Examination of fine‐scale spatial‐temporal overlap and segregation between two closely related congeners Gadus morhua and Gadus ogac in coastal Newfoundland

The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high‐resolution radio‐acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 (G. morhua) and 14·4 days (G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions (KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length (L_T) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 L_T s^?1, respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species.     

Aerobic scope for activity in age 0 year Atlantic cod Gadus morhua

Key components of swimming metabolism: standard metabolism (R_s), active metabolism (R_a) and absolute aerobic scope for activity (R_a–R_s) were determined for small age 0 year Atlantic cod Gadus morhua. Gadus morhua juveniles grew from 0·50 to 2·89 g wet body mass (M_WB) over the experimental period of 100 days, and growth rates (G) ranged from 1·4 to 2·9% day^?1, which decreased with increasing size. Metabolic rates were recorded by measuring changes in oxygen consumption over time at different activity levels using modified Brett‐type respirometers designed to accommodate the small size and short swimming endurance of small fishes. Power performance relationships were established between oxygen consumption and swimming speed measurements were repeated for individual fish as each fish grew. Mass‐specific standard metabolic rates () were calculated from the power performance relationships by extrapolating to zero swimming speed and decreased from 7·00 to 5·77 μmol O₂ g^?1 h^?1, mass‐specific active metabolic rates () were calculated from extrapolation to maximum swimming speed (U_max) and decreased from 26·18 to 14·35 μmol O₂ g^?1 h^?1 and mass‐specific absolute scope for activity was calculated as the difference between active and standard metabolism () and decreased from 26·18 to 14·35 μmol O₂ g^?1 h^?1 as M_WB increased. Small fish with low R_s had bigger aerobic scopes but, as expected, R_s was higher in smaller fish than larger fish. The measurements and results from this study are unique as R_s, R_a and absolute aerobic scopes have not been previously determined for small age 0 year G. morhua.     

Differences in the energetic cost of swimming in turbulent flow between wild,farmed and domesticated juvenile Atlantic salmon Salmo salar

Domestication has been shown to have an effect on morphology and behaviour of Atlantic salmon (Salmo salar). We compared swimming costs of three groups of juvenile Atlantic salmon subject to different levels of domestication: (1) wild fish; (2) first generation farmed fish origination from wild genitors; and (2) seventh generation farmed fish originating from Norwegian aquaculture stocks. We assessed swimming costs under two types of turbulent flow (one mean flow velocity of 23 cm s^?1 and two standard deviations of flow velocity of 5 and 8 cm s^?1). Respirometry experiments were conducted with fish in a mass range of 5–15 g wet at a water temperature of 15° C. Our results confirm (1) that net swimming costs are affected by different levels of turbulence such that, for a given mean flow velocity, fish spent 1·5‐times more energy as turbulence increased, (2) that domesticated fish differed in their morphology (having deeper bodies and smaller fins) and in their net swimming costs (being up to 30·3% higher than for wild fish) and (3) that swimming cost models developed for farmed fish may be also be applied to wild fish in turbulent environments.     

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.     

Heart rate as an indicator of metabolic rate and activity in adult Atlantic salmon, Salmo salar

Telemetered heart rate (f_H) was examined as an indicator of activity and oxygen consumption rate (VO₂) in adult, cultivated, Atlantic salmon, Salmo salar L. Heart rate was measured during sustained swimming in a flume for six fish at 10° C [mean weight, 1114 g; mean fork length (f. l.), 50·6 cm] and seven fish at 15° C (mean weight, 1119 g; mean f. l., 50·7 cm) at speeds of up to 2·2 body lengths/s. Semi–logarithmic relationships between heart rate and swimming speed were obtained at both temperatures. Spontaneously swimming fish in still water exhibited characteristic heart rate increases associated with activity. Heart rate and Vo₂ were monitored simultaneously in a 575–1 circular respirometer for six fish (three male, three female) at 4° C (mean weight, 1804 g; mean F. L., 62· cm) and six fish (three male, three female) at 10° C (mean weight, 2045 g; mean f. l., 63·2 cm) during spontaneous but unquantified activity. Linear regressions were obtained by transforming data for both f_H and Vo₂ to log values. At each temperature, slopes of the regressions between f_H and Vo₂ for individual fishes were not significantly different, but in some cases elevations were. All differences in elevation were between male and female fish. There were no significant differences in regression slope or elevation for fish of the same sex at the two temperatures and so regressions were calculated for the sexes, pooling data from 4 and 10° C. There was no significant difference in the mean ± S. D. Vo₂ between the sexes at 4° C (male, 66·0 ± 59·6 mgO₂ kg^?1 h^?1; female, 88·0 ± 60·1 mgO₂ kg^?1 h^?1) or 10° C (male, 166·2 ± 115·4 mgO₂ kg^?1 h^?1; female, 169·2 ± 111–1 mgO₂ kg^?1h^?1). Resting Vo₂ (x?± s. d.) at 4°C was 36·7 ± 8.4 mgO₂ kg^?1 h^?1, and 10° C was 72·8 ± 11·9 mgO₂ kg^?1 h^?1. Maximum Vo₂ (x?± S. D.) at 4° C was 250·6 ± 40·2 mgO₂ kg^?1 h^?1, and at 10° C was 423·6 ± 25·2 mgO₂ kg^?1 h^?1. Heart rate appears to be a useful indicator of metabolic rate over the temperature range examined, for the cultivated fish studied, but it is possible that the relationship for wild fish may differ.     

