Turning radius of yellowfin tuna (Thunnus albacares) in unsteady swimming manoeuvres

The specific turning radius of yellowfin tuna Thunnus albacares Cuvier is large relative to that of other fish (0.47 total body length ± 0.18, mean ± 2 s.e .). We argue that specializations for efficient steady swimming compromise performance in transient turning manoeuvres.     

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.     

The effects of body mass and feeding on metabolic rate in small juvenile Atlantic cod

Apparent specific dynamic action (SDA) amplitude in young juvenile Atlantic cod Gadus morhua (1 to 8 g wet mass), fed a standardized meal and then exercised in a circular swimming respirometer at a constant swimming speed of 0·5 ± 0·3 body lengths s^-1, occurred within l h after feeding in all juveniles. SDA amplitude were 1·4 to 1·8 times higher in fed fish compared to unfed fish, and rates of oxygen consumption decreased as body mass increased. SDA duration had a tendency to decrease with increasing body mass and was shortest, at 6 h, in the smallest fish (1–1·5 g), but increased to 10–11 h in the largest fish. Apparent SDA in fed fish ( R _r) scaled with a mass exponent of 0·89, while maximum metabolic rate ( R _max) determined by chasing fish to exhaustion and then measuring oxygen consumption for 12 h, and unfed routine metabolic rate (R_r) scaled with a mass exponent of 0·79 and 0·76 respectively. Relative aerobic scope ( R _max– unfed R _r) did not appear to vary over the 1 to 8 g increase in wet mass. These results show that as body mass increased in young juvenile Atlantic cod: (1) apparent SDA ( R _f) increased more rapidly than R _max, and (2) apparent SDA took up >98% of the relative aerobic scope and that young Atlantic cod allocated most of the energy to growth, and left little for other metabolic activities.     

Effects of angling on feeding by largemouth bass

Angling practice significantly effected the time required for largemouth bass Micropterus salmoides to begin feeding. Mean ± s.e. time until feeding resumed was longest for fish that experienced a simulated tournament (15·6 ± 2·2 h) followed by fish that were caught and released (8·4 ± 2·2 h) and controls (0·3 ± 1·6 h). Effects on feeding related to angling practices were maintained throughout the 48 h observation period. Using multiple logistic regression and bioenergetics simulations, decreased growth in fish subjected to competitive or catch-and-release angling events was predicted. Fish subjected to multiple captures in a pond experiment had greater mass loss than those not captured, supporting model predictions.     

TURNING MANEUVERS IN STELLER SEA LIONS (EUMATOPIAS JUBATUS)

Steller sea lions are highly maneuverable marine mammals (expressed as minimum turning radius). Video recordings of turns ( n = 195) are analyzed from kinematic measurements for three captive animals. Speed-time plots of 180° turns have a typical "V-shape." The sea lions decelerated during the first half of the turn, reached a minimum speed in the middle of the curved trajectory and reaccelerated by adduction of the pectoral flippers. The initial deceleration was greater than that for passive gliding due to pectoral flipper braking and/or change in body contour from a stiff, straight streamlined form. Centripetal force and thrust were determined from the body acceleration. Most thrust was produced during the power phase of the pectoral flipper stroke cycle. Contrary to previous findings on otariids, little or no thrust was generated during initial abduction of the pectoral flippers and during the final drag-based paddling phase of the stroke cycle. Peak thrust force at the center of gravity occurs halfway through the power phase and the centripetal force is maximal at the beginning of the power stroke. Performance is modulated by changes in the duration and intensity of movements without changing their sequence. Turning radius, maximum velocity, maximum acceleration and turning duration were 0.3 body lengths, 3.5 m/s, 5 m/s², and 1.6 s, respectively. The relative maneuverability based on velocity and length specific minimum turning radius is comparable to other otariids, superior to cetaceans but inferior to many fish.     

Evacuation of pelleted feed and the suitability of titanium(IV) oxide as a feed marker for gut kinetics in Nile tilapia

The present study assessed the suitability of titanium(IV) oxide, TiO₂, as a digesta passage marker in Nile tilapia Oreochromis niloticus and studied the shape of the evacuation curve in this species. In three separate trials, fish were given one dose of either 0·5, 0·25 or 0·1% of their body mass (% BME) of feed marked with 1% TiO₂ or 0·5% BME of the same feed without marker. The fish were serially slaughtered at intervals after feeding and the stomach contents analysed for dry mass and marker content. The data for individual trials were analysed with the linear, square root, surface area and exponential evacuation models and parameter comparisons showed that, although the marker interfered slightly with the evacuation process, true meal size could be predicted more accurately from the marker data. The results of an analysis of the combined data sets suggested that stomach evacuation in this species is dependent more on food particle surface area (surface area model) than on stomach content mass (exponential model) as is generally assumed. On the basis of these results, it was concluded that TiO₂ at an inclusion level of 1% is an acceptable marker for quantifying evacuation with a view to predicting food consumption but should be used with caution in digestibility studies.     

Reduced swimming performance in delta smelt infected with Mycobacterium spp.

