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This paper is not meant to be a review article. Instead, it gives an overview of the major research projects that the author, together with his students, colleagues and collaborators, has worked on. Although the main focus of the author's work has always been the fish lateral line, this paper is mainly about all the other research projects he did or that were done in his laboratory. These include studies on fishing spiders, weakly electric fish, seals, water rats, bottom dwelling sharks, freshwater rays, venomous snakes, birds of prey, fire loving beetles and backswimmers. The reasons for this diversity of research projects? Simple. The authors's lifelong enthusiasm for animals, and nature's ingenuity in inventing new biological solutions. Indeed, this most certainly was a principal reason why Karl von Frisch and Alfred Kühn founded the Zeitschrift für vergleichende Physiologie (now Journal of Comparative Physiology A) 100 years ago. [ABSTRACT FROM AUTHOR]

Data on the role of brain regions (forebrain, midbrain and other structures) in the control of schooling behavior of fish has been systematized. Data have been presented on the influence of the presence in the food of certain substances (docosahexaenoic acid) accumulating in the brain on the rate of formation of schooling behavior in fish ontogeny. The neurohormonal system may be involved in the regulation of schooling behavior. The individual behavior of fish in a school depends on the lateralization of brain functions. Attention has been drawn to the extremely poor knowledge of the processes of central and hormonal regulation of schooling behavior of fish. Vision is the leading, and most often the only sensory system that enables fish to demonstare schooling behavior. Monomodality distinguishes schooling behavior from other complex forms of fish behavior. Visual deprivation or deterioration of the conditions for visual reception makes schooling reactions of fish difficult or completely impossible. Existing assumptions about the possible participation in schooling behavior of other sensory systems of fish—lateral line, hearing, olfaction, electroreception—have been critically analyzed. Strict evidence of the real involvement of these sensory systems in the mediation of schooling contacts in fish is still lacking. [ABSTRACT FROM AUTHOR]

The zebrafish is increasingly employed in behavioral neuroscience as a translationally relevant model organism for human central nervous system disorders. One of the most prevalent CNS disorders representing an unmet medical need is the disorder cluster defined under the umbrella term anxiety disorders. Zebrafish have been shown to respond to a variety of anxiety and fear inducing stimuli and have been suggested for modeling human anxiety. Here, we describe a simple method with which we intend to induce fear/anxiety responses in this species. The method allows us to deliver a visual and lateral line stimulus (vibration or "tapping") to the fish with the use of a moving object, a ball colliding with the side glass of the experimental tank. We describe the hardware construction of the apparatus and the procedure of the behavioral paradigm. We also present data on how zebrafish respond to the tapping. Our results demonstrate that the method induces significant fear/anxiety responses. We argue that the simplicity of the method and the efficiency of the paradigm should make it popular among those who plan to use zebrafish as a tool in anxiety research. [ABSTRACT FROM AUTHOR]

Threespine stickleback exhibit a row of superficial neuromasts that project through the bony plates on each side of the trunk and which constitute an important sensory modality for detection of near-field water motion. Previously, we have shown that numbers of neuromasts on each structural plate are highly variable among populations. In the current paper, we expand this study to evaluate the extent of deviation from bilateral symmetry of 4344 fish in 57 natural and three transplant populations of threespine stickleback from lakes, streams and oceanic habitats of coastal British Columbia, predicting that neuromasts would be largely bilaterally symmetrical for optimal detection of external stimuli. In contrast, we found asymmetry in all populations, the greatest amount occurring on the anterior buttressing lateral plates and on populations with the fewest neuromasts. We found no consistent trends of signed (directional) asymmetry (SA) among the populations while relative absolute asymmetry (RAA) is lower in dystrophic (stained) habitats than in clearwater habitats (p < 0.001), except for fish with few neuromasts. Sexual dimorphism in RAA is also greater in dystrophic habitats (p < 0.001). Transplants from stained lakes to unstained ponds resulted in a 0.1% to 14% difference in RAA from the source population in less than 12 generations but varied in direction among experiments. Our data suggest a widespread tendency for populations exposed to reduced photic information to exhibit reduced asymmetry in their lateral line system, which can change rapidly in response to a new environment. [ABSTRACT FROM AUTHOR]

The mechanosensory lateral line of fishes is a flow sensing system and supports a number of behaviors, e.g. prey detection, schooling or position holding in water currents. Differences in the neuromast pattern of this sensory system reflect adaptation to divergent ecological constraints. The threespine stickleback, Gasterosteus aculeatus, is known for its ecological plasticity resulting in three major ecotypes, a marine type, a migrating anadromous type and a resident freshwater type. We provide the first comparative study of the pattern of the head lateral line system of North Sea populations representing these three ecotypes including a brackish spawning population. We found no distinct difference in the pattern of the head lateral line system between the three ecotypes but significant differences in neuromast numbers. The anadromous and the brackish populations had distinctly less neuromasts than their freshwater and marine conspecifics. This difference in neuromast number between marine and anadromous threespine stickleback points to differences in swimming behavior. We also found sexual dimorphism in neuromast number with males having more neuromasts than females in the anadromous, brackish and the freshwater populations. But no such dimorphism occurred in the marine population. Our results suggest that the head lateral line of the three ecotypes is under divergent hydrodynamic constraints. Additionally, sexual dimorphism points to divergent niche partitioning of males and females in the anadromous and freshwater but not in the marine populations. Our findings imply careful sampling as an important prerequisite to discern especially between anadromous and marine threespine sticklebacks. [ABSTRACT FROM AUTHOR]

Abstract: The emergence of genomics and its use in combination with high-resolution bioimaging for the study of animal development mechanisms provide scientists with information on gene sets and regulation thereof during development. This enabled the identification of the core set of transcription factors involved in the development of invertebrates and vertebrates. This approach was particularly efficient due to the widespread use of transparent embryos of zebrafish and other bony fishes in these studies. These embryos can be used as model systems for the analysis of vertebrate development, even at the level of individual cells, as the various processes of development unfold in vivo. [ABSTRACT FROM AUTHOR]