Evaluation of swimming performance for fish passage of longnose dace Rhinichthys cataractae using an experimental flume

The swimming performance of longnose dace Rhinichthys cataractae, the most widely distributed minnow (Cyprinidae) in North America, was assessed in relation to potential passage barriers. The study estimated passage success, maximum ascent distances and maximum sprint speed in an open‐channel flume over a range of water velocities and temperatures (10·7, 15·3 and 19·3° C). Rhinichthys cataractae had high passage success (95%) in a 9·2 m flume section at mean test velocities of 39 and 64 cm s^–1, but success rate dropped to 66% at 78 cm s^–1. Only 20% of fish were able to ascend a 2·7 m section with a mean velocity of 122 cm s^–1. Rhinichthys cataractae actively selected low‐velocity pathways located along the bottom and corners of the flume at all test velocities and adopted position‐holding behaviour at higher water velocities. Mean volitional sprint speed was 174 cm s^–1 when fish volitionally sprinted in areas of high water velocities. Swimming performance generally increased with water temperature and fish length. Based on these results, fishways with mean velocities <64 cm s^–1 should allow passage of most R. cataractae. Water velocities >100 cm s^–1 within structures should be limited to short distance (<1 m) and structures with velocities ≥158 cm s^–1 would probably represent movement barriers. Study results highlighted the advantages of evaluating a multitude of swimming performance metrics in an open‐channel flume, which can simulate the hydraulic features of fishways and allow for behavioural observations that can facilitate the design of effective passage structures.     

Heart rates of Atlantic salmon Salmo salar during a critical swim speed test and subsequent recovery

In this study, heart rate (HR) bio-loggers were implanted in the abdominal cavity of 12 post-smolt Atlantic salmon Salmo salar weighing 1024 ± 31 g and acclimated to 12°C sea water. One week after the surgical procedure, a critical swim speed (U_crit) test was performed on tagged and untagged conspecifics, whereafter tagged fish were maintained in their holding tanks for another week. The U_crit was statistically similar between tagged and untagged fish (2.67 ± 0.04 and 2.74 ± 0.05 body lengths s⁻¹, respectively) showing that the bio-logger did not compromise the swimming performance. In the pre-swim week, a diurnal cycle was apparent with HR peaking at 65 beats min⁻¹ during the day and approaching 40 beats min⁻¹ at night. In the U_crit test, HR increased approximately exponentially with swimming speed until a plateau was reached at the final speed before fatigue with a maximum of 85.2 ± 0.7 beats min⁻¹. During subsequent recovery tagged fish could be divided into a surviving group (N = 8) and a moribund group (N = 4). In surviving fish HR had fully recovered to pre-swim levels after 24 h, including reestablishment of a diurnal HR cycle. In moribund fish HR never recovered and remained elevated at c. 80 beats min⁻¹ for 4 days, whereafter they started dying. We did not identify a proximal cause of death in moribund fish, but possible explanations are discussed. Tail beat frequency (TBF) was also measured and showed a more consistent response to increased swimming speeds. As such, when exploring correlations between HR, TBF and metabolic rates at different swimming speeds, TBF provides better predictions. On the contrary, HR measurements in free swimming fish over extended periods of time are useful for other purposes such as assessing the accumulative burden of various stressors and recovery trajectories from exhaustive exercise.     