Delta smelt Hypomesus transpacificus infected with Mycobacterium spp. swam significantly more slowly (mean ± s.e ., 24±5 ± 1·2 cm s ⁻¹) than uninfected fish (30·0 ± 1·7 cm s ⁻¹). Differences in swimming performance were not attributable to differences in fish size ( L _s or wet mass), condition factor or laboratory holding duration. Similar proportions of non-fatigue-related swimming failure among the uninfected and infected fish indicated that mycobacteriosis did not affect the willingness of delta smelt to swim in the flume. Level of infection, measured for the dominant M. chelonae pathogen using enzyme-linked immunosorbent assay (ELISA), did not affect critical swimming velocity.     

Some aspects of sustained training of rainbow trout, Salmo gairdneri Richardson

Groups of 6-7 cm length rainbow trout, Salmo gairdneri Richardson, were simultaneously trained at four water velocities (0, 1·4, 2·2 and 3·5 Ls^-1) for a period of 46 days. Oxygen consumption and swimming ability (fatigue time) were then measured. Only training at 3·5 Ls^-1 increased the swimming ability of the fish. A study of the relative proportion of the white and red muscles indicated that the white muscle was increasing its mass at velocities in excess of 2·2 Ls^-1. The oxygen consumption rate of the trained fish was lower than that of the untrained fish when considered over the whole velocity range.     

Differential digestion and evacuation rates of prey in a warm-temperate grouper, gag Mycteroperca microlepis (Goode & Bean)

Prey-specific gastric evacuation rates and digestion state indices were modelled for gag Mycteroperca microlepis , a large warm-temperate grouper, consuming meals of either baitfish (scaled sardine Harengula jaguana ) or crab (purple swimmer crab Portunus gibbesii ). Power exponential models best fit the wet and dry mass gastric evacuation data and the average digestion indices over post-prandial time (PPT), regardless of prey type or gag size (Adjusted R² ≥ 0·79). Gag mass ( M ) or total length ( L _T) incorporated into an expanded power exponential model, along with exponential scalars, resulted in highly predictive ( R² ≥ 0·87) gastric evacuation and average digestion state models. The expanded power exponential models fit to the baitfish and crab wet mass gastric evacuation data differed significantly (Kimura's likelihood ratio test (LRT), both P < 0·001). Gag consuming crab showed a digestive lag period of at least 4 h (wet mass) and took a longer time to complete digestion relative to gag consuming baitfish. Gag, as well as many other warm-temperate and tropical groupers, consume a mixture of fish and crab prey and they will therefore require the development of a consumption model that incorporates mixed-prey gastric evacuation models.     

Big and beautiful? Quantitative genetic parameters for appearance of large rainbow trout

A quantitative genetic analysis of body condition, body shape, skin colour and spottiness of large, farmed rainbow trout Oncorhynchus mykiss showed that the traits can be modified through selective breeding. This was indicated by their high heritabilities ( h ² = 0·46–0·61 on the underlying liability scale and 0·29–0·50 on the observed scale). Correlations calculated using linear models showed that skin colour and the amount of spots displayed positive phenotypic ( r _P = 0·33) and genetic correlations ( r _A = 0·83), the relationship being advantageous for the genetic improvement of the traits. Body shape and condition factor displayed disadvantageous correlations with body mass at both ages, the genetic correlations between the traits ranging from 0·36 to 0·57. It was concluded that there are no strong genetic constraints for the genetic improvement of appearance, the only limitation being that rapidly growing fish become rotund.     

The effects of vision on the general locomotor behaviour of the goldfish, Carassius auratus

Comparison of the locomotor behaviour of normal, unilaterally and bilaterally blinded goldfish (Carassius auratus) demonstrated the roles of perspective vision (depth perception), which requires binocular vision, and of vision provided by only one eye, in the control of locomotion. Because normal and bilaterally blinded fish exhibited similar size and direction of angles of turn, a similar number of consecutive turns in the same direction and the same turning frequency, normal, binocular vision plays no role in the control of turning behaviour. Unilaterally blinded fish exhibited a strong bias in turning behaviour which resulted in their displaying circus movements toward the blinded side, a direction opposite to that reported by others for both invertebrates and vertebrates with unilateral sensory elimination. The mean step length was significantly increased by both uni- and bilateral blinding, and its temporal relationship with turning frequency and distance swum was also changed. Perspective vision (binocular) therefore controls these parameters. The significantly lower velocity of bilaterally blinded fish and the similarity between the other two test groups, indicated that sight by one eye only was sufficient to mediate velocity control.     