The saddleback syndromes were observed in several commercial fishes obtained from Saudi Arabian coast of the Arabian Gulf. These deformities resulting in missing dorsal spines or rays, sometimes accompanied by a depression in the dorsal profile, were found in ten fish species from seven families. Other morphological abnormalities such as scale disturbances, lateral line deformity, and kyphosis, the presence of a lesion, slight ambicoloration, and supraneural deformities accompanying the saddleback deformity were also observed. The occurrence of similar deformities across such a spectrum of fishes from the same location suggests that the abnormalities were induced by something in the environment common to all these species. [ABSTRACT FROM AUTHOR]

Fish use their mechanosensory lateral line amongst others for the detection of vortices shed by an upstream object and/or for the detection of vortices caused by the tail fin movements of another fish. Thus, vortices are one type of hydrodynamic stimuli to which fish are exposed in their natural environment. We investigated the responses of medullary lateral line units of common rudd, Scardinius erythrophthalmus, and common nase, Chondrostoma nasus (Cyprinidae), to water flow (9.5–13.3 cm−1) that contained vortices (a Kármán vortex street) shed by an upstream cylinder (diameter 2 cm). The distance between the cylinder and the tip of the fish’s snout varied between 8 and 24 cm. 21 out of 42 units (S. erythrophthalmus), respectively, 9 out of 39 units (Chondrostoma nasus) responded to the vortices shed by the cylinder. Up to a cylinder distance of 24 cm, interburst intervals revealed the vortex shedding frequency, i.e., burst frequency was similar to or identical with the vortex shedding frequency. [ABSTRACT FROM AUTHOR]

Nkx5 family members are homeobox transcription factors important for sensory organ development. Several members of the Nkx5 family are expressed in the eye, brain, developing ear, and lateral line. Members of this family have been previously identified in medaka, chick, and mouse. Here, we characterize two members of the Nkx5 family, Nkx5.3 and SOHo, in Xenopus laevis. We verify the identity of X. laevis Nkx5.3 and SOHo by phylogenetic comparison to chicken, medaka, and zebrafish orthologs. Both Nkx5.3 and SOHo are expressed in the developing eye, ear, lateral line system, and cranial neurons as determined by in situ hybridization. [ABSTRACT FROM AUTHOR]

Rheotaxis is a widespread behavior with many potential benefits for fish and other aquatic animals, yet the sensory basis of rheotaxis under different fluvial conditions is still poorly understood. Here, we examine the role that vision and the lateral line play in the rheotactic behavior of a stream-dwelling species (Mexican tetra, Astyanax mexicanus) under both rectilinear and turbulent flow conditions. Turbulence lowered the flow speed at which threshold levels of rheotactic performance were elicited, an effect that was independent of sensory condition. Compared to fish with access to visual information, fish without access exhibited cross-stream casting behaviors and a decrease in the accuracy with which they oriented upstream. Visual deprivation effects were independent of availability of lateral line information and whether flow was rectilinear or turbulent. Fish deprived of lateral line information exhibited no measureable deficits under any of the conditions of this study. This study indicates that rheotactic abilities persist in the absence of both vision and lateral line under both turbulent and non-turbulent conditions, but that turbulence enhances either the motivation or ability of fish to orient to slow currents. [ABSTRACT FROM AUTHOR]

We investigated the responses of medullary lateral line units of the rudd, Scardinius erythrophthalmus, to bulk water flow (7 cm s) and to water flow that contained vortices shed by an upstream half cylinder (diameter 1, 2, and 3 cm). Thirty-five percent of the medullary units either increased or decreased their discharge rate with the increasing cylinder diameter. In some units, the spike patterns revealed the vortex shedding frequency, i.e., in these units the amplitude of spike train frequency spectra was similar or identical to the vortex shedding frequency. [ABSTRACT FROM AUTHOR]

Two sand-dwelling cichlids from Lake Malawi ( Aulonocara stuartgranti, Tramitichromis sp.) that feed on benthic invertebrates, but have different lateral line phenotypes, use lateral line and/or visual cues to detect prey under light versus dark conditions. The current study examined how ecologically relevant variation in light intensity [0-800 lux (lx)] influences detection of prey (mobile, immobile) in each species by analyzing six behavioral parameters. Both species fed at light intensities ≥1 lx and trends in behavior among light intensities were informative. However, prey type and/or time of day (but not light intensity) predicted all four parameters analyzed with generalized linear mixed models in A. stuartgranti, whereas the interaction of light intensity and time of day predicted three of these parameters in Tramitichromis sp. Data suggest that the critical light intensity is 1-12 lx for both species, that the integration of visual and lateral line input explains differences in detection of mobile and immobile prey and behavioral changes at the transition from 1 to 0 lx in A. stuartgranti, and that Tramitichromis sp. likely uses binocular vision to locate prey. Differences in the sensory biology of species that exploit similar prey will have important implications for the trophic ecology of African cichlid fishes. [ABSTRACT FROM AUTHOR]

We explored how lateral line cues interact with visual cues to mediate flow sensing behaviors in the nocturnal developing frog, Xenopus laevis, by exposing animals to current flows under different lighting conditions and after exposure to the ototoxin gentamicin. Under dark conditions, Xenopus tadpoles move downstream at the onset of current flow, then turn, and orient toward the direction of the flow with high accuracy. Postmetamorphic froglets also exhibit positive rheotaxis but with less accuracy and longer latency. The addition of discrete light cues to an otherwise dark environment disrupts rheotaxis and positioning. Orientation is less accurate, latency to orient is longer, and animals do not move as far downstream in the presence of light. Compared with untreated tadpoles tested in the dark, tadpoles exposed to gentamicin show less accurate rheotaxis with longer latency and do not move as far downstream in response to flow. These effects are compounded by the presence of light cues. The disruptive effects of light on flow sensing in Xenopus emphasize the disturbances to natural behaviors that may be produced by anthropogenic illumination in nocturnal habitats. [ABSTRACT FROM AUTHOR]

