Effect of position-fixing interval on estimated swimming speed and movement pattern of fish tracked with a stationary positioning system

Ultrasonic telemetry using stationary positioning systems allows several fish to be tracked simultaneously, but systems that are incapable of sampling multiple frequencies simultaneously can record data from only one transmitter (individual) at a time. Tracking several individuals simultaneously thus results in longer intervals between successive position fixes for each fish. This deficiency leads to loss of detail in the tracking data collected, and may be expected to cause loss of accuracy in estimates of the swimming speeds and movement patterns of the fish tracked. Even systems that track fish on multiple frequencies are not capable of continuous tracking due to technical issues. We determined the swimming speed, area occupied, activity rhythm and movement pattern of cod (Gadus morhua) using a stationary single-channel positioning system, and analysed how estimates of these behavioural parameters were affected by the interval between successive position fixes. Single fish were tracked at a time, and position fixes were eliminated at regular intervals in the original data to generate new data sets, as if they had been collected in the course of tracking several fish (2–16). In comparison with the complete set, these data sets gave 30–70% decreases in estimates of swimming speed depending on the number of fish supposedly being tracked. These results were similar for two individuals of different size and activity level, indicating that they can be employed as correction factors to partly compensate for underestimates of swimming speed when several fish are tracked simultaneously. Tracking `several' fish only slightly affected the estimates of area occupied (1–15%). The diurnal activity rhythm was also similar between the data sets, whereas details in search pattern were not seen when several fish were tracked simultaneously.     

Relating the swimming movements of green sturgeon to the movement of water currents

Animals swimming in tidal environments continuously interact with water currents which may either hinder or aid their movement. It is difficult to observe the orientation of an organism relative to the current when it is swimming in the wild without specialized telemetry; however, using the total recorded movement vector and the current vector, one can use vector analysis to calculate the actual movement of the animal. Here, we apply this method to six tracks of green sturgeon (Acipenser medirostris) in the San Francisco Estuary, using current vectors derived from a hydrodynamic model. Three movements were near the surface in deeper, high-current regions of the bay and three were near the bottom in shallow, low-current areas. The total displacement over ground was faster at the surface (0.9 m sec⁻¹ versus 0.5 m sec⁻¹) and occurred in stronger currents (0.7 m sec⁻¹ versus 0.4 m sec⁻¹), but the swimming speeds of the fish were similar between surface and bottom movements (0.5 m sec⁻¹ versus 0.6 m sec⁻¹). All surface movements were in the direction of the current, and two of the fish also oriented closely to the flow. In contrast, none of the three benthic movements were in the direction of the current, and two were oriented opposite to the flow. It seems plausible that green sturgeon orient to and make use of water currents to efficiently move through tidal habitats, riding the flow in high-current areas, and moving independently of, or even into, the flow in slower currents.     

Temperature influences swimming speed, growth and larval duration in coral reef fish larvae

The effects of temperature on growth, pelagic larval duration (PLD) and maximum swimming speed were compared in the tropical fish marine species Amphiprion melanopus, to determine how temperature change affects these three factors critical to survival in larvae. The effects of rearing temperature (25 and 28 °C) on the length of the larval period and growth were examined in conjunction with the effects of swimming temperature (reared at 25 °C, swum at 25 and 28 °C, reared at 28 °C, swum at 25 and 28 °C) on critical swimming speed (U-crit). Larvae reared at 25 °C had a 25% longer pelagic larval duration (PLD) than larvae reared at 28 °C, 12.3 (±0.3) days compared with 9 (±0.6) days at 25 °C. To offset this effect of reduced developmental rate, growth and U-crit were measured in larvae reared at 28 and 25 °C at the same absolute age (7 days after hatching (dah)) and same developmental age (7 dah at 28 °C cf. 11 dah at 25 °C), corresponding to the day before metamorphosis. Larvae reared at 25 °C were smaller than larvae reared at 28 °C at the same absolute age (7 dah at 25 °C cf. 7 dah at 28 °C), yet larger at similar developmental age (11 dah at 25 °C cf. 7 dah at 28 °C) when weight and standard length were compared. This stage-specific size increase did not result in better performance in larvae at the same developmental age, as there was no difference in U-crit in premetamorphic larvae reared at either temperature (7 dah at 28 °C c.f 11 dah at 25 °C). However, U-crit was considerably slower in 7-day-old larvae reared at 25 °C than larvae of the same absolute age (7 dah) reared at 28 °C. Swimming temperature controls demonstrated that a change in temperature immediately prior to swimming tests did not effect swimming performance for larvae reared at either temperature.A decreased in rearing temperature resulted in longer larval durations, reduced growth rates and slower swimming development in larvae. However, the magnitude of the response of each of these traits varied considerably. As such, larvae reared at the lower temperature were a larger size at metamorphosis but had poorer relative swimming capabilities. This study highlights the importance of measuring a range of ecologically relevant traits in developing larvae to properly characterise their relative condition and performance in response to environmental change.     

