Archerfish Research Articles

Deep learning based classification of COVID-19 severity using hierarchical deep maxout model

COVID-19 is a huge pandemic disease and is gradually growing into our daily lives. It has affected us all in different ways, which the World Health Organization classified as a pandemic in 2020. A number of deep learning methods have been developed to identify COVID-19 in chest X-rays, but very few techniques are used to estimate the severity of COVID-19. Additionally, it is very complex to effectively train the data, resulting in slower convergence and time complexities. Therefore, to overcome these drawbacks, this study proposes a unique model to classify the severity of Covid-19 using a deep learning method. The pre-processing step includes image enhancement and noise reduction using the Amended Bilateral Filter (ABF). The relevant features are then extracted using an ensemble-based deep learning model, which includes the DenseNet-201, ResNet-152 and VGG-19 models, which are integrated via an ensemble average approach. The most optimal features are selected using the Modified Archer Fish Optimization Algorithm (Mod-AFO). The proposed optimization algorithm exhibits high convergence and reduced model complexity. COVID-19 severity classification can be effectively categorized using a Multihead attention-assisted hierarchical deep-maxout network model (Multi-HDM). The proposed classification model is comparatively faster in severity estimation and high in performance. Using Python, the proposed model performances are analyzed and compared with the existing models to demonstrate the superiority of the proposed model. The proposed model achieved 98.2% accuracy, 98.5% sensitivity, 96.4% specificity and 96.4% precision in COVID-19 severity estimation using the COVID-19 Chest X-ray images and Lung masks dataset.

Monitoring the Biological Aspects of Banded Archer Fish (Toxotes jaculatrix Pallas, 1767) in Bilah River, Labuhanbatu Regency, Indonesia

Banded archer fish (Toxotes jaculatrix Pallas, 1767) is one of the leading commodities of Indonesian ornamental fish. Its production so far is still from the catch of nature. Banded archer fish based on IUCN data has been included in the red list with the Least Concern (LC) category. Currently one of its habitats is found in the Bilah River, Labuhanbatu Regency. The purpose of the study was to information the condition of biological factors related to the relationship of weight length, sex ratio and factors of banded archer fish conditions in the Bilah River. Determination of observation station points by purposive sampling method, where in this study there are 3 stations. Fish sampling in January-March 2022. Fish are caught using splint nets. The entire number of fish caught was measured using a ruler with a length of 30 cm and weight using a digital balance sheet with a precision of 0.01 g. Next the data is tabulated and analyzed using the Microsoft Excel 2013 application. The data of the results of the study is displayed based on each month of observation. The results of the analysis of banded archer fish research data for the long weight relationship from January-March 2022 are negative alometric. The sex ratio of banded archer fish in January 2022 (0.69:1), February 2022 (0.47:1), and March 2022 (0.5:1). The value of the banded archer fish condition factor in January 2022 (1.0304), February 2020 (1.0338), and March 2022 (0.0954). It was concluded that the biological aspects of banded archer fish in the Bilah River still their growth and reproductioan.

Jumping archer fish exhibit multiple modes of fin–fin interaction

Aquatic organisms jumping for aerial prey require high-performance propulsion, accurate aim, and trajectory control to succeed. Archer fish, capable of jumping up to twice their body length out of the water, address these considerations through multifaceted fin and body kinematics. In this study, we utilized 3D synthetic aperture particle image velocimetry to visualize the wakes of archer fish throughout the jumping process. We found that multiple modes of interaction between the anal and caudal fins occur during jump behaviors. Time-resolved volumetric measurements presented herein illustrate the hydrodynamics of each interaction mode in detail. Additionally, regardless of which fin uses and interactions were exhibited during a jump, we found similar relationships between the cumulative impulse of multiple propulsive vortices in the wake and the instantaneous ballistic momentum of the fish. Our results suggests that fin use may compensate for variations in individual kinematic events and in the aiming posture assumed prior to jumping and highlight how interactions between tailbeats and other fins help the archer fish reach necessary prey heights in a spatially- and visually-constrained environment. In the broader context of bioinspired propulsion, the archer fish exemplifies that multiple beneficial hydrodynamic interactions can be generated in a high-performance scenario using a single set of actuators.