Lymphocyte antigen-6 (Ly-6) superfamily members have been identified in zebrafish, but the expression and function of these Ly-6 genes remain largely unknown. Posterior lateral line (pLL) system is produced by migrating pLL primordium (pLLp). Chemokine signaling, Notch, Wnt, and fibroblast growth factor (FGF) signaling regulate migration of pLLp cells and formation of neuromasts. However, the mechanism of neuromast deposition remains to be explored. Identification of novel genes expressed in pLLp will certainly help the study of such a process. Here we identified a Ly-6 gene called neuromast-expressed gpi-anchored lymphocyte antigen-6 ( negaly6), which was specifically expressed in neuromast. Quantitative real-time PCR (qRT-PCR) analysis showed that negaly6 started to be expressed at 24 hpf, and whole-mount in situ hybridization analysis indicated that negaly6 was highly expressed in the trailing zone of pLLp and mature neuromast. Furthermore, negaly6 expression was inhibited by FGF signaling antagonist but not by Wnt signaling agonist or antagonist. Collectively, these data indicate that negaly6 may be associated with the regulation of neuromast deposition via FGF signaling pathway. [ABSTRACT FROM AUTHOR]

The roles of vision and the lateral-line system in fish-screen avoidance behaviors were investigated in Sacramento splittail ( Pogonichthys macrolepidotus). Fish were viewed swimming in front of water-diversion-type fish screens in a laboratory flume during the day (lit condition) and night (darkened condition, using infrared equipment). Streptomycin-sulfate treatments were used to block the fish's lateral-line systems. Lateral line neuromasts were labeled with 2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide (DASPEI) to assess the streptomycin treatment's effectiveness. Splittail contacted the screens infrequently during the day, but contacted the screens significantly more often during the night. Also, in darkened conditions, streptomycin-treated splittail contacted the screens significantly more often than did control fish. Furthermore 60 % of the streptomycin-treated fish became impinged (stuck) to the screens during night experiments, compared to 15 % of the untreated fish. These findings suggest that splittail use their lateral-line system to detect and avoid objects (screens) in the absence of vision. Splittail displayed no response to stimuli generated from a piston-driven vibrator mounted to the center of the screens. Our findings are the first to show how fish can use different sensory systems to detect and avoid fish screens in the presence or absence of light, and they should benefit fisheries and water resources managers, regarding the timing of water extractions through screened water diversions. [ABSTRACT FROM AUTHOR]

Comparative studies of the mechanosensory lateral line (MLL) have provided valuable insights into the predatory, escape and navigation behaviours of teleost and elasmobranch fishes. Recent work on the MLL in elasmobranchs has focused on canal morphology and pore topography in batoid species, with considerably less detailed examination of the canal system of sharks. In this study, the spatial arrangement of MLL canals and pit organs, and the morphology of the sensory neuromasts, are described for two species of wobbegong shark: the spotted wobbegong Orectolobus maculatus and the ornate wobbegong O. ornatus. Wobbegongs are benthic species that employ an ambush feeding strategy, and it is hypothesised that the MLL will be adapted for both these ecological traits. The spatial distribution of the MLL system in both species is broadly similar to other elasmobranchs, with a dorsal concentration of canals and pit organs that is ideally suited for detecting water flow over the top of the head. This arrangement may facilitate the detection of prey and predators swimming above and in front of the shark. The non-pored canals positioned directly above the mouth may be used as mechanotactile receptors to optimise 'touch' sensation when feeding. Wobbegong canal and pit organ neuromast hair cell morphology is typical of other sharks; however, canal neuromast sensory tissue differs from other elasmobranch species in that it is not continuous throughout the canals. The study provides evidence that the MLL system of wobbegong sharks is well adapted for their rather unique feeding mode and benthic lifestyle. [ABSTRACT FROM AUTHOR]

Xenopus laevis employs mechano-sensory lateral lines to, for instance, capture arthropods on the surface of turbid waters with poor visibility based on incoming wave signals. To characterise central representations of surface waves emitted from different locations, responses to several wave parameters were extracellularly recorded across brainstem, midbrain and thalamic areas. Overall, 339 of 411 statistically analysed responses showed significantly altered spike rates during the presentation of surface waves. Of these units, 45.1 % were obtained in the torus semicircularis including its laminar subnucleus (23.3 %) that is known to process auditory cues. Wave parameters contributing to central object representations were indicated by response rates that systematically varied with amplitude (76.3 % of 160 tested units), frequency (74.4 % of 270 tested units), source angle (93.7 % of 79 tested units), or source distance (63.8 % of 218 tested units). Map-like parameter representations were rather diffuse, yet an increased fraction of units tuned to frontal source angles was observed at deeper tissue layers (>180 μm), and an increased fraction of best neuronal responses to low wave frequencies (≤25 Hz) at rostral midbrain sections. Responses to wave frequencies remained largely robust across tested unit samples independent of source angles, and distances ( N = 62). In comparison, spatial response characteristics seemed fragile across different wave frequencies in 68.3 % of 41 recordings. [ABSTRACT FROM AUTHOR]

The ontogeny of the ear, swim bladder and laterophysic connection was investigated in the spotfin butterflyfish, Chaetodon ocellatus in order to determine how the development of the laterophysic connection (a Chaetodon synapomorphy) is correlated with ontogenetic changes in the hearing capabilities in these abundant and ecologically important coral reef fishes. Histological and cleared and stained material revealed that the medial opening in the lateral line canal in the supracleithrum (which defines the laterophysic connection), an inflated physoclistous swim bladder, and the three otolithic organs are already present in the smallest individuals examined (7-15 mm SL). The medial opening in the supracleithrum increases in size and the cylindrical swim bladder horns form after the loss of the head plates characteristic of the tholichthys stage, in individuals ≥29 mm SL. The three sensory maculae of the ear increase in size, and the shape of the sacculus changes most dramatically with fish growth; hair cell density is highest in the utriculus. Physiological analysis of the reponse to sound pressure showed that larval and juvenile C. ocellatus had a hearing sensitivity peak at 100-200 Hz, which was ~30-40 dB more sensitive than that measured in larval coral reef fishes (e.g., damselfishes) that lack swim bladder horns. C. ocellatus did not show any ontogenetic changes in sensitivity to sound pressure, which may be explained by the fact that the growth of the swim bladder horns maintains the small distance between the swim bladder and ear that was established earlier during the larval stage. The timing of the development of the swim bladder horns suggests that if the laterophysic connection has a sensory acoustic function, its presence in individuals >29 mm SL suggests that its role is limited to post-settlement, reef-based behaviors. [ABSTRACT FROM AUTHOR]

