A hydro-mechanical approach to the scaling of swimming performance in the sand flathead Platycephalus bassensis Cuvier: effects of changes in morphological features based on fish size

The swimming performance of Platycephalus bassensis at steady speed was assessed with an emphasis on hydrodynamics. The minimum swimming speed to maintain hydrostatic equilibrium for P. bassensis of 0·271 m total length ( L _T) was calculated to be 1·06 L _T s⁻¹. At this speed, the required lift to support the mass of the fish was equivalent to 6·6% of the fish mass; 82·7% of which was created by the body as a hydrofoil, and the rest of which was created by the pelvic fins as hydrofoils. The minimum swimming speed decreased with the L _T of the fish and ranged from 1·15 L _T s⁻¹ for a fish of 0·209 m to 0·89 L _T s⁻¹ for a fish of 0·407 m. The forward movement per tail-beat cycle ( i.e. stride length) was described with an equation including quantities of morphological and hydro-mechanical relevance. This equation explained that stride length was increased by the effect of turbulence characterized by the Reynolds number and demonstrated the morphological and hydro-mechanical functional design of the fish for maximizing thrust and minimizing drag. The larger span of the caudal fin and caudal tail-beat amplitude was associated with larger stride length, whereas greater frictional drag was associated with smaller stride length.     

Swimming performance and metabolism of 0+ year Thymallus arcticus

The prolonged swimming speed and metabolic rate of 0+ year Arctic grayling Thymallus articus were examined with respect to current velocity, water temperature and fish size, and compared to conditions fish occupy in the river. Oxygen consumption (mg O₂ h⁻¹) increased with fish mass and temperature (6–23° C), with a steep increase in metabolic rate between 12 and 16° C. Absolute prolonged swimming speed (cm s⁻¹) increased rapidly with fish size (total length, L _T, and mass), however, fish in the natural stream habitat occupied current velocities between 15 and 25 cm s⁻¹ or 4  L _T s⁻¹, approximately half their potential prolonged swimming speed (10  L _T s⁻¹).     

Effect of temperature on swimming performance of sea bass juveniles

At four temperatures ( T= 15, 20, 25 and 28° C) swimming performance of Dicentrarchus labrax was significantly correlated with total length (23–43 mm L _T); r²=0.623–0.829). The relative critical swimming speed ( RU _crit= U _crit L _T⁻¹), where U _crit is the critical swimming speed, was constant throughout the L _T range studied. The significant effect of temperature on the relative critical swimming speed was described binomially: RU _crit=−0.0323T²+ 1.578 T −10.588 (r²=1). The estimated maximum RU _crit (8.69 L _T s⁻¹) was achieved at 24.4° C, and the 90% performance level was estimated between 19.3 and 29.6° C.     

Endurance swimming of European eel

A long‐term swim trial was performed with five female silver eels Anguilla anguilla of 0·8–1·0 kg ( c . 80 cm total length, L _T) swimming at 0·5 body lengths (BL) s⁻¹, corresponding to the mean swimming speed during spawning migration. The design of the Blazka‐type swim tunnel was significantly improved, and for the first time the flow pattern of a swim tunnel for fish was evaluated with the Laser‐Doppler method. The velocity profile over three different cross‐sections was determined. It was observed that 80% of the water velocity drop‐off occurred over a boundary layer of 20 mm. Therefore, swim velocity errors were negligible as the eels always swam outside this layer. The fish were able to swim continuously day and night during a period of 3 months in the swim tunnel through which fresh water at 19° C was passed. The oxygen consumption rates remained stable at 36·9 ± 2·9 mg O₂ kg⁻¹ h⁻¹ over the 3 months swimming period for all tested eels. The mean cost of transportation was 28·2 mg O₂ kg⁻¹ km⁻¹. From the total energy consumption the calculated decline in fat content was 30%. When extrapolating to 6000 km this would have been 60%, leaving only 40% of the total energy reserves for reproduction after arriving at the spawning site. Therefore low cost of transport combined with high fat content are crucial for the capacity of the eel to cross the Atlantic Ocean and reproduce.     

