Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Effects of surgically implanted acoustic transmitters >2% of body mass on the swimming performance, survival and growth of juvenile sockeye and Chinook salmon

The influence of surgical implantation of an acoustic transmitter on the swimming performance, growth and survival of juvenile sockeye salmon Oncorhynchus nerka and Chinook salmon Oncorhynchus tshawytscha was examined. The transmitter had a mass of 0·7 g in air while sockeye salmon had a mass of 7·0–16·0 g and Chinook salmon had a mass of 6·7–23·1 g (a transmitter burden of 4·5–10·3% for sockeye salmon and 3·1–10·7% for Chinook salmon). Mean critical swimming speeds (U_crit) for Chinook salmon ranged from 47·5 to 51·2 cm s^?1 [4·34–4·69 body lengths (fork length, L_F) s^?1] and did not differ among tagged, untagged and sham‐tagged groups. Tagged sockeye salmon, however, did have lower U_crit than control or sham fish. The mean U_crit for tagged sockeye salmon was 46·1 cm s^?1 (4·1 L_F s^?1), which was c. 5% less than the mean U_crit for control and sham fish (both groups were 48·6 cm s^?1 or 4·3 L_F s^?1). A laboratory evaluation determined that there was no difference in L_F or mass among treatments (control, sham or tag) either at the start or at the end of the test period, suggesting that implantation did not negatively influence the growth of either species. None of the sockeye salmon held under laboratory conditions died from the influence of surgical implantation of transmitters. In contrast, this study found that the 21 day survival differed between tagged and control groups of Chinook salmon, although this result may have been confounded by the poor health of Chinook salmon treatment groups.     

Critical swimming speeds of wild‐caught sand‐smelt Atherina presbyter larvae

Swimming abilities of wild‐caught sand‐smelt Atherina presbyter larvae were assessed as critical swimming speed (U_crit) throughout ontogeny. The mean U_crit increased with size, ranging from 3·6 to 18·7 cm s^?1, over the size range of 6·6–21·0 mm L_T. This indicates that at hatching A. presbyter larvae, far from being passive floaters, are already capable of active behaviours, which may influence their dispersal patterns.     

Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O₂ h^?1 at 30 cm s^?1 (c. 0·5 BL s^?1) to 3347 mg O₂ h^?1 at 170 cm s^?1 (c. 2·3 BL s^?1). Corrected for fish mass, these values ranged from 122 to 670 mg O₂ kg^?1 h^?1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s^?1, and a third‐order polynomial regression model fitted the data best. The upper critical swim speed (U_crit) of fish tested at two laboratories averaged 155 cm s^?1 (2·1 BL s^?1), but U_crit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s^?1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s^?1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s^?1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the U_crit for the fish used in the EMG trials (mean U_crit 168·2 cm s^?1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ≥80% of the U_crit.     

Swimming performance and associated ionic disturbance of juvenile pink salmon Oncorhynchus gorbuscha determined using different acceleration profiles

Swimming performance was assessed in juvenile pink salmon Oncorhynchus gorbuscha (body mass <5·0 g) using five different protocols: four constant acceleration tests each with a different acceleration profile (rates of 0·005, 0·011, 0·021 and 0·053 cm s^?2) and a repeated ramped‐critical swimming speed test. Regardless of the swim protocol, the final swimming speeds did not differ significantly (P > 0·05) among swim tests and ranged from 4·54 to 5·20 body lengths s^?1. This result supports the hypothesis that at an early life stage, O. gorbuscha display the same fatigue speeds independent of the swimming test utilized. Whole body and plasma [Na⁺] and [Cl^?] measured at the conclusion of these tests were significantly elevated when compared with control values (P < 0·05) and appear to be predominantly associated with dehydration rather than net ion gain. Given this finding for a small salmonid, estimates of swim performance can be accurately measured with acceleration tests lasting <10 min, allowing a more rapid processing than is possible with a longer critical swim speed test.     

