Signal detection theory, lateral-line excitation patterns and prey capture behaviour of mottled sculpin

Blind cavefish evolved higher foraging responses to chemo- and mechanostimuli

In nature, animals must navigate to forage according to their sensory inputs. Different species use different sensory modalities to locate food efficiently. For teleosts, food emits visual, mechanical, chemical, and/or possibly weak-electrical signals, which can be detected by optic, auditory/lateral line, and olfactory/taste buds sensory systems. However, how fish respond to and use different sensory inputs when locating food, as well as the evolution of these sensory modalities, remain unclear. We examined the Mexican tetra, Astyanax mexicanus, which is composed of two different morphs: a sighted riverine (surface fish) and a blind cave morph (cavefish). Compared with surface fish, cavefish have enhanced non-visual sensory systems, including the mechanosensory lateral line system, chemical sensors comprising the olfactory system and taste buds, and the auditory system to help navigate toward food sources. We tested how visual, chemical, and mechanical stimuli evoke food-seeking behavior. In contrast to our expectations, both surface fish and cavefish did not follow a gradient of chemical stimulus (food extract) but used it as a cue for the ambient existence of food. Surface fish followed visual cues (red plastic beads and food pellets), but, in the dark, were likely to rely on mechanosensors-the lateral line and/or tactile sensor-as cavefish did. Our results indicate cavefish used a similar sensory modality to surface fish in the dark, while affinity levels to stimuli were higher in cavefish. In addition, cavefish evolved an extended circling strategy to forage, which may yield a higher chance to capture food by swimming-by the food multiple times instead of once through zigzag motion. In summary, we propose that ancestors of cavefish, similar to the modern surface fish, evolved extended food-seeking behaviors, including circling motion, to adapt to the dark.

Individual based models for the simulation of fish movement near barriers: Current work and future directions

River fragmentation is an increasing issue for water managers and conservationists. Barriers such as dams interfere with freshwater fish migration, leading to drastic population declines. While there are a range of widely implemented mitigation approaches, e.g. fish passes, such measures are often inefficient due to suboptimal operation and design. There is increasing need to be able to assess mitigation options prior to implementation. Individual based models (IBMs) are a promising option. IBMs can simulate the fine-scale movement of individual fish within a population as they attempt to find a fish pass, incorporating movement processes themselves. Moreover, IBMs have high transferability to other sites or conditions (e.g. changing mitigation, change in flow conditions), making them potentially valuable for freshwater fish conservation yet their application to the fine-scale movement of fish past barriers is still novel. Here, we present an overview of existing IBMs for fine-scale freshwater fish movement, with emphasis on study species and the parameters driving movement in the models. In this review, we focus on IBMs suitable for the simulation of fish tracks as they approach or pass a single barrier. The selected IBMs for modelling fine-scale freshwater fish movement largely focus on salmonids and cyprinid species. IBMs have many applications in the context of fish passage, such as testing different mitigation options or understanding processes behind movement. Existing IBMs include movement processes such as attraction and rejection behaviours, as reported in literature. Yet some factors affecting fish movement e.g. biotic interactions are not covered by existing IBMs. As the technology available for fine scale data collection continues to advance, such as increasing data linking fish behaviour to hydraulics, IBMs could become a more common tool in the design and implementation of fish bypass structures.

Real-time parametric estimation of periodic wake-foil interactions using bioinspired pressure sensing and machine learning

Periodic wake-foil interactions occur in the collective swimming of bio-inspired robots. Wake interaction pattern estimation (and control) is crucial to thrust enhancement and propulsive efficiency optimization. In this paper, we study the wake interaction pattern estimation of two flapping foils in tandem configurations. The experiments are conducted at a Reynolds number of 1.41 × 10⁴in a water channel. A modified wake-foil phase parameter Φ, which unifies the influences of inter-foil distanceL_x, motion phase difference Δφand wake convection velocityU_v, is introduced to describe the wake interaction patterns parametrically. We use a differential pressure sensor on the downstream foil to capture wake interaction characteristics. Data sets at different tandem configurations are collected. The wake-foil phase Φ is used to label the pressure signals. A one-dimensional convolutional neural networks (1D-CNN) model is used to learn an end-to-end mapping between the raw pressure measurements and the wake-foil phase Φ. The trained 1D-CNN model shows accurate estimations (average error 3.5%) on random wake interaction patterns and is fast enough (within 40 ms). Then the trained 1D-CNN model is applied to online thrust enhancement control of a downstream foil swimming in a periodic wake. Synchronous force monitoring and flow visualization demonstrate the effectiveness of the 1D-CNN model. The limitations of the model are discussed. The proposed approach can be applied to the online estimation and control of wake interactions in the collective swimming and flying of biomimetic robots.

