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The marine environment imposes severe constraints on the means by which location information can be obtained from submerged, freely swimming animals. Standard methods of tracking marine organisms are often labour intensive, expensive, or of low spatial and temporal resolution. Here, we describe a new method by which larger species of fish that live in shallow or surface waters can be tracked using an inexpensive telemetry device based on the global positioning system (GPS). We fixed small GPS data-logger units configured to record position fixes at 90 to 150 s intervals to low-drag tow-bodies and then attached these units by means of a tether to New Zealand eagle rays Myliobatis tenuicaudatus. After deployment periods lasting up to 29 h we recovered the tracking gear and downloaded the location data, which were stored onboard. The GPS units worked well, with mean fix-success rates >90%, and allowed accurate reconstruction of the movements of the rays throughout an estuary in Northland, New Zealand. Although our method is restricted to animals that swim on or near the surface of the water, it does provide a means of cheaply describing the movement patterns of suitable species for substantial periods of time at heretofore unprecedented spatial and temporal scales.

Ambient sound intensity in coastal waters typically increases by as much as 2 to 3 orders of magnitude (20 to 30 dB) immediately after sunset and before sunrise in what is known as a dawn and evening chorus. The dominant feature of the chorus is most often a dramatic increase in spec- trum level usually in a narrow frequency range of around 400 to 4000 Hz. While the sources of some choruses have been identified, the sources of many choruses remain unidentified. Here we confirm that in New Zealand, the sound is the feeding noises of sea urchins for which frequencies in the range of 800 to 2800 Hz are amplified by the ovoid calcareous skeleton, or 'test', of urchins acting as a Helmholtz resonator. Furthermore, the timing of the dawn and dusk choruses is related to the crepus- cular feeding activity of sea urchins. Underwater sound recordings from individual sea urchins of a range of sizes confirm earlier speculation that the urchin test acts as a Helmholtz resonance chamber capable of generating sufficient acoustic power to create these choruses. These results indicate the potential importance of coastal urchin populations as a major contributor to the underwater choruses, which appear to be important in assisting the larvae of key reef species, such as fishes, crabs, and lobsters, to locate suitable settlement sites.

The importance of the acoustic cuescape is often overlooked in studies of animal orientation. Recent studies have shown that reef noise affects the behaviour and orientation of settlement-stage coral reef fish. This response may simply facilitate orientation to reefs; alternatively, acoustic habitat cues could also facilitate the remote selection of suitable settlement habitats. To test which components of reef noise evoke behavioural responses in larval fish, we used light traps to measure the responses of a diverse range of settlement-stage fish to the filtered ‘high’ (570–2000 Hz)- and ‘low’ ( 10 individuals, four (Pomacentridae, Apogonidae, Lethrinidae and Gobiidae) were caught in significantly greater numbers in the high-frequency traps than either the low-frequency or the silent traps. The Syngnathidae preferred high- to low-frequency traps, while the Blenniidae preferred high-frequency to silent traps. Only the Siganidae showed no preference between any of the sound treatments. Although some species-level variation in response was found, the general trend was a preference for high-frequency traps. This study suggests that most settlement-stage fish select the higher-frequency audible component of reef noise, which is produced mainly by marine invertebrates, as a means of selectively orienting towards suitable settlement habitats. The results highlight potential impacts of anthropogenic noise pollution and habitat modification in affecting the natural behaviour of reef fish at a critical stage in their life history.

Short-tailed stingrays (Dasyatis brevicaudata) are the largest stingrays in the world. They are common in New Zealand waters and aggregate seasonally in large numbers at the Poor Knights Islands Marine Reserve (PKMR), where they are a major attraction. Pop-up satellite archival tags (PSAT) were attached to two female short-tailed stingrays at two New Zealand offshore islands (within and nearby the PKMR) to investigate patterns of movement. These are the first PSAT data published for a stingray species. The rays were tagged for 62 and 151 days using a novel method of tag attachment developed specifically for ray species. Analyses of geolocation, depth and behavioural data indicate neither ray moved large distances (≤ 25 km) from the tagging locations. However, they showed a seasonal shift to deeper waters, progressively increasing time spent at greater depths and decreasing time spent at shallow depths towards winter. In addition, one ray displayed strong diel vertical movements. The method developed for PSAT attachment to stingrays proved successful and can be applied for long-term (> 6 months) movement and behavioural studies.

Interspecific variation in relative brain size (encephalization), the relative size of the five major brain areas (the telencephalon, diencephalon, mesencephalon, cerebellum, and medulla) and the level of cerebellar foliation was assessed in over 20 representative species of batoid (skates and rays), from eight families. Using species as independent data points and phylogenetically independent contrasts, relationships among each of the neuroanatomical variables and two ecological variables, habitat and lifestyle, were assessed. Variation in relative brain size and brain organization appears to be strongly correlated with phylogeny. Members of the basal orders Rajiformes and Torpediniformes tend to have relatively small brains, with relatively small telencephalons, large medullas, and smooth, unfoliated cerebellums. More advanced Myliobatiformes possess relatively large brains, with relatively large telencephalons, small medullas, and complex, heavily foliated cerebellums. Increased brain size, telencephalon size, and cerebellar foliation also correlate with living in a complex habitat (such as in association with coral reefs) and an active, benthopelagic lifestyle, but as primary habitat and lifestyle also closely match phylogenetic relationships in batoids, it is difficult to separate the influence of phylogeny and ecological factors on brain organization in these animals. However, the results of two forms of multivariate analysis (principal component analysis and cluster analysis) reveal that certain species are clustered with others that share ecological traits, rather than with more closely related species from the same order. This suggests that ecological factors do play a role in defining patterns of brain organization and there is some evidence for ‘cerebrotypes’ in batoids.