The critical swimming speed of Iberian barbel Barbus bocagei in relation to size and sex

The swimming capacity of Barbus bocagei was measured with the critical swimming speed (U_crit) standard test in a modified Bla?ka‐type swim tunnel. Sixty B. bocagei were tested and they exhibited a mean ±s .d . U_crit of 0·81 ± 0·11 m s^?1 or 3·1 ± 0·86 total lengths per second (L_T s^?1). Sex had no effect on U_crit but significant differences were found between the swimming performance of fish with distinct sizes.     

Effects of age and size on critical swimming speed of juvenile Chinese sturgeon Acipenser sinensis at seasonal temperatures

Changes in the critical swimming speed (U_crit, cm s^?1) with ontogeny of 2·5–12·5 month‐old juvenile anadromous Chinese sturgeon Acipenser sinesis were measured in a modified Blazka‐type swimming tunnel. The absolute U_crit increased with length, mass and age; the relative U^′_crit (body lengths, s^?1), however, decreased. Juvenile A. sinesis did not display a parr–smolt transformation at the length or age threshold to tolerate full‐strength seawater.     

Diel vertical migrations of bathypelagic perch fry

The behaviour of young‐of‐the‐year (YOY) perch Perca fluviatilis as a dominant species in the assemblage of fry in the pelagic of Slapy Reservoir (Czech Republic), was studied during late May and mid‐June 2002 using acoustic methods and complementary net catches. During the day, perch fry were present simultaneously in littoral, epipelagic and bathypelagic habitats. Bathypelagic perch fry, forming a scattering layer, migrated vertically each day between the epilimnion and hypolimnion, with an amplitude of 11·0 m in May and 12·5 m in June. At dusk, the migratory bathypelagic fry mixed in the epilimnion with non‐migrating epipelagic fry and spent the night close to the thermocline (abundance maximum at 3–4 m in May, 0–2 m in June). In June, shoaling behaviour by some of the bathypelagic perch fry was also observed: the shoaling fry remained higher in the water column than the non‐shoaling fry. Both depths of the scattering layer and the depths of the fry shoals were strongly controlled by the light intensity. The contribution of the bathypelagic part of the population to the total numbers of pelagic perch fry decreased from 28·1% in May to 4·7% in June, while the density of all pelagic perch fry increased (c. 96 000 individuals ha^?1 in May and 142 000 individuals ha^?1 in June). In May, the bathypelagic (average total length, L_T, 11·9 mm) and epipelagic (average L_T 14·6 mm) perch fry differed in size while, in June, the epipelagic fry were divided into two distinct size groups. The more abundant group, of small epipelagic perch fry (average L_T 14·6 mm), was similar in size to the bathypelagic fry (average L_T 14·6 mm) while the less abundant group, of larger epipelagic fry (average L_T 34·4 mm), was similar in size to littoral perch fry (average L_T 35·0 mm). The results suggest that in perch fry three different survival strategies with different risks can be used in the same locality, time and year.     

The effects of temperature on swimming performance of juvenile shortnose sturgeon (Acipenser brevirostrum)

The swimming performance of juvenile shortnose sturgeon (～16 cm TL, ～20 g), Acipenser brevirostrum, was quantified with regards to temperature (5 to 25°C) using both increased (U_crit) and fixed velocity (endurance) tests in a laboratory setting. Sturgeons were found to show reduced U_crit values at 5 and 10°C (25.99 and 28.86 cm s^?1 respectively), with performance beginning to plateau at 15°C through 25°C (33.99 cm s^?1). For the endurance protocol, fish were tested at speeds of 35, 40 and 45 cm s^?1 at 5, 15 and 25°C. Performance within a single speed was similar at all temperatures, indicating the usage of anaerobic metabolism to fuel locomotion at these higher velocities. Overall, shortnose sturgeon demonstrated high tolerance towards a wide range of temperatures but showed few differences between performance levels at colder or warmer water conditions.     