We recorded the responses of lateral line units in the midbrain torus semicircularis of goldfish, Carassius auratus, to a 50-Hz vibrating sphere and determined the unit's spatial receptive fields for various distances between fish and sphere and for different directions of sphere vibration. All but one unit responded to the vibrating sphere with an increase in discharge rate. Only a proportion (25 %) of the units exhibited phase-locked responses. Receptive fields were narrow or broad and contained one, two or more areas of increased discharge rate. The data show that the receptive fields of toral lateral line units are in many respects similar to those of brainstem units but differ from those of afferent nerve fibres. The responses of primary afferents represent the pressure gradient pattern generated by a vibrating sphere and provide information about sphere location and vibration direction. Across the array of lateral line neuromasts, the fish brain in principle can derive this information. Nevertheless, toral units tuned to a distinct sphere location or sensitive to a distinct sphere vibration direction were not found. Therefore, it is conceivable that the torus semicircularis uses a population code to determine spatial location and vibration direction of a vibrating sphere. [ABSTRACT FROM AUTHOR]

The lateral line system, including the distribution and counts of canal and superficial neuromasts, in a Japanese tripterygiid Enneapterygius etheostomus was studied. Although the basic topography of the lateral line canals was typical of teleosts, preopercular, mandibular, parietal, predorsal and caudal fin groupings of superficial neuromasts were recognized for the first time in addition to the previously reported groupings in Tripterygiidae. Comparisons of neuroanatomical characteristics with those of New Zealand tripterygiids previously reported revealed significant differences, thereby indicating that detailed examination of the lateral line system could provide new information useful for taxonomic studies. [ABSTRACT FROM AUTHOR]

We studied the role of the lateral line system for detection and discrimination of dipole stimuli in the oscar, Astronotus ocellatus (Family Cichlidae), and determined detection thresholds in still water and frequency discrimination capabilities in still and turbulent water. Average detection threshold of six animals for a 100-Hz dipole stimulus was 0.0059 μm peak-to-peak water displacement at the surface of the fish. After inactivation of the neuromast receptor organs of the lateral line system with the antibiotic streptomycin, dipole detection was reduced, but recovered within 2-4 weeks. This suggests that the oscar relied strongly on hydrodynamic information received by the lateral line system. Five oscars learned to discriminate a 100-Hz stimulus from 70 Hz and lower frequencies. When turbulence was introduced into the experimental tank, fish were still able to discriminate 100 Hz from frequencies 70 Hz and lower indicating that frequency discrimination mediated by the lateral line system was not reduced in turbulent water. [ABSTRACT FROM AUTHOR]

Blind cavefish use a form of active sensing in which burst-coast swimming motions generate flow signals detected by the lateral line. To determine if blind cavefish have evolved behavioral specializations for active flow-sensing, including the ability to regulate flow signal production through lateral line feedback, the swimming kinematics of blind and sighted morphs of Astyanax were compared before and after 24 h of familiarization with a novel, dark environment and with and without lateral line functionality. Although both morphs showed little difference in the vast majority of kinematic parameters measured, blind morphs differed significantly from sighted morphs in having a much higher incidence of swim cycle sequences devoid of sharp turns. Both lateral line deprivation and familiarization with the arena led to significant declines in this number for blind, but not sighted morphs. These findings suggest that swimming kinematics are largely conserved, but that blind morphs have nevertheless evolved enhanced abilities to use lateral line feedback when linking swim cycles into continuous, straight trajectories for exploratory purposes. This behavioral specialization can best be understood in terms of the intermittent and short-range limitations of active flow-sensing and the challenges they pose for spatial orientation and navigation. [ABSTRACT FROM AUTHOR]

Blind Mexican cave fish ( Astyanax fasciatus) lack a functional visual system and have been shown to sense their environment using a technique called hydrodynamic imaging, whereby nearby objects are detected by sensing distortions in the flow field of water around the body using the mechanosensory lateral line. This species has also been noted to touch obstacles, mainly with the pectoral fins, apparently using this tactile information alongside hydrodynamic imaging to sense their surroundings. This study aimed to determine the relative contributions of hydrodynamic and tactile information during wall following behaviour in blind Mexican cave fish. A wall was custom built with a 'netted' region in its centre, which provided very similar tactile information to a solid tank wall, but was undetectable using hydrodynamic imaging. The fish swam significantly closer to and collided more frequently with the netted region of this wall than the solid regions, indicating that the fish did not perceive the netted region as a solid obstacle despite being able to feel it as such with their pectoral fins. We conclude that the touching of objects with the pectoral fins may be an artefact of the intrinsic link between pectoral fin extensions and tail beating whilst swimming, and does not function to gather information. During wall following, hydrodynamic information appears to be used strongly in preference to tactile information in this non-visual system. [ABSTRACT FROM AUTHOR]

Morphology of two endemic eastern Pacific species of eelpouts-blackbelly Lycodes pacificus Collett, 1879 and bigfin L. cortezianus Gilbert, 1891-were studied. It was shown that these two species are characterized by unreduced seismosensory system of the head and belong to a species group with a double lateral line. It was suggested that the ancestral form of this species group could have possibly dispersed in the Atlantic Ocean through the Panama Canal in the pre-Pleistocene time. It is likely that the antitropical distribution of the Newfoundland eelpout L. terranovae is related this event. [ABSTRACT FROM AUTHOR]