Bioenergetic model of planktivorous fish feeding, growth and metabolism: theoretical optimum swimming speed of fish larvae

The feeding activity of an individual fish larva is described by an equation which includes parameters for the area successfully searched, probability of food capture multiplied by the cross-sectional perceptive visual field, larval swimming speed and the time required to consume a unit of food energy. The proportion of ingested food energy used for metabolism increases exponentially with increasing swimming speed. The model predicts that food consumption rate increases asymptotically whereas metabolic rate increases exponentially. This results in a predicted growth rate curve that reaches a maximum at a certain swimming speed and decreases at both higher and lower speeds. The model can be used to predict the influence of type of prey, prey density, water temperature etc. on larval growth. An expression describing how many hours per day fish larvae must forage in order to grow at a certain daily body weight gain allows the limits of environmental conditions for positive, zero and negative growth rate to be set. Results of simulations demonstrated that the optimum swimming speed for maximum growth of coregonid larvae increased with an increase in food density, decrease in water temperature or decrease of prey vulnerability. At optimum ‘theoretical’ swimming speed an increase in water temperature from 5 to 17° C required the food density to be increased from 20 to 80 copepods l^?1 in order to maintain a daily growth increment of 2%. The minimum Artemia density required for maintenance metabolism increased from 10 to 30 items 1¹ over the same temperature increase from 5 to 17° C, and food densities required for 8% growth rates were 26 and 56 Artemia nauplii l^?1 at 5 and 17° C, respectively. Contrary to previous findings, results of the present study suggest that metabolic rates of actively feeding fish larvae may be from 5 to 50 times the standard metabolic rate: earlier studies suggested that a factor of 2–3 may be generally applicable.     

Costs of swimming measured at optimum speed: scale effects, differences between swimming styles, taxonomic groups and submerged and surface swimming

1. Data on swimming energy expenditure of 30 submerged and nine surface swimmers, covering different swimming styles and taxonomic groups, are selected from the literature. 2. The costs of transport at the optimum speed are compared and related to body mass and Re numbers. 3. Fish and turtles use relatively less and most surface swimmers slightly more energy than the other submerged swimmers; man and mink are poorly adapted to swimming. 4. The metabolic rate in W at optimum speed is approximately equal to the body mass in kg for fish and turtles and three times the mass figure for the other submerged swimmers.     

Sperm morphology and its influence on swimming speed in Atlantic cod

A protocol for staining fish spermatozoa using Hemacolor-stain was developed for light microscopy and successfully applied to Atlantic cod ( Gadus morhua ). Sperm head morphology was characterized by size (length, width, area and perimeter) and shape (ellipticity, rugosity, elongation and regularity) (n   =   6500 spermatozoa), and tail length (n   =   260 spermatozoa) of 12 individual cod. Two spermatozoa heads sperm were clearly identified: round and elongated, being this last one more abundant (86.3%). No evidence was detected in tail length for both head types. Tails were 96.4% length of sperm and no difference in tail length was detected between head types. A positive correlation existed between head and tail length, with variability existing among males. Sperm swimming speeds varied among males with a maximum curvilinear velocity between 151.5 and 201.5  μ m s⁻¹. Mean swimming speed declined by 8.2% from 30 to 70 s post-activation. Spermatocrit was negatively correlated with curvilinear velocity at 30 s post-activation. Males with short sperm heads maintained their swimming velocity for longer periods that those with long heads. Fulton's condition factor was negatively correlated with straightness of path.     

Computational and mathematical modeling of the effects of tailbeat frequency and flexural stiffness in swimming fish

In this paper we describe how we combine computational and mathematical models to form virtual fish to explore different hypotheses about the impact of centra. We show how we create simulation models using a combination of a mathematical model of a fish-like robot using caudal fin propulsion, a propulsion model, and an optimizer, to explore the impact of centra under various scenarios. The optimizer uses the mathematical model to construct valid configurations of the digital robot and uses the utility function and propulsion model to evaluate the performance of each configuration. The evaluations are used to explore the adaptive landscape and find high-performing configurations. Our results show that the high-performing configurations have both increased (flexural) stiffness of the tail and higher tailbeat frequencies.     