Tilting behaviour of the Atlantic mackerel, Scomber scombrus, at low swimming speeds

Negatively-buoyant Atlantic mackerel, Scomber scombrus L., (fork length 30–39 cm) tilt their bodies with the head up while swimming at speeds below 0.8 body length per second (B.L. s⁻¹). This behaviour is quantitatively described by the body attack angle and swimming speed measured from film records. The maximum recorded body attack angle was 27° in a 32 cm-long fish swimming at 0.45 B.L. s⁻¹ while its nose followed a course close to the horizontal. In general, larger body attack angles were shown at lower swimming speeds and were associated with denser bodies at each speed. We consider that this behaviour pattern allows the fish to maintain a chosen swimming depth while its body creates lift by acting as a hydrofoil. Lift from the fins is insufficient at low swimming speeds.     

The effect of external dummy transmitters on oxygen consumption and performance of swimming Atlantic cod

Decreased critical swimming speed and increased oxygen consumption (     ) was found for externally tagged Atlantic cod Gadus morhua swimming at a high speed of 0·9 body length (total length, L _T) s⁻¹. No difference was found in the standard metabolic rate, indicating that the higher     for tagged cod was due to drag force rather than increased costs to keep buoyancy.     

Anaemia and salmonid swimming performance: the potential effects of sub‐lethal sea lice infection

The effect of two known rates of repeated blood loss on rainbow trout Oncorhynchus mykiss swimming performance was measured and blood‐feeding rates of sea lice Lepeophtheirus salmonis were calculated to predict the point at which blood ingestion causes anaemia in infected fish. Known quantities of blood were sampled from rainbow trout over a 5 day period followed by critical swimming performance ( U _crit) testing. A predictive equation was developed using masses of blood‐feeding sea lice and host blood loss calculated for increasing levels of sea lice infection. Blood loss of 8% total blood volume caused a decrease in U _crit for rainbow trout. Total blood volume losses of 3·2% reduced erythrocyte stores, but did not affect fish swimming performance. The predictive feeding rate model suggests that 15–25% of the tissue consumed by sea lice is blood. This consumption of blood at higher sub‐lethal infection levels (≥0·5 sea lice g⁻¹) may cause anaemia and a further decrease in swimming performance. Anaemia would compound the osmotic balance problems due to infection and potentially precipitate the morbidity seen at lethal sea lice levels (0·75–1·0 lice g⁻¹).     

Effects of the brain parasite Myxobolus arcticus on sockeye salmon

Parasitism with Myxobolus arcticus did not affect smolt size of sockeye salmon or their osmocompetence, but had a deleterious effect ( P <0.001) on the swimming speed of naturally infected smolts. Parasitized fish had a mean swimming speed of 2.89 fork length s⁻¹ (L_F s⁻¹) compared with 4.37 L _F s⁻¹ for unparasitized fish. The parasite probably impairs swimming ability by affecting the central nervous system, but this effect does not appear severe enough to limit the parasite's usefulness in stock separation.     

Diet of brown trout in relation to variation in abundance and size of pelagic fish prey

The seasonal diet of a predator, brown trout Salmo trutta [total length ( L _T) 17–69 cm] and simultaneous density and size‐structure of prey populations, vendace Coregonus albula and smelt Osmerus eperlanus (4–16 cm L _T), in a large boreal lake were analysed and compared in 2001 and 2002. The upper L _T limit for consumed prey was c . 40% of the predator L _T. All brown trout, however, preferred small (<10 cm L _T) and avoided large (≥10 cm L _T) prey. The results also suggested that equal densities of similar‐sized (4–10 cm L _T) fish of the two prey species led to random foraging on these species by brown trout, but if either one of the prey species predominated (>50%) in the lake, brown trout shifted to foraging on this species almost exclusively. Brown trout diets thus reflected the density dynamics of the two alternative prey species.     

Gait transition and oxygen consumption in swimming striped surfperch Embiotoca lateralis Agassiz