Components of the lateral line system and their innervation were studied in Odontobutis obscura (Odontobutidae) and Pterogobius elapoides (Gobiidae), which are benthic and pelagic species, respectively. Innervation of the superficial neuromasts constituting the trunk lateral line system by way of three continuous longitudinal series (dorsal, middle, and ventral series: ld, lm, and lv series, respectively) became apparent for the first time. Innervation patterns indicated that the ld and lv series represented a mixture of displaced rows (from lm series) and new additional rows. In O. obscura, the ld and lv series were poorly developed, whereas both series were well developed in the pelagic P. elapoides, possibly as an adaptation to receive stimuli from above and below. Two extremely elongated nerve branches derived from the lateral ramus of the posterior lateral line nerve innervated the ld and lv series, respectively, in P. elapoides. Homologies of the neuromast rows on the head and body were discussed on the basis of their innervation patterns. [ABSTRACT FROM AUTHOR]

When introduced into a novel environment that limits or prevents vision, a variety of species including Mexican blind cavefish ( Astyanax mexicanus) exhibit wall-following behaviors. It is often assumed that wall following serves an exploratory function, but this assertion remains untested against alternative artifactual explanations. Here, we test whether wall following by cavefish is a purposeful behavior in which fish actively maintain a close relationship with the wall, or an artifactual consequence of being enclosed in a small concave arena, in which fish turn slightly to avoid the wall whenever it impedes forward movement. Wall-following abilities of fish were tested in a large, goggle-shaped arena, where forward motion along the convex wall was unimpeded. In this circumstance, cavefish continued to follow the wall at frequencies significantly above chance levels. Lateral line inactivation significantly reduced the ability of fish to follow convex, but not concave or straight, walls. Wall-following abilities of normal fish decreased with decreasing radius of wall convex curvature. Our results demonstrate that cavefish actively follow walls of varying contours. Radius-of-curvature effects coupled with the difficulties posed by convex walls to lateral line-deprived fish suggest a partially complementary use of tactile and lateral line information to regulate distance from the wall. [ABSTRACT FROM AUTHOR]

Morphology of a rare species-large-scale eelpout Lycodes macrolepis Taranetz et Andriashev, 1935-has been studied. It was shown that the main lateral line of this species has a ventrolateral configuration rather than medial, as was considered previously. Large-scale eelpout is an endemic species of the Sea of Okhotsk; evidence of its finding in the Sea of Japan is based on the erroneous classification of another eelpout species. [ABSTRACT FROM AUTHOR]

Branching patterns of the trunk lateral line nerves were studied in 46 pleuronectiform species, representing nine families in two suborders. The dorsal fin longitudinal ramus (DFLR), derived from the main nerve (horizontal septum lateral line nerve), passed closely along the course of the middle trunk lateral line in all specimens examined, the dorsal longitudinal collector nerve (DLCN) partly coalescing with the DFLR along the arched part of the lateral line in Psettodes erumei (Psettodoidei), compared with the entire length of the latter in all other species (Pleuronectoidei). Citharidae, Paralichthyidae, and Pleuronectidae were characterized by having a simple, elongated dorsal ramule; Bothidae was unique in having more than one dorsal ramule, forming a ladder-like network and peripherally giving off numerous minute branches; Poecilopsettidae and Samaridae possessed a few, short dorsal ramules; Soleidae and Cynoglossidae were characteristic in having a dendritic dorsal ramule. Secondary modifications of the course of the middle trunk lateral line were detected by nerve information, the arched part of the lateral line having been secondarily highly elevated in some genera of Pleuronectidae, but secondarily straightened in Samaridae. [ABSTRACT FROM AUTHOR]

We revisit the method of conformal mapping and apply it to the setting found in mechanosensory detection systems such as the lateral-line system of fish. We derive easy-to-use equations capable of describing analytically the influence of the stimulus shape on the flow field and thus on the input to the lateral line. The present approach shows that the shape of a submerged moving object affects its perception if its distance to a detecting animal does not exceed the object’s body length. [ABSTRACT FROM AUTHOR]

The auditory pressure thresholds of red sea bream were examined using cardiac response in the field by placing fish subjects far from the sound source to prevent particle motion. Pressure and particle motion thresholds were also obtained using the auditory brainstem response (ABR) technique. The thresholds at 100 and 200 Hz were significantly higher when measured using the cardiac response in the far field than those obtained in previously conducted experiments in experimental tub. However, thresholds obtained using ABR from 200 to 500 Hz were not remarkably lower, although significantly different (0.01 < P < 0.05), compared with those obtained using cardiac response in the far field. Furthermore, calculated particle velocity thresholds indicated that fish probably detected particle motion within the frequency range of 50–200 Hz, even in fish with a deactivated lateral line. Although the ABR method is widely applied in fish auditory study, hearing thresholds are apparently affected by particle motion. [ABSTRACT FROM AUTHOR]

Structure of nonmodified scales and lateral-line scales ( Sll) is compared in 179 species of 105 genera of 13 families of the order Pleuronectiformes. Morphological diversity of Sll depends on the level of development and of interaction of two component parts—the scale plate and the tubular part. Of the considered characters, the most individually variable character is whether the tubular part is complete or incomplete. The interspecies differences may manifest themselves in structure of the scale plate, the level of unification of opening of the tubular part and of the cutaneous canaliculus, or in completeness or incompleteness of the tubular part. As a rule, Sll in species of the same genus is similar in structure. In some cases, special traits of this structure may be diagnostic characters of genera and contribute to the solution of controversial issues of generic position of species. The families of Pleuronectiformes are characterized by a different ratio of taxa with certain involved characters of nonmodified scales and Sll. However, their distribution in this order does not give a simple idea on their relationships and on the direction of evolutionary transformations. This follows from the fact that the structure of Sll depends on a wide complex of factors—morphogenesis of nonmodified scales, level of ossification of trunk canal, time of anlage, and mutual influence of these structures at early stages of ontogenesis. [ABSTRACT FROM AUTHOR]

