David J. Coughlin

Swimming and search behaviour in clownfish, Amphiprion perideraion, larvae

The swimming behaviour and search patterns of pink clownfish larvae, Amphiprion perideraion, were examined using a novel filming apparatus that permits three-dimensional tracking of free swimming zooplankters. Analysis of the resulting search paths included swimming speed and average turning angle, as well as a new approach to the study of search dynamics, fractal analysis. Amphiprion perideraion larvae display a clear shift in behaviour at the onset of feeding, with a drop in overall complexity of their swimming paths and an increase in their swimming speed. Similar to other foraging animals, clownfish larvae display at least two search modes after the onset of feeding: a highly linear ranging mode used to locate patches of food and a highly complex, convoluted searching mode used to exploit those patches once they are located. Conventional analysis did not adequately discriminate between foraging modes, creating the need for fractal analysis. Unlike other foraging animals, clownfish larvae increase swimming speed when they encounter patches of high food abundance. This response is proposed to be the result of hydrodynamic constraints imposed upon the fish because of their relatively small size.

Zooplankton capture by a coral reef fish : an adaptive response to evasive prey

SynopsisHigh-speed cinematography and video using modified Schlieren optics and laser illumination helped elicit details of prey capture mechanisms used by Chromis viridis while feeding on calanoid copepods and Artemia. Chromis viridis is capable of a ram-jaw, low-suction feeding, as well as a typical suction feeding behavior described for other species of planktivores. By adjusting the degree of jaw protrusion and amount of suction used during a feeding strike, this fish can modulate its feeding strikes according to the prey type being encountered. The ram-jaw feeding mode enables C. viridis to capture highly evasive calanoid copepods within 6 to 10 msec. The use of specialized feeding behavior for evasive prey and the ability to vary feeding behavior are adaptations for feeding on evasive prey.

A cellular basis for polarized-light vision in rainbow trout

Polarized light sensitivity was examined in single units of the rainbow trout (Oncorhynchus mykiss) torus semicircularis, a sub-tectal visual area with a high degree of ultraviolet sensitivity. First, chromatically isolated torus units with inputs from each of the four cone mechanisms found in the trout visual system were separately examined for e-vector sensitivity. UV ON-response units showed polarization sensitivity for vertical ly (0° and 180°) polarized stimuli, while ON-response units of the short, middle and long cone mechanisms were not polarization sensitive. No OFF-response units of the UV or short cone mechanism were observed, but OFF-response units of the middle and long cone mechanisms show polarization sensitivity for horizontally (90°) polarized stimuli. Second, e-vector sensitivity was observed in color-coded units which received inputs from more than one cone mechanism and showed different sign responses (ON or OFF) at different points of the spectral sensitivity curve. Biphasic units which had ON input from the UV cone mechanism and OFF inputs from the middle and long cone mechanisms showed polarization opponency. This opponency was observed with a 380 nm stimulus when the threshold sensitivities of the alpha-band absorption peak of the UV mechanism and the beta-band absorption peak of the middle and long cone mechanisms were equal. We believe that biphasic torus units provide a possible cellular basis for polarized light vision in rainbow trout.

The Contribution of Ultraviolet and Short-Wavelength Sensitive Cone Mechanisms to Color Vision in Rainbow Trout

Color vision in rainbow trout was studied by characterizing the spectral sensitivity of single units in three areas of visual processing: optic nerve; optic tectum; and torus semicircularis. Sensitivity to medium wavelength stimuli was a common feature of all single units examined. Additionally, long wavelength sensitivity was found in all units that were not medium wavelength-only or monophasic. Ultraviolet and short-wavelength sensitivity was common in small, juvenile trout, with ultraviolet sensitive units found in the optic nerve and torus, and short wavelength sensitivity found in the optic nerve and tectum. The shorter wavelength inputs were excitatory and, if found in the same unit, synergistic. The most common type of unit in the trout tectum and optic nerve is trichromatic, with ON inputs from the long and short cone mechanisms and an OFF input from the medium mechanism. In contrast, goldfish color vision is dominated by L and M opponent units without S input. The segregation of ultraviolet sensitivity in the torus but not in the tectum relates to functional differences of these two areas. While the tectum serves the function of wavelength discrimination, ultraviolet inputs to the torus may contribute to prey detection and orientation.