In the adaptive filter model of the cerebellum, the granular layer performs a recoding which expands incoming mossy fibre signals into a temporally diverse set of basis signals. The underlying neural mechanism is not well understood, although various mechanisms have been proposed, including delay lines, spectral timing and echo state networks. Here, we develop a computational simulation based on a network of leaky integrator neurons, and an adaptive filter performance measure, which allows candidate mechanisms to be compared. We demonstrate that increasing the circuit complexity improves adaptive filter performance, and relate this to evolutionary innovations in the cerebellum and cerebellum-like structures in sharks and electric fish. We show how recurrence enables an increase in basis signal duration, which suggest a possible explanation for the explosion in granule cell numbers in the mammalian cerebellum.

The top predators in coastal marine ecosystems, such as whales, dolphins, seabirds, and large predatory fishes (including sharks), may compete with each other to exploit food aggregations. Finding these patchy food sources and being first to a food patch could provide a significant competitive advantage. Our hypothesis is that food patches have specific sound signatures that marine predators could detect and that acoustic sources and animal sensory capabilities may contribute to competition dynamics. Preliminary analysis shows that diving gannets have a distinct spectral signature between 80 and 200 Hz, which falls within the hearing sensitivity of large pelagic fishes. Therefore, we suggest that diving birds may contribute to the sound signatures of food aggregations, linking competition dynamics both above and below the water surface.

Soundscapes provide a new tool for the study of fish communities. Bigeyes (Pempheris adspersa) are nocturnal planktivorous reef fish, feed in loose shoals and are soniferous. These vocalisations have been suggested to be contact calls to maintain group cohesion, however direct evidence for this is absent, despite the fact that contact calls are well documented for many other vertebrates, including marine mammals. For fish, direct evidence for group cohesion signals is restricted to the use of visual and hydrodynamic cues. In support of adding vocalisation as a contributing cue, our laboratory experiments show that bigeyes significantly increased group cohesion when exposed to recordings of ambient reef sound at higher sound levels while also decreasing vocalisations. These patterns of behaviour are consistent with acoustic masking. When exposed to playback of conspecific vocalisations, the group cohesion and vocalisation rates of bigeyes both significantly increased. These results provide the first direct experimental support for the hypotheses that vocalisations are used as contact calls to maintain group cohesion in fishes, making fish the evolutionarily oldest vertebrate group in which this phenomenon has been observed and adding a new dimension to the interpretation of nocturnal reef soundscapes.

Juvenile and adult reef fishes often undergo migration, ontogenic habitat shifts, and nocturnal foraging movements. The orientation cues used for these behaviours are largely unknown. In this study, the use of sound as an orientation cue guiding the nocturnal movements of adult and juvenile reef fishes at Lizard Island, Great Barrier Reef was examined. The first experiment compared the movements of fishes to small patch reefs where reef noise was broadcast, with those to silent reefs. No significant responses were found in the 79 adults that were collected, but the 166 juveniles collected showed an increased diversity each morning on the reefs with broadcast noise, and significantly greater numbers of juveniles from three taxa (Apogonidae, Gobiidae and Pinguipedidae) were collected from reefs with broadcast noise. The second experiment compared the movement of adult and juvenile fishes to reefs broadcasting high (>570 Hz), or low (

The dwarf scorpionfish Scorpaena papillosa detected the hydrodynamic signals produced by prey with the mechanosensory lateral line. This species displayed a pause and move search pattern that is consistent with a saltatory search. The pause phase of the search cycle was probably used to detect prey because pauses often ended early in order to initiate an approach at prey and prey were detected throughout the search space. The move phase of the search cycle repositioned the fish so that it moved approximately a third of the reactive distance. Move distance was found to be the most important factor in gaining novel search space. Turning was shown to be relatively unimportant in gaining novel search space with a high frequency of low turn angles made by the fish. The dwarf scorpionfish, however, exhibited a spiralling or looping pattern over a search path exhibiting a turn bias towards either the left or right. The dwarf scorpionfish adopted a search behaviour that is consistent with a saltatory search and efficient for lateral line predation.

Underwater breathing apparatus (UBA) has played a vital role in the study of aquatic environments, and is commonly used in visual census of mobile aquatic animals. The possibility of artifacts arising from diver presence and from the noise produced by UBA have long been recognised but not systematically studied. Here we analyse the noise produced by the three types of UBA used for research; self-contained underwater breathing apparatus (SCUBA), semi-enclosed circuit re-breather (SECR), and fully enclosed circuit re-breather (FECR) systems. There were significant differences in the source levels (SL) produced by the different UBA for both mean SL (p

The larvae or phyllosomes of many species of spiny lobsters (Palinuridae) are known to complete their development in offshore oceanic waters. Phyllosomes metamorphose to non‐feeding, nektonic post‐larvae or pueruli, which move into shallow coastal waters where they settle to become benthic dwelling juveniles. There is growing evidence that the movement of pueruli is directed toward the coast rather than a process of random dispersal. The migration inshore by the non‐feeding pueruli is likely to be one of the more extreme examples of onshore orientation among marine organisms, but is still poorly understood. This article provides a synthesis of the current state of knowledge of the possible cues and sensory mechanisms that might be used by pueruli of spiny lobsters for orienting toward the coast from offshore waters. The review is used to identify the potential cues that would benefit from future research efforts.