Mexican blind cavefish exhibit an unconditioned wall-following behavior in response to novel environments. Similar behaviors have been observed in a wide variety of animals, but the biological significance and evolutionary history of this behavior are largely unknown. In this study, the behaviors of Mexican blind cavefish ( Astyanax sp.) and sighted Mexican tetra ( Astyanax mexicanus) were videotaped after fish were introduced into a novel environment under dark (infrared) or well-lit conditions. Under dark conditions, both sighted and blind morphs exhibited wall-following behaviors with subtle but significant differences. Blind morphs swam more nearly parallel to the wall, exhibited greater wall-following continuity and reached higher levels of sustained swimming speeds more quickly than sighted morphs. In contrast, sighted morphs in the light remained motionless near the wall for long periods of time or moved slowly around the center of the tank without entraining to the walls. These results are consistent with the idea that wall-following is a shared, primitive trait that serves an exploratory function under dark conditions to compensate for the absence of vision. This behavior has become more honed in blind morphs for exploratory purposes—in large part due to the enhanced, active-flow sensing abilities of the lateral line. [ABSTRACT FROM AUTHOR]

Information contained in the spatial excitation pattern along arrayed sensors in the lateral line system of Lake Michigan mottled sculpin, as well as other surface-feeding fish and amphibians, is thought to play a fundamental role in guiding prey-orienting behaviors. However, the way in which prey location is encoded by the excitation pattern and used by the nervous system to direct orienting behaviors is largely unknown. In this study, we test the hypothesis that mottled sculpin use excitation peaks (local ‘hot spots’) to determine the somatotopic location of an artificial prey (vibrating sphere/dipole source) along the body surface. Dipole orientation (axis of sphere vibration re: long axis of the fish) is manipulated to produce excitatory peaks in different body locations without changing the actual sphere location. Our results show that orienting accuracy is largely independent of source orientation, but not source distance and that turning directions are not guided by local hot spots in the somatotopic activation pattern of the lateral line. [ABSTRACT FROM AUTHOR]

Lamprey metamorphosis leads to considerable changes in morphology and behavior. We have recently reported that larval lampreys possess a functional lateral line system. Here we investigated metamorphic morphological changes in the lateral line system using light and electron microscopy. Functional modifications were studied by recording the trunk lateral line nerve activity of larvae and adults while stimulating neuromasts with approximately sinusoidal water motion. We found a general re-patterning of neuromasts on the head and trunk including an increase in numbers, redistribution within the pit lines, and shifts of the pit lines relative to external features. The trunk lateral line nerve response was qualitatively similar in adults and larvae. Both showed two neuronal populations responding to opposite directions of water flow. Magnitude of the response increased monotonically with stimulus amplitude. At low frequencies, the response lag relative to the stimulus maximum was approximately 220°, and the gain depended approximately linearly on frequency, confirming that superficial neuromasts are velocity detectors. Changes in phase lag with increasing stimulus frequency were steeper in larvae, suggesting slower afferent conductance. The response gain with frequency was smaller for adults, suggesting a narrower frequency discrimination range and decreased sensitivity. These changes may be adaptations for the active lifestyle of adult lampreys. [ABSTRACT FROM AUTHOR]

Aquatic predators like Xenopus laevis exploit mechano-sensory lateral lines to localise prey on the water surface by its wave emissions. In terms of distance, hypothetically, the source of a concentric wave could be centrally represented based on wave curvatures: for Xenopus, we present a first sample of 98 extracellularly recorded brainstem and midbrain responses to waves with curvatures ranging from 22.2–11.1 m−1. At the frog, concurrently, wave amplitudes and their spectral composition were kept stable. Notably, 61% of 98 units displayed curvature-dependent spike rates, suggesting that wave curvatures could support an extraction of source distances in the amphibian brain. [ABSTRACT FROM AUTHOR]

The zebrafish is a valuable model for studying hair cell development, structure, genetics, and behavior. Zebrafish and other aquatic vertebrates have hair cells on their body surface organized into a sensory system called the lateral line. These hair cells are highly accessible and easily visualized using fluorescent dyes. Morphological and functional similarities to mammalian hair cells of the inner ear make the zebrafish a powerful preparation for studying hair cell toxicity. The ototoxic potential of drugs has historically been uncovered by anecdotal reports that have led to more formal investigation. Currently, no standard screen for ototoxicity exists in drug development. Thus, for the vast majority of Food and Drug Association (FDA)-approved drugs, the ototoxic potential remains unknown. In this study, we used 5-day-old zebrafish larvae to screen a library of 1,040 FDA-approved drugs and bioactives (NINDS Custom Collection II) for ototoxic effects in hair cells of the lateral line. Hair cell nuclei were selectively labeled using a fluorescent vital dye. For the initial screen, fish were exposed to drugs from the library at a 100-μM concentration for 1 h in 96-well tissue culture plates. Hair cell viability was assessed in vivo using fluorescence microscopy. One thousand forty drugs were rapidly screened for ototoxic effects. Seven known ototoxic drugs included in the library, including neomycin and cisplatin, were positively identified using these methods, as proof of concept. Fourteen compounds without previously known ototoxicity were discovered to be selectively toxic to hair cells. Dose–response curves for all 21 ototoxic compounds were determined by quantifying hair cell survival as a function of drug concentration. Dose–response relationships in the mammalian inner ear for two of the compounds without known ototoxicity, pentamidine isethionate and propantheline bromide, were then examined using in vitro preparations of the adult mouse utricle. Significant dose-dependent hair cell loss in the mouse utricle was demonstrated for both compounds. This study represents an important step in validating the use of the zebrafish lateral line as a screening tool for the identification of potentially ototoxic drugs. [ABSTRACT FROM AUTHOR]