Morphological malleability of the lateral line allows for surface fish (Astyanax mexicanus) adaptation to cave environments

The lateral line is the primary modality fish use to create a hydrodynamic image of their environment. These images contribute to a variety of behaviors, from rheotaxis to escape responses. Here we discern the contributions of visual and lateral line modalities in hunting behavior of larvae that have developed under different photic conditions. In particular, cave animals have a hypertrophied sense of mechanosensation, and we studied the common animal model cavefish Astyanax mexicanus and its closest related surface relative. We raised larvae in a diurnal light-dark regimen and in complete darkness. We then examined the distribution of neuromasts in their lateral lines, and their hunting performance in light and dark conditions, with and without the contribution of the lateral line. We report that all larva depend on the lateral line for success in hunting and that surface fish raised in the dark have a greater dependency on the lateral line.

Signal detection: applying analysis methods from psychology to animal behaviour

Conspecific acceptance thresholds (Reeve 1989 Am. Nat. 133, 407-435), which have been widely applied to explain ecological behaviour in animals, proposed how sensory information, prior information and the costs of decisions determine actions. Signal detection theory (Green & Swets 1966 Signal detection theory and psychophysics; SDT), which forms the basis of CAT models, has been widely used in psychological studies to partition the ability to discriminate sensory information from the action made as a result of it. In this article, we will review the application of SDT in interpreting the behaviour of laboratory animals trained in operant conditioning tasks and then consider its potential in ecological studies of animal behaviour in natural environments. Focusing on the nest-mate recognition systems exhibited by social insects, we show how the quantitative application of SDT has the potential to transform acceptance rate data into independent indices of cue sensitivity and decision criterion (also known as the acceptance threshold). However, further tests of the assumptions underlying SDT analysis are required. Overall, we argue that SDT, as conventionally applied in psychological studies, may provide clearer insights into the mechanistic basis of decision making and information processing in behavioural ecology. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

Canal neuromasts enhance foraging in zebrafish (Danio rerio)

Aquatic animals commonly sense flow using superficial neuromasts (SNs), which are receptors that extend from the body's surface. The lateral line of fishes is unique among these systems because it additionally possesses receptors, the canal neuromasts (CNs), that are recessed within a channel. The lateral line has inspired the development of engineered sensors and concepts in the analysis of flow fields for submersible navigation. The biophysics of CNs are known to be different from the SNs and thereby offer a distinct submodality. However, it is generally unclear whether CNs play a distinct role in behavior. We therefore tested whether CNs enhance foraging in the dark by zebrafish (Danio rerio), a behavior that we elicited with a vibrating rod. We found that juvenile fish, which have only SNs, bite at this rod at about one-third the rate and from as little as one-third the distance of adults for a high-frequency stimulus (50  <  f   <  100 Hz). We used novel techniques for manipulating the lateral line in adults to find that CNs offered only a modest benefit at a lower frequency (20 Hz) and that foraging was mediated entirely by cranial neuromasts. Consistent with our behavioral results, biophysical models predicted CNs to be more than an order of magnitude more sensitive than SNs at high frequencies. This enhancement helps to overcome the rapid spatial decay in high-frequency components in the flow around the stimulus. These findings contrast what has been previously established for fishes that are at least ten-times the length of zebrafish, which use trunk CNs to localize prey. Therefore, CNs generally enhance foraging, but in a manner that varies with the size of the fish and its prey. These results have the potential to improve our understanding of flow sensing in aquatic animals and engineered systems.

Modeling Fish Movement Trajectories in Relation to Hydraulic Response Relationships in an Experimental Fishway

This study developed an IBM (individual-based model) to model fish movement trajectories integrating hydraulic stimulus variables (turbulent kinetic energy (TKE), velocity (V) and strain rate (SR)) to which fish responded, and the rules for individual fish movement. The fish movement trajectories of the target fish, silver carp (Hypophthalmichthys molitrix), were applied to model fish trajectories in a 1% vertical slot fishway at a discharge of 13.5 L/s. Agreement between measured and simulated trajectories implied the plausibility of the movement rules, which illustrated that the fish movement trajectories model has the preliminary ability to track individual fish trajectories for this fishway.

