Free-swimming Fish Research Articles

Effect of water velocity on swimming behavior of juvenile Megalobrama amblycephala

To investigate the swimming behavior of juvenile Megalobrama amblycephala, a tracking analysis device was designed to monitor behavior indicators including velocity (V), swimming distance (SD), turn angle (TA), distance to center-point (DC) and swimming track (ST) at different flow rates (0, 0.1, 0.2, 0.3 and 0.4 m/s) at 25℃. Results showed that indicator values all increased with increasing flow rate. Values of V, SD and TA showed no significant differences among the flow rates of 0, 0.1 and 0.2 m/s, respectively (P>0.05). However, they increased obviously at flow rates of 0.3 and 0.4 m/s (P<0.05), with no significant differences found between these two flow rates (P>0.05). The SD value did not change markedly according to flow rates (P>0.05), while ST showed complex patterns corresponding to increasing flow rate. A significant linear positive correlation occurred in free-swimming fish between V and SD, while a negative relationship was found between V and TA. No regular relationship was deduced between swimming speed and DC.

SEEING WHAT FISH THINK

![][1] Have you ever wondered about what goes through a fish's head? Recent advances in molecular biology and genetics are now making it possible to look at the activity of single neurons in free-swimming fish. Akira Muto from the National Institute of Genetics in Shizuoka, Japan, and

In situ analysis of cadmium uptake in four sections of the gastro-intestinal tract of rainbow trout (Oncorhynchus mykiss)

This study links results from past in vitro and in vivo experiments, by implementing an in situ experiment in order to determine the relative importance for cadmium (Cd) uptake of different sections of the gastro-intestinal tract (GIT) of rainbow trout. Transport of Cd from four sections of the GIT of adult rainbow trout (∼220g) was individually examined by infusing ligated sections of the GIT in live, free-swimming fish with 50μM Cd spiked with radiolabelled 109Cd (0.5μCiml−1). Fish were exposed for an 8-h period. The percentage of the total injected 109Cd which was internalized from the different segments was only between ∼0.1 and ∼7%, indicating low uptake efficiency. The stomach is the most important GIT segment for Cd transport into the internal compartment of the animal, while the posterior intestine also plays a significant role. The majority of 109Cd recovered at the end of the flux period was detected within gut material (ranging from 28 to 95%); the portion of Cd which was internalized was largely found in the carcass (32 to 60%). Distribution between the measured organs varied with uptake from the various GIT sections. Our results also confirm that the GIT acts as a protective barrier against Cd uptake from dietary exposure.

Swimming activity of migrating Chinook salmon in a regulated river

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 17:47-56 (2012) - DOI: https://doi.org/10.3354/ab00460 Swimming activity of migrating Chinook salmon in a regulated river Caleb T. Hasler1,*, Brent Mossop2, David A. Patterson3, Scott G. Hinch4, Steve J. Cooke1 1Fish Ecology and Conservation Physiology Laboratory, Department of Biology and Institute of Environmental Science, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada 2BC Hydro, 6911 Southpoint Drive, Burnaby, British Columbia V3N 4X8, Canada 3Fisheries and Oceans Canada, Science Branch, Pacific Region, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada 4Centre for Applied Conservation Research, Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada *Email: cthasler@gmail.com ABSTRACT: Adult Pacific salmon Oncorhynchus spp. have a fixed amount of energy available to fuel their freshwater spawning migration, so they must optimize their activity in a manner that conserves energy to ensure successful spawning. The flow regime in the Puntledge River in British Columbia, Canada, is regulated for hydropower production, and this has resulted in alterations in discharge and water temperature. The purpose of this study was to assess the relative changes to locomotory activity in Puntledge River summer-run Chinook salmon O. tshawytscha at varying discharges, temperatures, and reaches. Coded electromyogram (EMG) radio transmitters were used to evaluate aerobic swimming-muscle activity of free-swimming fish. Because transmitter calibration was not possible, a standardized EMG (SEMG) value was used to relate relative activity to variability among individuals, reaches, encountered temperatures, and discharge variables. A random forest algorithmic modeling analysis was used to account for the non-independence of predictor variables and activity values repeatedly recorded on the same fish. The model accounted for 57.6% of the variance in SEMG and revealed that individuals accounted for most of the variation in SEMG, followed by reach, temperature, and discharge. These findings indicate that individual variability in swimming strategies, migratory behaviors, and habitat use may influence swimming activity to a greater degree than river conditions. If such findings are confirmed in other regulated systems, this would have important implications for how alterations in flow and their biological consequences are evaluated. KEY WORDS: Adult Pacific salmon · Upriver migration · Energy use · Electromyogram · EMG · Individual variation · Temperature · Discharge Full text in pdf format PreviousNextCite this article as: Hasler CT, Mossop B, Patterson DA, Hinch SG, Cooke SJ (2012) Swimming activity of migrating Chinook salmon in a regulated river. Aquat Biol 17:47-56. https://doi.org/10.3354/ab00460 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 17, No. 1. Online publication date: October 17, 2012 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2012 Inter-Research.