Scientists detail jumping physics of tiny fish

Researchers model the jumping kinematics of archer fish to understand how these tiny aquatic creatures achieve their aerodynamic feats as they breach the water-air interface.

Water exit dynamics of jumping archer fish: Integrating two-phase flow large-eddy simulation with experimental measurements

Archer fish jumping for prey capture are capable of achieving accelerations that can reach 12 times gravitational from a stationary start at the free surface. This behavior is associated with nontrivial production of hydrodynamic thrust. In this work, we numerically investigate the hydrodynamic and aerodynamic performance of a jumping smallscale archer fish (Toxotes microlepis) to elucidate the propulsive mechanisms that contribute to the rapid acceleration and the considerable jump accuracy. We conduct high-fidelity, two-phase flow, large-eddy simulation (LES) of an anatomically realistic archer fish using detailed jump kinematics in water, through the water/air interface, and in air. The complex fish body kinematics are reconstructed using high-speed imaging. The LES results during the water phase of the jump are compared with particle image velocimetry measurements of a live jumping archer fish, and excellent agreement is found. The numerical simulations further enable detailed analysis of the flow dynamics and elucidate for the first time the dynamics of the coherent vortical structures in both the water and air phases. In particular, the pectoral fins are shown to contribute to the initial spike in acceleration before water exit and to enhance the overall jumping performance of the fish.

A computer based experiment to show that Snell’s law follows from Fermat’s principle

Understanding reflection and refraction are an integral part of school and college learning. In nature even birds and fish (Archer fish) very skillfully use refraction to strike down prey present above or below the water surface. Fermat’s principle allows one to look beyond the reasons behind the laws governing the reflection and refraction. A pedagogical computer based experiment (CBE) is proposed to demonstrate the simplicity of usage of Fermat’s principle for undergraduate physics students in universities and school students pursuing secondary education by implementing a program written in open source software Scilab and also through MS Excel/Open Office. In this work we probe: (i) the refraction across a plane interface and (ii) reflection from a parabolic mirror and arrive at many useful propositions.

Multi-camera volumetric PIV for the study of jumping fish

Archer fish accurately jump multiple body lengths for aerial prey from directly below the free surface. Multiple fins provide combinations of propulsion and stabilization, enabling prey capture success. Volumetric flow field measurements are crucial to characterizing multi-propulsor interactions during this highly three-dimensional maneuver; however, the fish’s behavior also drives unique experimental constraints. Measurements must be obtained in close proximity to the water’s surface and in regions of the flow field which are partially-occluded by the fish body. Aerial jump trajectories must also be known to assess performance. This article describes experiment setup and processing modifications to the three-dimensional synthetic aperture particle image velocimetry (SAPIV) technique to address these challenges and facilitate experimental measurements on live jumping fish. The performance of traditional SAPIV algorithms in partially-occluded regions is characterized, and an improved non-iterative reconstruction routine for SAPIV around bodies is introduced. This reconstruction procedure is combined with three-dimensional imaging on both sides of the free surface to reveal the fish’s three-dimensional wake, including a series of propulsive vortex rings generated by the tail. In addition, wake measurements from the anal and dorsal fins indicate their stabilizing and thrust-producing contributions as the archer fish jumps.

Endogenous orienting in the archer fish

The literature has long emphasized the neocortex's role in volitional processes. In this work, we examined endogenous orienting in an evolutionarily older species, the archer fish, which lacks neocortex-like cells. We used Posner's classic endogenous cuing task, in which a centrally presented, spatially informative cue is followed by a target. The fish responded to the target by shooting a stream of water at it. Interestingly, the fish demonstrated a human-like "volitional" facilitation effect: their reaction times to targets that appeared on the side indicated by the precue were faster than their reaction times to targets on the opposite side. The fish also exhibited inhibition of return, an aftermath of orienting that commonly emerges only in reflexive orienting tasks in human participants. We believe that this pattern demonstrates the acquisition of an arbitrary connection between spatial orienting and a nonspatial feature of a centrally presented stimulus in nonprimate species. In the literature on human attention, orienting in response to such contingencies has been strongly associated with volitional control. We discuss the implications of these results for the evolution of orienting, and for the study of volitional processes in all species, including humans.

Archer fish jump as well as shoot.