Model-based observer and feedback control design for a rigid Joukowski foil in a Kármán vortex street

Obstacles and swimming fish in flow create a wake with an alternating left/right vortex pattern known as a Kármán vortex street and reverse Kármán vortex street, respectively. An energy-efficient fish behavior resembling slaloming through the vortex street is called Kármán gaiting. This paper describes the use of a bioinspired array of pressure sensors on a Joukowski foil to estimate and control flow-relative position in a Kármán vortex street using potential flow theory, recursive Bayesian filtering, and trajectory-tracking feedback control. The Joukowski foil is fixed in downstream position in a flowing water channel and free to move on air bearings in the cross-stream direction by controlling its angle of attack to generate lift. Inspired by the lateral-line neuromasts found in fish, the sensing and control scheme is validated using off-the-shelf pressure sensors in an experimental testbed that includes a flapping device to create vortices. We derive a potential flow model that describes the flow over a Joukowski foil in a Kármán vortex street and identify an optimal path through a Kármán vortex street using empirical observability. The optimally observable trajectory is one that passes through each vortex in the street. The estimated vorticity and location of the Kármán vortex street are used in a closed-loop control to track either the optimally observable path or the energetically efficient gait exhibited by fish. Results from the closed-loop control experiments in the flow tank show that the artificial lateral line in conjunction with a potential flow model and Bayesian estimator allow the robot to perform fish-like slaloming behavior in a Kármán vortex street. This work is a precursor to an autonomous robotic fish sensing the wake of another fish and/or performing pursuit and schooling behavior.

From Biological Cilia to Artificial Flow Sensors: Biomimetic Soft Polymer Nanosensors with High Sensing Performance

We report the development of a new class of miniature all-polymer flow sensors that closely mimic the intricate morphology of the mechanosensory ciliary bundles in biological hair cells. An artificial ciliary bundle is achieved by fabricating bundled polydimethylsiloxane (PDMS) micro-pillars with graded heights and electrospinning polyvinylidenefluoride (PVDF) piezoelectric nanofiber tip links. The piezoelectric nature of a single nanofiber tip link is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Rheology and nanoindentation experiments are used to ensure that the viscous properties of the hyaluronic acid (HA)-based hydrogel are close to the biological cupula. A dome-shaped HA hydrogel cupula that encapsulates the artificial hair cell bundle is formed through precision drop-casting and swelling processes. Fluid drag force actuates the hydrogel cupula and deflects the micro-pillar bundle, stretching the nanofibers and generating electric charges. Functioning with principles analogous to the hair bundles, the sensors achieve a sensitivity and threshold detection limit of 300 mV/(m/s) and 8 μm/s, respectively. These self-powered, sensitive, flexible, biocompatibale and miniaturized sensors can find extensive applications in navigation and maneuvering of underwater robots, artificial hearing systems, biomedical and microfluidic devices.

Assessing hydrodynamic space use of brown trout, Salmo trutta, in a complex flow environment: a return to first principles

It is commonly assumed that stream-dwelling fish should select positions where they can reduce energetic costs relative to benefits gained and enhance fitness. However, the selection of appropriate hydrodynamic metrics that predict space use is the subject of recent debate and a cause of controversy. This is for three reasons: (1) flow characteristics are often oversimplified, (2) confounding variables are not always controlled and (3) there is limited understanding of the explanatory mechanisms that underpin the biophysical interactions between fish and their hydrodynamic environment. This study investigated the space use of brown trout, Salmo trutta, in a complex hydrodynamic flow field created using an array of different sized vertically oriented cylinders in a large open-channel flume in which confounding variables were controlled. A hydrodynamic drag function (D) based on single-point time-averaged velocity statistics that incorporates the influence of turbulent fluctuations was used to infer the energetic cost of steady swimming. Novel hydrodynamic preference curves were developed and used to assess the appropriateness of D as a descriptor of space use compared with other commonly used metrics. Zones in which performance-enhancing swimming behaviours (e.g. Kármán gaiting, entraining and bow riding) that enable fish to hold position while reducing energetic costs (termed 'specialised behaviours') were identified and occupancy was recorded. We demonstrate that energy conservation strategies play a key role in space use in an energetically taxing environment with the majority of trout groups choosing to frequently occupy areas in which specialised behaviours may be adopted or by selecting low-drag regions.