A flow-through respirometer and swim tunnel was used to estimate the gait transition speed ( U _p-c) of striped surfperch Embiotoca lateralis , a labriform swimmer, and to investigate metabolic costs associated with gait transition. The U _p-c was defined as the lowest speed at which fish decrease the use of pectoral fins significantly. While the tail was first recruited for manoeuvring at relatively low swimming speeds, the use of the tail at these low speeds [as low as 0·75 body (fork) lengths s⁻¹, L _F s⁻¹) was rare (<10% of the total time). Tail movements at these low speeds appeared to be associated with occasional slow manoeuvres rather than providing power. As speed was increased beyond U _p-c, pectoral fin (PF) frequencies kept increasing when the tail was not used, while they did not when PF locomotion was aided by the tail. At these high speeds, the tail was employed for 40–50% of the time, either in addition to pectoral fins or during burst-and-coast mode. Oxygen consumption increased exponentially with swimming speeds up to gait transition, and then levelled off. Similarly, cost of transport ( C _T) decreased with increasing speed, and then levelled off near U _p-c. When speeds ≥ U _p-c are considered, C _T is higher than the theoretical curve extrapolated for PF swimming, suggesting that PF swimming appears to be higher energetically less costly than undulatory swimming using the tail.     

The muscle twitch and the maximum swimming speed of giant bluefin tuna, Thunnus thynnus L.

Sustained swimming of bluefin tuna was analysed from video recordings made of a captive patrolling fish school [lengths (L) 1.7–3.3 m, body mass (M) 54–433 kg]. Speeds ranged from 0.6 to 1.2 L s⁻¹ (86–260 km day⁻¹) while stride length during steady speed swimming varied between 0.54 and 0.93 L. Maximum swimming speed was estimated by measuring twitch contraction of the anaerobic swimming muscle in pithed fish 5 min after death. Muscle contraction time increased from the shortest just behind the head (30–50 ms at 20% L) to the longest at the tail peduncle (80–90 ms at 80% L) (all at 28°C). A fish (L = 2.26 m) with a muscle contraction time of 50 ms at 25% L can have a maximum tail beat frequency of 10 Hz and maximum swimming speed of 15m s⁻¹ (54km h⁻¹) with a stride length of 0.65L. With a stride length of 1 L a speed of 22.6 m s⁻¹ (81.4 km h⁻¹) is possible. Power used at maximum speed was estimated for this fish at between 10 and 40 kW, with corresponding values for the drag coefficient at a Reynolds number of 4.43 × 10⁷ of 0.0007 and 0.0027.     

Is tilting behaviour at low swimming speeds unique to negatively buoyant fish? Observations on steelhead trout,Oncorhynchus mykiss,and bluegill,Lepomis macrochirus

When swimming at low speeds, steelhead trout and bluegill sunfish tilted the body at an angle to the mean swimming direction. Trout swam using continuous body/caudal fin undulation, with a positive (head-up) tilt angle ( 0 , degrees) that decreased with swimming speed ( u , cm s⁻¹) according to: 0 =(164±96).u^{(−1.14±0.41)} (regression coefficients; mean±2 s.e. ). Bluegill swimming gaits were more diverse and negative (head down) tilt angles were usual. Tilt angle was −3·0 ± 0.9° in pectoral fin swimming at speeds of approximately 0.2–1.7 body length s⁻¹ (Ls⁻¹; 3–24 cm s⁻¹), −4.5 ±2.6° during pectoral fin plus body/caudal fin swimming at 1·2–1·7 L s⁻¹ (17–24cm s⁻¹), and −5.0± 1.0° during continuous body/caudal fin swimming at 1.6 and 2.5 L s⁻¹ (22 and 35cm s⁻¹). At higher speeds, bluegill used burst-and-coast swimming for which the tilt angle was 0.1±0.6°. These observations suggest that tilting is a general phenomenon of low speed swimming at which stabilizers lose their effectiveness. Tilting is interpreted as an active compensatory mechanism associated with increased drag and concomitant increased propulsor velocities to provide better stabilizing forces. Increased drag associated with trimming also explains the well-known observation that the relationship between tail-beat frequency and swimming speed does not pass through the origin. Energy dissipated because of the drag increases at low swimming speeds is presumably smaller than that which would occur with unstable swimming.     

The swimming endurance of threespine sticklebacks, Gasterosteus aculeatus L., from the Afon Rheidol, Wales

The endurance of threespine sticklebacks, Gasterosteus aculeatus , swimming with pectoral fin locomotion at 20° C in a laboratory flume was measured. Each trial lasted a maximum of 480 min. At a speed of 4 body lengths per sec (L s⁻¹) all fish were still swimming at the end of the trial, but endurance decreased at higher speeds. At speeds of 5 or 6 L s⁻¹ (20–30 cm s⁻¹) a few fish still maintained labriform locomotion for the 480 min. However, at a speed of 7 L s⁻¹ all fish furled their pectoral fins and used body and caudal fin propulsion but fatigued rapidly. During sustained swimming, fish could cover distances of 6 km or more. No significant differences between males and females were found.     