The development of robust morphometric indices from accurate and precise measurements of free-swimming whale sharks using laser photogrammetry

To enable the study of population dynamics of wild animals the determination of the age, growth rate and maturity status of a sample of the individuals present is required; consequently, obtaining repeated accurate and precise total length (TL) measurements for individuals over time can be especially valuable. However, there are limited easily applied methods to ascertain the TL of large free-swimming fish, especially the largest extant species of fish, the whale shark (Rhincodon typus). This study expands on previous work and presents the results of a robust laser photogrammetry system developed to achieve accurate TL, pre-caudal length (PCL) and further morphometric measurements of whale sharks observed between 2009 and 2011 in seasonal feeding aggregations located in the Seychelles and Djibouti. Calculations for repeatability (r) indicated a high level of precision for the system with r approaching 1 for both TL and PCL, increasing further with the use of morphometric measurements. TL measurements of ‘straight sample sharks’ also provided geometric mean linear regression equations to enable the prediction of TL from defined morphological indices. Continuous validation of the system against objects of a fixed length also indicated a high level of accuracy for the method of measurement. We concluded that the laser photogrammetry system can be confidently employed to obtain accurate in-water TL, PCL and morphometric measurements for R. typus, with wide ranging implications and applications for the study of R. typus, and other large marine fauna.

Organic matter dynamics and stable isotope signature as tracers of the sources of suspended sediment

Abstract. Suspended sediment (SS) and organic matter in rivers can harm brown trout Salmo trutta by affecting the health and fitness of free swimming fish and by causing siltation of the riverbed. The temporal and spatial dynamics of sediment, carbon (C), and nitrogen (N) during the brown trout spawning season in a small river of the Swiss Plateau were assessed and C isotopes as well as the C/N atomic ratio were used to distinguish autochthonous and allochthonous sources of organic matter in SS loads. The visual basic program IsoSource with 13Ctot and 15N as input isotopes was used to quantify the temporal and spatial sources of SS. Organic matter concentrations in the infiltrated and suspended sediment were highest during low flow periods with small sediment loads and lowest during high flow periods with high sediment loads. Peak values in nitrate and dissolved organic C were measured during high flow and high rainfall, probably due to leaching from pasture and arable land. The organic matter was of allochthonous sources as indicated by the C/N atomic ratio and δ13Corg. Organic matter in SS increased from up- to downstream due to an increase of pasture and arable land downstream of the river. The mean fraction of SS originating from upper watershed riverbed sediment decreased from up to downstream and increased during high flow at all measuring sites along the course of the river. During base flow conditions, the major sources of SS are pasture, forest and arable land. The latter increased during rainy and warmer winter periods, most likely because both triggered snow melt and thus erosion. The measured increase in DOC and nitrate concentrations during high flow support these modeling results. Enhanced soil erosion processes on pasture and arable land are expected with increasing heavy rain events and less snow during winter seasons due to climate change. Consequently, SS and organic matter in the river will increase, which will possibly affect brown trout negatively.