Prey aggregation is an effective olfactory predator avoidance strategy

Predator–prey interactions have a major effect on species abundance and diversity, and aggregation is a well-known anti-predator behaviour. For immobile prey, the effectiveness of aggregation depends on two conditions: (a) the inability of the predator to consume all prey in a group and (b) detection of a single large group not being proportionally easier than that of several small groups. How prey aggregation influences predation rates when visual cues are restricted, such as in turbid water, has not been thoroughly investigated. We carried out foraging (predation) experiments using a fish predator and (dead) chironomid larvae as prey in both laboratory and field settings. In the laboratory, a reduction in visual cue availability (in turbid water) led to a delay in the location of aggregated prey compared to when visual cues were available. Aggregated prey suffered high mortality once discovered, leading to better survival of dispersed prey in the longer term. We attribute this to the inability of the dead prey to take evasive action. In the field (where prey were placed in feeding stations that allowed transmission of olfactory but not visual cues), aggregated (large groups) and semi-dispersed prey survived for longer than dispersed prey—including long term survival. Together, our results indicate that similar to systems where predators hunt using vision, aggregation is an effective anti-predator behaviour for prey avoiding olfactory predators.

Toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the peripheral nervous system of developing red seabream (Pagrus major)

We investigated 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced effects on the morphology of peripheral nervous system (PNS) in the developing red seabream (Pagrus major) embryos. The embryos at 10h post-fertilization (hpf) were treated with 0, 0.1, 0.4 or 1.7 μg/L of TCDD in seawater for 80 min. The morphology of PNS was microscopically observed with florescence staining using an anti-acetylated tubulin antibody at 48, 78, 120 and 136 hpf. Axon length of facial nerve (VII) was found to be shortened by TCDD exposure. Axon guidance in the glossopharyngeal nerve (IX) and vagus nerve (X) was altered at 120 and 136 hpf in a TCDD dose-dependent manner. Lowest observable effect level of TCDD (0.1 μg/L) that induced the morphological alteration of PNS was lower than those of other endpoints on morphological deformities so far reported. Given that the growth cone at the tip of growing nerve axons advances under the influence of its surrounding tissues, we hypothesized that TCDD exposure would affect (1) the nerve cell proliferation/differentiation, (2) the structure of muscle as an axon target and (3) the nerve guidance factor in the embryos. By the immunostaining of embryos with an antibody against the neuronal specific RNA-binding protein, HuD, and an antibody against the sarcomeric myosin, no morphological effects were observed on the neural proliferation/differentiation and the structure of facial muscles of TCDD-treated embryos. In contrast, whole mount in situ hybridization of semaphorin 3A (Sema3A), a secretory axon repulsion factor, revealed the altered expression pattern of its transcripts in TCDD-treated embryos. Our findings suggest that TCDD treatment affects the projection of PNS in the developing red seabream embryos through the effects on the axonal growth cone guidance molecule such as Sema3A, but not on the neuronal differentiation/proliferation and axon target. The PNS in developing embryos may be one of the most sensitive biomarkers to the exposure of dioxin-like compounds.

Histochemical analysis of glycoproteins in the secretory cells in the epidermis of the head skin of Indian Major Carp, Labeo rohita

A series of histochemical procedures were employed to localise and characterise glycoprotein (GP) classes produced by the epithelial cells, the type A and the type B mucous goblet cells (MGCs) and the club cells in the epidermis of Labeo rohita. The epithelial cells secreted GPs with oxidizable vicinal diols and GPs with sialic acid residues without O-acyl substitution in low concentrations. The type A MGCs and the type B MGCs, in contrast, produced these GPs in high concentrations. Further, these MGCs produced GPs with O-sulphate esters as well. GPs with O-sulphate esters were produced in high concentration by the type A MGCs and in low concentration by the type B MGCs. The club cells produced GPs with oxidizable vicinal diols in trace amounts. Production of more than one type of GPs suggested a basis for functional discrimination in their role in the mucous secretions at the skin surface. This is considered an adaptation to environment inhabited by the fish and is discussed in relation to their role in lubrication, protection and inhibition of the invasion and proliferation of pathogenic micro-organisms.