Parapercis colias (blue cod) and Cheimarrichthys fosteri (torrentfish) are two members of the family Pinguipedidae. They reside in habitats with different background levels of hydrodynamic activity and differ in their feeding ecology. The peripheral morphology of the mechanosensory lateral line system was investigated in each species. The torrentfish is the only freshwater member of this otherwise exclusively marine family. It resides in turbulent fast flowing habitats and feeds nocturnally on stream drift. Torrentfish have many superficial neuromasts and a simple unbranched canal system. In comparison the blue cod resides in sub-tidal slow flowing habitats, is a diurnal predator and has relatively few superficial neuromasts and a well-developed branching canal system. For these two species the background level of hydrodynamic activity does not appear to be the dominant selection pressure on lateral line morphology, in the case of the torrentfish in particular it is more compelling to view lateral line morphology in the light of environmental pressures that have favoured the evolution of nocturnal feeding.

The detection of food odour by the freshwater eels, Anguilla australis and Anguilla dieffenbachii released a behavioural response to flow that resulted in direct upstream movement toward the odour source. Changes in various orientation parameters were observed as eels neared the source. Eels had substantially lower swimming velocities and considerably more variable heading and course angles close to the odour source (!0"9 m) than further away (>0"9 m). Observed changes in orientation parameters were primarily due to changes in the behaviour of a searcher following odour loss. Cross-stream movements were initiated when the eel moved beyond the lateral margins of the odour plume. The behavioural switch from odour-conditioned rheotaxis to cross-stream casting following odour loss occurred more frequently close to the odour source where the plume was most narrow. Odour-conditioned rheotaxis enables the searcher to move quickly and efficiently toward the odour source without the need to extract directional information from a highly intermittent and complex chemical signal.

The response properties of anterior lateral line afferent neurones in Trematomus bernacchii were recorded extracellularly while stimulating the fish with unidirectional water flows of varying velocity. Afferent neurone responses were either flow-sensitive or flow-insensitive. Flow-sensitive neurones showed linear increases in response magnitude with increasing flow rate and tonic non-adapting response properties. These findings indicate that flow-sensitive afferent neurones originate from lateral line receptors that detect absolute flow velocity. The likely explanation is that flow-sensitive afferent neurones innervate neuromasts located superficially on the skin and flow-insensitive neurones innervate neuromasts situated in sub-epidermal fluid-filled canals.

The sensory basis of olfactory search behavior was investigated in the banded kokopu, Galaxias fasciatus, using a flow tank. In the presence of a 2 cm s(-1) current flow, banded kokopu use both water current and chemical information to locate a food odor source. The superficial neuromasts of the lateral line system mediate the rheotactic component of the odor search. A physical block of one olfactory nostril did not affect the olfactory search strategy employed by banded kokopu in still water or in the presence of a current flow. Thus, there is no evidence that banded kokopu perform a bilateral comparison of the olfactory stimulus during their odor search. Previously, olfaction and gustation have been the only sensory systems shown to directly mediate orientation and movement towards odor sources in fish. The use of hydrodynamic cues by fish in location of an olfactory source has been previously proposed, but without direct experimental identification of the sensory systems employed. This study identifies the contributing roles of both olfactory and hydrodynamic sensory systems to the olfactory search repertoire of fish.

Water movements, of both abiotic and biotic origin, provide a wealth of information of direct relevance to the guidance of prey capture behavior. To gather hydrodynamic information, fish have sensors of two basic types: those scattered over the surface of the body known as superficial neuromasts and similar sensors embedded in subdermal lateral line canals. Recently, the anatomical dichotomy between superficial and canal neuromasts has been matched by demonstrations of a corresponding functional dichotomy. Prey detection and localization are evidently mediated by canal neuromasts, whereas superficial neuromasts are more sensitive to water flows over the surface of the fish and participate in the orientation to water currents, a behavior known as rheotaxis. However, rheotaxis in combination with chemosensory inputs can also guide fish to their prey. Thus there is evidence that both lateral line sub-modalities either alone or in concert with other senses play a role in prey capture. Are there circumstances where prey capture requires integration of information from both lateral line sub- modalities? Recent evidence shows that fish are capable of tracking other fish on the basis of the hydrodynamic trails left behind by their swimming motion. Pharmacological and physical ablation of lateral line end organs shows that indeed integration of information from both sub-modalities is required for the complex hydrodynamic task of natural prey capture in the dark. Furthermore, these experiments provide an excellent demonstration of the integration of hydrodynamic, chemosensory, tactile and visual information for the multimodal guidance of prey capture behavior.

We draw inspiration from the fish “hearing” organ, the otolith, to create a portable engineering device that can augment a human diver’s ability to hear underwater. The otolith is an inertial displacement sensor, consisting of a dense bony mass that acts as a reference to the surrounding sensory hair cells. The challenges in adapting the otolith into a hearing device are discussed. For our proposed sensor, we have explored the use of capacitive sensing for measuring displacement. A proof of concept prototype and a finite element model of the sensor are presented.

The potential for cadmium to produce sensory deficits in the mechanosensory lateral line and olfactory systems was examined in migratory Galaxias fasciatus juveniles or ‘whitebait’. Using a two-choice chamber apparatus, three groups of whitebait were tested for a known attraction to adult pheromones and then exposed to either 0.1, 0.5 or 1 μg Cd+2 l-1 for 48 h and retested. The attraction to adult pheromones had been eliminated after exposure to concentrations of 0.5 and 1 μg Cd+2 l-1, indicating these levels of cadmium exposure had impaired olfactory function. Rheotaxis trials were conducted to determine the level of cadmium exposure which would inhibit lateral line function. The lateral line system was not blocked until a concentration of 2 μg Cd+2 l-1. The blocking of the lateral line and olfactory sensory systems was reversible. After 14 days recovery in clean freshwater both rheotaxis and the attraction to adult pheromones had returned. Whitebait were also tested for a preference/avoidance response at 2 μg Cd+2 l-1. Fish showed neither a preference for, or an avoidance of, a concentration which would disable both the lateral line and olfactory sensory systems. The disabling of these sensory systems may render migratory cues undetectable, affecting habitat selection by whitebait, which may ultimately affect the distribution of banded kokopu populations.