Modelling energetic costs of fish swimming

The oxygen consumption rates of two cyprinid fishes, carp (Cyprinus carpio L.) and roach (Rutilus rutilus (L.)), were analysed for a wide range of body mass and swimming speed by computerized intermittent-flow respirometry. Bioenergetic models were derived, based on fish mass (M) and swimming speed (U), to predict the minimal speed and mass-specific active metabolic rate (AMR) in these fishes (AMR=aMbUc). Mass and speed together explained more than 90% of the variance in total swimming costs in both cases. The derived models show that carp consume far more oxygen at a specific speed and body mass, thus being less efficient in energy use during swimming than roach. It was further found that in carp (AMR=0.02M0.8U0.95) the metabolic increment during swimming is more strongly effected by speed, whereas in roach (AMR=0.02M0.93U0.6) it is more strongly effected by body mass. The different swimming traits of carp and roach are suitable for their respective lifestyles and ecological demands.     

Light-oriented swimming of schooling fish in continuous channels

Synopsis Fish groups were tested both in a circular and in a figure eight-shaped channel. In both cases fish showed a long lasting, constant direction swimming provided that illumination was maintained at a constant angle around the channel. In the circular channel, fish did not reverse direction, as would be expected, when light angle was shifted from one side to the other in the channel. However, direction reversals did occur when these illumination shifts were performed on the eight-shaped channel. We suggest that constant-oriented swimming reflects a sun-compass oriented behavior, but swimming at a constant angle in the circular channel produces an irreversible disarrangement of the inertial-orientation system, which does not occur in the eight-shaped channel due to the geometrical relationship between the light and the shape of the channel.     

A gravity-induced regulation of swimming speed in Euglena gracilis

We investigated the autotrophic flagellate Euglena gracilis for gravity-induced modulation of the speed of swimming as previously documented for larger protozoan cells. Methods of video-tracking of swimming and sedimenting cells under 1 g and hypergravity up to 2 g, and computer-assisted data processing were applied. The vertical and horizontal swimming speed, and sedimentation rates of immobilized cells, were found to be linear functions of acceleration. Accounting for sedimentation in the observed upward and downward movements of Euglena, the active component of speed (propulsion) rose in proportion to acceleration. No saturation of gravikinesis was seen within the g-range tested. Gravity-dependent augmentation of speed was maximal in upward swimmers and decreased continuously over horizontal to downward swimmers. Linear extrapolations of the data to zero-g conditions suggest the absence of a threshold of gravikinesis in Euglena. Energetic considerations indicate a high sensitivity of gravitransduction near the level of Brownian molecular motion. Accepted: 22 August 1999     

Energetic advantages of burst swimming of fish

It is shown theoretically that fish can swim more efficiently by alternating periods of accelerated motion and powerless gliding. Analysis of the mechanics of swimming shows that large savings of over 50% in the energy required to traverse a given distance can be obtained by such means. In calculations based upon measured data for salmon and haddock, the possibility of range increases of up to three times the range at constant speed are demonstrated.     

Optimal shape and motion of undulatory swimming organisms

Undulatory swimming animals exhibit diverse ranges of body shapes and motion patterns and are often considered as having superior locomotory performance. The extent to which morphological traits of swimming animals have evolved owing to primarily locomotion considerations is, however, not clear. To shed some light on that question, we present here the optimal shape and motion of undulatory swimming organisms obtained by optimizing locomotive performance measures within the framework of a combined hydrodynamical, structural and novel muscular model. We develop a muscular model for periodic muscle contraction which provides relevant kinematic and energetic quantities required to describe swimming. Using an evolutionary algorithm, we performed a multi-objective optimization for achieving maximum sustained swimming speed U and minimum cost of transport (COT)--two conflicting locomotive performance measures that have been conjectured as likely to increase fitness for survival. Starting from an initial population of random characteristics, our results show that, for a range of size scales, fish-like body shapes and motion indeed emerge when U and COT are optimized. Inherent boundary-layer-dependent allometric scaling between body mass and kinematic and energetic quantities of the optimal populations is observed. The trade-off between U and COT affects the geometry, kinematics and energetics of swimming organisms. Our results are corroborated by empirical data from swimming animals over nine orders of magnitude in size, supporting the notion that optimizing U and COT could be the driving force of evolution in many species.     

Methods of measuring swimming speed of spermatozoa.

Three basic approaches for determining the mean swimming speed of a suspension of microorganisms were compared, using bull and ram spermatozoa. Number fluctuation counting was performed automatically on a Quantimet 720 image analysing computer, the mean speed being obtained using 'probability after' statistics. The other two approaches were photomicrographic: number flux counting was performed on single photomicrographs; on the same photomicrographs, the mean speed was estimated from measurement of 'whole' and 'half' track lengths. These results were compared with each other and with the Quantimet results. The 'probability after' method was also compared, on additional samples, with cine-photomicrographic tracking. The mean speeds predicted by the 'probability after' method compared favourably with the other methods (range 68 mum/sec to 162 mum/sec). The results also suggested that, on single photomicrographs, measurement of 'half' track lengths or number flux counting were generally preferable to measurement of whole track lengths.     