Feeding in the dark: lateral-line-mediated prey detection in the peacock cichlid Aulonocara stuartgranti

The cranial lateral line canal system of teleost fishes is morphologically diverse and is characterized by four patterns. One of these, widened lateral line canals, has evolved convergently in a wide range of teleosts, including the Lake Malawi peacock cichlids (Aulonocara), and has been attributed to its role in prey detection. The ability to study Aulonocara in the laboratory provides an opportunity to test the hypothesis that their reported ability to feed on invertebrate prey living in sandy substrates in their natural habitat is the result of lateral-line-mediated prey detection. The goal of this study was to determine whether Aulonocara stuartgranti could detect hydrodynamic stimuli generated by tethered brine shrimp (visualized using digital particle image velocimetry) under light and dark conditions, with and without treatment with cobalt chloride, which is known to temporarily inactivate the lateral line system. Fish were presented with six pairs of tethered live and dead adult brine shrimp and feeding behavior was recorded with HD digital video. Results demonstrate that A. stuartgranti: (1) uses the same swimming/feeding strategy as they do in the field; (2) detects and consumes invertebrate prey in the dark using its lateral line system; (3) alters prey detection behavior when feeding on the same prey under light and dark conditions, suggesting the involvement of multiple sensory modalities; and (4) after treatment with cobalt chloride, exhibits a reduction in their ability to detect hydrodynamic stimuli produced by prey, especially in the dark, thus demonstrating the role of the lateral line system in prey detection.

Developmentally regulated multisensory integration for prey localization in the medicinal leech

Medicinal leeches, like many aquatic animals, use water disturbances to localize their prey, so they need to be able to determine if a wave disturbance is created by prey or by another source. Many aquatic predators perform this separation by responding only to those wave frequencies representing their prey. As leeches' prey preference changes over the course of their development, we examined their responses at three different life stages. We found that juveniles more readily localize wave sources of lower frequencies (2 Hz) than their adult counterparts (8-12 Hz), and that adolescents exhibited elements of both juvenile and adult behavior, readily localizing sources of both frequencies. Leeches are known to be able to localize the source of waves through the use of either mechanical or visual information. We separately characterized their ability to localize various frequencies of stimuli using unimodal cues. Within a single modality, the frequency-response curves of adults and juveniles were virtually indistinguishable. However, the differences between the responses for each modality (visual and mechanosensory) were striking. The optimal visual stimulus had a much lower frequency (2 Hz) than the optimal mechanical stimulus (12 Hz). These frequencies matched, respectively, the juvenile and the adult preferred frequency for multimodally sensed waves. This suggests that, in the multimodal condition, adult behavior is driven more by mechanosensory information and juvenile behavior more by visual. Indeed, when stimuli of the two modalities were placed in conflict with one another, adult leeches, unlike juveniles, were attracted to the mechanical stimulus much more strongly than to the visual stimulus.

Evolution of a behavioral shift mediated by superficial neuromasts helps cavefish find food in darkness

How cave animals adapt to life in darkness is a poorly understood aspect of evolutionary biology [1]. Here we identify a behavioral shift and its morphological basis in Astyanax mexicanus, a teleost with a sighted surface-dwelling form (surface fish) and various blind cave-dwelling forms (cavefish) [2-4]. Vibration attraction behavior (VAB) is the ability of fish to swim toward the source of a water disturbance in darkness. VAB was typically seen in cavefish, rarely in surface fish, and was advantageous for feeding success in the dark. The potential for showing VAB has a genetic component and is linked to the mechanosensory function of the lateral line. VAB was evoked by vibration stimuli peaking at 35 Hz, blocked by lateral line inhibitors, first detected after developmental increases in superficial neuromast (SN) number and size [5-7], and significantly reduced by bilateral ablation of SN. We conclude that VAB and SN enhancement coevolved to compensate for loss of vision and to help blind cavefish find food in darkness.

