticulata, Poecilidae). Induction to anaesthesia, recovery from anaesthesia and survival of fish were determined for five concentrations (20 mg/L, 30 mg/L, 40 mg/L, 80 mg/L, and 160 mg/L). A 20 mg/L clove oil concentration was not sufficient to induce a loss of reflex reactivity within 10 min for most individuals (> 85%) in the eight species examined. Effective clove oil concentrations for anaesthesia induction and recovery (40–80 mg/L) for seven out of the eight species examined overlap with those reported for other tropical freshwater fish species. Differences in induction and recovery times among treatments were not always independent of fish size for G. bellendenensis, M. splendida, O. lineolatus, and P. mariae, emphasizing the importance of taking biological and environmental factors into account when determining and applying effective clove oil concentrations for anaesthesia in fish. In contrast, long recovery times and mortality for T. tandanus in even relatively low concentrations suggests that clove oil may not be an appropriate anaesthetic for at least some fish species.

Intraspecific Sexual Size and Shape Dimorphism in an Australian Freshwater Fish Differs with Respect to a Biogeographic Barrier and Latitude

Geographically structured variation in morphology is a common phenomenon in animals with environmental factors covarying with both latitude and biogeographic barriers having profound impacts on body size and shape. The Pacific blue-eye (Pseudomugil signifer) is a freshwater fish that lives along Australia’s east coast and occurs on either side of a terrestrial barrier, the Burdekin Gap. By quantifying the size and shape of males and females from 10 populations we found that Pacific blue-eyes are not sexually size dimorphism north of the Burdekin Gap whereas the degree of dimorphism was dependent upon latitude south of the barrier. Rensch’s rule was not supported as the degree of male-biased size dimorphism did not increase with increasing population mean body size. Body shape was related to body size and was sexually dimorphic south of the Burdekin Gap but not north of it. Our study represents a rare case of identifying how both body size and shape differ with respect to latitude and a major terrestrial biogeographic barrier and lends further support to the notion that P. signifer may comprise two species, or incipient species, that are separated by the Burdekin Gap.

Sensory ecology in a changing world: salinity alters conspecific recognition in an amphidromous fish, Pseudomugil signifer

Group fission and fusion processes are driven by state dependence, risk and the availability of information from others. Yet the availability of information changes under different environmental conditions, thus aiding or inhibiting group formation and maintenance. Chemical cues provide information on the location of individuals and can act as a mechanism for individuals to group together, although they can be greatly affected by environmental conditions. Using a flow channel, we studied how one shoaling fish species, the Pacific blue-eye (Pseudomugil signifer), responds to conspecific chemical cues (CCCs) in different environmental conditions (salinities). This species lives in estuarine environments, ranging in salinity from fresh to fully marine. P. signifer responded to CCCs in freshwater but not in saltwater. Furthermore, P. signifer did not respond to saltwater with CCCs added from freshwater. It took significantly longer for fish in saltwater, than in freshwater, to locate and join a shoal when only CCCs from the shoal were present. Finally, fish formed more cohesive shoals in freshwater than in brackish or saltwater. These results suggest that these fish do not rely on chemical cues in saltwater to locate conspecific shoals. Furthermore, the reduced amounts of these cues in saltwater may inhibit the maintenance of tight shoal structures. We suggest that fish utilise different sensory modalities in fresh or saltwater in order to locate one another, or the social structure of these groups is fundamentally different between these two water

Females prefer athletes, males fear the disadvantaged: different signals used in female choice and male competition have varied consequences

The most commonly assumed cost for exaggerated male ornamentation is increased predation pressure owing to decreased locomotor performance or increased conspicuousness to predators. Despite its intuitive basis, the locomotor costs of male ornamentation are not well established. We tested the hypothesis that multiple male signals that are used independently during female choice and male competition could lead to varied locomotor costs. Multiple signals with varied costs could provide a more detailed indicator of overall male quality, as only the highest-quality individuals could support all costs. To test this idea, we investigated the burst locomotor consequences of multiple ornaments for males of the pacific blue-eye (Pseudomugil signifer). We evaluated five competing models relating body size, ornament size and performance traits to field measures of dominance and attractiveness. Non-propulsive male fin ornaments used during male competition were different from those used in female choice. First dorsal fin length was the most important predictor of male attractiveness, while dominance was only associated with anal fin length. Furthermore, first dorsal fin length was positively correlated with swim speed, while anal fin length was negatively associated with speed. Our study shows that multiple male signals that are used independently during male competition and female choice also differ in their associated costs. This provides a mechanism for understanding why locomotor costs for exaggerated male ornamentation are not often empirically demonstrated.

