Investigation on the Lateral Line Systems of Two Cavefish： Sinocyclocheilus Macrophthalmus and S. Microphthalmus （Cypriniformes： Cyprinidae）

Cavefish, with sensitive lateral lines, can swim freely and locate preys in invisible and complex cave environments, though their eyes are greatly degenerated. Investigations on the morphology and distribution characteristics of their lateral line systems would benefit our understanding of the high-sensitivity mechanism of the fish. In this study, the arrangement and morphology of the lateral lines are described for two species ofSinocyclocheilus： S. macrophthalmus and S. microphthalmus, which live in the karst caves in Guangxi, China. The behavior experiments indicate that the lateral line system of the S. macrophthalmus is more sensitive at a low vibration frequency range from 20 Hz to 70 Hz. The cephalic and trunk lateral line systems both contribute to the efficient object-locating capability. For both of the two species of cavefish, the diameter of the lateral canal nearby the neuromasts is narrower than that nearby the canal pores. This variation can increase the normal pressure to the surface of the cupula, and increase the sensitivity of the canal lateral line system.

An artificial lateral line system using IPMC sensor arrays

Most fish and aquatic amphibians use the lateral line system,consisting of arrays of hair-like neuromasts,as an important sensory organ for prey/predator detection,communication,and navigation.In this paper a novel bio-inspired artificial lateral line system is proposed for underwater robots and vehicles by exploiting the inherent sensing capability of ionic polymer-metal composites(IPMCs).Analogous to its biological counterpart,the IPMC-based lateral line processes the sensor signals through a neural network.The effectiveness of the proposed lateral line is validated experimentally in the localization of a dipole source(vibrating sphere)underwater.In particular,as a proof of concept,a prototype with body length(BL)of 10 cm,comprising six millimeter-scale IPMC sensors,is constructed and tested.Experimental results have shown that the IPMC-based lateral line can localize the source from 1-2 BLs away,with a maximum localization error of 0.3 cm,when the data for training the neural network are collected from a grid of 2 cm by 2 cm lattices.The effect of the number of sensors on the localization accuracy has also been examined.

Lateral line system of fish

The lateral line is a sensory system that allows fishes to detect weak water motions and pressure gradients.The smallest functional unit of the lateral line is the neuromast,a sensory structure that consists of a hair cell epithelium and a cupula that connects the ciliary bundles of the hair cells with the water surrounding the fish.The lateral line of most fishes consists of hundreds of superficial neuromasts spread over the head,trunk and tail fin.In addition,many fish have neuromasts embedded in lateral line canals that open to the environment through a series of pores.The present paper reviews some more recent aspects of the morphology,behavioral relevance and physiology of the fish lateral line.In addition,it reports some new findings with regard to the coding of bulk water flow.

Morphological structure and peripheral innervation of the lateral line system in the Siberian sturgeon (Acipenser baerii)

Light and scanning electron microscopy(SEM)were used to study the epidermal lateral line system of the Si-berian sturgeon(Acipenser baerii Brandt,1869).This system consists of mechanoreceptive neuromasts,ampul-lae and the electroreceptive organ.The neuromasts are located in 5 pairs of cephalic and 1 pair of trunk canals and superficially in the middle and posterior pit lines that lie dorsomedially along the top of the skull immedi-ately adjacent to the otic ampullae field.Both canal neuromasts and pit organ superficial neuromasts have oppo-site polarized hair cells that are parallel along the axis of the canal and pit line,respectively.However,they dif-fer in both size and shape and in the density and length of the hair bundles.The ampullae are confined on the head,adjacent to the neuromast lines.The morphological structure of the ampullae in the Siberian sturgeon is similar to the ampullae in elasmobranchs and other primitive fish.Nevertheless,it has a relatively large mucus-filled ampulla,and a shorter and narrower canal leading to a small opening to the outer epidermal surface.We also present new information concerning the peripheral innervation of lateral line receptors in sturgeons.The re-ceptors of the lateral line system are innervated by 2 pairs of cranial nerves:anterior and posterior lateral line nerves.The peripheral processes of the anterior lateral line nerve form superficial ophthalmic,buccal,otic and anteroventral rami.The peripheral processes of the posterior lateral line nerve form middle,supratemporal and lateral rami.