The mechanosensory lateral line is a distributed, hair-cell based system which detects the water flow regime at the surface of the fish. Superficial neuromasts densely scattered over the surface of some cave fish detect the pattern of flow over the surface of the body and are important in rheotactic behaviors and perhaps in the localization of small vibrating sources. Canal neuromasts are very likely also involved in the detection of small planktonic prey, but seem also to play an essential role in replacing vision as the major sense by which blind cave-fish perceive their surroundings. The flow-field that exists around a gliding fish is perturbed by objects in the immediate vicinity, these perturbations are detected by the lateral line system. In this way the fish can build up a ‘picture’ of its environment, a process that has been called active hydrodynamic imaging. None of the lateral line behaviors exhibited by blind cave fish are necessarily exclusive to these species, but there is some evidence that their lateral line capabilities are enhanced with respect to their sighted relatives.

Our understanding of habitat selection by reef fish larvae has changed dramatically in the last 10 years. Fish larvae have long been considered passive particles at the mercy of ocean currents, tides and weather events. For reef fishes, ecological evidence has shown that passive dispersal alone often cannot explain larval distributions, suggesting active behaviour by reef fish larvae. While behaviourally modified passive transport may be important, recent work demonstrates that some reef fish larvae have the capability to actively swim to settlement habitat. They can orientate to reefs from distances of at least 1 km and can swim at speeds of 13.5 cm s ‐1 for several days. The question then becomes, what are the cues that fish larvae use to orientate to reefs? Ambient reef sound has been shown to be attractive to reef fish larvae, and current research aims to understand better the nature and use of these acoustic cues. Other potential cues include chemoreception /olfaction, wave cues and visual location of reefs. A better understanding of active habitat selection and the underlying sensory and behavioural mechanisms will improve our knowledge of recruitment processes in reef fish ecology, and may have implications for active management of reef fish populations.

Juvenile migratory Galaxias fasciatus juveniles or whitebait were attracted to odours produced by adults. The attraction was dependent on concentration with an upstream movement and attraction to the odour chamber at intermediate level concentrations. At a high concentration the migratory response of whitebait was retarded with the majority of fish not moving upstream but remaining in the lower section of the apparatus. There was no response to odours from adults of other galaxiid species, the inanga G. maculatus or koaro G. brevipinnis at any concentration. These results demonstrate G. fasciatus whitebait have the ability to discriminate species-specific pheromones during their migratory phase, providing evidence of a pheromonal attraction in migratory amphidromous fish which could possibly provide a basis for effective habitat selection.

Elasmobranchs possess a multiplicity of mechanisms controlling posture and short distance orientation. Visual–vestibular contributions to posture and locomotion are well documented. So too, are the contributions of vision, olfaction and the octavolateralis senses to short distance orientation, particularly orientation to specific environmental stimuli such as those generated by prey. Less well understood are the mechanisms guiding orientation over longer distances. Anecdotal and systematic observations of behaviour show tidal, daily, repeat long distance, and even seasonal movement patterns. True navigation has not been demonstrated in elasmobranchs and the sensory mechanisms underlying the above movement patterns remain largely speculative. However, they are likely to include responses to water currents, and physical parameters such as temperature, pressure, and the geomagnetic field. Of particular interest in elasmobranchs is that geomagnetic orientation could be mediated directly via a magnetite based sensory system, or indirectly via the electrosensory system. Systematic studies of movement patterns and experimental studies of the underlying mechanisms of orientation are required to gain an increased understanding of orientation and navigation in this intriguing group.

The sensory basis of rheotaxis (orientation to currents) was investigated in the blind Mexican cave fish, Astyanax fasciatus. An unconditioned rheotactic response to uniform velocity flows was exhibited, with a threshold of less than 3 cm s−1. Disabling the entire lateral line or the superficial neuromast receptor class increased the rheotactic threshold to greater than 9 cm s−1. A pharmacological block of the lateral line canal system alone had no effect. These results demonstrate that the superficial lateral line system controls rheotaxis at low current velocities. The effect of pairing an odor stimulant with the water current dropped the rheotactic threshold to less than 0.4 cm s−1. This study provides a clear behavioral role for the superficial neuromasts where none previously existed, and also establishes a link between the mechanosensory lateral line and olfactory systems in the olfactory search behavior of the cave fish.

The sensory basis of rheotaxis was investigated in Pagothenia borchgrevinki utilising a laminar flow chamber. The threshold for P. borchgrevinki to exhibit an unconditioned rheotactic response lay between 1 and 2 cm s−1. Disabling the entire lateral line or the superficial neuromast receptors increased the rheotactic threshold to greater than 5 cm s−1. Pharmacological blocking of the lateral line canal system alone had no effect. This study provides a direct demonstration that the superficial lateral line system is involved in mediating rheotaxis. These results, coupled with previous work on Antarctic fishes, suggest a division of labour exists between the two submodalities of the lateral line system. Superficial neuromasts are more responsive to unmodulated flows (DC) and mediate behaviour such as rheotaxis, whereas canal neuromasts detect acceleration components of modulated flows (AC) and are more concerned with behaviour such as feeding.