Temporal patterns of growth in larval cohorts of the Japanese sardine Sardinops melanostictus in a coastal nursery area

Growth patterns of larval sardine Sardinops melanostictus were studied in a coastal nursery area, in southern Japan for four monthly hatch cohorts of larvae (November, December, January and February) for the 2003–2004 and 2004–2005 seasons. Laird–Gompertz models were fitted to each cohort using both total length (L_T)‐at‐age at capture and mean L_T‐at‐age data derived from backcalculations. In both approaches, the absolute daily growth rates (G_R) and absolute daily growth rates at the inflection point (G_XO) were estimated. In parallel, individual growth rates (G_I) were derived from backcalculated L_T (L_B). Growth showed the following general common patterns irrespective of hatch month, season and methods: (1) significant Laird–Gompertz fits, (2) asymptotic growth, (3) a decrease in G_R after the inflexion point, except for February for the 2003–2004 season that showed an apparent constant growth pattern, (4) six in eight cohorts showed G_XO ranging from 0·8 to 1·2 mm day^?1 and (5) a decreasing tendency of G_I from 1·75 to 0·24 mm day^?1, from first feeding through the first month of larval life. The contrasting pattern between the 2003–2004 and the 2004–2005 seasons were: (1) allometric v. logarithmic (ln) L_T and otolith radius relationships, (2) low G_XOv. high G_XO, (3) high G_Rv. low G_R when growth turned asymptotic, (4) low G_XOv. high G_XO when monthly hatch cohorts were combined and (5) L_B and G_I not differing among monthly hatch cohorts. The differences in growth patterns and growth rates between seasons seemed to be linked to the influx of warmer and oligotrophic waters of the Kuroshio Current that triggered an increase of 3° C in the coastal area for the 2003–2004 seasons. In the overall context, however, the high G_XO, within cohorts and seasons reported in the current study, suggests that either sea surface temperature (SST) or food availability, or both are in the optimal range of preferences for S. melanostictus larvae. Consequently, nearshore coastal areas seem to be playing an important role as a nursery area for the larval stage of this species.     

Stem water storage capacity and efficiency of water transport: their functional significance in a Hawaiian dry forest

We investigated the contribution of internal water storage and efficiency of water transport to the maintenance of water balance in six evergreen tree species in a Hawaiian dry forest. Wood‐saturated water content, a surrogate for relative water storage capacity, ranged from 70 to 105%, and was inversely related to its morphological correlate, wood density, which ranged between 0·51 and 0·65 g cm^?3. Leaf‐specific conductivity (k_L) measured in stem segments from terminal branches ranged from 3 to 18 mmol m^?1 s^?1 MPa^?1, and whole‐plant hydraulic efficiency calculated as stomatal conductance (g) divided by the difference between predawn and midday leaf water potential (Ψ_L), ranged from 70 to 150 mmol m^?2 s^?1 MPa^?1. Hydraulic efficiency was positively correlated with k_L (r² = 0·86). Minimum annual Ψ_L ranged from ? 1·5 to ? 4·1 MPa among the six species. Seasonal and diurnal variation in Ψ_L were associated with differences among species in wood‐saturated water content, wood density and k_L. The species with higher wood‐saturated water content were more efficient in terms of long‐distance water transport, exhibited smaller diurnal variation in Ψ_L and higher maximum photosynthetic rates. Smaller diurnal variation in Ψ_L in species with higher wood‐saturated water content, k_L and hydraulic efficiency was not associated with stomatal restriction of transpiration when soil water deficit was moderate, but avoidance of low minimum seasonal Ψ_L in these species was associated with a substantial seasonal decline in g. Low seasonal minimum Ψ_L in species with low k_L, hydraulic efficiency, and wood‐saturated water content was associated with higher leaf solute content and corresponding lower leaf turgor loss point. Despite the species‐specific differences in leaf water relations characteristics, all six evergreen tree species shared a common functional relationship defined primarily by k_L and stem water storage capacity.     