Vibratory sources as compound stimuli for the octavolateralis systems: dissection of specific stimulation channels using multiple behavioral approaches

Underwater vibratory sources simultaneously present acoustic and hydrodynamic disturbances. Because vibratory dipole sources are poor sonic projectors, most researchers have assumed that such sources are of greatest relevance to the lateral line system. Both hydroacoustic principles and empirical studies have shown that dipole sources are also a potent stimulus to the inner ear. Responses to vibratory sources in mottled sculpin (Cottus bairdi) were assessed using unconditioned orienting, differential and nondifferential conditioning. Orienting responses are dominated by lateral line inputs and eliminated by lateral line inactivation. Simple conditioning depends on inputs from other systems and was not affected by lateral line inactivation. Differential conditioning alters behavioral control, and sculpin could be conditioned to ignore substrate-borne vibrations and respond only to hydroacoustic stimulation of the ear. The lateral line and inner ear of mottled sculpin do not necessarily exhibit range fractionation, as both systems operate over a similar distance (within 1.5 body lengths) and respond to many of the same sources. Vibratory dipole sources generate compound stimuli that simultaneously activate multiple octavolateralis systems, and sculpin make use of the channels differentially under different behavioral tasks.

Sensitivity of the anterior lateral line to natural stimuli in the oyster toadfish, Opsanus tau (Linnaeus)

Inductive neural telemetry was used to record from microwire electrodes chronically implanted into the anterior lateral line nerve of the oyster toadfish, Opsanus tau (L.). The lateral lines of free-ranging toadfish were stimulated by the swimming movements of a prey fish (Fundulus heteroclitus), and the corresponding neural activity was quantified. Both spontaneously active and silent afferent fibers experienced an increase in neural firing as the prey approached the lateral line. Activity was evoked when the prey fish approached to within 8-12 cm of the neuromast, with increases in nerve firing rates directly correlated with diminishing distance. Thus, adult toadfish (28 cm standard length; 33 cm total length) were only able to detect mobile prey that approached within approximately 40% of their body length. Both spontaneously active and silent afferent fibers also experienced a dramatic increase in firing during predatory strikes, indicating that the fibers were not inhibited during rapid body movement. This study investigates, for the first time, the neural response of the anterior lateral line to prey stimuli in free-ranging fish.

Impact of acute cadmium exposure on the trunk lateral line neuromasts and consequences on the "C-start" response behaviour of the sea bass (Dicentrarchus labrax L.; Teleostei, Moronidae)

Behavioural responses of sea bass Dicentrarchus labrax were investigated after exposure to cadmium ions in laboratory-controlled conditions. The aim of this study was to discover whether environmental exposure to cadmium ions inactivates fish lateral line system neuromasts, and to determine the behavioural consequences of such a sensory blockage. For this, fish escape behaviour in response to an artificial water jet was recorded using a 25-frames s(-1) analog video camera before and after cadmium exposure. Experimental set up was tested with fish whose lateral line system was artificially inactivated by antibiotics (gentamicin and streptomycin). Histological analyses with scanning electron microscopy showed antibiotic treatment destroyed lateral line system neuromasts. In addition, these fish did not respond to stimulations provoked by the water jet after antibiotic treatment. Fish escape behaviour was then recorded before and after cadmium exposure at two different concentrations. When fish were exposed to the first concentration of cadmium tested (0.5 microg l(-1), which represents the maximal cadmium concentration encountered in contaminated estuaries), no alteration in neuromast tissue was observed. In addition, before cadmium exposure, fish responded positively in 98.41 +/- 4.95% of lateral line system stimulations (escape behaviour in response to the water jet). After cadmium exposure, no behavioural modification could be detected: the fish responded positively in 95.16 +/- 9.79% of stimulations (chi(2) = 2.464, p = 0.116). In contrast, the high cadmium concentration used (5 microg l(-1), which represents 10 times the concentration occurring in highly polluted estuarine areas) involved severe neuromast tissue damage. Just after such cadmium exposure, fish showed only 41.67 +/- 35.36% of positive responses to their lateral line system stimulations, while they responded positively in 95.93 +/- 9.10% of stimulations under control conditions (chi(2) = 24.562, p < 0.0001). Their lateral line system neuromasts seemed to regenerate about 1 month after cadmium exposure. Associated with this regeneration, from the 21st day after cadmium exposure, their escape behaviour had recovered and was not significantly different from that recorded under control conditions (86.74 +/- 20.82%, chi(2) = 2.876, p = 0.090). This study shows that although 5 microg l(-1) cadmium is able to damage lateral line system neuromasts and causes fish behavioural alterations, fish exposed to 0.5 microg l(-1) cadmium displayed neither tissue neuromast nor behavioural modification.

