Water Current Direction Research Articles

Migration patterns and navigation cues of Atlantic salmon post-smolts migrating from 12 rivers through the coastal zones around the Irish Sea.

The freshwater phase of the first seaward migration of juvenile Atlantic salmon (Salmo salar) is relatively well understood when compared with our understanding of the marine phase of their migration. In 2021, 1008 wild and 60 ranched Atlantic salmon smolts were tagged with acoustic transmitters in 12 rivers in England, Scotland, Northern Ireland and Ireland. Large marine receiver arrays were deployed in the Irish Sea at two locations: at the transition of the Irish Sea into the North Atlantic between Ireland and Scotland, and between southern Scotland and Northern Ireland, to examine the early phase of the marine migration of Atlantic salmon smolts. After leaving their natal rivers' post-smolt migration through the Irish Sea was rapid with minimum speeds ranging from 14.03 to 38.56 km.day-1 for Atlantic salmon smolts that entered the Irish Sea directly from their natal river, to 9.69-39.94 km.day-1 for Atlantic salmon smolts that entered the Irish Sea directly from their natal estuary. Population minimum migration success through the study area was strongly correlated with the distance of travel, populations further away from the point of entry to the open North Atlantic exhibited lower migration success. Post-smolts from different populations experienced different water temperatures on entering the North Atlantic. This was largely driven by the timing of their migration and may have significant consequences for feeding and ultimately survivorship. The influence of water currents on post-smolt movement was investigated using data from previously constructed numerical hydrodynamic models. Modeled water current data in the northern Irish Sea showed that post-smolts had a strong preference for migrating when the current direction was at around 283° (west-north-west) but did not migrate when exposed to strong currents in other directions. This is the most favorable direction for onward passage from the Irish Sea to the continental shelf edge current, a known accumulation point for migrating post-smolts. These results strongly indicate that post-smolts migrating through the coastal marine environment are: (1) not simply migrating by current following (2) engage in active directional swimming (3) have an intrinsic sense of their migration direction and (4) can use cues other than water current direction to orientate during this part of their migration.

New insights into methylmercury induced behavioral and energy-related gene transcriptional responses in European glass eel (Anguilla anguilla)

The effect of methylmercury (MeHg) was investigated in glass eel migration behavior and metabolism. To migrate up estuary, glass eels synchronize their swimming activity to the flood tide and remain on or in the substratum during ebb tide. Following seven days of exposure to MeHg (100 ng L−1), glass eels migration behavior was expressed by their swimming synchronization to the water current reversal every 6.2 h (mimicking the alternation of flood and ebb tides) and their swimming activity level. In relation to their behavior, we then analyzed the energy-related gene expression levels in individual head, viscera and muscle. Results showed that MeHg decreased the number of glass eels synchronized to the change in water current direction and their swimming activity level. This last effect was more pronounced in non-synchronized fish than in synchronized ones, supporting the idea that non-synchronized glass eels could be more vulnerable to stress. As regard the expression of energy-related genes, no significant difference was observed between control and MeHg-exposed fish. In contrast, when the swimming activity levels were plotted against transcriptional responses, positive correlations were evidenced in viscera and especially in the head of exposed glass eels but not in control. Finally, it is noteworthy that non-synchronized glass eels displayed lower expression level of metabolism genes than their synchronized counterpart, but only in the head. Altogether, these results support the interest of focusing on the head to investigate the facultative migration behavior in glass eels and the effect of environmental stressors on this rhythmic behavior.

Some Aspects Regarding Torque Study and Elaboration of the Blades Orientation Mechanism for Microhydropower Plant

The analysis of hydraulic energy conversion systems has demonstrated the opportunity for the development of water kinetic energy conversion systems compared to potential energy conversion systems. Insistent searches of authors have led to the design and licensing of some advanced technical solutions for outflow micro hydroelectric power plants. They are based on the hydrodynamic effect, generated by the hydrodynamic profile of blades and by the optimal blades' orientation towards water streams with account of energy conversion at each rotation phase of the turbine rotor. The basic advantage of the flow microhydropower plant is the increase of the conversion efficiency by the simultaneous use of the pressure effects of water streams on the blade surface and of the hydrodynamic effect generated by the hydrodynamic profile of the blade with continuous blade orientation. The most important nodes of the microhydropower plant are the hydrodynamic rotor with vertical axis and the mechanism of continuous orientation of the blades depending on the direction of water currents. The paper makes an analysis of the brief torque and of the forces applied on the hydrodynamic blades located in the transition zone from the upstream area to the downstream area, by positioning the blades according to the flow velocity of the water flow which leads to increased hydrodynamics forces developed by each blade and the simultaneous reduction of the hydraulic resistance forces to the rotation of the blades, based on which the mechanism of orienting the blades in optimal positions against water currents was designed, developed, and manufactured.