Exquisite structure of the lateral line system in eyeless cavefish Sinocyclocheilus tianlinensis contrast to eyed Sinocyclocheilus macrophthalmus(Cypriniformes:Cyprinidae)

In this study,the lateral line systems in Chinese cavefish eyeless Sinocyclocheilus tianlinensis and eyed Sinocyclocheilus macrophthalmus were investigated to reveal their morphological changes to survive in harsh environments.Compared with the eyed cavefish S.macrophthalmus(atypical),the lateral line system in the eyeless cave-fish S.tianlinensis(typical)has certain features to adapt to the dark cave environments:the superficial lateral line system in the eyeless species possesses a higher number of superficial neuromasts and more hair cells within an individual neuromast,and the trunk lateral line canal system in S.tianlinensis exhibits larger canal pores,higher canal diameter and more pronounced constrictions.Fluid–structure interaction analysis suggested that the trunk lateral line canal system in the eyeless S.tianlinensis should be more sensitive than that in the eyed S.macrophthalmus.These morphological features of the lateral line system in the eyeless S.tianlinensis probably enhance the functioning of the lateral line system and compensate for the lack of eyes.The revelation of the form–function relationship in the cavefish lateral line system provides inspiration for the design of sensitive artificial flow sensors.

Effects of Toluene on the Development of the Inner Ear and Lateral Line Sensory System of Zebrafish

Objective The aim of this study was to explore the ototoxicity of toluene in the early development of zebrafish embryos/larvae.Methods Zebrafish were utilized to explore the ototoxicity of toluene. Locomotion analysis,immunofluorescence, and q PCR were used to understand the phenotypes and molecular mechanisms of toluene ototoxicity.Results The results demonstrated that at 2 mmol/L, toluene induced zebrafish larvae death at 120 hours post fertilization(hpf) at a rate of 25.79% and inhibited the rate of hatching at 72 hpf.Furthermore, toluene exposure inhibited the distance travelled and average swimming velocity of zebrafish larvae while increasing the frequency of movements. As shown by fluorescence staining of hair cells, toluene inhibited the formation of lateral line neuromasts and middle line 1(Ml1) neuromasts in 3 days post fertilization larvae in a concentration-dependent manner. Toluene altered the expression level of genes involved in ear development/function in zebrafish, among which the m RNA levels of cd164 l2,tekt3, and pcsk5 a were upregulated, while the level of otofb was downregulated, according to the q PCR results.Conclusion This study indicated that toluene may affect the development of both the inner ear and lateral line systems in zebrafish, while the lateral line system may be more sensitive to toluene than the inner ear.

Simulation of detection and scattering of sound waves by the lateral line of a fish

A solvable model of lateral line of a fish based on a wave equation with additional boundary conditions on a set of isolated points is proposed.Within the framework of this model it is shown that the ratio of pressures on lateral lines on different fish flanks,as well as the cross section of sound scattering on both the lines,strongly depends on angles of incidence of incoming sound waves.The strong angular dependence of the pressure ratio seems to be sufficient for the fish to determine the directions from which the sound is coming.

Measurements on the Turtle’s Shell that Help Illuminate How the Fishes Lateral Line Function Was Replaced by the Reptilian Hearing Organ

The acoustic sense of fish, embodied in the lateral line, no longer worked when amphibians ventured onto the land. The new acoustic environment where sound traveled in the thin medium of air rather than the relatively dense medium of water presented a major challenge. The multiple sensors of the lateral line were replaced by one gross sensor, the tympanic membrane or eardrum. We show acoustical measurements on the turtle shell that can suggest a possible explanation of how the turtle dealt with the issue of sensing the directionality of incoming sounds.