Video-tape recordings of prey-capture behaviour were made to demonstrate that stargazers can detect and capture prey in the dark and to determine the range of prey movement velocities that resulted in prey capture. Electrophysiological recording techniques were then used to determine how an artificial source (a sphere), moving at speeds within the range of recorded prey movement velocities, was encoded by anterior lateral line nerve fibres innervating the preopercular-mandibular canals on the head. A vibrating sphere was also used to measure frequency–response characteristics to determine the bandwidth of response and fibre origin (type of neuromast and location). In order to measure the relevant stimulus parameters likely to govern neural responses, the pressure-gradient pattern produced by the moving sphere was characterised with a pair of miniature hydrophones separated by approximately the same distance as head lateral line canal pores on stargazers. At least four different features of neural response patterns, including direction-dependent changes in the overall envelope of the firing rate pattern, could be predicted on the basis of measured pressure-gradient patterns. The dominant features of both the pressure-gradient and neural response patterns were produced by the wake behind the moving sphere, but behavioural observations indicated that stargazers were responding to the bow of an approaching prey, rather than its wake. Although the form of the wake behind the moving sphere is unlikely to be a good match for the stimulus mediating prey detection, these results clearly establish that pressure-gradient patterns are good predictors of neural response patterns. Thus, similar measurements of pressure-gradient patterns produced by more biologically relevant sources can be used to predict peripheral lateral line responses and stimulus features likely to be of key importance.

This chapter summarizes what is known about the role of lateral line flow sensors in different types of fish orienting behaviors and the spatiotemporal characteristics of flow patterns that guide fish. Where possible, fundamental and shared principles of flow guidance are identified for behaviors as diverse as rheotaxis, prey orientation, and predator avoidance. Multisensory, egocentric direction maps in the midbrain optic tectum are thought to underlie oriented movements toward discrete targets of interest (e.g., prey), whereas differential biasing of bilaterally paired Mauthner cells by multisensory inputs are involved in fast-start oriented behaviors such as predator avoidance. Wide-field integration of global flow fields inspired by optic flow studies in flies is suggested as a central mechanism by which cells are tuned to expected flow patterns over large body regions during common motion states, such as forward translational movement. Disruptions in those patterns caused by, e.g., the destabilizing influences of currents could then be used as part of closed-loop feedback control for corrective actions. Flow guidance of behaviors is likely to be best understood when viewed from a multisensory, evolutionary perspective in which nonvisual and visual systems work in tandem to guide behavior.

Some vertebrates can navigate over long distances using the Earth's magnetic field, but the sensory system that they use to do so has remained a mystery. Here we describe the key components of a magnetic sense underpinning this navigational ability in a single species, the rainbow trout ( Oncorhynchus mykiss). We report behavioural and electrophysiological responses to magnetic fields and identify an area in the nose of the trout where candidate magnetoreceptor cells are located. We have tracked the sensory pathway from these newly identified candidate magnetoreceptor cells to the brain and associated the system with a learned response to magnetic fields.

Rheotaxis is a behavioural orientation to water currents1. It has been demonstrated physiologically that some lateral-line receptors are particularly well suited to provide information on water currents2, but their contribution to rheotaxis has been largely overlooked. The accepted view is that rheotaxis is mediated by visual and tactile cues1, and that in rheotactic orientation “the lateral lines play only a minor role”3. Here we provide a direct demonstration that rheotaxis can be mediated by the lateral line, and indeed by one specific receptor class of this system. In three diverse fish species, pharmacological block of the entire lateral-line system substantially increases the velocity threshold for rheotactic behaviour. The same effect is observed when only superficial neuromasts are ablated, whereas blockade of the other receptor class, canal neuromasts, has no such effect. Our results therefore demonstrate that superficial neuromasts make an important contribution to rheotactic behaviour in fish.

In 1996 Montgomery proposed an ontogenetic shift in the use of visual and non-visual senses in Antarctic notothenioid fishes, with visual dominance in larval fishes giving way to non-visual senses in adults. One prediction of the hypothesis is timing differences in the development of the respective sensory systems, with the visual system expected to develop earlier than the other systems. The volume of certain brain centres can be determined from fixed material and should correlate with sensory development. This study determined the relative volumes of visual and lateral line brain areas, and relative eye size as a function of fish length in Pleuragramma antarcticum.The relative volume of optic tectum was largest in larval fish, exhibiting a negative allometry with growth. The eminentia granularis, and crista cerebellaris (lateral line associated areas) were not recognisable in the smallest larvae; they became differentiated at standard lengths of 10–20 mm and their relative volumes continued to increase over the size range of fish studied (up to 150 mm standard length). Relative eye diameter decreased dramatically over the size range 5–25 mm and then increased such that relative eye diameter doubled over the size range 25–30 mm. A similar, but less extreme, pattern was seen over the size range 30–60 mm. Above 60 mm relative eye diameter increased slightly with size. Our interpretation is that eye growth and somatic growth are on separate trajectories, and the breaks in the relative eye diameter curve result from overwinter periods when somatic growth is static, but the eye continues to grow. These results provide support for the ontogenetic shift hypothesis, and indicate that the timing of the shift probably occurs after the second winter.

Dwarf scorpion fish live in broken rocky reef areas at depths of 5–25 m. By day they are found in crevices and beneath rock overhangs, whereas at night they are observed sitting in the open. Gut samples show that feeding occurs predominantly at night with the most common prey items being crabs and brittlestars. In the laboratory experiments, under an artificial day/night light regime (LD 12:12) the prey species show a strong daily rhythm of activity, with activity confined to the period of darkness. Activity is controlled by light level. An artificial “sunset”; in the middle of the day has both crabs and brittlestars emerging from cover at ambient light levels of about 4 × 10‐2μE.m‐2.s‐1 but not becoming fully active until dark. Under similar conditions, the dwarf scorpion fish's visual threshold for response to a moving visual target occurs at light levels of about 7 × 10‐3μE.m‐2.s‐1. Field measurements show light levels between these two values occur only for a limited period after sunset, and that ligh...