Parvalbumin correlates with relaxation rate in the swimming muscle of sheepshead and kingfish.

SUMMARY Parvalbumin is a muscle protein that aids in relaxation from contraction. Parvalbumin binds myoplasmic Ca2+ during contractions, reducing calcium concentration and enhancing relaxation. Different isoforms of parvalbumin have varying affinities for calcium, and relaxation rates in skeletal muscle may be affected by variations in the isoforms of parvalbumin expressed. This study examines the effect of expression levels of parvalbumin isoforms on relaxation rate in the sheepshead, Archosargus probatocephalus (Pisces, F. Sparidae). We measured relaxation rate of each of the three fiber types, white (fast-twitch), red (slow-twitch) and pink (intermediate), from three longitudinal body positions. Sheepshead show a significant longitudinal shift in relaxation rate in red muscle, with anterior muscle displaying faster rates of relaxation than posterior, but this pattern was not significant in the pink and white muscle. We hypothesized that patterns of parvalbumin expression determine relaxation rate along the length of the fish. The prediction is that total parvalbumin content and the relative expression of parvalbumin isoforms will differ between the anterior and posterior red muscle, but little longitudinal variation will be observed in parvalbumin expression in white and pink muscle. We successfully employed protein electrophoresis (SDS–PAGE) with western blots to identify two parvalbumin isoforms in each muscle fiber type. SDS–PAGE and densitometry were used to determine the relative expression levels of the two parvalbumin isoforms and total parvalbumin expression. Red muscle displays a significant shift, from anterior to posterior, in the relative expression of the two isoforms, both in their relative contribution and in total parvalbumin content, but white and pink muscle did not. The red muscle of southern kingfish, Menticirrhus americanus (Pisces, F. Scianidae) showed a pattern similar to the red muscle of sheepshead.

Ultraviolet sensitivity in the torus semicircularis of juvenile rainbow trout (Oncorhynchus mykiss)

The spectral sensitivity of single units in the torus semicircularis (TS) of small (< 30 g) and large (> 60 g) juvenile rainbow trout, Oncorhynchus mykiss, was investigated. All examined units (n = 39) showed inputs from the long and medium cone mechanisms. In addition, a majority of units (28 of 39) in both size groups of fish had inputs from the UV cone mechanism, and both groups had several types of color-coded units. The TS of large trout differed from small fish by having a significantly higher proportion of luminance or non-color-coded units relative to color-coded units. Additionally, large fish had a reduced number of UV-sensitive units and an increased number of short-wavelength-sensitive units relative to small fish.

Muscle Activity in Steady Swimming Scup, Stenotomus chrysops, Varies With Fiber Type and Body Position

The red and pink aerobic muscle fibers are used to power steady swimming in fishes. We examined red and pink muscle recruitment and function during swimming in scup, Stenotomus chrysops, through electromyography and high-speed ciné. Computer analysis of electromyograms (EMGs) allowed determination of initial speed of muscle recruitment and duty cycle and phase of muscle electromyographic activity for both fiber types. This analysis was carried out for three longitudinal positions over a range of swimming speeds. Fiber type and longitudinal position both affected swimming speed of initial recruitment. Posterior muscle is recruited at the lowest swimming speed, whereas more anterior muscle is not initially recruited until higher speeds. At more anterior positions, the initial recruitment of pink muscle occurs at a higher swimming speed than the recruitment of red muscle. The duty cycle of pink muscle EMG activity is significantly shorter than that of red muscle, reflecting a difference in the onset time of activation during each cycle of length change: pink muscle onset time follows that of red. The different patterns of usage of red and pink muscle reflect differences in their contraction kinetics. Because pink muscle generates force more rapidly than red muscle, it can be activated later in each tailbeat cycle. Pink muscle is used to augment red muscle power production at higher swimming speeds, allowing a higher aerobically based steady swimming speed than that possible by red muscle alone.