![Figure][1] An archer fish take-off. Photo credit: Anna Shih. While spitting is taboo in some human cultures, a few species have honed it to a fine art, from cobras that eject venom into the eyes of their victims to archer fish that down their prey with a precisely aimed jet of water. In

Archer fish jumping prey capture: kinematics and hydrodynamics.

Smallscale archer fish, Toxotes microlepis, are best known for spitting jets of water to capture prey, but also hunt by jumping out of the water to heights of up to 2.5body lengths. In this study, high-speed imaging and particle image velocimetry were used to characterize the kinematics and hydrodynamics of this jumping behavior. Jumping used a set of kinematics distinct from those of in-water feeding strikes and was segmented into three phases: (1) hovering to sight prey at the surface, (2) rapid upward thrust production and (3) gliding to the prey once out of the water. The number of propulsive tail strokes positively correlated with the height of the bait, as did the peak body velocity observed during a jump. During the gliding stage, the fish traveled ballistically; the kinetic energy when the fish left the water balanced with the change in potential energy from water exit to the maximum jump height. The ballistic estimate of the mechanical energy required to jump was comparable with the estimated mechanical energy requirements of spitting a jet with sufficient momentum to down prey and subsequently pursuing the prey in water. Particle image velocimetry showed that, in addition to the caudal fin, the wakes of the anal, pectoral and dorsal fins were of nontrivial strength, especially at the onset of thrust production. During jump initiation, these fins were used to produce as much vertical acceleration as possible given the spatial constraint of starting directly at the water's surface to aim.

Visual pop-out in barn owls: Human-like behavior in the avian brain.

Visual pop-out is a phenomenon by which the latency to detect a target in a scene is independent of the number of other elements, the distractors. Pop-out is an effective visual-search guidance that occurs typically when the target is distinct in one feature from the distractors, thus facilitating fast detection of predators or prey. However, apart from studies on primates, pop-out has been examined in few species and demonstrated thus far in rats, archer fish, and pigeons only. To fill this gap, here we study pop-out in barn owls. These birds are a unique model system for such exploration because their lack of eye movements dictates visual behavior dominated by head movements. Head saccades and interspersed fixation periods can therefore be tracked and analyzed with a head-mounted wireless microcamera--the OwlCam. Using this methodology we confronted two owls with scenes containing search arrays of one target among varying numbers (15-63) of similar looking distractors. We tested targets distinct either by orientation (Experiment 1) or luminance contrast (Experiment 2). Search time and the number of saccades until the target was fixated remained largely independent of the number of distractors in both experiments. This suggests that barn owls can exhibit pop-out during visual search, thus expanding the group of species and brain structures that can cope with this fundamental visual behavior. The utility of our automatic analysis method is further discussed for other species and scientific questions.

Pharmacological study of direction selectivity in the archer fish retina.

Direction selective cells have been found in the retina, the first level of the visual system, in mammals and recently also in the archer fish. These cells are involved in a variety of fast neural computation processes, from the control of eye movements to the detection of prey by the archer fish. The standard model for this mechanism in mammalian retina is well understood and is based on the asymmetry of inhibitory and excitatory inputs to the retinal ganglion cells. However, it remains unclear whether the mechanism that underlies direction selectivity is similar across animal classes. This study reports a pharmacological investigation designed to elucidate the mechanism that underlies motion detection in the archer fish retina. Direction selectivity in the retina was characterized under the influence of specific channel blockers that are known to be present in the different types of neurons of the retina. The results show that the direction-selective mechanism in the archer fish retina is modified only when the inhibitory channels of GABA and Glycine are manipulated. This suggests that the mechanism of direction selectivity in the archer fish retina is fundamentally different from the mechanism of direction selectivity in the mammalian retina.