Effect of fish length and nutritional condition on the fecundity of distressed Atlantic cod Gadus morhua from the Baltic Sea

The disappearance of larger individuals and the decrease in individual body condition suffered by Atlantic cod Gadus morhua in the eastern Baltic during the past two decades can be expected to affect the stock reproductive output. To investigate this, female G. morhua were collected during the spawning and pre‐spawning period in 2015?2016. The current individual potential fecundity (F_P) of eastern Baltic G. morhua was estimated and analysed in relation to total length (L_T) and indices of nutritional status such as body condition (K) and hepato‐somatic index (I_H) using generalized linear models. In addition, the current prevalence of atresia and its potential relation to K were investigated. Moreover, a calibration curve to estimate F_P from oocyte diameter, based on the autodiametric oocyte counting method, was established for the first time for eastern Baltic G. morhua and can be used for future fecundity studies on this stock. The results showed that F_P was mainly positively related to fish length, but K and I_H also contributed significantly to the variation in F_P. The model predicted that fish with K = 1·2 have a F_P 51% higher than fish of the same L_T with K = 0·8. The prevalence of fecundity regulation by atresia was 5·8%, but it was found only in fish in the pre‐spawning maturity stage and with low K. Temporal changes in biological features such as the length composition and individual body condition of eastern Baltic G. morhua, should be accounted for when estimating stock reproductive potential.     

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.     

Scaling effects on the neuromuscular system,twitch kinetics and morphometrics of the cod,Gadus morhua

Size related changes in muscle twitch kinetics, morphometrics and innervation have been examined in cod, Gadus morhua. Fish size ranged from 9 cm to 45 cm in total length (L).

Twitch contraction time (time to 90% relaxation), scaled in proportion to L^0.29. Scaling of morphometric parameters was essentially geometric. Mean cross‐sectional area and weight of the myotomal muscle scaled in proportion to L^2.05 and L^3.08 respectively. These results are discussed in the light of alterations in length specific swimming performance and kinematics as fish grow.

During growth, the number of endplates terminating on each fast fibre increased, from around 10 on fibres 2 mm in length (～10 cm fish) to 20 on 10 mm fibres (—40 cm fish). However, mean spacing between endplates increased from around 0.25 mm to 0.50 mm. The functional significance of polyneuronal innervation in teleost fast muscle fibres is discussed.     

Reproductive biology of albacore Thunnus alalunga

Reproductive variables in albacore Thunnus alalunga were evaluated by gonad histology in samples of 132 males (58–118 cm fork length, L_F) and 112 females (59–101 cm L_F) that were collected from the western North Pacific Ocean from 2001 to 2006. In the sex ratio examination, males greatly outnumbered females in large adult fish (L_F > 100 cm). Thunnus alalunga exhibited a protracted spawning period from March to September in the waters off eastern Taiwan and the Philippines, and the peak spawning activity occurred in March and April. Minimum sizes associated with the classification of mature fish were 78 and 83 cm L_F for males and females, respectively. In addition, the largest L_F of immature fish were 93 cm for males and 94 cm for females. The spawning frequency estimate in April was 1·7 days. Batch‐fecundity estimates of 21 females (89–99 cm L_F) ranged between 0·17 and 1·66 million eggs (mean ±s.d . = 0·94 ± 0·43). The relative fecundity estimates of the 21 females ranged between 9·2 and 92·4 oocytes g^?1 body mass (mean ±s.d . = 50·5 ± 22·8). The results presented in this study provide increased information regarding this species' reproductive‐related characteristics than are currently available in stock status determinations.     

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.     

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.     

Population biology of an endangered species: the common guitarfish Rhinobatos rhinobatos in Lebanese marine waters of the eastern Mediterranean Sea

This study focuses on the population biology of the common guitarfish Rhinobatos rhinobatos, a cartilaginous fish listed as Endangered in the International Union for the Conservation of Nature (IUCN) Red List. Between December 2012 and January 2014, 67 individuals were collected by bottom longlining in coastal Lebanese marine waters at different ports at depths ranging from 10 to 110 m. The total length (L_T) of the specimens ranged from 50 to 143 cm, and the mean ± s.d . was 76·2 ± 19·7 cm. The most common L_T classes were between 60 and 70 cm. The total mass of the specimens ranged from 410 to 10 000 g, and the mean ± s.d . was 1841 ± 1987 g. A total of 34 males and 33 females were collected, and the sex ratio was not significantly different from 1:1. The mass and L_T relationship showed positive allometric growth (b = 3·096 and r² = 0·99), and the mean ± s.d . L_T at which 50% of the individuals were sexually mature was 84·73 ± 5·81 cm for females and 78·57 ± 4·88 cm for males. The gonado‐somatic and hepato‐somatic indices were determined along with a condition factor, and parturition appeared to occur in winter. The primary prey items found in the fish stomachs during the autumn and winter seasons were Penaeidae. The results of this study will help to parameterize models of the population dynamics for this exploited fish stock to ensure the long‐term sustainability of its fishery.     