Research on Artificial Lateral Line Perception of Flow Field based on Pressure Difference Matrix

In nature,with the help of lateral lines,fish is capable of sensing the state of the flow field and recognizing the surrounding near-fleld hydrodynamic environment in the condition of weak light or even complete darkness.In order to study the application of lateral lines,an improved pressure distribution model was proposed in this paper,and the pressure distributions of the lateral line carrier under different working conditions were obtained using hydrodynamic simulations.Subsequently,a visualized pressure difference matrix was constructed to identify the flow fields under different working conditions.The role of the lateral lines was investigated from a visual image perspective.Instinct features of different flow velocities,flow angles and obstacle offset distances were mapped into the pressure difference matrix.Lastly,a four-layer Convolutional Neural Network(CNN)model was built as a recognition tool to evaluate the effectiveness of the pressure difference matrix method.The recognition results demonstrate that the CNN can identify the flow field state with 2 s earlier than the current time.Hence,the proposed method provides a new way to identify flow field information in engineering applications.

Underwater Positioning Based on an Artificial Lateral Line and a Generalized Regression Neural Network

Taking advantage of the lateral line organ, fish can navigate, feed, and avoid predators and obstacles by sensing surrounding flow fields. The lateral line organ provides an important reference for the development of new underwater detection technology. Inspired by the lateral line organ, in this paper, for the sake of localizing the target dipole source in three-dimensional underwater space, an artificial lateral line consisting of nine underwater pressure sensors forming a cross-shaped sensor array is applied. Combined with the method of gener- alized regression neural network, which is suitable for solving nonlinear pattern recognition problems, a corresponding experimental platform has been built to sample data for training the neural network from a 12 cm by 12 cm by 24 cm cuboid space. The experimental results indicate that the cross-shaped artificial lateral line can localize the target dipole source two body-lengths away. The well- performing perceptual distance is below 13 cm away from the sensing array. Moreover, decreasing the data sampling interval and in- creasing the number of sensors utilized can help improve the positioning accuracy.

Fish Lateral Line Inspired Flow Sensors and Flow-aided Control: A Review

Any phenomenon in nature is potential to be an inspiration for us to propose new ideas.Lateral line is a typical example which has attracted more interest in recent years.With the aid of lateral line,fish is capable of acquiring fluid information around,which is of great significance for them to survive,communicate and hunt underwater.In this paper,we briefly introduce the morphology and mechanism of the lateral line first.Then we focus on the development of artificial lateral line which typically consists of an array of sensors and can be installed on underwater robots.A series of sensors inspired by the lateral line with different sensing principles have been summarized.And then the applications of artificial lateral line systems in hydrodynamic environment sensing and vortices detection,dipole oscillation source detection,and autonomous control of underwater robots have been reviewed.In addition,the existing problems and future foci in this field have been further discussed in detail.The current works and future foci have demonstrated that artificial lateral line has great potentials of applications and contributes to the development of underwater robots.

TGFβ1a regulates zebrafish posterior lateral line formation via Smad5 mediated pathway

The zebrafish sensory posterior lateral line(pLL)has become an attractive model for studying collective cell migration and cell morphogenesis.Recent studies have indicated that chemokine,Wnt/β-catenin,Fgf,and Delta-Notch signaling pathways participate in regulating pLL development.However,it remains unclear whether TGFβsignaling pathway is involved in pLL development.Here we report a critical role of TGFβ1 in regulating morphogenesis of the pLL primordium(pLLP).The tgfβ1a gene is abundantly expressed in the lateral line primordium.Knockdown or knockout of tgfβ1a leads to a reduction of neuromast number,an increase of inter-neuromast distance,and a reduced number of hair cells.The aberrant morphogenesis in embryos depleted of tgfβ1a correlates with the reduced expression of atoh1a,deltaA,and n-cadherin/cdh2,which are known important regulators of the pLLP morphogenesis.Like tgfβ1a depletion,knockdown of smad5 that expresses in the pLLP,affects pLLP development whereas overexpression of a constitutive active Smad5 isoform rescues the defects in embryos depleted of tgfβ1a,indicating that Smad5 mediates tgfβ1a function in pLLP development.Therefore,TGFβ/Smad5 signaling plays an important role in the zebrafish lateral line formation.