Distribution of Mangrove Red Snapper Lutjanus argentimaculatus in response to hydrodynamic condition at the reef patches of Lankayan, Sugud Islands Marine Conservation Area, Sabah, Malaysia

The species Lutjanus argentimaculatus is a prized food-fish in the tropical and subtropical fisheries, as well as the aquaculture industry. This study investigated the distribution of L. argentimaculatus at three patch reefs of Lankayan Island, within the Sugud Islands Marine Conservation Area. Fish surveys of this species were conducted 12 times at each of the selected patch reefs, from August 2016 until March 2017. In addition to taking underwater video footages, hydrodynamic parameters, i.e. water current direction and current speed were recorded during each survey. The distribution patterns of the fish were then plotted against these parameters to determine any correlation, in response to these parameters. As a result, we found a significant relationship between the current direction and the position of L. argentimaculatus at the reef where the schoolings were found to occur. We found that regardless of the current speed, the schools of L. argentimaculatus were always present at the reef slope facing the incoming current. This finding is important for the management and conservation of this species, which is a targeted species in the Live Reef Fish Food Trade (LRFFT), and is useful for the manager of a Marine Protected Area (MPA) in general. This finding is also important as it provides useful insights into the ecology of Lutjanus spp.

Looking at the complex relationships between migration behavior and conditional strategy based on energy metabolism in the European glass eel (Anguilla anguilla)

Diadromy in eel is facultative and the diverse propensities in glass eel estuarine migration may lead to a large spatial dispersion, which may has profound influences on the species sex determination. In this study, we sought to clarify the relationship between European glass eel energetics and their pattern of migration behavior, in the framework of the conditional strategy. Marine glass eels were sampled in autumn and spring, stratifying high and low energetic status, respectively. Their migration behavior was determined in experimental installations that mimic tides using a change in water current direction every 6.2 h. When synchronized to the current reversal, glass eels were called active while individuals hiding in the substratum were considered as non-active. Then, for each active fish, a level of swimming activity was determined and both migration behavior and level of swimming activity were correlated to the individual wet weight (used as a proxy of energy stores), standard metabolic rate (relative SMR) and transcriptomic profile of metabolism related genes. Results showed that spring glass eels presented a lower probability to migrate, a lower wet weight and a higher expression of genes involved in energy stress resistance than autumn ones, supporting a conditional strategy based on individual's energy status. However, within each season, no wet weight difference was observed between active and non-active fish. In autumn glass eels, migration behavior was weakly related to relative SMR while in spring, none of the parameters analyzed allows discriminating active and non-active glass eels. The level of swimming activity in active fish was related to their relative SMR in autumn and to their wet weight in spring. Altogether, our results could not validate a conditional strategy but spring glass eels displayed some signs of energy distress and a lower level of swimming activity than autumn ones.

Habitat characteristic of two selected locations for sea cucumber ranching purposes

Sea cucumbers face heavily overfished because of their high prices and very strong market demand. One effort suggested to overcome this problem is sea ranching. The objectives of present works were to determine biological, physical, and chemical characteristics of prospective location for sea ranching of sea cucumber Holothuria atra. Two location at Jepara Waters (Teluk Awur and Bandengan WateRs of Jepara Regency) were selected. The determination of chemical (salinity, temperature, dissolved oxygen of water, phosphate, nitrate, nitrite and ammonium of water and sediment, organic matters of sediment), physical (transparancy, sedimen grains size, water current direction and its velocity), biologycal characteristic (coverage of seagrass and its macroalgae associated, phytoplankton as well as chlorophyl-a and phaeopytin of water and sediment) ware determined. The result of present work showed that some characteristic were matched with requirement as sea ranching location of sea cucumber because the density of sea cucumber in the sea is a function of habitat features. For sediment feeding holothurians of the family Aspidochirotida, the biologycal characteristic act as very important considerations by providing sea cucumber food. High cholophyl-a and phaeopytin in sediment also represent a prosperous habitat for sea cucumber ranching.