Wireless Biosensor System for Real-Time L-Lactic Acid Monitoring in Fish

We have developed a wireless biosensor system to continuously monitor l-lactic acid concentrations in fish. The blood l-lactic acid level of fish is a barometer of stress. The biosensor comprised Pt-Ir wire (φ0.178 mm) as the working electrode and Ag/AgCl paste as the reference electrode. Lactate oxidase was immobilized on the working electrode using glutaraldehyde. The sensor calibration was linear and good correlated with l-lactic acid levels (R = 0.9959) in the range of 0.04 to 6.0 mg·dL−1. We used the eyeball interstitial sclera fluid (EISF) as the site of sensor implantation. The blood l-lactic acid levels correlated closely with the EISF l-lactic acid levels in the range of 3 to 13 mg·dL−1 (R = 0.8173, n = 26). Wireless monitoring of l-lactic acid was performed using the sensor system in free-swimming fish in an aquarium. The sensor response was stable for over 60 h. Thus, our biosensor provided a rapid and convenient method for real-time monitoring of l-lactic acid levels in fish.

Development of a biocompatible glucose biosensor for wireless and real time blood glucose monitoring of fish

We developed glucose biosensors coated with biocompatible polymers to rapidly monitor glucose levels in free-swimming fish. Biocompatible polymers have a similar structure to living organisms and are thus used to make metallic materials more compatible with the living body. We focused on three widely used biocompatible polymers, 2-methacryloyloxyethyl phosphorlycholine (MPC) polymers, polypyrroles, and polyurethanes, to achieve biocompatibility of our glucose biosensor. The developed glucose biosensor has a Pt-Ir wire (φ0.178 mm) as the working electrode and Ag/AgCl paste as the reference electrode. The biosensor was first coated with Nafion to prevent coexisting substances such as ascorbic acid and uric acid from interfering with the sensor output current, and then glucose oxidase (GOx) was fixed on top of the Nafion layer along with biocompatible polymers. The sensor was inserted into the fish eyeball interstitial scleral fluid (EISF), which contains low levels of proteins and correlates well with the glucose levels in the whole blood. Those three sensors were tested for durability and sensors coated with MPC polymers (Nafion/GOx/MPC sensor) proved to be most durable: the sensor output current maintained 93% output for 15 h in standard glucose solution, and 80% in EISF for 8 h, whereas the output current of the other sensors decreased more rapidly overtime. We then inserted Nafion/GOx/MPC sensor to wirelessly monitor EISF glucose levels in free-swimming fish. One-point calibration method was used to calibrate the sensor output current. As a result, 24 h of wireless monitoring was successfully achieved.

Mediator-type biosensor for real-time wireless monitoring of blood glucose concentrations in fish

We developed a wireless mediator-type biosensor system to rapidly monitor blood glucose concentrations in free-swimming fish. Glucose oxidase was used to determine the glucose concentration, but fluctuations in the oxygen concentrations in the samples affected the measurements. In this work, we used a mediator, a synthetic electron acceptor, as a substitute in the oxidation–reduction reaction, thus ensuring that changes in the concentration of oxygen do not affect the measurements of glucose concentration performed by the sensor. We especially focused on the use of ferrocene as a mediator. The resulting enzyme sensor utilized a Pt–Ir wire (diameter 0.178 mm) as the working electrode and Ag/AgCl paste as the reference electrode. Chitosan was used to fix ferrocene and glucose oxidase to the working electrode. The characteristics of the sensor were tested, and it was found to be capable of measuring glucose independent of the oxygen concentration of the sample. Its reproducibility was also tested, and the results showed that the sensor was suitable for performing measurements in vivo. The sensor was then inserted into to eyeball interstitial sclera fluid in order to wirelessly monitor the glucose concentration in free-swimming fish. Measurements were taken for a total of 48 h. During these measurements, artificial stress was applied to the fish. The glucose concentrations of fish rise with their stress levels. The output current from the sensor gradually increased during the application of stress, which hinted that the stress was monitored by this system.