A cinematographic comparison of behavior by the calanoid copepod Centropages hamatus Lilljeborg: tethered versus free-swimming animals

Many previous cinematographic studies of copepod behavior have used animals tethered to dog or cat hairs to keep them in focus. We compared behavior of tethered and free-swimming specimens of the calanoid copepod Centropages hamatus Lilljeborg using cinematographic methods. Precise quantification was made of the time allocated to four modes of behavior: slow-swim (movement of feeding appendages only), break (no appendages moving), fast-swim (posteriorally-directed movement of first antennae and pereiopods), and groom (brushing of first antennae through feeding appendages). Ten copepods each were used for tethered and free-swimming filming. Under both experimental regimes, copepods spent < 1 % of total amount of time in fast-swimming and grooming behavior. Most of the time (50.7–95.5%) animals were on break. The rest of the time (3.8–48.9%) animals were in the slow-swimming mode, moving only feeding appendages. There were no significant differences between tethered and free-swimming animals in mean time allocations to slow-swimming and break behavioral modes. However, individual variability of tethered animals was higher than that of free-swimming ones. We conclude that, while mean time allocation to slow-swimming and break behaviors were similar between free-swimming and tethered animals, the variability between tethered individuals is a factor to be considered when designing experiments.

Foraging to the rhythm of ocean waves: porcelain crabs and barnacles synchronize feeding motions with flow oscillations

Abstract Suspension-feeding activity patterns of four benthic crustacean species (2 porcellanid crabs and 2 balanomorph barnacles) were studied in simulated wave-action (oscillating flow in a laboratory flow tank). The hypothesis that the frequency of rhythmic suspension-feeding motions observed in oscillating flow depends on the frequency of flow oscillation was tested. Also, we examined the effect of flow oscillation frequency on time allocation to food-particle-trapping versus non-trapping components of feeding behavior, as an indication of how the energetic gain-to-cost ratio of feeding varies with flow regime. A newly developed flow pattern generator, consisting of computer programs interfaced with a flow tank motor, was used to produce various oscillating flow regimes (0.16–0.65 Hz. 6.2–12.1 cm·s −1 maximum velocity). Laser-optics, fiber optics, and video equipment were used to record behavior and to determine water flow velocities non-intrusively, by tracking the video-recorded movement of back-lit particles suspended in flowing seawater. All animals tested rhythmically reoriented suspension-feeding fans in oscillating flow so that the cup-shaped fans faced concave-upstream. At all test frequencies, the frequency of the cyclic motions of feeding append ages matched the frequency of flow directional oscillation precisely. Also, all species behaviorally anticipated changes in flow direction, by beginning to reorient feeding fans to changing flow direction before the water itself had reversed flow direction (i.e the animals responded when water was decelerating). This anticipatory behavior allowed animals feeding in wave-action to avoid missing full fan extension during part of the peak velocity range of an upcoming pulse of flow, as would have happened if they had waited until flow direction changed to reorient appendages. That animals actively track wave frequency so precisely with their feeding fan movements suggests than, in natural habitats, wave frequency is a critical factor for certain consumers that affects the energetics of feeding activity. Video analysis showed that as flow oscillation frequency decreased, all animals spent a greater fraction of feeding time trapping suspended food particles with fans fully extended into flow, and a corresponding smaller fraction of time engaged in the muscular activity of removing trapped particles and reorienting feeding fans. These changes suggest an increase in energetic feeding gain-to-cost ratio with a decrease in flow oscillation frequency.

Rainbow trout Oncorhynchus mykiss consume less energy when swimming near obstructions.

The effect of obstructions in steady flow on swimming by rainbow trout Oncorhynchus mykiss was examined in a respirometry swim tunnel to test the prediction that fish interacting with obstructions require less energy to hold station. When an obstruction was present, O. mykiss altered the kinematics of swimming and the rate of oxygen consumption was significantly reduced. The fish employed both entrainment and Kármán gait swimming strategies, permitting greater locomotor efficiency.