Lateral line stimulation patterns and prey orienting behavior in the Lake Michigan mottled sculpin (Cottus bairdi)

Sound and sturgeon: Bioacoustics and anthropogenic sounda)

Sturgeons are basal bony fishes, most species of which are considered threatened and/or endangered. Like all fishes, sturgeons use hearing to learn about their environment and perhaps communicate with conspecifics, as in mating. Thus, anything that impacts the ability of sturgeon to hear biologically important sounds could impact fitness and survival of individuals and populations. There is growing concern that the sounds produced by human activities (anthropogenic sound), such as from shipping, commercial barge navigation on rivers, offshore windfarms, and oil and gas exploration, could impact hearing by aquatic organisms. Thus, it is critical to understand how sturgeon hear, what they hear, and how they use sound. Such data are needed to set regulatory criteria for anthropogenic sound to protect these animals. However, very little is known about sturgeon behavioral responses to sound and their use of sound. To help understand the issues related to sturgeon and anthropogenic sound, this review first examines what is known about sturgeon bioacoustics. It then considers the potential effects of anthropogenic sound on sturgeon and, finally identifies areas of research that could substantially improve knowledge of sturgeon bioacoustics and effects of anthropogenic sound. Filling these gaps will help regulators establish appropriate protection for sturgeon.

A multisensory perspective on near-field detection and localization of hydroacoustic sourcesa)

This paper gives a brief synopsis of the research career of S.C. in fish bioacoustics with an emphasis on dipole near fields. The hydroacoustic nature of the dipole near field and the effective stimuli to lateral line and auditory systems combine to produce a multisensory, range-fractionated region that is critically important to many fish behaviors. The mottled sculpin and goldfish lateral lines encode the spatial complexities of the near field as spatial excitation patterns along the body surface to provide instantaneous snapshots of various source features such as distance, orientation, and direction of movement. In contrast, the pressure-sensitive channel of the goldfish auditory system [the anterior swim bladder (SB)-saccule complex] encodes the spatial complexities in a temporal fashion whenever the position or orientation of the source changes with respect to the anterior SB. A full appreciation for how these somatotopic and egocentric representations guide fish behavior requires an understanding of how multisensory information, including vision, is combined in sensorimotor regions of the brain to effect behavior. A brief overview of vertebrate brain organization indicates that behaviors directed to or away from hydroacoustic sources likely involve a variety of mechanisms, behavioral strategies, and brain regions.

A Novel Obstacle Localization Method for an Underwater Robot Based on the Flow Field

Because the underwater environment is complex, autonomous underwater vehicles (AUVs) have difficulty locating their surroundings autonomously. In order to improve the adaptive ability of AUVs, this paper presents a novel obstacle localization strategy based on the flow features. Like fish, the strategy uses the flow field information directly to locate the object obstacles. Two different localization methods are provided and compared. The first method, which is named the Method of Spatial Distribution (MSD), is based on the spatial distribution of the flow field. The second method, which is named the Method of Amplitude Variation (MAV), is provided by the amplitude variation of the flow field. The flow field around spherical targets is obtained by a numerical method, and both methods use the parallel velocity component on the virtual lateral line. During the study, different target numbers, detective ratios, spacing ratios, and flow velocities are taken into account. It is demonstrated that both methods are able to locate object obstacles. However, the prediction accuracy of MAV is higher than that of MSD. That implies that MAV is more robust than MSD. These new findings indicate that the object obstacles can be directly located based on the flow field information and robust flow sensing is perhaps not based on the spatial distribution of the flow field but rather, on its fluctuation range.

Flow field perception based on the fish lateral line system

Fish are able to perceive the surrounding weak flow and pressure variations with their mechanosensory lateral line system, which consists of a superficial lateral line for flow velocity detection and a canal lateral line for flow pressure gradient perception. Achieving a better understanding of the flow field perception algorithms of the lateral line can contribute not only to the design of highly sensitive flow sensors, but also to the development of underwater smart skin with good hydrodynamic imaging properties. In this review, we discuss highly sensitive flow-sensing mechanisms for superficial and canal neuromasts and flow field perception algorithms. Artificial lateral line systems with different transduction mechanisms are then described with special emphasis on the recent innovations in the field of polymer-based artificial flow sensors. Finally, we discuss our perspective of the technological challenges faced while improving flow sensitivity, durability, and sensing fusion schemes.

The mechanosensory lateral line is used to assess opponents and mediate aggressive behaviors during territorial interactions in an African cichlid fish

Fish must integrate information from multiple sensory systems to mediate adaptive behaviors. Visual, acoustic and chemosensory cues provide contextual information during social interactions, but the role of mechanosensory signals detected by the lateral line system during aggressive behaviors is unknown. The aim of this study was first to characterize the lateral line system of the African cichlid fish Astatotilapia burtoni and second to determine the role of mechanoreception during agonistic interactions. The A. burtoni lateral line system is similar to that of many other cichlid fishes, containing lines of superficial neuromasts on the head, trunk and caudal fin, and narrow canals. Astatotilapia burtoni males defend their territories from other males using aggressive behaviors that we classified as non-contact or contact. By chemically and physically ablating the lateral line system prior to forced territorial interactions, we showed that the lateral line system is necessary for mutual assessment of opponents and the use of non-contact fight behaviors. Our data suggest that the lateral line system facilitates the use of non-contact assessment and fight behaviors as a protective mechanism against physical damage. In addition to a role in prey detection, the diversity of lateral line morphology in cichlids may have also enabled the expansion of their social behavioral repertoire. To our knowledge, this is the first study to implicate the lateral line system as a mode of social communication necessary for assessment during agonistic interactions.