Carbon nanotube enhanced mediator-type biosensor for real-time monitoring of glucose concentrations in fish

We have developed a mediator-type biosensor to rapidly monitor blood glucose concentrations in fish, which are an indicator of stress. Glucose oxidase was used to detect glucose concentrations and ferrocene was used to limit the effect of oxygen. We also improved the sensitivity and durability of the sensor for better performance. Single-walled carbon nanotubes were used to enhance sensor sensitivity. Affixing the carbon nanotubes (30 mg ml(-1)) to the working electrode increased the sensor sensitivity to 61.9 mM nA(-1) mm(-2), twice the value for the sensor without single-walled carbon nanotubes. A fabricated mediator-type biosensor sensor was used to perform real-time in vivo measurements. The sensor was implanted into the interstitial fluid of a fish eyeball, and detection was transmitted to a personal computer by a wireless potentiostat. Continuous measurement of the glucose concentration was possible for 78 hours. Stress was artificially applied to the fish during the measurement, and the change of blood glucose concentrations were observed. Our proposed sensor is applicable for effectively monitoring stress in free-swimming fish.

Autonomous measurement of ingestion and digestion processes in free swimming sharks

Direct measurement of predator feeding events would represent a major advance in marine trophic ecology. To date, devices available for empirically quantifying feeding in free-swimming fishes have relied on measuring stomach temperature, pH or physical motility, each of which has major practical limitations. We hypothesized that the considerable physical changes that occur in the stomachs of carnivorous predators during the processes of ingestion and digestion should be quantifiable using bulk electrical impedance measured across paired electrodes. We used a prototype archival data logging tag to record changes in impedance inside the stomachs of captive free-swimming tiger and sandbar sharks over multiple, successive feeding events. Feeding and digestion events produced characteristic changes in electrical impedance of the stomach contents, identifiable as five successive phases: (1) pre-ingestion (empty stomach), (2) ingestion, (3) chemical 'lag', (4) mechanical 'chyme' and (5) stomach emptying. The duration of the chyme phase was positively related to meal size.

Precision measurement of electric organ discharge timing from freely moving weakly electric fish

Physiological measurements from an unrestrained, untethered, and freely moving animal permit analyses of neural states correlated to naturalistic behaviors of interest. Precise and reliable remote measurements remain technically challenging due to animal movement, which perturbs the relative geometries between the animal and sensors. Pulse-type electric fish generate a train of discrete and stereotyped electric organ discharges (EOD) to sense their surroundings actively, and rapid modulation of the discharge rate occurs while free swimming in Gymnotus sp. The modulation of EOD rates is a useful indicator of the fish's central state such as resting, alertness, and learning associated with exploration. However, the EOD pulse waveforms remotely observed at a pair of dipole electrodes continuously vary as the fish swims relative to the electrodes, which biases the judgment of the actual pulse timing. To measure the EOD pulse timing more accurately, reliably, and noninvasively from a free-swimming fish, we propose a novel method based on the principles of waveform reshaping and spatial averaging. Our method is implemented using envelope extraction and multichannel summation, which is more precise and reliable compared with other widely used threshold- or peak-based methods according to the tests performed under various source-detector geometries. Using the same method, we constructed a real-time electronic pulse detector performing an additional online pulse discrimination routine to enhance further the detection reliability. Our stand-alone pulse detector performed with high temporal precision (<10 μs) and reliability (error <1 per 10(6) pulses) and permits longer recording duration by storing only event time stamps (4 bytes/pulse).