Endurance swimming of diploid and triploid Atlantic salmon

When groups of diploid (mean ±  s . e . fork length, L _F) 33·0 ± 1·4 cm and triploid (35·3 ± 0·5 cm) Atlantic salmon Salmo salar were forced to swim at controlled speeds in a carefully monitored 10 m diameter 'annular' tank no significant difference was found between the maximum sustained swimming speeds ( U _ms, maintainable for 200 min) where the fish swam at the limit of their aerobic capability. Diploids achieved 2·99 body lengths per second (bl s⁻¹)(0·96 m s⁻¹) and triploids sustained 2·91 bl s⁻¹(1·02 m s⁻¹). The selection of fish for the trials was based on their ability to swim with a moving pattern projected from a gantry rotating at the radius of the tank and the selection procedure did not prove to be significant by ploidy. A significant difference was found between the anaerobic capabilities of the fish measured as endurance times at their prolonged swimming speeds. During the course of the experimentation the voluntary swimming speed selected by the fish increased and the schooling behaviour improved. The effect of the curvature of the tank on the fish speeds was calculated (removing the curved effect of the tank increased the speed in either ploidy by 5·5%). Implications of the endurance times and speeds are discussed with reference to the aquaculture of triploid Atlantic salmon.     

The effect of temperature and acclimation period on repeat swimming performance in cutthroat trout

Hatchery cutthroat trout Oncorhynchus clarki clarki were used to examine the effects of 48 h and 3 week temperature acclimation periods on critical swimming speed ( U _crit). The U _crit was determined for fish at acclimation temperatures of 7, 14 and 18° C using two consecutive ramp‐ U _crit tests in mobile Brett‐type swim tunnels. An additional group was tested at the stock's ambient rearing temperature of 10° C. The length of the temperature acclimation period had no significant effect on either the first or the second U _crit( U _crit‐1 and U _crit‐2, respectively) or on the recovery ratio (the quotient of U _crit‐2  U _crit‐1⁻¹). As anticipated, there was a significant positive relationship between U _crit‐1 and temperature ( P  < 0·01) for both acclimation periods, and an increasing, though non‐significant, trend between U _crit‐2 and temperature ( P  = 0·10). Acclimation temperature had no significant effect ( P  = 0·71) on the recovery ratio. These results indicate that a 48 h acclimation to experimental temperatures within the range of −3 to +8° C of the acclimation temperature may be sufficient in studies of swimming performance with this species. This ability to acclimate rapidly is probably adaptive for cutthroat trout and other species that occupy thermally variable environments.     

Effect of rearing density on thyroid and interrenal gland activity and plasma and hepatic metabolite levels in rainbow trout, Salmo gairdneri Richardson

There were significant inverse correlations between rearing density of rainbow trout, Salmo gairdneri Richardson, and final body weight, plasma L-thyroxine (T₄), trüodo-L-tryronine (T₃), cortisol and protein concentrations, plasma T₄/T₃ ratios and thyroid epithelial cell height. In addition, hepatosomatic indices and plasma free fatty acid concentrations were higher in fish reared at low (134 g 1⁻¹) density compared with groups reared at medium (210g1⁻¹) or high density (299g 1⁻¹), and the post-feeding (3.5-4h) elevation in plasma glucose and triglyceride levels evident in trout maintained at low rearing density was not found in those fish reared at higher densities. There were no significant effects of rearing density on hematocrit, carcass composition, hepatic glycogen and lipid levels and interregnal nucleus size.     