Sharks detect their prey using an extremely sensitive electrosensory system that is capable of distinguishing weak external stimuli from a relatively strong background noise generated by the animal itself. Experiments indicate that part of the shark’s hindbrain, the dorsal octavolateralis nucleus (DON), is responsible for extracting the external stimulus using an adaptive filter mechanism to suppress signals correlated with the shark’s breathing motion. The DON’s principal neuron integrates input from afferents as well as many thousands of parallel fibres transmitting, inter alia, breathing-correlated motor command signals. There are a number of models in the literature, studying how this adaptive filtering mechanisms occurs, but most of them are based on a spike-train model approach. This paper presents a biophysically based computational simulation which demonstrates a mechanism for adaptive noise filtering in the DON. A spatial model of the neuron uses the Hodgkin–Huxley equations to simulate the propagation of action potentials along the dendrites. Synaptic inputs are modelled by applied currents at various positions along the dendrites, whose input conductances are varied according to a simple learning rule. Simulation results show that the model is able to demonstrate adaptive filtering in agreement with previous experimental and modelling studies. Furthermore, the spatial nature of the model does not greatly affect its learning properties, and in its present form is effectively equivalent to an isopotential model which does not incorporate a spatial element.

Recordings were made from primary afferent fibres and secondary projection neurones (crest cells) in the mechanosensory lateral line system of the dwarf scorpionfish. Crest cells were identified by antidromic stimulation from the contralateral midbrain. Differences between primary afferent fibre and crest cell response characteristics are indicative of signal processing by the neuronal circuitry of the medial octavolateralis nucleus. There are a number of differences between primary afferent fibres and crest cells. Primary afferents have relatively high levels of spontaneous activity (mean close to 40 impulses s−1) and many of them are strongly modulated by ventilation. By contrast, crest cells have a much lower rate of spontaneous activity that is not obviously modulated by ventilation. Primary afferents show a simple tonic response to a maintained stimulus, whereas crest cells show a variety of temporal response properties, but in general show a phasic/tonic response to the same prolonged stimulus. Afferents are most sensitive to frequencies of stimulation around 100 Hz; in contrast, crest cells show a strong suppression of activity at this frequency. Crest cells are most responsive around 50 Hz. These afferent/secondary comparisons show similarities with those reported for allied electrosensory and auditory pathways.

The sensory ecology and neuroethology of the lateral line provides an overview of the role of the lateral line in natural fish behaviour. The approach is more conceptual than comprehensive, choosing representative behaviors and especially those that lend themselves to a neuroethological analysis. This approach provides a clear focus for the determination of the relevant parameters of the physical stimulus, the physical and physiological mediation of stimulus encoding, and a targeted approach as to how the central nervous system processes and transforms sensory inputs to behavioral action. Like all major sensory systems, the lateral line makes an important contribution to the sensory capabilities of fish and aquatic amphibians and contributes to a wide range of core behaviors. This overview covers the role of the lateral line in: feeding, avoidance of predators, communication, hydrodynamic imaging, and orientation to slow and turbulent flows.

The cerebellum is well developed in cartilaginous fishes, with the same cell types (barring basket cells) and organizational features found in other vertebrate groups, including mammals. In particular, the lattice-like organization of cerebellar cortex (with a molecular layer of parallel fibers, interneurons, spiny Purkinje cell dendrites, and climbing fibers) is a defining characteristic. In addition to the cerebellum, cartilaginous fishes have cerebellum-like structures in the dorsolateral wall of the hindbrain. These structures are adjacent to and, in part, contiguous with the cerebellum. They are cerebellum-like in that they have a molecular layer of parallel fibers and inhibitory interneurons that has striking organizational similarities to the molecular layer of the cerebellar cortex. However, these structures also have characteristics that differ from the cerebellum. For example, cerebellum-like structures do not have climbing fibers and are clearly sensory. They receive direct afferent input from peripheral sensory receptors and relay their outputs to midbrain sensory areas. As a consequence of this close sensory association and the ability of researchers to characterize signal processing in these structures in a behaviorally relevant context, good progress has been made in determining the fundamental processing algorithm of the cerebellum-like structures. This algorithm enables the molecular layer to act as an adaptive filter that cancels self-generated noise in electrosensory and lateral line systems. Given the fundamental similarities of the molecular layer across these structures and the phylogeny of these structures across basal vertebrates, it is clear that these structures share a common genetic-developmental program. Syngeny is a term that has been used to describe similarity of structure due to a shared genetic-developmental program, whether the structures are phylogenetically homologous or not. Given that the cerebellum and cerebellum-like structures are physically adjacent, we propose that cerebellum-like structures were the evolutionary antecedent of the cerebellum and that the cerebellum arose through a change in the genetic-developmental program, amounting to a duplication of existing structure. Such duplication to form adjacent structures can be considered a special case of syngeny. On this view, the cerebellum is an evolutionary innovation in gnathostomes that is literally superimposed on pre-existing underlying brain structures and pathways. From this perspective, the cerebellum can be considered an example of ‘subsumption architecture’, a term that describes the addition of modules that add computational power while maintaining existing fundamental functionality. This addition is reflected in the finding that in elasmobranchs with relatively large brains, the size of the telencephalon and cerebellum enlarge disproportionately, while those parts of the brain that contain more direct sensory and motor connections do not. Added ‘computational’ power in the chondrichthyan brain and the comparative function and evolution of the cerebellum and cerebellum-like structures across the cartilaginous fishes supports the idea of the cerebellum as an example of subsumption architecture.