Numerical analysis of particulate organic waste diffusion in an aquaculture area of Gokasho Bay, Japan

Particulate organic waste, originating from fish cultured in cages, often brings about negative effects on the structure of bottom sediments. These effects result in deterioration of the aquatic environment. In the present study, a three-dimensional numerical model was coupled with developed submodels of fish cage drag and aquaculture waste diffusion to simulate the hydrodynamic environment and distribution of particulate organic waste. Numerical simulation results showed that fish cages exerted an influence on both the velocity and direction of water current; the reduction of water current velocity was a maximum of approximately 38%. The contribution of fish fecal matter was dominant during winter (ca. 80%), whereas waste fish feed was the main source in other seasons. The distribution of organic waste near the sea bottom indicated that organic waste not only loaded mainly on the sea floor just beneath the fish cages but also diffused towards the coastlines.

Radiolitid rudist colonisation strategies and biostrome development in moderate-energy inner-platform environments (Campanian, Brač Island, Croatia)

During the Late Cretaceous radiolitid rudist bivalves were abundant calcifiers on Tethyan shallow-water carbonate platforms. Previous studies have demonstrated various low to high-energetic subtidal environments in which vertically growing rudist bivalves lived. However, the precise mode of colonisation in moderate to higher energetic environments remains unclear. The purpose of this study is to elucidate the attachment of rudist juveniles and colonisation strategies on loose grain sediment using three-dimensional reconstructions and other quantitative approaches. The present data demonstrate that small and thinly walled rudists colonised energetic environments over several generations. The main contributors to the biostrome, Distefanella, Bournonia, and Pseudopolyconites, followed different strategies within the same ecosystem. For instance, cylindrical elevator morphotype Distefanella built up a generally loose but anchored framework to resist sedimentation and wave energy. In contrast, Bournonia and Pseudopolyconites followed a solitary strategy of settlement on any hard substrate. Preferred growth direction affecting all genera was possibly linked to a predominant direction of water currents.

Investigations on Mass Mortalities among Oreochromis Niloticus at Mariotteya Stream, Egypt: Parasitic Infestation and Environmental Pollution Impacts

The present study was carried out to determine the possible causes of an emergent event of respiratory distress with consequent mass mortalities among Nile fish, Oreochromis niloticus (O. niloticus) at Mariotteya stream, an intrastate tributary of River Nile, Egypt. The area of incident extended from Shabramant till Abouseer city (along 4 km distance) with the direction of water current. Field visits have recorded thousands of dead large sized fish on both sides of the stream while huge numbers of fish of different size accumulated on the water surface showing typical signs of asphyxia. It was also noted that Mariotteya water body is being subjected to multiple sources of pollution through the dumping of improperly treated organic and inorganic chemical wastes in addition to sewage materials. Results of field and laboratory investigations have revealed that, all the examined 60 fish samples were heavily infested with different types of parasites including zoonotic species: Cichlidogyrus arthracanthu(monogenea), Lamproglena monody and Ergasilus sarsi (Copepod), Myxobolus dermatobia, Chilodonella hexastica, Trichodina truttae, Trichodina fultoni, Cryptosporidium spp. and Balantidium spp. (Protozoa), Acanthosentis tilapae. (Acanthocephala), Clinostomum spp., Euclinostomum spp., Heterophid and Prohemistomatid metacercarae (larval of Trematodes). The physical and chemical examinations of water samples and the analysis of heavy metals concentration indicated marked abnormal water quality parameters and environmental pollution which might be incriminated as a primary stress factor that promoted the invasion of parasites as a secondary stress factor. The study concluded that both factors would have interacted to produce this catastrophic intense case of respiratory distress and mass mortalities. The impact of the recorded parasitic infestation and environmental pollution was briefly discussed.

Investigations on Mass Mortalities among Oreochromis niloticus at Mariotteya Stream, Egypt: Parasitic Infestation and Environmental Pollution Impacts