Archerfish predict where prey will land to outwit rivals

Archerfish predict where prey will land to outwit rivals

One shot, one kill: the forces delivered by archer fish shots to distant targets

Archer fishes are skillful hunters of terrestrial prey, firing jets of water that dislodge insects perched on overhead vegetation. In the current investigation, we sought an answer to the question: are distant targets impractical foraging choices? Targets far from the shooter might not be hit with sufficient force to cause them to fall. However, observations from other investigators show that archer fish fire streams of water that travel in a non-ballistic fashion, which is thought to keep on-target forces high, even to targets that are several body lengths distant from the fish. We presented targets at different distances and investigated three aspects of foraging behavior: (i) on-target forces, (ii) shot velocity, (iii) a two-target choice assay to determine if fish would show any preference for downing closer targets or more distant targets. In general, shots from our fish (Toxotes chatareus) showed a mild decrease (less than 15% on average) in on-target forces at our most distant target offered (5.8 body lengths) with respect to the closest target offered (2.3 body lengths). One individual in our investigation showed slightly, but significantly, greater on-target forces as target distance increased. Forces on the furthest targets offered were found to double that of attachment forces for 200mg insects, even for individuals whose on-target forces showed mild decreases with increases in target distance. High-speed video analysis of jet impact with the target revealed that the shot was traveling in a non-ballistic manner, even to our most distant target offered, corroborating previous suppositions that on-target forces should remain high. Fish were able to accomplish this without large changes to shot velocity, but we did find evidence that the water jets appeared to differ in the timing of their acceleration as target distance increased. Our two-target choice experiment revealed that fish show preference for downing the closer target first, even though impact forces on distant targets only showed mild decreases. Our overall findings (and the findings of others) suggest that archer fish modulate many aspects of their shooting behavior: from target selection to active control over the water jet that allows the fish to deliver reliably forceful impacts to prey over a wide range of distances.

Pop-out in visual search of moving targets in the archer fish

Pop-out in visual search reflects the capacity of observers to rapidly detect visual targets independent of the number of distracting objects in the background. Although it may be beneficial to most animals, pop-out behaviour has been observed only in mammals, where neural correlates are found in primary visual cortex as contextually modulated neurons that encode aspects of saliency. Here we show that archer fish can also utilize this important search mechanism by exhibiting pop-out of moving targets. We explore neural correlates of this behaviour and report the presence of contextually modulated neurons in the optic tectum that may constitute the neural substrate for a saliency map. Furthermore, we find that both behaving fish and neural responses exhibit additive responses to multiple visual features. These findings suggest that similar neural computations underlie pop-out behaviour in mammals and fish, and that pop-out may be a universal search mechanism across all vertebrates.

Life & evolution: Archerfish mouth reveals spit secret: Shooting gobs of water at prey requires rapid oral acrobatics

Life & evolution: Archerfish mouth reveals spit secret: Shooting gobs of water at prey requires rapid oral acrobatics

Archer fish show how to sharpshoot

Archer fish show how to sharpshoot

How archer fish gun down prey from a distance

How archer fish gun down prey from a distance

Visual receptive field properties of cells in the optic tectum of the archer fish

The archer fish is well known for its extreme visual behavior in shooting water jets at prey hanging on vegetation above water. This fish is a promising model in the study of visual system function because it can be trained to respond to artificial targets and thus to provide valuable psychophysical data. Although much behavioral data have indeed been collected over the past two decades, little is known about the functional organization of the main visual area supporting this visual behavior, namely, the fish optic tectum. In this article we focus on a fundamental aspect of this functional organization and provide a detailed analysis of receptive field properties of cells in the archer fish optic tectum. Using extracellular measurements to record activities of single cells, we first measure their retinotectal mapping. We then determine their receptive field properties such as size, selectivity for stimulus direction and orientation, tuning for spatial frequency, and tuning for temporal frequency. Finally, on the basis of all these measurements, we demonstrate that optic tectum cells can be classified into three categories: orientation-tuned cells, direction-tuned cells, and direction-agnostic cells. Our results provide an essential basis for future investigations of information processing in the archer fish visual system.

Inhibition of return in the archer fish

Inhibition of return is the inhibitory tagging of recently attended locations or objects. It was previously suggested that inhibition of return is a foraging facilitator in visual search. Inhibition of return was first discovered in humans and was demonstrated also in monkeys, yet it has never been demonstrated in non-primates. Here we report the presence of inhibition of return in the archer fish, which shoots down prey on overhanging vegetation, using squirts of water spouted from its mouth. Moreover, we find similar attentional effects for fish as for human participants. Our results show that the generation of inhibition of return does not require a fully developed cortex and strengthen the view that inhibition of return functions as a foraging facilitator.