Exercise metabolism in two species of cod in arctic waters

The northern range of Atlantic cod (Gadus morhua), overlaps the southern range of the Greenland cod (Gadus ogac), in the coastal waters of Western Greenland. The availability of a temperate water species (G. morhua) in the same area and oceanographic conditions as a polar species (G. ogac) presented us with the ideal circumstances to test the hypothesis of metabolic cold adaptation (MCA) since many of the problems associated with MCA studies (adaptation of the animals beyond their normal temperature range or mathematical extrapolation of data to common temperatures) could thus be avoided. We therefore used a swim tunnel to measure oxygen consumption in fish at 4°C over a range of swimming speeds and following exhaustion, monitored the size of the oxygen debt and time of oxygen debt repayment. There were no significant differences in standard (60–72 mg O₂ kg^–1· hr^–1), routine (76 mg O₂ kg^–1·hr^–1), active (137mg O₂ kg^–1·hr^–1), or maximal (157 mg O₂ kg^–1·hr^–1) metabolic rate, metabolic scope (2.5) or critical swimming speed (2.2 BL·s^–1) between the two species. Following exhaustive swimming, however, the half-time for oxygen debt repayment in G. ogac (43 min) was almost twice that of G. morhua (25 min). Despite its circumpolar distribution, therefore, there was no evidence of MCA in G. ogac.     

Characterizing the escape response of juvenile summer flounder Paralichthys dentatus to diel‐cycling hypoxia

Swimming speed, angular correlation and expected displacement were measured in juvenile summer flounder Paralichthys dentatus acclimated to either oxygen saturation (c. 7·8 mg O₂ l^?1; saturation‐acclimated fish) or diel‐cycling hypoxia (cycling between 11·0 and 2·0 mg O₂ l^?1) for 10 days and subsequently exposed to more severe diel‐cycling hypoxia (cycling between 7·0 and 0·4 mg O₂ l^?1). Saturation‐acclimated P. dentatus exhibited an active response to declining dissolved oxygen (DO) by increasing swimming speed, angular correlation and expected displacement to peak levels at 1·4 mg O₂ l^?1 that were 3·5, 5·5 and 4·2 fold, respectively, greater than those at DO saturation. Diel‐cycling hypoxia‐acclimated P. dentatus also exhibited an active response to declining DO, although it was relatively less pronounced. Diel‐cycling hypoxia‐acclimated P. dentatus swimming speed, however, still doubled as DO decreased from 7·0 to 2·8 mg O₂ l^?1. Diel‐cycling hypoxia‐acclimated P. dentatus did not recover as well from low DO exposure as did saturation‐acclimated fish. This was reflected in their relatively more random swimming (low angular correlation between successive moves) and poor maintenance of rank order between individuals during the recovery phase. Even saturation‐acclimated P. dentatus did not resume swimming at speeds observed at saturation until DO was 4·2 mg O₂ l^?1. Paralichthys dentatus were very sensitive to decreasing DO, even at DO levels that were not lethal or growth limiting. This sensitivity and their poor recovery may preclude juvenile P. dentatus from using highly productive nursery habitats affected by diel‐cycling hypoxia.     

Ontogeny of critical and prolonged swimming performance for the larvae of six Australian freshwater fish species

Critical (<30 min) and prolonged (>60 min) swimming speeds in laboratory chambers were determined for larvae of six species of Australian freshwater fishes: trout cod Maccullochella macquariensis, Murray cod Maccullochella peelii, golden perch Macquaria ambigua, silver perch Bidyanus bidyanus, carp gudgeon Hypseleotris spp. and Murray River rainbowfish Melanotaenia fluviatilis. Developmental stage (preflexion, flexion, postflexion and metalarva) better explained swimming ability than did length, size or age (days after hatch). Critical speed increased with larval development, and metalarvae were the fastest swimmers for all species. Maccullochella macquariensis larvae had the highest critical [maximum absolute 46·4 cm s^?1 and 44·6 relative body lengths (L_B) s^?1] and prolonged (maximum 15·4 cm s^?1, 15·6 L_B s^?1) swimming speeds and B. bidyanus larvae the lowest critical (minimum 0·1 cm s^?1, 0·3 L_B s^?1) and prolonged swimming speeds (minimum 1·1 cm s^?1, 1·0 L_B s^?1). Prolonged swimming trials determined that the larvae of some species could not swim for 60 min at any speed, whereas the larvae of the best swimming species, M. macquariensis, could swim for 60 min at 44% of the critical speed. The swimming performance of species with precocial life‐history strategies, with well‐developed larvae at hatch, was comparatively better and potentially had greater ability to influence their dispersal by actively swimming than species with altricial life‐history strategies, with poorly developed larvae at hatch.     