SummaryThe auditory evoked potential technique has been used for the past 30 years to evaluate the hearing ability of fish. The resulting audiograms are typically presented in terms of sound pressure (dB re 1 µPa) with the particle motion (dB re 1 ms-2) component largely ignored until recently. When audiograms have been presented in terms of particle acceleration, one of two approaches has been used for stimulus characterization: measuring the pressure gradient between two hydrophones or using accelerometers. With rare exceptions these values are presented from experiments using a speaker as the stimulus, thus making it impossible to truly separate the contribution of direct particle displacement and pressure detection in the response. Here we compare the particle acceleration and pressure auditory thresholds of three species of fish with differing hearing specialisations, Goldfish (Carassius auratus; weberian ossicles), bigeye (Pempheris adspersus hearing specialisation) and a third species with no swim bladder, the common triplefin (Forstergyian lappillum), using three different methods of determining particle accelerations. In terms of particle acceleration all three fish species have similar hearing thresholds, but when expressed as pressure thresholds goldfish are the most sensitive followed by bigeye, with triplefin the least sensitive. It is suggested here that all fish have a similar ability to detect the particle motion component of the sound field and it is their ability to transduce the pressure component of the sound field to the inner ear via ancillary hearing structures that provides the differences in hearing ability. Therefore, care is needed in stimuli presentation and measurement when determining hearing ability of fish and when interpreting comparative hearing abilities between species.

The yellowtail kingfish, Seriola lalandi , shows a distribution of anaerobic and aerobic (red and pink) muscle fibres along the trunk that is characteristic of active pelagic fishes. The athletic capacity of S. lalandi is also shown by its relative high standard metabolic rate and optimal (i.e. least cost) swimming speed. To test the hypothesis that lateral line afferent information contributes to efficient locomotion in an active pelagic species, the swimming performance of S. lalandi was evaluated after unilateral disruption of trunk superficial neuromasts (SNs). Unilaterally disrupting the SNs of the lateral line impaired both swimming performance and energetic efficiency. The critical swimming speed ( U crit; mean ± s.d., N =12) for unilaterally SN-disrupted fish was 2.11±0.96 fork lengths (FL) s−1, which was significantly slower than the 3.66±0.19 FL s−1 U crit of sham SN-disrupted fish. The oxygen consumption rate (mg O2 kg−1 min−1) of the unilaterally SN-disrupted fish in a speed range of 1.0–2.2 FL s−1 was significantly greater than that of the sham SN-disrupted fish. The least gross cost of transport (GCOT; N =6) for SN-disrupted fish was 0.18±0.06 J N−1 m−1, which was significantly greater than the 0.11±0.03 J N−1 m−1 GCOT for sham SN-disrupted fish. The factorial metabolic scope ( N =6) of the unilaterally SN-disrupted fish (2.87±0.78) was significantly less than that of sham controls (4.14±0.37). These data show that an intact lateral line is important to the swimming performance and efficiency of carangiform swimmers, but the functional mechanism of this effect remains to be determined. * a,b,c : parameters in a power function of swimming speed and body mass for oxygen consumption A c : cross-sectional area of the flow chamber Af : cross-sectional area of the fish AMR : active metabolic rate AMRmax : maximum active metabolic rate ![Graphic][1] : mean maximum active metabolic rate AMRopt : active metabolic rate at optimal swimming speed CPG : central pattern generator d : maximum depth of the fish body FL : fork length of the fish FMS : fractional metabolic scop ![Graphic][2] : mean FMS GCOT : gross cost of transport GCOTmin> : minimum GCOT based on a power model of ![Graphic][3] ![Graphic][4] : mean minimum GCOT g : gravitational acceleration M : mass of the fish ![Graphic][5] : mass-specific oxygen consumption rate P O2 : partial pressure of oxygen at 100% air saturation SMR : standard metabolic rate SN : superficial neuromasts t f : elapsed time from the velocity increase to fatigue of the fish in the U crit test t i : time between the velocity increments in the critical swimming speed test U : flow velocity or swimming speed when the fish held its station relative to the flume U crit : critical swimming speed Ū crit : mean critical swimming speed U i : velocity increment in the U crit test U max : maximum swimming speed at which the fish was able to complete 30-min period of swimming in the U crit test Ū max : mean maximum swimming speed U opt : optimal swimming speed based on a power model of ![Graphic][6] Ū opt : mean optimal swimming speed U w : flow velocity without fish V w : volume of the respirometer WPM : cost of swimming as work per metre βwO2 : capacitance coefficient of oxygen in water at a certain salinity Δsat : change in % of air saturation per second [1]: /embed/inline-graphic-42.gif [2]: /embed/inline-graphic-43.gif [3]: /embed/inline-graphic-44.gif [4]: /embed/inline-graphic-45.gif [5]: /embed/inline-graphic-46.gif [6]: /embed/inline-graphic-47.gif

As part of a study of signal processing in the electro- and mechanosensory systems we have screened the octavolateralis column of the skate for GABA A , muscarinic cholinergic, excitatory amino acid, neurotensin and opiate binding sites using autoradiography following in vitro labelling of cryostat sections with tritiated ligands. The presence and distribution of these binding sites is compared between the octavolateralis column and the corpus cerebellum. GABA A binding sites were located in high concentrations in the granule cell regions of the cerebellum and octaval columns, with much lower concentrations in the Purkinje cell layer of the corpus cerebellum. Little or no labelling was evident in all molecular layer areas. Displacement studies using the discriminating ligand CL218,872 indicated that the GABA A binding sites were predominantly of the GABA A /benzodiazepine Type II variety. M 1 muscarinic cholinergic binding sites were found in high concentrations in all granule cell areas and in lower concentrations in the molecular layer of the octavolateralis column, with an absence of labelling in the molecular layer of the corpus cerebellum. Kainic acid and AMPA binding sites were present in very high concentrations in all molecular layer areas. Glutamate binding was present in the molecular layer of the octavolateralis column and in some restricted regions of the dorsal granular ridge, whereas phencyclidine binding sites were sparse or absent. Neurotensin binding sites were strongly present in all granule cell areas and evident in the molecular layer of the octavolateralis column. There was evidence for opiate binding sites in the molecular layer of both the dorsal and medial octavolateralis nucleus. The results of these studies show the presence of a wide variety of putative neurotransmitter binding sites in the corpus cerebellum and octavolateral column of the skate.