The lateral line is a hydrodynamic sensory system that allows fishes and aquatic amphibians to detect the water motions caused, for instance, by conspecifics, predators or prey. Typically the peripheral lateral line of fishes consists of several hundred neuromasts spread over the head, trunk, and tail fin. Lateral line neuromasts are mechanical low-pass filters that have an operating range from <1 Hz up to about 150 Hz. Within this frequency range, neuromasts encode the duration, local direction, amplitude, frequency, and phase of a hydrodynamic stimulus. This paper reviews the peripheral and central processing of lateral line information in fishes. Special attention is given to the coding of simple and complex hydrodynamic stimuli, to parallel processing, the roles of the various brain areas that process hydrodynamic information and the centrifugal (efferent) control of lateral line information. The review argues that in order to fully comprehend peripheral and central lateral line information processing, it is imperative to do comparative studies that take into account the ecology of fishes, meaning that natural stimulus and noise conditions have to be considered. [ABSTRACT FROM AUTHOR]

Fish acquire information about their aquatic environment by means of their mechanosensory lateral-line system. This system consists of superficial and canal neuromasts that sense perturbations in the water surrounding them. Based on a hydrodynamic model presented here, we propose a mechanism through which fish can localize the source of these perturbations. In doing so we include the curvature of the fish body, a realistic lateral line canal inter-pore distance for the lateral-line canals, and the surface boundary layer. Using our model to explore receptor behavior based on experimental data of responses to dipole stimuli we suggest that superficial and canal neuromasts employ the same mechanism, hence provide the same type of input to the central nervous system. The analytical predictions agree well with spiking responses recorded experimentally from primary lateral-line nerve fibers. From this, and taking into account the central organization of the lateral-line system, we present a simple biophysical model for determining the distance to a source. [ABSTRACT FROM AUTHOR]

Cave fishes need to rely on non-visual senses, such as the sense of smell or the lateral line to communicate in darkness. In the present study, we investigated sex identification by females of a cave-dwelling livebearing fish, Poecilia mexicana (cave molly), as well as its surface-dwelling relatives. Unlike many other cave fishes, cave mollies still possess functional eyes. Three different modes of presentation of the stimulus fish (a male and an equally sized female) were used: ( i) the stimulus fish were presented behind wire-mesh in light, allowing the focal female to perceive multiple cues, ( ii) the experiment was carried out under infrared conditions, such that only non-visual cues could be perceived and ( iii) the stimulus fish were presented in light behind transparent Plexiglas, allowing for the use of visual cues only. Females of all populations examined preferred to associate with the stimulus female in at least one of the treatments, but only when visible light was provided, suggesting that far-range sex recognition is limited or even absent in the cave molly under naturally dark conditions. [ABSTRACT FROM AUTHOR]

The investigation of small physiological mechano-sensory systems, such as hair cells or their accessory structures in the inner ear or lateral line organ, requires mechanical stimulus equipment that allows spatial manipulation with micrometer precision and stimulation with amplitudes down to the nanometer scale. Here, we describe the calibration of a microfluid jet produced by a device that was designed to excite individual cochlear hair cell bundles or cupulae of the fish superficial lateral line system. The calibration involves a precise definition of the linearity and time- and frequency-dependent characteristics of the fluid jet as produced by a pressurized fluid-filled container combined with a glass pipette having a microscopically sized tip acting as an orifice. A procedure is described that can be applied during experiments to obtain a fluid jet’s frequency response, which may vary with each individual glass pipette. At small orifice diameters (<15 μm), the fluid velocity of the jet is proportional to the displacement of the piezoelectric actuator pressurizing the container’s volume and is suitable to stimulate the hair bundles of sensory hair cells. With increasing diameter, the fluid jet velocity becomes proportional to the actuator’s velocity. The experimentally observed characteristics can be described adequately by a dynamical model of damped fluid masses coupled by elastic components. [ABSTRACT FROM AUTHOR]

Morphology of larval lampreys’ neuromasts was found to be very similar to that of adults. Activity in the lateral line nerve, elicited by a vibrating ball, indicated a functional lateralis system. Analysis revealed at least two populations of afferents, responding to opposite directions of water flow, with adapting responses. The response magnitude increased monotonically with stimulus amplitude. Larval lampreys’ neuromasts were less sensitive than those of teleosts. At low frequencies the response showed a phase lead of 200–220° with respect to the maximum of the ball displacement and a gain that was approximately linearly proportional to frequency. [ABSTRACT FROM AUTHOR]

Displacements of cupulae in the supraorbital lateral line canal in ruffe (Gymnocephalus cernuus) have been measured using laser interferometry and by applying transient as well as sinusoidal fluid stimuli in the lateral line canal. The cupular displacement in response to impulses of fluid velocity shows damped oscillations at approximately 120 Hz and a relaxation time-constant of 4.4 ms, commensurate with a quality factor of approximately 1.8. These values are in close agreement with the frequency characteristics determined via sinusoidal fluid stimuli, implying that the nonlinearity of cupular dynamics imposed by the gating apparatus of the sensory hair cells is limited in the range of cupular displacements and velocities measured (100-300 nm; 100-300 µm/s). The measurements also show that cupular displacement instantaneously follows the initial waveform of transient stimuli. The functional significance of the observed cupular dynamics is discussed. [ABSTRACT FROM AUTHOR]

The Eph family is the largest known group of structurally related receptor tyrosine kinases (RTKs). Each Eph receptor has a specific Ephrin ligand, and these function to define spatial boundaries during development. Analyses of EphA4 in mouse, chick, frog and zebrafish embryos have implicated this gene in a number of developmental processes, including maintenance of segmental boundaries, axon guidance, limb development, neural crest migration and patterning of the ear. In order to determine which components of EphA4 function may be primitive for gnathostomes, we cloned EphA4 from the lesser spotted catshark (Scyliorhinus canicula) and examined its expression pattern during shark embryonic development. Consistent with the patterns reported for bony fish and tetrapods, we observed segmental expression of EphA4 in the developing hindbrain and later in the pharyngeal arches of shark embryos. EphA4 was also detected during sensory organogenesis, in the developing ear, eye, nasal pits and lateral line. A dynamic pattern of EphA4 expression occurs during shark fin development, suggesting an early role in outgrowth and patterning of the fin buds and a later role in tissue differentiation. We also observed several novel domains of EphA4 expression that have not been reported in other vertebrates, including external gill buds, dermal denticles, median fins and claspers. While some of these domains may reflect co-option of EphA4 expression to novel sites for development of shark-specific characters, others are more likely to be ancestral patterns of expression that were lost in other vertebrate lineages. [ABSTRACT FROM AUTHOR]