Extraordinary growth in tiger sharks Galeocerdo cuvier from the South Atlantic Ocean

Two tagged‐and‐recaptured tiger sharks Galeocerdo cuvier, measuring 172 and 304 cm total length (L_T) and at age 0·75 and 3·50 years, exhibited unmatched growth rates of 118·4 and 55·5 cm year^?1, respectively. The larger fish was nearly mature, indicating that G. cuvier off Brazil could mature considerably earlier than conspecifics from other regions.     

Postprandial metabolic increment of southern bluefin tuna Thunnus maccoyii ingesting high or low‐lipid sardines Sardinops sagax

This study examined the postprandial metabolism and swimming speed of southern bluefin tuna Thunnus maccoyii when fed sardines Sardinops sagax of either high‐lipid and high‐energy content or low‐lipid and low‐energy content. Five groups of two or three T. maccoyii (mean ±s.e. mass = 19·8 ± 0·5 kg, n = 14) were fed either low [2·2% lipid, 5·5 MJ kg^?1 gross energy (GE)] or high‐lipid (12·9%, 9·2 MJ kg^?1 GE) S. sagax. Before feeding, T. maccoyii swam at 0·74 ± 0·03 body lengths s^?1 (n = 5) and their routine metabolic rate was 305 ± 15 mg kg^?1 h^?1. Swimming speed and metabolic rate of T. maccoyii increased following feeding. Thunnus maccoyii swam 1·3 and 1·8 times faster during digestion of low and high‐lipid S. sagax, respectively. Postprandial peak metabolic rate, duration of elevated metabolism and total postprandial metabolic increment were all greater for T. maccoyii that ingested high‐lipid S. sagax. When total postprandial increment is represented as a proportion of ingested energy, there was no difference between high and low‐lipid meals, equating to between 30 and 35% of ingested energy. It was estimated that increased postprandial swimming costs account for 25 and 46% of the total postprandial metabolic response for low and high‐lipid S. sagax meals, respectively. Specific dynamic action (SDA) accounts for c. 20% of ingested energy regardless of S. sagax lipid level. These results confirm that the postprandial metabolic increment of T. maccoyii is greater than most other fish species. Much of the high cost of postprandial metabolic increment can be attributed to increased postprandial swimming costs. For T. maccoyii, it appears that activity and SDA are not independent, which complicates bioenergetic evaluation. High postprandial metabolic costs accentuate the great energetic requirements of T. maccoyii.     

Effects of Temperature and Body Size on the Swimming Speed of Larval and Juvenile Atlantic Cod (Gadus Morhua): Implications for Individual-based Modelling

Synopsis The routine swimming speed (S) of three groups of 4, 9 and 32 cm total length (L_T) juvenile cod (Gadus morhua) was quantified in the laboratory at 6 – 10 different temperatures (T) between 3.2 and 16.7°C. At temperatures between 5 and 15°C, mean group S increased exponentially with increasing T (S=a e^bT) and the effect of temperature (b = 0.082, Q₁₀ = 2.27) was not significantly different among the groups (over the 8-fold difference in fish sizes of early- and post-settlement juveniles). Differences in mean S among individuals within each group were quite large (coefficient of variation = 40 – 80%). Swimming data for juveniles and those collected for groups of 0.4, 0.7 and 0.9 cm standard length (L_S) larvae were combined to assess the effect of body size on S. At 8°C, S (mm s⁻¹) increased with L_S (mm) according to: S = 0.26L_S^Φ−5.28L_S⁻¹, where Φ = 1.55L_S^−0.08. Relative S (body lengths s⁻¹) was related to L_S by a dome-shaped relationship having a maximum value (0.49 body lengths s⁻¹) at 18.5 – 19 mm L_S corresponding to the sizes of fish at the end of larval-juvenile metamorphosis. Previous larval cod IBM’s using a cruise-predator mode likely overestimated rates of foraging (prey searching and encounters) by a factor of ~2, whereas foraging rates in pause-travel models are closer to estimates of swimming velocities obtained in this and other laboratory studies.