The effects of temperature and swimming speed on instantaneous fuel use and nitrogenous waste excretion of the Nile tilapia.

The effects of acclimation temperature (30 degrees, 20 degrees, and 15 degrees C) and swimming speed on the aerobic fuel use of the Nile tilapia (Oreochromis niloticus; 8-10 g, 8-9-cm fork length) were investigated using a respirometric approach. As acclimation temperature was decreased from 30 degrees C to 15 degrees C, resting oxygen consumption (Mo2) and carbon dioxide excretion (Mco2) decreased approximately twofold, while nitrogenous waste excretion (ammonia-N plus urea-N) decreased approximately fourfold. Instantaneous aerobic fuel usage was calculated from respiratory gas exchange. At 30 degrees C, resting Mo2 was fueled by 42% lipids, 27% carbohydrates, and 31% protein. At 15 degrees C, lipid use decreased to 21%, carbohydrate use increased greatly to 63%, and protein use decreased to 16%. These patterns at 30 degrees C and 15 degrees C in tilapia paralleled fuel use previously reported in rainbow trout acclimated to 15 degrees C and 5 degrees C, respectively. Temperature also had a pronounced effect on critical swimming speed (UCrit). Tilapia acclimated to 30 degrees C had a UCrit of 5.63+/-0. 06 body lengths/s (BL/s), while, at 20 degrees C, UCrit was significantly lower at 4.21+/-0.14 BL/s. Tilapia acclimated to 15 degrees C were unable or unwilling to swim. As tilapia swam at greater speeds, Mo2 increased exponentially; Mo2min and Mo2max were 5.8+/-0.6 and 21.2+/-1.5 micromol O2/g/h, respectively. Nitrogenous waste excretion increased to a lesser extent with swimming speed. At 30 degrees C, instantaneous protein use while swimming at 15 cm/s ( approximately 1.7 BL/s) was 23%, and at UCrit (5.6 BL/s), protein use dropped slightly to 17%. During a 48-h swim at 25 cm/s (2.7 BL/s, approximately 50% UCrit), Mo2 and urea excretion remained unchanged, while ammonia excretion more than doubled by 24 h and remained elevated 24 h later. These results revealed a shift to greater reliance on protein as an aerobic fuel during prolonged swimming.     

Influence of the uterine environment on rat sperm motility and swimming speed

The present study compared several rat sperm parameters in semen samples recovered from a natural uterine environment (i.e., intact estrous female) to those recovered from an artificially induced uterine environment (i.e., ovariectomized hormonally primed female). The sperm parameters measured were percent motile, percent exhibiting forward progressive motility, actual swimming speed, and linear swimming speed. The comparisons were conducted at four postcopulatory time points (0.25, 1.5, 3, and 6 hours) in order to detect differences as a function of residence time within the uterus. No significant differences (P less than 0.05) in the parameters were seen between the two types of uterine environments. Residence time within the reproductive tract had no significant effect on the parameters with the exception of percent motile, which was significantly increased (P less than 0.01) at the 1.5-hour postcopulatory time point.     

Brain function in antarctic fish: Activity of central vestibular neurons in relation to head rotation and eye movement

Summary Recordings were made from central vestibular neurons responding to horizontal head rotation in antarctic fish,Pagothenia borchgrevinki, at a temperature close to 0 °C. The spontaneous activity of these units varied between 0 and 56 Imp/s with a mean value of 20. Almost all units responded to horizontal rotation with a maximum firing rate that was approximately in phase with head velocity, either towards the recording side (type I units) or away from the recording side (type II), with no alteration of firing pattern during saccadic eye movements. The mean gain of these units was 2.6 Imp/s//s at 0.35 Hz which is higher than that reported for central vestibular neurons in other fish.     

A combined neuronal and mechanical model of fish swimming

A simulated neural network has been connected to a simulated mechanical environment. The network is based on a model of the spinal central pattern generator producing rhythmic swimming movements in the lamprey and the model is similar to that used in earlier simulations of fictive swimming. Here, the network has been extended with a model of how motoneuron activity is transformed via the muscles to mechanical forces. Further, these forces are used in a two-dimensional mechanical model including interaction with the surrounding water, giving the movements of the different parts of the body. Finally, these movements are fed back through stretch receptors interacting with the central pattern generator. The combined model provides a platform for various simulation experiments relating the currently known neural properties and connectivity to the behavior of the animalin vivo. By varying a small set of parameters, corresponding to brainstem input to the spinal network, a variety of basic locomotor behaviors, like swimming at different speeds and turning can be produced. This paper describes the combined model and its basic properties.