Measurements of aerobic metabolism of a school of horse mackerel at different swimming speeds

Oxygen consumption rates were measured in a school of 56 horse mackerel Trachurus trachurus while at rest and while swimming at steady sustained speeds. Resting values of 38.76 and 42.10mg O₂ kg^?1 h^?1 were measured in a sealed cylindrical tank (535 l) while observing that the fish school remained neutrally buoyant and inactive with only gentle pectoral fin movements and no swimming motion. The same school was trained to swim with projected light patterns within a 10-m diameter annular doughnut respirometer. The oxygen consumption increased from the resting level through 51 mg O₂ kg^?1 h^?1 at the slowest swimming speeds of 0.29 m s^?1 (0.95 L s^?1) to around 259 mg O₂ kg^?1 h^?1 at the higher measured swimming speed of 0.87 m s^?1 (2.82 L s^?1). The data fitted a curve where oxygen consumption rose in proportion to velocity to the power of 2.56 with the intercept at the resting level. The maximum sustained speed (80 min) of 1.12 m s^?1 (3.63 Ls^?1) was not achieved within the respirometer but corresponded to an estimated oxygen consumption of 458.33 mg O₂ kg^?1 h^?1 giving a scope for aerobic activity of 419.02 mg O₂ kg^?1 h^?1. At a speed of 0.87 m s^?1, there was a lower bound on the aerobic efficiency of at least 38% and at 1.12 m s^?1, the highest aerobic speed, of 40%. Sustained speeds swum in a curved path as here should be increased by 5% for a straight path giving a maximum sustained 80 min speed of 1.18 m s^?1.     

Pelagic to demersal transition in a coral‐reef fish,the orbicular batfish Platax orbicularis

Behavioural and ecological observations were made on young, reared Platax orbicularis in Opunohu Bay, Moorea, French Polynesia, during their transition from the pelagic, dispersive stage to the reef‐orientated demersal stage. Seventy‐two young P. orbicularis (17–75 mm standard length, L_S) were released in the pelagic zone and 20 (40–70 mm L_S) adjacent to the reefs. Swimming speed was slow (mean 5·2 cm s^?1) and independent of size. An ontogenetic descent was observed: the smallest P. orbicularis swam at the surface, medium‐sized P. orbicularis swam in midwater (mean 5–13 m) and the largest P. orbicularis swam to the bottom, where many lay on their sides. Platax orbicularis swam southerly on average, away from the ocean and into the bay. Smaller P. orbicularis were more likely to swim directionally than larger individuals. Young P. orbicularis released near reef edges swam at similar, but more variable speeds (mean 6·6 cm s^?1). About half of those released near reefs swam away, but fewer swam away from an inshore fringing reef than from a patch reef near the bay mouth. Many P. orbicularis swam up the slope onto the reef top, but the little settlement observed was near the reef base. Average, near‐reef swimming direction was also southerly. Some reef residents, in particular the triggerfish Balistapus undulatus, harassed young P. orbicularis.     

Relationship between swimming capacities and morphological traits of fish larvae at settlement stage: a study of several coastal Mediterranean species

Experimental measurements were made in the laboratory to determine the swimming capacities of settlement-stage fish larvae of several Mediterranean coastal species collected from the nearshore waters of Corsica, France. Critical swimming speed (U_crit, cm s⁻¹) was measured to provide a realistic laboratory estimate of in situ swimming speed. Morphometric traits were measured to assess potential predictors of a species’ swimming ability and, when possible, daily otolith increments were used to estimate age. Observed swimming speeds were consistent with other temperate species and demonstrated that the tested species are competent swimmers and not passive components of their environment. Morphological traits varied in their correlation with U_crit across groups and species. Direct measurements of morphological traits were better predictors than calculated ratios. Pelagic larval duration had little relationship with swimming speed among species for which daily otolith increments were counted. In addition to expanding the database on swimming capacities of settlement-stage fish larvae in the Mediterranean Sea, this study also developed methods that simplify the assessment of larval fish swimming ability. Swimming speed data are essential for improving larval dispersal models and for predicting recruitment rates in coastal fish populations.     