Estimating position and velocity of a submerged moving object by the clawed frog Xenopus and by fish--a cybernetic approach

The lateral-line system is a unique facility of aquatic animals to locate predator, prey, or conspecifics. We present a detailed model of how the clawed frog Xenopus, or fish, can localize submerged moving objects in three dimensions by using their lateral-line system. In so doing we develop two models of a slightly different nature. First, we exploit the characteristic properties of the velocity field, such as zeros and maxima or minima, that a moving object generates at the lateral-line organs and that are directly accessible neuronally, in the context of a simplified geometry. In addition, we show that the associated neuronal model is robust with respect to noise. Though we focus on the superficial neuromasts of Xenopus the same arguments apply mutatis mutandis to the canal lateral-line system of fish. Second, we present a full-blown three-dimensional reconstruction of the source on the basis of a maximum likelihood argument.

Quantitative Aspects of the Spatial Distribution and Morphological Characteristics of the Sea Bass (Dicentrarchus labrax L.; Teleostei, Serranidae) Trunk Lateral Line Neuromasts

The results presented herein report quantitative data relative to the distribution and morphological characteristics of both types of neuromasts encountered on the trunk lateral line of the sea bass (Dicentrarchus labrax, L.). These data were obtained from scanning electron micrographs. They indicate that, as expected, each modified scale of the sea bass possessed a single canal neuromast with long axis oriented parallel to the fish's long axis. In contrast to several fish species, two thirds of superficial neuromasts observed herein were oriented perpendicular to the fish's long axis. However, whatever the main orientation of superficial neuromasts, two thirds of their hair bundles were oriented parallel to the long axis of the animal with approximately half of them in the direction of the head. Similar ratios were observed for canal neuromasts whatever the area of the maculae: central or peripheral. For both types of neuromasts it was not possible to clearly distinguish a paired organization of hair bundles with opposing polarities. Superficial neuromasts on each trunk canal scale were located on either the dorsal or ventral side of the canal and appeared to be distributed along the trunk lateral line with a higher probability to be encountered closer to the operculum. The frequency of presence and the average number of superficial neuromasts per scale increased with fish size. We observed a size gradient for canal neuromasts between the operculum and caudal peduncle. This gradation was correlated with a reduction of the width of the central area of the canal segment. Canal neuromasts were always localized in the larger portions of the canal segments. Taken together, these results point out some specific features associated with the sea bass trunk lateral line. With the previous report, they establish the first full description of the trunk lateral line of sea bass and will be useful for upcoming experiments regarding the function of the two types of neuromasts.

Spatial Distribution and Morphological Characteristics of the Trunk Lateral Line Neuromasts of the Sea Bass (Dicentrarchus labrax, L.; Teleostei, Serranidae)

The morphology and spatial distribution of the different types of neuromasts encountered on the trunk lateral line of the sea bass (Dicentrarchus labrax) were examined using scanning electron microscopy. The sea bass trunk lateral line exhibits a complete straight pattern. In their basic features, the two types of neuromasts present, canal and superficial, resemble what has been described in other fishes. They are similar in their general cellular organization but differ in sizes, and shapes, as well as in the densities and lengths of their hair bundles. However, the sea bass trunk lateral line distinguishes itself in several ways. For instance, the pores of the canal segments are partially obstructed due to the overlap of scales throughout the trunk. Moreover, based on the density and length of the hair bundles, two distinct areas, central and peripheral, could be distinguished within the maculae of canal neuromasts. Their cupulae are also peculiar as they possess two wing-like extensions and that their central core appears to be organized in layers instead of columns. In addition, the superficial neuromasts, up to 6 per scale, are either round or elliptical and seem to be distributed serendipitously. Finally, within the maculae of both types of neuromasts, a significant number of hair bundles do not follow the two-directional polarity pattern usually described. Although some hypotheses are proposed, the influence of these characteristics in terms of signal encoding and fish behavior is yet to be understood.