Signals and noise in the octavolateralis systems: What is the impact of human activities on fish sensory function?

The octavolateralis systems of fishes include the vestibular,auditory,lateral line and electrosensory systems.They are united by common developmental and neuro-computational features,including hair cell sensors and computations based on cross-neuron analyses of differential hair cell stimulation patterns.These systems also all use both spectral and temporal filters to separate signals from each other and from noise,and the distributed senses(lateral line and electroreception)add spatial filters as well.Like all sensory systems,these sensors must provide the animal with guidance for adaptive behavior within a sensory scene composed of multiple stimuli and varying levels of ambient noise,including that created by human activities.In the extreme,anthropogenic activities impact the octavolateralis systems by destroying or degrading the habitats that provide ecological resources and sensory inputs.At slightly lesser levels of effect,anthropogenic pollutants can be damaging to fish tissues,with sensory organs often the most vulnerable.The exposed sensory cells of the lateral line and electrosensory systems are especially sensitive to aquatic pollution.At still lesser levels of impact,anthropogenic activities can act as both acute and chronic stressors,activating hormonal changes that may affect behavioral and sensory function.Finally,human activities are now a nearly ubiquitous presence in aquatic habitats,often with no obvious effects on the animals exposed to them.Ship noise,indigenous and industrial fishing techniques,and all the ancillary noises of human civilization form a major part of the soundscape of fishes.How fish use these new sources of information about their habitat is a new and burgeoning field of study.

Function of lateral line canal morphology

Fish perceive water motions and pressure gradients with their lateral line.Lateral line information is used for prey detection,spatial orientation,predator avoidance,schooling behavior,intraspecific communication and station holding.The lateral line of most fishes consists of superficial neuromasts(SNs)and canal neuromasts(CNs).The distribution of SNs and CNs shows a high degree of variation among fishes.Researchers have speculated for decades about the functional significance of this diversity,often without any conclusive answers.Klein et al.(2013)examined how tubules,pore number and pore patterns affect the filter properties of lateral line canals in a marine teleost,the black prickleback(Xiphister atropurpureus).A preliminary mathematical model was formulated and biomimetic sensors were built.For the present study the mathematical model was extended to understand the major underlying principle of how canal dimensions influence the filter properties of the lateral line.Both the extended mathematical model and the sensor experiments show that the number and distribution of pores determine the spatial filter properties of the lateral line.In an environment with little hydrodynamic noise,simple and complex lateral line canals have comparable response properties.However,if exposed to highly turbulent conditions,canals with numerous widely spaced pores increase the signal to noise ratio significantly.

Hydrodynamic Perception Using an Artificial Lateral Line Device with an Optimized Constriction Canal

To perform flow-related behaviors in darkness,blind cavefish have evolved Lateral Line Systems(LLSs)with constriction canals to enhance hydrodynamic sensing capabilities.Mimicking the design principles,we developed a Canal-type Artificial Lateral Line(CALL)device featuring a biomimetic constriction canal.The hydrodynamic characterization results revealed that the sensitivity of the canal LLS increases with the decrease in the width(from 1 mm to 0.6 mm)and length(from 3 mm to 1 mm)of the constriction canal,which is in accordance with the modeling results of canal mechanics.The CALL device was characterized in Kármán vortex streets generated by a cylinder in a laminar flow.The CALL device was able to identify the diameter of the cylinder,with a mean identification error of approximately 2.5%.It also demonstrated the identification ability of wake width using the CALL device,indicating the potential for application in hydrodynamic perception.

Data Processing Methods of Flow Field Based on Artificial Lateral Line Pressure Sensors

The estimation of the type and parameter of flow field is important for robotic fish.Recent estimation methods cannot meet the requirements of the robotic fish due to the lack of prior knowledge or the under-fitting of the model.A processing method including data preprocessing,feature extraction,feature selection,flow type classification and flow field parameters estimation,is proposed based on the data of the pressure sensors in an artificial lateral line.Probabilistic Neural Network(PNN)is used to classify the flow field type and the Generalized Regressive Neural Network(GRNN)is the best choice for estimating the flow field parameters.Also,a few filtering methods for data preprocessing,three methods for feature selection and nine parameters estimation methods are analysis for choosing better method.The proposed method is verified by the experiments with both simulation and real data.