The present study was carried out to determine the possible causes of an emergent event of respiratory distress with consequent mass mortalities among Nile fish, Oreochromis niloticus (O. niloticus) at Mariotteya stream, an intrastate tributary of River Nile, Egypt. The area of incident extended from Shabramant till Abouseer city (along 4 km distance) with the direction of water current. Field visits have recorded thousands of dead large sized fish on both sides of the stream while huge numbers of fish of different size accumulated on the water surface showing typical signs of asphyxia. It was also noted that Mariotteya water body is being subjected to multiple sources of pollution through the dumping of improperly treated organic and inorganic chemical wastes in addition to sewage materials. Results of field and laboratory investigations have revealed that, all the examined 60 fish samples were heavily infested with different types of parasites including zoonotic species: Cichlidogyrus arthracanthus (monogenea), Lamproglena monody and Ergasilus sarsi (Copepod), Myxobolus dermatobia, Chilodonella hexastica, Trichodina truttae, Trichodina fultoni, Cryptosporidium spp. and Balantidium spp. (Protozoa), Acanthosentis tilapae. (Acanthocephala), Clinostomum spp., Euclinostomum spp., Heterophid and Prohemistomatid metacercarae (larval of Trematodes). The physical and chemical examinations of water samples and the analysis of heavy metals concentration indicated marked abnormal water quality parameters and environmental pollution which might be incriminated as a primary stress factor that promoted the invasion of parasites as a secondary stress factor. The study concluded that both factors would have interacted to produce this catastrophic intense case of respiratory distress and mass mortalities. The impact of the recorded parasitic infestation and environmental pollution was briefly discussed.

Testing the Accuracy of Different A-Axis Types for Measuring the Orientation of Bones in the Archaeological and Paleontological Record

Orientation of archaeological and paleontological materials plays a prominent role in the interpretation of site formation processes. Allochthony and authochthony are frequently assumed from orientation patterns or lack thereof. Although it is still debated to what extent orientation of items can be produced in original depositional contexts, the recent use of GIS tools to measure orientations has highlighted several ways of reproducing A-axes with which to address these taphonomic issues. In the present study, the three most relevant A-axis types are compared to test their accuracy in reproducing water current direction. Although results may be similar in specific bone shapes, differences are important in other shapes. As known in engineering working with wind and fluid mechanics (developing shape optimization), longitudinal symmetrical axes (LSA) are the one that best orient structures against or in the same direction of wind and water. The present work shows that this is also the case for bones (regardless of shape), since LSA produce the most accurate estimates of flow direction. This has important consequences for the interpretation of orientation patterns at sites, since this type of axis is still not properly reproduced by GIS available tools.

Size-specific locomotion rate and movement pattern of four common Indo-Pacific sea stars (Echinodermata; Asteroidea)

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 12:157-164 (2011) - DOI: https://doi.org/10.3354/ab00326 Size-specific locomotion rate and movement pattern of four common Indo-Pacific sea stars (Echinodermata; Asteroidea) Benjamin Mueller1,2,4,*, Arthur R. Bos2,3, Gerhard Graf1, Girley S. Gumanao2 1Marine Biology Department, Bioscience, University of Rostock, Albert-Einstein-Straße 3, 18059 Rostock, Germany 2Research Office, Davao del Norte State College, New Visayas, 8105 Panabo City, The Philippines 3Department of Marine Zoology, Netherlands Center for Biodiversity Naturalis, PO Box 9517, 2300 RA Leiden, The Netherlands 4Present address: Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands *Email: muellerb@ymail.com ABSTRACT: The ecology of sea stars appears to be related to their locomotive abilities. This relationship was studied for the sea stars Acanthaster planci, Archaster typicus, Linckia laevigata, and Protoreaster nodosus in the coastal waters of Samal Island, the Philippines between May and July 2008. In order to avoid the sensory interruptions that sea stars exhibit when moving across natural substrate, a tarpaulin (2 × 2 m) was placed on the seafloor to create a uniform habitat. Mean (±SD) locomotion rate of Archaster typicus was 45.8 ± 17.0 cm min–1 but increased with mean radius (R). Locomotion rate increased from 17.8 to 72.2 cm min–1 for specimens with R of 1 and 5 cm respectively. Mean locomotion rate of L. laevigata, P. nodosus, and Acanthaster planci was 8.1 ± 1.9, 18.8 ± 3.9, and 35.3 ± 10.0 cm min–1 respectively, and was not related to R. Maximum speed of Archaster typicus was 76.0 ± 31.9 cm min–1 and also increased with R. Maximum speed of L. laevigata, P. nodosus, and Acanthaster planci was 10.6 ± 2.7, 27.7 ± 7.5, and 50.9 ± 14.0 cm min–1 respectively. An inter-specific comparison of locomotion rates using the number of body moves per minute suggests that the effect of body size partially overrules morphological and behavioral adaptations. The movement patterns of Acanthaster planci, L. laevigata, and P. nodosus were highly directional (ratio of displacement to total distance traveled [D:Wall] ≥ 0.86), whereas Archaster typicus displayed a more random movement pattern (D:Wall = 0.51). Water-current direction did not affect movement directions of the 4 species. KEY WORDS: Acanthaster planci · Archaster typicus · Davao Gulf · Linckia laevigata · Protoreaster nodosus · Starfish · Speed Full text in pdf format PreviousNextCite this article as: Mueller B, Bos AR, Graf G, Gumanao GS (2011) Size-specific locomotion rate and movement pattern of four common Indo-Pacific sea stars (Echinodermata; Asteroidea). Aquat Biol 12:157-164. https://doi.org/10.3354/ab00326 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 12, No. 2. Online publication date: April 28, 2011 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2011 Inter-Research.