Rheotaxis and prey detection in uniform currents by Lake Michigan mottled sculpin (Cottus bairdi)

Lake Michigan mottled sculpin, Cottus bairdi, exhibit a lateral-line mediated, unconditioned orienting response, which is part of the overall prey capture behavior of this species and can be triggered in visually deprived animals by both live (e.g. Daphnia magna) and artificial (e.g. chemically inert vibrating sphere) prey. However, the extent to which background water motions (e.g. currents) might mask the detection of biologically significant stimuli like these is almost entirely unknown, despite the fundamental nature and importance of this question. To examine this question, the orienting response of mottled sculpin was used to measure threshold sensitivity to a nearby artificial prey (a 50 Hz vibrating sphere) as a function of background noise level (unidirectional currents of different flow velocities). Because many fish show unconditioned rheotaxis to uniform currents, we also measured the fish's angular heading relative to the oncoming flow in the absence of the signal. Frequency distributions of fish headings revealed positive rheotaxis to flows as low as 4 cm s(-1) and an increasing degree of alignment with the oncoming flow as a function of increasing flow velocity. Sculpin positioned in the upstream direction were able to detect relatively weak signals (estimated to be approx. 0.001-0.0001 peak-peak cm s(-1) at the location of the fish) in the presence of strong background flows (2-8 cm s(-1)), and signal levels at threshold increased by less than twofold for a fourfold increase in flow velocity. These results are consistent with the idea that lateral line canals behave as high-pass filters to effectively reject low frequency noises such as those caused by slow d.c. currents.

The orienting response of Lake Michigan mottled sculpin is mediated by canal neuromasts

Lake Michigan mottled sculpin, Cottus bairdi, exhibit a naturally occurring and unconditioned orienting response that can be triggered by both live prey and chemically inert vibrating spheres, even in blinded animals. CoCl(2)-induced reductions of the orienting response demonstrate that the lateral line is required for this behavior in the absence of non-mechanosensory cues (such as vision), but shed no light on the relative contributions of superficial and canal neuromasts to this behavior. To determine the relative roles of these two subsystems, we measured the frequency with which mottled sculpin oriented towards a small vibrating sphere before and after two treatments: (i) immersion of fish in a solution of gentamicin, an aminoglycoside antibiotic that damages hair cells in canal, but not superficial, neuromasts; and (ii) scraping the skin of the fish, which damages the superficial, but not the canal, neuromasts. To ensure that both superficial and canal neuromasts were adequately stimulated, we tested at different vibration frequencies (10 and 50 Hz) near or at the best frequency for each type of neuromast. At both test frequencies, response rates before treatment were greater than 70 % and were significantly greater than ‘spontaneous’ response frequencies measured in the absence of sphere vibration. Response rates fell to spontaneous levels after 1 day of gentamicin treatment and did not return to pre-treatment levels for 10–15 days. In contrast, response rates stayed approximately the same after superficial neuromasts had been damaged by skin abrasion. Scanning electron microscopy confirmed hair cell damage (loss of apical cilia) in canal, but not superficial, neuromasts of gentamicin-treated animals after as little as 24 h of treatment. The sensory epithelium of canal neuromasts gradually returned to normal, following a time course similar to behavioral loss and recovery of the orienting response, whereas that of superficial neuromasts appeared normal throughout the entire period. This study shows that the orienting response of the mottled sculpin is mediated by canal neuromasts.

Hydrodynamic image formation by the peripheral lateral line system of the Lake Michigan mottled sculpin, Cottus bairdi

Lake Michigan mottled sculpin (Cottus bairdi) have a lateral-line-mediated prey-capture behaviour that consists of an initial orientation towards the prey, a sequence of approach movements, and a final strike at the prey. This unconditioned behaviour can be elicited from blinded sculpin in the laboratory by both real and artificial (vibrating sphere) prey. In order to visualize what Lake Michigan mottled sculpin might perceive through their lateral line when approaching prey, we have combined anatomical, neurophysiological, behavioural and computational modelling techniques to produce three-dimensional maps of how excitation patterns along the lateral line sensory surface change as sculpin approach a vibrating sphere. Changes in the excitation patterns and the information they contain about source location are consistent with behavioural performance, including the approach pathways taken by sculpin to the sphere, the maximum distances at which approaches can be elicited, distances from which strikes are launched, and strike success. Information content is generally higher for laterally located sources than for frontally located sources and this may explain exceptional performance (e.g. successful strikes from unusually long distances) in response to lateral sources and poor performance (e.g. unsuccessful strikes) to frontal sources.