Artificial Hair-Like Sensors Inspired from Nature： A Review

Nature creatures have evolved excellent receptors, such as sensory hairs in arthropods, lateral line system of fishes. Researchers inspired by nature creatures have developed various mechanical sensors. Here, we provide an overview on the development of Artificial Hair-Like （AHL） sensors based on the inspiration of hair flow sensory receptors, especially sensory hairs in arthropods and lateral line systems of fishes. We classify the developed AHL sensors into several categories according to the operating principles they based on, for example, piezoresistive and piezoelectric effects. The current challenges and existing problems in the development of AHL sensors are also present, which were primarily restricted by the exploratory tools of sensing mechanism of creatures and current manufacturing technologies. In future, more efforts are required in order to further improve the performance of AHL sensors. We expect that intelligent multi-functional AHL sensors can be applied not only in applications like navigation of underwater automatic vehicles, underwater search and rescue, tap-water metering, air monitoring and even in medicare, but also potentially be used in space robots to detect complex to- pography.

Why do fish school？

Synchronized movements （schooling） emit complex and overlapping sound and pressure curves that might confuse the inner ear and lateral line organ （LLO） of a predator. Moreover, prey-fish moving close to each other may blur the elec- tro-sensory perception of predators. The aim of this review is to explore mechanisms associated with synchronous swimming that may have contributed to increased adaptation and as a consequence may have influenced the evolution of schooling. The evolu- tionary development of the inner ear and the LLO increased the capacity to detect potential prey, possibly leading to an increased potential for cannibalism in the shoal, but also helped small fish to avoid joining larger fish, resulting in size homogeneity and, accordingly, an increased capacity for moving in synchrony. Water-movements and incidental sound produced as by-product of locomotion （ISOL） may provide fish with potentially useful information during swimming, such as neighbour body-size, speed, and location. When many fish move close to one another ISOL will be energetic and complex. Quiet intervals will be few. Fish moving in synchrony will have the capacity to discontinue movements simultaneously, providing relatively quiet intervals to al- low the reception of potentially critical environmental signals. Besides, synchronized movements may facilitate auditory grouping of ISOL. Turning preference bias, well-functioning sense organs, good health, and skillful motor performance might be important to achieving an appropriate distance to school neighbors and aid the individual fish in reducing time spent in the comparatively less safe school periphery. Turning preferences in ancestral fish shoals might have helped fish to maintain groups and stay in for- mation, reinforcing aforementioned predator confusion mechanisms, which possibly played a role in the lateralization of the ver- tebrate brain [Current Zoology 58 （1）： 116-128, 2012].

Behavior and physiology of mechanoreception: separating signal and noise

The mechanosensory lateral line is found in all aquatic fish and amphibians.It provides a highly sensitive and versatile hydrodynamic sense that is used in a wide range of behavior.Hydrodynamic stimuli of biological interest originate from both abiotic and biotic sources,and include water currents,turbulence and the water disturbances caused by other animals,such as prey,predators and conspecifics.However,the detection of biologically important stimuli often has to occur against a background of noise generated by water movement,or movement of the fish itself.As such,separating signal and noise is“of the essence”in understanding the behavior and physiology of mechanoreception.Here we discuss general issues of signal and noise in the lateral-line system and the behavioral and physiological strategies that are used by fish to enhance signal detection in a noisy environment.In order for signal and noise to be separated,they need to differ,and we will consider those differences under the headings of:frequency and temporal pattern;intensity discrimination;spatial separation;and mechanisms for the reduction of self-generated noise.We systematically cover the issues of signal and noise in lateral-line systems,but emphasize recent work on self-generated noise,and signal and noise issues related to prey search strategies and collision avoidance.