50 kHz 체장어군탐지기용 분할 빔 음향 변환기의 지향성 보정 및 위치각 추정

The most satisfactory split-beam transducer for fish sizing maintains a wide bearing angle region for correct fish tracking without interference from side lobes and lower sensitivity to fish echoes outside of the main lobe region to correctly measure the angular location of free-swimming fishes in the sound beam. To evaluate the performance of an experimentally developed 50 kHz split-beam transducer, the angular location of a target was derived from the electrical phase difference between the resultant signals for the pair of transducer quadrants in the horizontal and vertical planes consisting of 32 transducer elements. The electrical phase difference was calculated by cross-spectral density analysis for the signals from the pair of receiving transducer quadrants, and the directivity correction factor for a developed split-beam transducer was estimated as the fourth-order polynomial of the off-axis beam angle for the angular location of the target. The experimental results demonstrate that the distance between the acoustic centers for the pair of receiving transducer quadrants can be controlled to less than one wavelength by optimization with amplitude-weighting transformers, and a smaller center spacing provides a range of greater angular location for tracking of a fish target. In particular, a side lobe level of -25.2 dB and an intercenter spacing of <TEX>$0.96\lambda$</TEX>(<TEX>$\lambda$</TEX>= wavelength) obtained in this study suggest that the angular location of fish targets distributing within a range of approximately <TEX>${\pm}28^{\circ}$</TEX> without interference from side lobes can be measured.

Comparison of salt marsh creeks and ditches as habitat for nekton

Salt marshes are dynamic systems supporting a diverse assemblage of resident and transient nekton (free-swimming fish and decapod crustaceans). Within a marsh, many sub-habitats are used by nekton, including ditches and natural creeks. While the use of natural creeks is well doc- umented, the role of ditches as habitat for nekton remains less well known. The present study describes the nekton-support function of this prolific marsh sub-habitat, and compares it to tidal creeks. Sampling was conducted in the summer of 2008 in a microtidal, polyhaline salt marsh on Fire Island, NY, USA. Ditches and creeks were found to have different nekton communities. Creeks had significantly higher species richness and represented nearly all ditch species. Prolonged anoxia (up to 18 h) in ditches is suggested as a significant factor contributing to differences in the creek and ditch nekton community. Upper portions of ditches and creeks differed for resident nekton species, with higher species richness and density of the mummichog Fundulus heteroclitus in the upper portion of creeks than in the upper portion of ditches. Additional differences were seen in the nekton commu- nity composition of open and naturally plugged ditches, where the densities of individual species (such as F. heteroclitus, which was more abundant in open ditches) also differed. Ditches are a major habitat type in salt marshes of the northeastern USA, such as at the Fire Island marsh site studied here, and as efforts are considered to remove ditches from marshes as a habitat restoration technique, their nekton support function should be considered.