The structure and physiology of the anterior lateral line canal systems were studied in six species of fish belonging to two different families within the suborder of antarctic fish Notothenioidei. Many of the canals within the species belonging to the genus Trematomus are relatively straight sided tubes with diameters around 0.4 mm. Some of the canals in Trematomus, and most of the canals in the icefishes (family Channichthyidae) are more complex. Relatively small pores lead into large tubules, the walls of which appear partially membranous, and the canals not much more than constrictions between adjacent tubules. Dissostichus mawsoni, a large species, has canals with distinctive wide and narrow sections, 1.8 mm and 0.48 mm, respectively. Despite these morphological differences the frequency response characteristics of anterior lateral line units are remarkably similar in all six species. In the case of D. mawsoni, this functional similarity results from narrow sections of the canals, which provide the viscous resistance to flow that preserves the mechanical filtering properties of the canal despite the huge size difference between D. mawsoni and the other species. It is argued that the most appropriate way to view canals is as high pass filters which attenuate lower frequencies, and that this effect is best illustrated by comparing the frequency response characteristics of superficial and canal neuromasts using a sinusoidal stimulus that has a constant peak-to-peak velocity. The functional contribution of canals is to attenuate low frequencies and improve the signal-to-noise ratio for biologically important signals in the presence of low frequency noise produced, for example, by the animal's own movements.

Extracellular recording techniques were used to measure frequency response functions of anterior and posterior lateral line nerve fibers innervating superficial neuromasts at five different locations on the head and trunk of an antarctic notothenioid fish, Trematomus bernacchii. Scanning electron microscopy was used to measure neuromast size according to location. Fibers innervating neuromasts from all locations were similar in showing equal responsiveness in the 10-30 Hz range to equal pk-pk velocity levels of a sinusoidally vibrating sphere. The mean cut-off frequency (CF) at which responsiveness declined to 50% of maximum was 46 Hz for all fibers combined. Superficial neuromasts located on the ventral trunk line were three to six times larger in surface area than most other neuromasts. The mean CF for fibers innervating these large neuromasts was 7-18 Hz lower than mean CF's corresponding to other superficial neuromast locations, but small differences in mean CF's were not consistently related to neuromast size. It is argued that fiber responses from different superficial neuromasts are more similar than dissimilar and that the evolution of large superficial neuromasts on the ventral trunk line is linked to a general paedomorphic trend among notothenioid fishes that may be essentially non-adaptive for the lateral line.

Hatchery reared juvenile rainbow trout of common parentage were reared on measured low or high rations, or fed ad libitum for 4.3 months to produce fish with different growth rates. Fish from the different groups differed in size by up to 40 and 290% for length and weight, respectively, by the end of the trial. Slow somatic growth was not accompanied by correspondingly slow growth of either the eyes, optic tectum or the cerebellum, suggesting that above a certain maintenance ration, growth of these parts of the CNS is strongly age-dependent. Retinal characteristics were also found to be age-dependent and not affected by the somatic growth rate of the fish. The corollary that age-dependent ocular growth should also be reflected in different relative eye sizes in fish with differential growth rates in the wild was tested by comparing fish of known age from lakes in which fish have markedly different growth profiles. Fish stocked from a single hatchery were recaptured from Lakes Okataina and Tarawera (rapid fish growth) and Lake Taharoa (slow fish growth) at times up to 5 years after release. As predicted, eye sizes of fish from Lakes Okataina and Tarawera were smaller for any given body size, than those of fish from Lake Taharoa. Absolute eye size was correlated with fish age, although there was some variation in eye size for any given age. Taken together, these results show that up to a certain level of food deprivation, growth of the eye is maintained at the expense, or in spite, of low somatic growth. However, there is a level of somatic growth below which ocular growth is affected.

Aggregations of organisms, ranging from zooplankton to whales, are an extremely common phenomenon in the pelagic zone; perhaps the best known are fish schools. Social aggregation is a special category that refers to groups that self-organize and maintain cohesion to exploit benefits such as protection from predators, and location and capture of resources more effectively and with greater energy efficiency than could a solitary individual. In this review we explore general aggregation principles, with specific reference to pelagic organisms; describe a range of new technologies either designed for studying aggregations or that could potentially be exploited for this purpose; report on the insights gained from theoretical modelling; discuss the relationship between social aggregation and ocean management; and speculate on the impact of climate change. Examples of aggregation occur in all animal phyla. Among pelagic organisms, it is possible that repeated co-occurrence of stable pairs of individuals, which has been established for some schooling fish, is the likely precursor leading to networks of social interaction and more complex social behaviour. Social network analysis has added new insights into social behaviour and allows us to dissect aggregations and to examine how the constituent individuals interact with each other. This type of analysis is well advanced in pinnipeds and cetaceans, and work on fish is progressing. Detailed three-dimensional analysis of schools has proved to be difficult, especially at sea, but there has been some progress recently. The technological aids for studying social aggregation include video and acoustics, and have benefited from advances in digitization, miniaturization, motion analysis and computing power. New techniques permit three-dimensional tracking of thousands of individual animals within a single group which has allowed novel insights to within-group interactions. Approaches using theoretical modelling of aggregations have a long history but only recently have hypotheses been tested empirically. The lack of synchrony between models and empirical data, and lack of a common framework to schooling models have hitherto hampered progress; however, recent developments in this field offer considerable promise. Further, we speculate that climate change, already having effects on ecosystems, could have dramatic effects on aggregations through its influence on species composition by altering distribution ranges, migration patterns, vertical migration, and oceanic acidity. Because most major commercial fishing targets schooling species, these changes could have important consequences for the dependent businesses.