Mechanosensory signaling as a potential mode of communication during social interactions in fishes

Signals produced during social interactions convey crucial information about the sender's identity, quality, reproductive state and social status. Fishes can detect near-body water movements via the mechanosensory lateral line system, and this sense is used during several common fish behaviors, such as schooling, rheotaxis and predator-prey interactions. In addition, many fish behaviors, such as aggressive lateral displays and reproductive body quivers, involve fin and body motions that generate water movements that can be detected by the lateral line system of nearby fish. This mechanosensory system is well studied for its role in obstacle avoidance and detection of inadvertent hydrodynamic cues generated during schooling and predator-prey interactions; however, little research has focused on the role of mechanosensory communication during social interactions. Here, we summarize the current literature on the use of mechanosensation-mediated behaviors during agonistic and reproductive encounters, as well as during parental care. Based on these studies, we hypothesize that mechanosensory signaling is an important but often overlooked mode of communication during conspecific social interactions in many fish species, and we highlight its importance during multimodal communication. Finally, we suggest potential avenues of future research that would allow us to better understand the role of mechanosensation in fish communication.

Smart Mechanical Dipole: a device for the measurement of sphere motion in behavioral and neurophysiological experiments

Fluid motion and pressure fields induced by vibrating spheres are frequently used to investigate the function of biological mechanosensory systems and artificial sensors. The calibration of the sphere motion amplitude (displacement, velocity, acceleration), time course and vibration direction often demands expensive equipment. To mitigate this requirement, we have developed a high-quality, low-cost device that we term a 'Smart Mechanical Dipole'. It provides real-time measurement of sphere acceleration along three axes and can be used to obtain an accurate stimulation trace. We applied digital filtering to equalize the frequency response of the vibrating sphere, which also reduced unwanted amplitude and frequency changes in the hydrodynamic signal. In addition, we show that the angular orientation of the rod to which the sphere was attached, i.e. axial versus transverse, but not the immersion depth of the sphere affected sphere vibration behavior.

Cobalt Chloride Treatment Used to Ablate the Lateral Line System Also Impairs the Olfactory System in Three Freshwater Fishes

Fishes use multimodal signals during both inter- and intra-sexual displays to convey information about their sex, reproductive state, and social status. These complex behavioral displays can include visual, auditory, olfactory, tactile, and hydrodynamic signals, and the relative role of each sensory channel in these complex multi-sensory interactions is a common focus of neuroethology. The mechanosensory lateral line system of fishes detects near-body water movements and is implicated in a variety of behaviors including schooling, rheotaxis, social communication, and prey detection. Cobalt chloride is commonly used to chemically ablate lateral line neuromasts, thereby eliminating water-movement cues to test for mechanosensory-mediated behavioral functions. However, cobalt acts as a nonspecific calcium channel antagonist and could potentially disrupt function of all superficially located sensory receptor cells, including those for chemosensing. Here, we examined whether CoCl2 treatment used to ablate the lateral line system also impairs olfaction in three freshwater fishes, the African cichlid fish Astatotilapia burtoni, goldfish Carassius auratus, and the Mexican blind cavefish Astyanax mexicanus. To examine the impact of CoCl2 on the activity of peripheral receptors, we quantified DASPEI fluorescence intensity of the olfactory epithelium from fish exposed to control and CoCl2 solutions. In addition, we examined brain activation in olfactory processing regions of A. burtoni immersed in either control or cobalt solutions. All three species exposed to CoCl2 had decreased DASPEI staining of the olfactory epithelium, and in A. burtoni, cobalt treatment caused reduced neural activation in olfactory processing regions of the brain. To our knowledge this is the first empirical evidence demonstrating that the same CoCl2 treatment used to ablate the lateral line system also impairs olfactory function. These data have important implications for the use of CoCl2 in future research and suggest that previous studies using CoCl2 should be reinterpreted in the context of both impaired mechanoreception and olfaction.

Coping with flow: behavior, neurophysiology and modeling of the fish lateral line system

With the mechanosensory lateral line fish perceive water motions relative to their body surface and local pressure gradients. The lateral line plays an important role in many fish behaviors including the detection and localization of dipole sources and the tracking of prey fish. The sensory units of the lateral line are the neuromasts which are distributed across the surface of the animal. Water motions are received and transduced into neuronal signals by the neuromasts. These signals are conveyed by afferent nerve fibers to the fish brain and processed by lateral line neurons in parts of the brainstem, cerebellum, midbrain, and forebrain. In the cerebellum, midbrain, and forebrain, lateral line information is integrated with sensory information from other modalities. The present review introduces the peripheral morphology of the lateral line, and describes our understanding of lateral line physiology and behavior. It focuses on recent studies that have investigated: how fish behave in unsteady flow; what kind of sensory information is provided by flow; and how fish use and process this information. Finally, it reports new theoretical and biomimetic approaches to understand lateral line function.