Laboratory Evaluation of the Effect of Alternative Prey and Vegetation on Predation of Culex annulirostris Immatures by Australian Native Fish Species

The impact of alternative prey and simulated vegetation on Culex annulirostris Skuse predation efficacy by Australian smelt, Retropinna semoni (Retropinnidae); crimson-spotted rainbowfish, Melanotaenia duboulayi (Melanotaeniidae); empire gudgeon, Hypseleotris compressa (Eleotridae); estuary perchlet, Ambassis marianus (Ambassidae); firetail gudgeon, Hypseleotris galii (Eleotridae); fly-specked hardyhead, Craterocephalus stercusmuscarum (Atherinidae); and Pacific blue-eye, Pseudomugil signifer (Atherinidae), was evaluated in Queensland, Australia. The presence of chironomid midge larvae and tusked frog, Adelotus brevis (Leptodactylidae), tadpoles did not have a significant negative impact on the predation rates of Cx. annulirostris by these 7 fish species. Hypseleotris galii, M. duboulayi, and R. semoni demonstrated strong preference for larvae of Cx. annulirostris over both alternative prey species. In the presence of alternative prey species, the mean predation rate of M. duboulayi on larvae of Cx. annulirostris remained greater than that of other fish species tested. When evaluated at varying densities of simulated vegetation, predation rates of all fish species were similar to those reported in open conditions.

Comparisons of fish catches using fyke nets and buoyant pop nets in a vegetated shallow water saltmarsh flat at Towra Point, NSW

The selection of appropriate sampling methods is a prerequisite for the design of any survey detailing nekton assemblages. In the present study two commonly used saltmarsh fish sampling methods, the fyke net and the buoyant pop net, were used to compare the assemblages of fish caught in a saltmarsh flat during monthly spring tides over a twelve month period. Both nets were made of 2mm mesh. A total of 3514 fish and crustaceans of 21 species were captured by 48 fyke net sets and 818 fish of 16 species were captured by 48 pop net releases. Fyke and pop nets recorded significantly different (ANOSIM: P<0.001) assemblages, with higher proportions of Pseudomugil signifer caught in the fyke nets and Ambassis jacksoniensis in the pop nets. Five species, Sillago cilliata, Rhabdosargus sarba, Redigobius macrostoma, Taeniodes mordax and Metapenaeus macleayi, were caught in the fyke nets only. Significant differences in the size of fish caught were recorded for two species, Gobiopterus semivestitus and Gerres subfasciatus, with larger fish on average caught in the pop nets. The result suggested that pop nets are less efficient at catching smaller fish.

Trophic relationships between itinerant fish and crab larvae in a temperate Australian saltmarsh

Comparisons of zooplankton inputs and outputs for a temperate Australian saltmarsh demonstrate a substantial contribution of crab larvae to the ebbing tide water, particularly during the cooler months. Few crab larvae were present in the incoming tide (mean abundance 4 m−3), whereas many crab larvae were present in the outgoing water (mean abundance 2124.63 m−3). Stomach content analysis of itinerant fish exiting the saltmarsh with the ebbing tide demonstrated extremely high proportions of crab larvae in the gut of glassfish (Ambassis jacksoniensis), as well as flat tail mullet (Liza argentea) and blue eye (Pseudomugil signifer). The results suggest a direct trophic link between secondary production of saltmarsh and itinerant fish, and a significant ecological role for burrowing crabs occupying saltmarshes in temperate Australia in the trophic food web of saltmarsh–estuarine systems.

Male competition is disruptive to courtship in the Pacific blue‐eye

The present study examined the effects of competition on male courtship in the Pacific blue‐eye Pseudomugil signifer, a species of fish where females have previously been shown to use courtship, but not male fighting prowess, as an important mate choice cue. Courtship bouts directed to a stimulus female were shortest when two males were allowed to freely interact (contact treatment) and longest when there was only one male (non‐interaction). Courtship length in trials where one of two males was confined to a clear cylinder (visual) was intermediate between the other two treatments. Courtship in visual and contact treatments was constantly disrupted. The percentage of interrupted courtships was higher for the contact compared to visual treatment where aggressive interactions were also longer in duration and took place more frequently. Within contact trials, dominant males courted longer than subordinates despite both males experiencing comparable rates of courtship disruption. These results suggest that male‐male competition can have important implications for adaptive female choice particularly in circumstances where the benefits being sought by females are unrelated to male fighting ability.

Sequential male mate choice in a fish, the Pacific blue-eye Pseudomugil signifer

Mate choice is not just a female preoccupation. Under some circumstances, males may also be choosy. However, studies of male mate choice have generally been confined to situations where males can make direct comparisons between potential partners. In contrast, sequential male mate choice has largely been overlooked despite its biologically importance, especially if current investment in mate attraction diminishes a male’s future mating opportunities. Using the Pacific blue-eye fish Pseudomugil signifer, we show that males are capable of exercising sequential mate choice. When presented sequentially with large and small females, males spent more effort courting the former. However, males did not appear to modify the time spent courting a given female based on the size of the female encountered previously. We suggest that greater attention to the sequential choice problem in males may help illuminate similarities and differences between the sexes when it comes to mating decisions.