Behavior of red king crab larvae: Phototaxis,geotaxis and rheotaxis

Zoeae of Paralithodes camtschatica were positively phototactic to white light intensities above 1 × 10¹³ q cm^?2 s^?1. Negative phototaxis occurred at low (1 × 10¹² q cm^?2 s^?1), but not high intensities (2.2 × 10¹⁶q cm^?2 s^?1). Phototactic response was directly related to light intensity. Zoeae also responded to red, green and blue light. Zoeae were negatively geotactic, but geotaxis was dominated by phototaxis. Horizontal swimming speed of stage 1 zoeae <4 d old was 2.4 ± 0.1 (SE) cms^?1 and decreased to 1.7 ± 0.1 cm s^?1 in older zoeae (P <0.01). Horizontal swimming speed of stage 2 zoeae was not significantly different from ≥4 d old stage 1 zoeae. Vertical swimming speed, 1.6 ± 0.1 cm s^?1, and sinking rate, 0.7 ± 0.1 cm s^?1, did not change with ontogeny. King crab zoeae were positively rheotactic and maintained position in horizontal currents less than 1.4 cm s^?1. Starvation reduced swimming and sinking rates and phototactic response.     

Interaction between migration behaviour and estuarine mortality in cultivated Atlantic salmon Salmo salar smolts

Migration behaviour and estuarine mortality of cultivated Atlantic salmon Salmo salar smolts in a 16 km long estuary were studied using two methods: (1) acoustic telemetry and (2) group tagging in combination with trap nets. Progression rates of surviving individuals through the estuary were relatively slow using both methods [0·38 L_T (total length) s^?1 v. 0·25 L_T s^?1]. In 2012, the progression rate was slow from the river to the estuary (0·55 L_T s^?1) and the first part of the estuary (0·31 L_T s^?1), but increased thereafter (1·45–2·21 L_T s^?1). In 2013, the progression rate was fast from the river to the estuary (4·31 L_T s^?1) but was slower thereafter (0·18–0·91 L_T s^?1). Survival to the fjord was higher in 2012 (47%) compared to 2013 (6%). Fast moving individuals were more likely to migrate successfully through the estuary compared to slower moving individuals. Adult recapture of coded‐wire‐tagged S. salar was generally low (0·00–0·04%). Mortality hot spots were related to topographically distinct areas such as the river outlet (in 2012) or the sill separating the estuary and the fjord (in 2013). At the sill, an aggregation of cod Gadus morhua predating on cultivated smolts was identified. The results indicate that slow progression rates through the estuary decreases the likelihood of smolts being detected outside the estuary. The highly stochastic and site‐specific mortality patterns observed in this study highlight the complexity in extrapolating mortality patterns of single release groups to the entire smolt run of wild S. salar.     

Comparison of fin ray sampling methods on white sturgeon Acipenser transmontanus growth and swimming performance

Effects of two fin‐ray sampling methods on swimming performance, growth and survival were evaluated for hatchery‐reared sub‐adult white sturgeon Acipenser transmontanus. Fish were subjected to either a notch removal treatment in which a small section was removed from an anterior marginal pectoral‐fin ray, or a full removal treatment in which an entire marginal pectoral‐fin ray was removed. Control fish did not have fin rays removed, but they were subjected to a sham operation. A modified 3230 l Brett‐type swim tunnel was used to evaluate 10 min critical station‐holding speeds (S_CSH) of A. transmontanus, immediately after the fin ray biopsies were obtained with each method. Survival and growth were evaluated over a 6 month period for a separate group of fish subjected to the same biopsy methods. Mean ± s.e . 10 min S_CSH were 108·0 ± 2·3, 110·0 ± 2·6 and 115·0 ± 3·5 cm s^?1 for the notch removal group, full removal group and control group, respectively, and were not significantly different among treatments. Behavioural characteristics including tail‐beat frequency and time spent hunkering were also not significantly different among treatment groups swimming at the same speeds. There were no mortalities and relative growth was similar among treatment groups. Average biopsy time for the notch removal method was lower and the wounds appeared to heal more quickly compared with the full removal method.     