Hydrodynamic perception in true seals (Phocidae) and eared seals (Otariidae)

Pinnipeds, that is true seals (Phocidae), eared seals (Otariidae), and walruses (Odobenidae), possess highly developed vibrissal systems for mechanoreception. They can use their vibrissae to detect and discriminate objects by direct touch. At least in Phocidae and Otariidae, the vibrissae can also be used to detect and analyse water movements. Here, we review what is known about this ability, known as hydrodynamic perception, in pinnipeds. Hydrodynamic perception in pinnipeds developed convergently to the hydrodynamic perception with the lateral line system in fish and the sensory hairs in crustaceans. So far two species of pinnipeds, the harbour seal (Phoca vitulina) representing the Phocidae and the California sea lion (Zalophus californianus) representing the Otariidae, have been studied for their ability to detect local water movements (dipole stimuli) and to follow hydrodynamic trails, that is the water movements left behind by objects that have passed by at an earlier point in time. Both species are highly sensitive to dipole stimuli and can follow hydrodynamic trails accurately. In the individuals tested, California sea lions were clearly more sensitive to dipole stimuli than harbour seals, and harbour seals showed a superior trail following ability as compared to California sea lions. Harbour seals have also been shown to derive additional information from hydrodynamic trails, such as motion direction, size and shape of the object that caused the trail (California sea lions have not yet been tested). The peculiar undulated shape of the harbour seals' vibrissae appears to play a crucial role in trail following, as it suppresses self-generated noise while the animal is swimming.

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.

Neuronal birth order identifies a dimorphic sensorineural map

Spatially distributed sensory information is topographically mapped in the brain by point-to-point correspondence of connections between peripheral receptors and central target neurons. In fishes, for example, the axonal projections from the mechanosensory lateral line organize a somatotopic neural map. The lateral line provides hydrodynamic information for intricate behaviors such as navigation and prey detection. It also mediates fast startle reactions triggered by the Mauthner cell. However, it is not known how the lateralis neural map is built to subserve these contrasting behaviors. Here we reveal that birth order diversifies lateralis afferent neurons in the zebrafish. We demonstrate that early- and late-born lateralis afferents diverge along the main axes of the hindbrain to synapse with hundreds of second-order targets. However, early-born afferents projecting from primary neuromasts also assemble a separate map by converging on the lateral dendrite of the Mauthner cell, whereas projections from secondary neuromasts never make physical contact with the Mauthner cell. We also show that neuronal diversity and map topology occur normally in animals permanently deprived of mechanosensory activity. We conclude that neuronal birth order correlates with the assembly of neural submaps, whose combination is likely to govern appropriate behavioral reactions to the sensory context.

Perception of frequency, amplitude, and azimuth of a vibratory dipole source by the octavolateralis system of goldfish (Carassius auratus)

Goldfish (Carassius auratus) were conditioned to suppress respiration to a 40-Hz vibratory source and subsequently tested for stimulus generalization to frequency, stimulus amplitude, and position (azimuth). Animals completely failed to generalize to frequencies separated by octave intervals both lesser and greater than the CS. However, they did appear to generalize weakly to an aerial loudspeaker stimulus of the same frequency (40 Hz) after conditioning with an underwater vibratory source. Animals had a gradually decreasing amount of generalization to amplitude changes, suggesting a perceptual dimension of loudness. Animals generalized largely or completely to the same underwater source presented at a range of source azimuths. When these azimuths were presented at a transect of 3 cm, some animals did show decrements in generalization, while others did not. This suggests that although azimuth may be perceived more saliently at distances closer to a dipole source, perception of position is not immediately salient in conditioned vibratory source detection. Differential responding to test stimuli located toward the head or tail suggests the presence of perceptual differences between sources that are rostral or caudal with respect to the position of the animal or perhaps the head.

Responses of brainstem lateral line units to different stimulus source locations and vibration directions

We recorded responses of lateral line units in the medial octavolateralis nucleus in the brainstem of goldfish, Carassius auratus, to a 50 Hz vibrating sphere and studied how responses were affected by placing the sphere at various locations alongside the fish and by different directions of vibration. In most units (88%), stimulation with the sphere from one or more spatial locations caused an increase and/or decrease in discharge rate. In few units (10%), discharge rate was increased by stimulation from one location and decreased by stimulation from an adjacent location in space. In a minority of the units (2%), changing sphere location did not affect discharge rates but caused a change in phase coupling. Units sensitive to a distinct sphere vibration direction were not found. The data also show that the responses of most brainstem units differ from those of primary afferent nerve fibers. Whereas primary afferents represent the pressure gradient pattern generated by the sphere and thus encode location and vibration direction of a vibrating sphere, most brainstem units do not. This information may be represented in the brainstem by a population code or in higher centers of the ascending lateral line pathway.

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.