Effect of immersion at low tide on distribution and movement of the mud snail, Ilyanassa obsoleta (Say), in the upper Bay of Fundy, eastern Canada

Habitat heterogeneity often affects movement behaviours of animals, and consequently their spatial distribution. We evaluated the effect of immersion at low tide on the distribution, fine-scale movement patterns and daily movement patterns of the mud snail Ilyanassa obsoleta on a mudflat in the upper Bay of Fundy, Canada. Mud snails migrate onto intertidal mudflats in the summer, and our field survey showed that their density was higher inside tide pools relative to adjacent areas that are exposed at low tide. Using time-lapse videography, we evaluated the effect of snail size, snail density, and immersion at low tide on fine-scale movement patterns of I. obsoleta. Time until snails stopped moving and burrowed was unaffected by snail size, but snails at low and high densities burrowed somewhat faster than those at intermediate densities. Snail size and snail density had no detectable effect on displacement speed or linearity of displacement. Immersion affected snail movement: snails within tide pools delayed burrowing and traveled in more convoluted paths compared to those on exposed mud. Snails increased their turning angles within tide pools, which is probably the mechanism by which aggregations are formed. We also performed a mark-recapture experiment to compare daily movement patterns of snails released inside and outside tide pools. Snails released in tide pools moved shorter distances, but did not orient themselves differently than snails released outside tide pools. Both groups exhibited significant directionality, moving against the mean water current direction over 24 h. In sum, immersion at low tide affected the behaviour and spatial distribution of snails, resulting in snail aggregations within tide pools. These snail aggregations, in turn, may be a major factor influencing spatial dynamics on mudflats, including causing changes in distribution patterns of the burrowing amphipod Corophium volutator, a dominant inhabitant and key species in the food web of mudflats.

Individual patterns of rhythmic swimming activity in Anguilla anguilla glass eels synchronised to water current reversal

The existence of distinct patterns of activity and swimming behaviour were tested in individual European glass eels by means of Bayesian inference mixture modelling. 36 glass eels were tagged using Visible Implant Elastomer and added to 36 untagged glass eels in February and April. Each group was presented with a change in water current direction every 6,2 h and videotaped during 2 weeks. Two hypotheses were tested: (i) all individuals display a similar pattern of behaviour within a tidal period, glass eels showing both positive and negative rheotaxis in opposite phase (M1 model) and (ii) individuals are distributed in two different groups, some glass eels swimming with and the others against the current (M2 model). Results showed that most glass eels displayed a positive or a negative rheotaxis and only a small number exhibited both behaviours. All swimming behaviours were synchronised to a change in current direction with a period close to the tidal one. Results are discussed in relation to synchronisation and migration behaviour.

Rhythmic swimming activity in Anguilla anguilla glass eels: Synchronisation to water current reversal under laboratory conditions

Synchronisation of swimming activity to water current reversal every 6.2 h was tested in the European glass eel ( Anguilla anguilla L.). When presented with a change in water current direction, glass eels exhibited rhythmic patterns of activity with a period close to the tidal one. Glass eels began to swim with the current and then alternated between positive and negative rheotaxis after each change in the water current direction. Results are discussed in relation to the flood tidal transport theory. Following synchronisation to current reversal, glass eels subjected to constant conditions displayed a weak rhythmic activity suggesting that locomotor behaviour might, in the wild, synchronise to several environmental cues related to the tide. Results obtained with different densities also suggest that social cues might improve the synchronisation.

Magnetic anisotropy indications of deformations associated with diagenesis

Abstract Anisotropy of magnetic susceptibility (AMS), as revealed by mathematical modelling and empirical studies, sensitively reflects initial ductile deformation associated with diagenesis and early tectonism. In rocks shortened vertically because of the gravitational loading by the weight of overlying strata, the degree of AMS increases and the magnetic fabric becomes more oblate. The magnetic foliation remains parallel to the bedding and the magnetic lineation remains near the water current directions. In rocks shortened laterally, usually by tectonic forces, the degree of AMS and the magnetic fabric oblateness initially decrease and only later increase. The magnetic lineation deflects from the water current direction and the magnetic foliation from the bedding, with its poles creating a girdle pattern. The AMS changes are due to the physical rotation of magnetic grains, which has serious implications for palaeomagnetism, but are major indicators of the change from a diagenetic to a tectonically controlled regime.