Comparative movements of four large fish species in a lowland river

A multi‐year radio‐telemetry data set was used to comparatively examine the concurrent movements of the adults of three large‐bodied Australian native freshwater fishes (Murray cod Maccullochella peelii, trout cod Maccullochella macquariensis and golden perch Macquaria ambigua) and the introduced carp Cyprinus carpio. The study was conducted over a reach scale in the regulated Murray River in south‐eastern Australia. Differences were identified in the movements among these species. The predominant behaviour was the use of small movements (<1 km) for all species, and although larger‐scale movements (>1 km) did occur, the frequency varied considerably among species. Large‐scale movements were least evident for M. macquariensis and more common for M. ambigua and C. carpio with these two species also having a greater propensity to change locations. Macquaria ambigua displayed the largest movements and more M. ambigua moved on a ‘continual’ basis. Although a degree of site fidelity was evident for all species, the highest levels were exhibited by M. macquariensis and M. peelii. Homing was also evident to some degree in all species, but was greatest for M. peelii.     

VOLVOX BARBERI,THE FASTEST SWIMMER OF THE VOLVOCALES (CHLOROPHYCEAE)1

Volvox barberi W. Shaw is a volvocalean green alga composed of biflagellated cells. Vovocales with 16 cells or more form spherical colonies, and their largest members have germ‐soma separation (all species in the genus Volvox). V. barberi is the largest Volvox species recorded in terms of cell number (10,000–50,000 cells) and has the highest somatic to reproductive cell ratio (S/R). Since they are negatively buoyant, Volvocales need flagellar beating to avoid sinking and to reach light and nutrients. We measured V. barberi swimming speed and total swimming force. V. barberi swimming speeds are the highest recorded so far for volvocine algae (～600 μm · s^?1). With this speed, V. barberi colonies have the potential to perform daily vertical migrations in the water column at speeds of 2–3 m · h^?1, consistent with what has been reported about Volvox populations in the wild. Moreover, V. barberi data fit well in the scaling relationships derived with the other smaller Volvox species, namely, that the upward swimming speed V_up∝N^0.28 and the total swimming force F_S∝N^0.77 (N = colony cell number). These allometric relationships have been important supporting evidence for reaching the conclusion that as size increases, colonies have to invest in cell specialization and increase their S/R to increase their motility capabilities to stay afloat and motile.     

Maximum sustainable swimming speeds of late-stage larvae of nine species of reef fishes

We examined the maximum sustainable swimming speed of late-stage larvae of nine species of tropical reef fishes from around Lizard Island, Great Barrier Reef, Australia. Larvae were captured in light traps and were swum in flumes at different experimental swimming speeds (of 5 cm s⁻¹ intervals) continuously for 24 h. Logistic regression was used to determine the speed at which 90% of larvae were able to maintain swimming, and this was used to indicate the maximum sustainable swimming speed for each species. Maximum sustainable swimming speeds varied among the species examined, with the lethrinid maintaining the fastest sustainable swimming speed (24 cm s⁻¹), followed by the Pomacentridae (10-20 cm s⁻¹) and the Apogonidae (8-12 cm s⁻¹). U-crit (maximum speed) explained 64% of the variation in sustainable speed among species, whereas total length only explained 33% of the variation in sustained swimming. A regression fitted across species suggests that 50% U-crit is a good approximation of the speed able to be maintained by these larvae for 24 h. A model based on a cubic relationship between sustained swimming time and speed was found to be more successful than either length or U-crit as a method of estimating sustainable swimming speed for most of the species examined. Overall, we found that swimming speed is an important factor when considering the potential for active swimming behaviour to influence dispersal patterns, recruitment success and levels of self-recruitment in reef fish larvae and needs to be carefully considered in models of larval dispersal.