Tadpoles (Xenopus laevis) have a lateral line system whose anatomical structure has been described, but whose functional significance has not been closely examined. These experiments tested the hypothesis that the lateral line system is involved in rheotaxis. Tadpoles in developmental stages 47-56 oriented toward the source of a water current. Orientation was less precise after treatment with cobalt chloride or streptomycin, but was similar to that of untreated animals after exposure to gentamicin. In no current conditions, tadpoles exhibited a characteristic head-down posture by which they held themselves in the water column at an angle around 45°. This body posture became significantly less tilted in the presence of water current. Treatment with cobalt chloride or streptomycin increased the angle of tilt close to that seen in no current conditions, while gentamicin treatment tended to decrease tilt angle. The data are consistent with anatomical and physiological findings that tadpole neuromasts are similar to superficial, but not canal, neuromasts in fishes, and they suggest that the lateral line system is involved in both directional current detection and current-related postural adjustments inXenopus. [ABSTRACT FROM AUTHOR]

We investigated how single units in the medial octavolateralis nucleus of the rainbow trout, Oncorhynchus mykiss, respond to a 50-Hz vibrating sphere in still and running water. Four types of units were distinguished. Type MI units (N=16) were flow-sensitive; their ongoing discharge rates either increased or decreased in running water, and as a consequence, responses of these units to the vibrating sphere were masked if the fish was exposed to water flow. Type MII units (N=7) were not flow-sensitive; their ongoing discharge rates were comparable in still and running water, and thus their responses to the vibrating sphere were not masked. Type MIII units (N=7) were also not flow-sensitive; nevertheless, their responses to the vibrating sphere were masked in running water. Type MIV units (N=14) were flow-sensitive, but their responses to the vibrating sphere were not masked. Our data confirm previous findings in the goldfish, Carassius auratus, indicating that the organization of the peripheral lateral line is reflected to a large degree in the medial octavolateralis nucleus. We compare data from goldfish and trout and discuss differences with respect to lateral line morphology, lifestyle and habitat of these species. [ABSTRACT FROM AUTHOR]

Mechanoreceptive hair cells are extremely sensitive to aminoglycoside antibiotics, including neomycin. Hair cell survival was assessed in larval wild-type zebrafish lateral line neuromasts 4 h after initial exposure to a range of neomycin concentrations for 1 h. Each of the lateral line neuromasts was scored in live fish for the presence or absence of hair cells using the fluorescent vital dye DASPEI to selectively label hair cells. All neuromasts were devoid of DASPEI-labeled hair cells 4 h after 500 microM neomycin exposure. Vital DASPEI staining was proportional to the number of hair cells per neuromast identified in fixed larvae using immunocytochemistry for acetylated tubulin and phalloidin labeling. The time course of hair cell regeneration in the lateral line neuromasts was also analyzed following neomycin-induced damage. Regenerated hair cells were first observed using live DASPEI staining 12 and 24 h following neomycin treatment. The potential role of proliferation in regenerating hair cells was analyzed. A 1 h pulse-fix protocol using bromodeoxyuridine (BrdU) incorporation was used to identify S-phase cells in neuromasts. BrdU incorporation in neomycin-damaged neuromasts did not differ from control neuromasts 4 h after drug exposure but was dramatically upregulated after 12 h. The proliferative cells identified during a 1 h period at 12 h after neomycin treatment were able to give rise to new hair cells by 24-48 h after drug treatment. The results presented here provide a standardized preparation for studying and identifying genes that influence vertebrate hair cell death, survival, and regeneration following ototoxic insults. [ABSTRACT FROM AUTHOR]

The lateral line of fish is composed of neuromasts used to detect water motions. Neuromasts occur as superficial neuromasts on the skin and as canal neuromasts in subepidermal canals. Fibres of the lateral line nerves innervate both. There have been extensive studies on the responses of lateral line nerve fibres to dipole stimuli applied in still water. However, despite the fact that many fish live in rivers and/or swim constantly, responses of lateral line nerve fibres to dipole stimuli presented in running water have never been recorded. We investigated how the peripheral lateral line of still water fish (Carassius auratus) and riverine fish (Oncorhynchus mykiss) responds to minute sinusoidal water motions while exposed to unidirectional water flow. Both goldfish and trout have two types of posterior lateral line nerve fibres: Type I fibres, which most likely innervate superficial neuromasts, were stimulated by running water (10 cm s–1). The responses of type I fibres to water motions generated by a vibrating sphere were masked if the fish was exposed to running water. Type II fibres, which most likely innervate canal neuromasts, were not stimulated by running water. Consequently, responses of type II fibres to a vibrating sphere were not masked under flow conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

ABSTRACT: The developmental processes of the olfactory organ, taste buds, lateral line system, and inner ear in the Japanese sardine Sardinops melanostictus were examined in reared and wild specimens. Both the ciliated and microvillous receptor cells in the olfactory organ were found shortly after hatching. Formation of the olfactory nostrils and lamellae began at about 20 mm standard length (SL). The calculated inflection points in the relationship between the number of olfactory lamellae and standard length were at 30.3 and 62.7 mm SL. Taste buds first appeared in a 16.1-day-old larva of 11.2 mm notochord length. Newly hatched larvae were equipped with 12 pairs of neuromasts on the head and trunk. The formation of the lateral line canal commenced at about 20 mm SL and the four canals had ossified by 32.5 mm SL. At hatching, the inner ear was an oval-shaped auditory vesicle with two otoliths. Three semicircular canals formed by the first-feeding stage, and larvae assumed an upright position. The pro-otic bulla was gas-filled and formation of the lagena pocket began at about 20 mm SL. The saccular sac was entirely formed by about 32 mm SL. From the present results, the basic structure of the sense organs was almost completed by 32 mm SL, and the adult condition might be attained at 60–70 mm SL, as suggested by the second inflection point in the relationship between the number of olfactory lamellae and SL. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]