Short‐term freshwater exposure benefits sea lice‐infected Atlantic salmon

Atlantic salmon Salmo salar were infected with sea lice Lepeophtheirus salmonis (0·08 ± 0·007 sea lice g⁻¹) over a period of 4 h. Both infected and non‐infected fish were swim tested in sea water (SW) and fresh water (FW). The ventral aorta of each fish was fitted with a Doppler cuff in order to measure cardiac output, stroke volume and heart rate during swim testing. Blood samples were taken at rest and after exercise. Critical swimming speed of infected fish in SW (2·14 ± 0·08 body lengths, bl s⁻¹) was significantly lower ( P  < 0·05) than infected fish switched to FW (2·81 ± 0·08 bl s⁻¹) and non‐infected fish in SW (2·42 ± 0·04 bl s⁻¹) and FW (2·61 ± 0·08 bl s⁻¹). Cardiac and blood results indicated infected fish exposed to FW did experience stress, but relief from osmotic and ionic distress probably reduces energy expenditure, allowing the increase in performance. As the performance of sea lice‐infected fish improved upon transfer to FW, it is likely that heavily infected salmonids do return to FW to restore compromised osmotic and ionic balance, and remove sea lice in the process.     

Swimming performance of European eel (Anguilla anguilla (L.)) elvers

To determine the relation between swimming endurance time and burst swimming speed, elvers of the European eel, Anguilla anguilla (L.), were made to swim at speeds from 3.6 to 7.2 L (body lengths) s⁻¹ in both fresh and sea water. Swimming endurance time of elvers averaging 7.2 cm total length decreased logarithmically with increased swimming speed from 3.0 min at 3.5 L s⁻¹ to 0.7 min at 5.0 L s⁻¹, and again logarithmically but with a lesser slope to 0.27 min at 7.5 L s⁻¹. No differences were found between fresh and sea water elvers. In still water, elvers could swim at high speeds for about 10–45m before exhaustion, depending upon speed. Elvers would be able to make virtually no progress against water currents >50 cm s⁻¹. Drift in coastal water currents and selective tidal transport probably involve swimming speeds below those tested in this study. Migration into freshwater streams undoubtedly involves avoidance of free stream speeds and a combination of burst and sustained swimming.     

Influence of spawning on swimming performance and muscle contractile properties in the short-horn sculpin

The total distance travelled during the first two kinematic stages of the escape response of short-horn sculpin was significantly greater in post spawning fish (0·41 L) than in gravid fish (0·23 L). The maximum velocity of the snout during the C-bend was significantly higher (5·6 L s⁻¹) in postspawning fish than in gravid fish (3·8 L s⁻¹). To investigate some of the mechanisms underlying changes in swimming performance, the contractile properties of fast muscle fibres were determined in fish of similar body length. The rate of tetanic force relaxation (time from last stimulus to 50% peak force) was 34% faster in gr avid than in postspawning fish. Maximum contraction velocity, determined by the slack-test method, was significantly higher in gravid than in postspawning fish (6·8 v . 5·9 muscle lengths s⁻¹). In contrast, both maximum isometric stress and power output (determined from the force–velocity relationship) were >50% higher in fibres from postspawning than from gravid fish, even though myofibrillar protein and water contents were similar (120 mg g⁻¹ wet mass and 86% of body mass, respectively). The results show that swimming performance and the contractile properties of fast muscle fibres vary with the reproductive cycle in short-horn sculpin acclimated to the same photoperiodic and temperature regime.     

Cardiorespiratory status of triploid brown trout during swimming at two acclimation temperatures

At 14° C, standard metabolic rate (75·1 mg O₂ h⁻¹ kg⁻¹), routine metabolic rate (108.8 mg O₂ h⁻¹ kg⁻¹), active metabolic rate ( c . 380 mg O₂ h⁻¹ kg⁻¹), critical swimming speed (U_crit 1·7 BL s⁻¹), heart rate 47 min⁻¹), dorsal aortic pressure (3·2 kPa) and ventilation frequency (63 min⁻¹) for triploid brown trout Salmo trutta were within the ranges reported for diploid brown trout and other salmonids at the same temperature. During prolonged swimming ( c . 80% U _crit), cardiac output increased by 2·3-fold due to increases in heart rate (1·8-fold) and stroke volume (1·2-fold). At 18° C, although standard and routine metabolic rates, as well as resting heart rate and ventilation frequency increased significantly, active metabolic rate and certain cardiorespiratory variables during exercise did not differ from those values for fish acclimated to 14° C. As a result, factorial metabolic scope was reduced (2·93-fold at 18° C v . 5·13-fold at 14° C). Therefore, it is concluded that cardiorespiratory performance in triploid brown trout was not unusual at 18° C, but that reduced factorial metabolic scope may be a contributing factor to the mortality observed in triploid brown trout at temperatures near 18° C.