A note on Aaptosyax grypus, a very rare, unique cyprinid fish

Rainboth (1991) described a new cyprinid fish, Aaptosyax grypus, from the Mekong River in Thailand, establishing a new monotypic genus. I was very interested in his figures of the species, which was similar to Chanos chanos in general appearance, and visited the fishermen’s base at Khong Chiam, eastern Thailand, several times from April 1998 to January 1999. Then I obtained a total of ten specimens of A. grypus: two from Khong Chiam and eight from the lower reaches near Khone Falls, Laos. All specimens were adult and larger than 700 mm in standard length (SL). One specimen was obtained in August (Khong Chiam), while the others were all obtained from the end of November to December, which may be the spawning season of the species, when the temperature of the Mekong decreases to 20 C, the coolest period (see ‘‘Ecological notes’’). Since Rainboth (1991) first described the superficial characters of A. grypus in detail, little biological information has accumulated for this species (e.g., it is categorized as ‘‘Data Deficient’’ in the IUCN Red List; Kottelat 1996). Here, I report some of the anatomical characteristics and other biological aspects of this very rare fish. Although the specimen for anatomical observation was not kept, another specimens were deposited in Lake Biwa Museum, Shiga, Japan [LBM 1210014953 (740 mm SL), 1210014954 (916 mm SL); tissue for DNA analysis, 1210015335; pharyngeal teeth, 1210026911, 1210047434; all from the Mekong River, Laos]. Mouth parts. In most free-swimming cyprinid fishes, the upper jaw can protrude through the action of the kinethmoid (Alexander 1966). In A. grypus, however, the upper jaw curves strongly and the postero-dorsal end of the premaxillary is supported by a large, curved, arched plate (probably corresponding to the kinethmoid) posteriorly, limiting the antero-posterior movement of the premaxillary. This structure seems to be associated with the biting jaw movement of this species, instead of protrusion (Fig. 1). Weberian ossicles. The claustrum is tightly connected to the supraneural by ligamentous tissue, in contrast to its free state in other cyprinid fishes (Fig. 1). There are also differences in the base of the scaphium and intercalarium, which are not pointed but wide. The connection of the tripus to the air bladder is remarkable. There is no flexible elongation of the transformer process in the end of the tripus; the latter is located free in a thick ligamentous mass that fills the gap between the air bladder and the os suspensorium anteriorly and the vertebral column dorsally. This thick mass is covered with an overhanging curtain from the centrum. There is neither a sagittally running slit in the antero-dorsal corner of the tunica externa nor a thinned area of the tunica interna coinciding with the slit in the tunica externa of the air bladder, which are widely seen in cyprinid fishes (Alexander 1962); these imply that pressure transmission is less effective. All of these characters suggest that the Weberian ossicles of A. grypus are incomplete in communicating sound from the air bladder to the inner ear. Filamentous bones. In lower teleosts, such as Sardinops and other clupeoid fishes, a dense growth of filamentous bones called the osseous brush and the filamentiferous rod (Phillips 1942) develops in the dorso-anterior region of the vertebral column. These bones are not generally found in cyprinid fishes. However, A. grypus possesses well-developed dense filamentous bones similar to those of clupeoids, which are attached to the posterior region of the neurocranium and extend into the trunk muscles (Fig. 1). Y. Tomoda (&) 415-76 Hamabun, Imazu, Takashima, Shiga 520-1604, Japan

A digital stereo-video camera system for three-dimensional monitoring of free-swimming Pacific bluefin tuna,Thunnus orientalis, cultured in a net cage

We used a digital stereo-video camera system for three-dimensional monitoring of cultured Pacific bluefin tuna, Thunnus orientalis, swimming freely in a net cage. We estimated the fork length and length frequency distribution of individual fish using the direct linear transformation (DLT) method. Information obtained from stereo images is useful for managing the growth of tuna during rearing. Our aim was to develop a simple method involving a combination of DLT and commercial image-processing software to enable aquaculturists to obtain three-dimensional measurements of fish. In this study, we used a stereo-video camera system to evaluate the precision and validity of fish size estimates determined from repeated measurements. Of the total assessed individuals swimming within a distance of <5.5 m from the camera system, estimates for 99% (106/107) were found to be valid, with an error ratio (standard error/mean) of <5%. Therefore, we believe that our proposed simple method for monitoring free-swimming fish could be very useful for aquaculture management.