Superior fighters make mediocre fathers in the Pacific blue-eye fish

It is widely assumed that male competition and female choice select for elaboration of the same male traits and that fighting ability is synonymous with high quality in terms of benefits to females. Under these assumptions, females are expected to use the same traits that reflect fighting ability to choose the most dominant male, even if females are not privy to actual male–male interactions. Few studies, however, have explicitly investigated female choice in relation to male fighting ability. I conducted experiments separating the effects of male competition and female choice in a freshwater fish, the Pacific blue-eye, Pseudomugil signifer, to test whether females prefer dominant males and whether females obtain higher egg hatching success by being choosy. When females were precluded from witnessing agonistic encounters between two potential mates, they did not appear to use traits correlated with fighting ability to choose competitively superior males. However, even when females were privy to competition, witnessing male interactions did not induce a preference for dominant individuals. Lack of preference for superior fighters may be because there was no difference in hatching success between eggs guarded by dominant and subordinate males. Instead, females appeared to prefer males that spent a greater proportion of time engaged in courtship and, in so choosing, enjoyed higher egg hatching success. These results indicate that dominant males are not necessarily more attractive than subordinates nor do the former necessarily guarantee or deliver the kind of benefits that females may seek.

Costs influence male mate choice in a freshwater fish.

It is well known that female mate choice decisions depend on the direct costs of choosing (either because of search costs or male-imposed costs). Far less is known about how direct fitness costs affect male mate choice. We conducted an experiment to investigate male mate choice in a fish, the Pacific blue-eye (Pseudomugil signifer). Preferred females were larger, probably because larger females are also more fecund. Males, however, were consistent in their choice of female only when the costs of associating with prospective mates were equal. By contrast, males were far less consistent in their choice when made to swim against a current to remain with their initially preferred mate. Our results suggest that males may also respond adaptively to changes in the costs of choosing.

Extensive genetic divergence among populations of the Australian freshwater fish, Pseudomugil signifer (Pseudomugilidae), at different hierarchical scales

The 'island' nature of river systems limits the possibility of dispersal in freshwater fish species, with many displaying extensive genetic subdivision across their ranges. We examined the population genetic structure of the predominantly freshwater fish, Pseudomugil signifer, at fine, medium and broad scales using allozyme and mitochondrial DNA techniques. Extensive genetic subdivision across the range (FST = 0.6) at six polymorphic allozyme loci was partitioned mostly among river-system drainages (42%). Patterns of mitochondrial DNA sequences, which mirrored previous taxonomic designations and a terrestrial biogeographic barrier, identified two major groups. The level of divergence between the groups implied a considerable period of isolation. At a more localized scale, significant genetic differences between adjacent drainages implied that flood events are not effective transport mechanisms and indicate that populations of P. signifer in different drainages are essentially independent units. The history of P.�signifer appears to be dominated, at different spatial scales, by long periods of isolation among drainages mediated by changes in sea-level, which merge and isolate drainages haphazardly over time. The chance nature of dispersal, coupled with isolation and potential population size fluctuations, probably leads to the observed complex patterns of genetic divergence.

Within-drainage population genetic structure of the freshwater fish Pseudomugil signifer (Pseudomugilidae) in northern Australia

Dendritic channel patterns have the potential to isolate populations within drainages, depending on the relative position within the stream hierarchy of the populations. We investigated the extent of genetic subdivision in the Australian freshwater fish Pseudomugil signifer (Kner) (Pseudomugilidae) from two drainages in northern Queensland, Australia, using allozyme techniques. The drainages were adjacent and had similar channel patterns each with two major subcatchments coalesced to an estuarine confluence. Analysis of 30 sites across the two drainages revealed that although there was significant genetic variation among sites in both drainages, this was not between the two subcatchments in either case. This result did not support predictions of the stream hierarchy model (SHM), which would predict higher levels of variation among subcatchments than within them, nor did it suggest that estuarine conditions represent a significant barrier to dispersal in this species. More variation was among sites within each subcatchment. Multidimensional scaling plots revealed that, although most sites within a drainage were similar to one another, outlier sites occurred in each drainage, so correlations between genetic distance and geographic distance were weak. We suggest that the distance between sites and the probability of connectivity between sites may better explain the observed distribution of genetic diversity.

Factors Influencing Fish Composition in an Australian Intermittently Open Estuary. Is Stability Salinity-Dependent?

The ichthyofauna of the intermittently open Shellharbour Lagoon in southeastern Australia was sampled over 14 months to investigate factors influencing species composition. Zostera capricorni and bare sand habitats were sampled every two months with a fine-mesh seine. Of the 10277 fish caught representing 19 families and 27 species, the most numerically dominant species were Pseudogobius olorum and Pseudomugil signifer. The most abundant economically important species were Acanthopagrus australis, Mugil cephalus and Myxus elongatus. Mean number of fish and species was significantly higher over Zostera than bare sand during months immediately after the estuary opened when juvenile marine fishes recruited, demonstrating the estuary's nursery function. In contrast to other intermittently open estuaries in Australia and South Africa, Shellharbour Lagoon's fish assemblage appears resilient to perturbation and does not undergo distinct seasonal variations. This may be a result of the estuary's short open phases providing less opportunity for marine fishes to enter. Perhaps more importantly, the less dramatic fluctuations in salinity between open and closed phases maintains salinity at a level intermediate of the tolerances of both marine and estuarine fishes.