Remanent magnetization of ash from the 18 May 1980 eruption of Mount St. Helens

Ash from the 18 May 1980 eruption of Mount St. Helens deposited from air faithfully records the direction of the local geomagnetic field in eastern Washington, whereas ash settled from suspension in water in fluvial environments exhibits significant inclination and current‐rotation errors in magnetic direction similar to those reported in other subaqueously deposited sediments. The current‐rotation errors are associated with partial alignment of the major axes of magnetic susceptibility in the direction of water currents. Subaerial deposition produces strong stable remanent magnetization in ash with or without postdepositional wetting by rain.

Waves, weather, and ocean bottom microseisms

The latest model of the Lamont Geological Observatory Ocean Bottom Geophysical Station (OBS III), located approximately 200 km WNW of San Francisco at a depth of 3.9 km, has been in operation since May 1966. In addition to long- and short-period seismic data, this station provides data on water current direction and speed, water temperature, long- and short-period pressure variations, and horizontal and vertical accelerations at tidal periods. Twenty-three microseismic storms have been detected on the seismic and pressure sensors during the first eight months of operation (May-December 1966). The characteristics of two of these storms have been studied in detail, and the results have been compared with data from the Berkeley seismographs. Both peaks in microseismic activity appear to be related to specific weather systems, one local and one distant. Correlation between local water waves and microseismic amplitudes is observed in one case but not in the other. Particle motion amplitudes on the ocean bottom were 3 to 5 times larger than those at a near-land station (Berkeley) for the vertical component and 7 to 10 times larger for the horizontal component. Predominant periods (6 to 8 sec) were the same at both sites. Ratios of horizontal to vertical particle motion and pressure to vertical motion were measured for microseisms and compared with theoretical values for Rayleigh waves. The combination of these two ratios proves to be a very sensitive method of determining sediment properties. Coherence between pressure and vertical motion is consistently high. It is concluded that (1) the observed microseisms propagate primarily as Rayleigh waves of the fundamental mode, and (2) the thickness of the sediment layer is 0.65 km. The predominant direction of microseismic propagation during both storms was approximately perpendicular to the coastline. Study of the average phase relationship of pressure, vertical particle motion, and horizontal particle motion shows that the direction of propagation is from sea to land if fundamental mode Rayleigh waves are assumed. The microseismic energy flux was approximately 4 times larger in the oceanic structure than in the continental structure near Berkeley for both storms.

Electrical Responses from Dually Innervated Tactile Receptors on the Thorax of the Crayfish

ABSTRACT Electrophysiological recordings have been obtained from tactile receptors which occur in shallow pits on the crayfish carapace. Controlled mechanical stimulation has established that each receptor is innervated by a pair of sensory neurons. One of these neurons responds when the receptor is moved anteriorly, and the partner cell responds to displacement in the opposite direction. The receptors are sensitive to motion of the fluid medium in which they are immersed, and they may provide the animal with a means for determining the speed and direction of water currents. Vital staining procedures have confirmed the presence of two bipolar sensory cells associated with each receptor. An abrupt increase in the diameter of the sensory axons occurs several hundred microns proximal to the cell bodies of the neurons, and it is suggested that this is the locus of spike initiation.

魚類の游泳生態に関する研究-I

The author considered that the subject of behavior of oceanic surface fishes give clues to settle the problem of locomotion, gathering and scattering of fish school. How do fishes hold their position against movements of water masses and partial water currents? As only a few investigations regarding the above problem have been already carried, more investigations are expected in the near future. The author examined the relationship between the side of the net on which the fishes were entangled and the direction of water current. This gave the following results;…… 1) In the case of the investigation carried out during the daytime in the area over 30 miles off shore, over 95-99% of the number of the catches were entangled to the net on the tide ward side, and small number on the lee tide side. 2) In the allied case carried out during the daytime in the coasting area less than 15 miles off shore, in general, majority of the catches were entangled to the net on the tide ward side, as much as 78% and the rest from the lee tide side, however, very few cases should be high percentage on the lee tide side. 3) In the off shore area over 30 miles, the investigations during the daytime (involving the daybreak and twilight) were carried out in June and July. It is supposed that the flying fish would move keeping the direction of body parallel to that of the current.