Elaboration of equipment and methods of continuous recording of electric activity of clariid catfish (Clariidae, Siluriformes) in social and reproductive behavior

Equipment and methods of simultaneous continuous long-term recording of electric activity of clariid catfish (Clariidae) is elaborated. All electric organ discharges (EOD) in any position and orientation of free swimming fish are fixed by simultaneous recording of electric voltage with two mutually perpendicular pairs of electrodes. Light-emitting diodes controlled by a microprocessor allow for the possibility to observe the moments of discharge emission both in real time and during scanning of videorecords. According to its parameters, the created equipment corresponds to characteristics of EOD of clariid catfish, performs primary treatment of signals, and stores in its inner flash memory all discharges recorded in a prolonged experiment (duration up to several days, number of EOD up to several tens of thousands). Various examples of EOD are presented recorded by means of the elaborated methods in clariid catfish (C. macrocephalus, C. batrachus, C. fuscus, and hybrids C. gariepinus × C. macrocephalus) when they manifested aggressive-defensive and spawning behavior. The procedure of treatment of EOD is suggested, including that of special bursts of EODs generated by females in pairing.

Studies of hydrodynamics in fishlike swimming propulsion

In this paper, we will attempt to provide an overview on the hydrodynamics of fishlike swimming propulsion based on our recent work performed experimentally, numerically and theoretically. We mainly present some typical work, including measurement on kinematics of free-swimming fish and prediction of dynamics acting on an arbitrarily deformable body, numerical and experimental simulations of flow over flapping and traveling wavy bodies, and the relevant biomimetic technology.

Functional morphology of the flounder allows stable and efficient gliding: an integrated analysis of swimming behaviour

Although technologies such as archival tags have been developed to monitor the behav- iour of free-swimming fish, more advanced techniques are required in order to understand the basis of their behaviour. To assess the glide behaviour of the negatively buoyant Japanese flounder Paralichthys olivaceus, we adopted a new approach to examine the importance of the physical aspects of its swimming performance by integrating in situ bio-logging data from free-swimming fish with corresponding computational fluid dynamics (CFD) analyses. Field data from the data loggers revealed that flounder commenced powerless glides after swimming upwards. A theoretical simula- tion of this glide using CFD analysis revealed that the body angle producing the maximum lift/drag ratio was in agreement with the field data and that, during a glide, the moment equilibrium body angle of the flounder resulted in the longest glide distance. This suggests that the morphology of the flounder confers stability on its glide, making this mode of movement more energetically efficient.

Lack of arterial PO2 downregulation in Atlantic salmon (Salmo salar L.) during long-term normoxia and hyperoxia

Regulation of arterial partial pressure of O2 (PaO2) in Atlantic salmon (Salmo salar) was investigated during resting conditions in normoxic and hyperoxic water. Dorsal aorta cannulated adult Atlantic salmon (1.2-1.6 kg, n=8) were exposed to 2 week sequential periods of normoxia [16.7±1.1 kPa (mean±SD)] and hyperoxia (34.1±4.9 kPa) in individual tanks containing seawater (33.7±0.2 ppt) at stable temperature conditions (8.7±0.7°C) and a light regime of L:D=12:12. Tank design and sampling procedures were optimized to provide suitable shelter and current for the fish, and to allow repeated, undisturbed sampling of blood from free-swimming fish. Fish were sampled regularly through the experimental period. PwO2, PaO2, blood ion composition (Na+, K+, Cl-), acid-base status (pH, PCO2, HCO3-), haematocrit and glucose were measured. The most frequently observed PaO2 values were in the range of 60-80% of PwO2, both during normoxia and hyperoxia, and PaO2 values were significantly lower during normoxia than during hyperoxia. Blood pH, PCO2 and HCO3- were significantly elevated during hyperoxia, while, Na+, Cl- and Hct were significantly lower. K+ and glucose showed no significant differences. This study demonstrates a lack PaO2 regulation in Atlantic salmon to low partial pressures, in contrast to previous reports for many aquatic gill breathing animals. Both during normoxia and hyperoxia, PaO2 reflects PwO2, and alterations in external PO2 consequently result in proportional arterial PO2 changes. Physiological adaptation to hyperoxia, as illustrated by changes in several blood parameters, does not include down-regulation of PaO2 in Atlantic salmon. The lack of PaO2 regulation may make Atlantic salmon vulnerable to the oxidative stress caused by increased free radical formation in hyperoxic conditions.