Cyclic feeding and subsequent compensatory growth do not significantly impact standard metabolic rate or critical swimming speed in rainbow trout

Standard metabolic rate ( R _s) and critical swimming speed ( U _crit) were used to assess the aspects of physiological status (stamina) of rainbow trout Oncorhynchus mykiss . Fish were fed either 1·5% body mass daily, 1·5% body mass cyclically (3 weeks of food deprivation followed by 3 weeks of refeeding), a ration based on Stauffer's formula (a maximum temperature-specific ration level) daily or on Stauffer's ration cyclically for 18 weeks. It was hypothesized that if cyclic feeding had no impact on the status of the fish, R _s and U _crit would not cycle with the feeding regime. This hypothesis was supported. No significant difference was found between the mean mass and the fork length of the four groups at the end of the experiment ( P > 0·05). Feeding had no effect on changes in R _s among the four groups, which were significantly different throughout the experiment ( P ≤ 0·05). No significant difference in U _crit was found ( P > 0·05) until at week 12 between groups fed 1·5% body mass ration cyclically and Stauffer's ration daily ( P ≤ 0·05). For groups fed a 1·5% body mass ration cyclically and daily, significant differences occurred at week 15 ( P ≤ 0·05) but no significant difference was found by week 18 ( P > 0·05), suggesting that cyclic feeding does not affect the aspects of physiological status (stamina) of the fish.     

Reproductive ecology of cultured fish in the wild

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.     

Compensatory growth of juvenile brown flounder Paralichthys olivaceus (Temminck & Schlegel) following thermal manipulation

The compensatory growth of juvenile brown flounder Paralichthys olivaceus (body mass c. 12 g) following different thermal exposure was investigated. Fish were exposed to one of the five temperatures: 8·5 ( T _8·5), 13·0 ( T _13·0), 17·5 ( T _17·5), 22·0 ( T _22·0) and 26·5° C ( T _26·5) for 10 days and fish grew best at 22·0° C. Then the water temperature in all treatments was equably adjusted to 22·0° C over 3 days. At the end of the following 30 days after temperature adjustment, there were no significant differences between body masses of fish in the different treatments (wet body mass at the end of the experiment ranged from 22·13 to 24·56 g). Results indicated that the juvenile P. olivaceus achieved complete compensatory growth. Analysis of the dynamics of the feeding rates and feed conversion efficiencies indicated that compensatory growth of the fish experienced low temperature ( T _8·5, T _13·5 and T _17·5) or high temperature ( T _26·5) exposure was mainly dependent on increasing feed intake (hyperphagia) and possibly by improvement in feed conversion efficiency. The moisture content was not affected by different temperature exposure significantly. The lipid and energy content of juvenile P. olivaceus in T _8·5, however, were significantly lower than other treatment. Results of the current study indicate that a short period of low or high temperature exposure may not affect annual growth, but may affect lipid and energy deposition.     

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.     

Food consumption and growth of two piscivorous fishes, the mandarin fish and the Chinese snakehead

Rates of maximum food consumption and growth were determined for immature mandarin fish Siniperca chuatsi (47·2—540·2 g) and Chinese snakehead Channa argus (45·0—546·2 g) at 10, 15, 20, 25, 30 and 35) C. The relationship between maximum rate of food consumption ( C max), body weight ( W ) and temperature ( T ) was described by the multiple regression equations: In C max=−4·880+0·597 In W +0·284 T −0·0048 T ² for the mandarin fish, and In C max=−6·718+ 0·522 In W +0·440 T −0·0077 T ² for the Chinese snakehead. The optimum temperature for consumption was 29·6) C for the mandarin fish and 28·6) C for the Chinese snakehead. The relationship between growth rate ( G ), body weight and temperature was ln( G +0·25)=−0·439−0·500 ln W +0·270 T −0·0046 T ² for the mandarin fish, and ln( G +0·25)=−6·150+ (0·175−0·026 T ) ln W +0·571 T −0·0078 T ² for the Chinese snakehead. The weight exponent in the growth–weight relationship was −0·83 for the mandarin fish, but decreased with increasing temperature for the Chinese snakehead. The optimum temperature for growth was 29·3) C for the mandarin fish, but tended to decrease with increasing weight for the Chinese snakehead, being 30·3) C for a 45-g fish, and 26·1°C for a 550-g fish.     

Finlets and the steady swimming performance of Thunnus albacares

The functional significance of finlets on the steady swimming performance of yellowfin tuna Thunnus albacares was evaluated by measuring the speed and tail‐beat frequency of the fish with and without them. It was hypothesized that if finlets do improve swimming performance, fish without finlets would have to work harder to maintain the same swimming speed as fish with them and that this would be reflected in kinematic differences. Two‐way ANOVA showed significant effects between individuals on speed (d.f. = 5 and 228, P  < 0·001) and tail‐beat frequency (d.f. = 5 and 48, P  < 0·001), but no significant effects of treatment on speed (d.f. = 1 and 228, P  = 0·25) and tail‐beat frequency (d.f. = 1 and 48, P  > 0·1). No interaction effects on speed (d.f. = 5 and 228, P  > 0·1) and tail‐beat frequency (d.f. = 5 and 48, P  > 0·25) were found. This suggested that finlets were unlikely to function as significant drag reduction and thrust enhancing devices in routine steady swimming. Though not statistically significant, small percentage differences between the mean swimming speeds and tail‐beat frequency of the untreated and treated groups (fish with and without finlets respectively) of the order of 0·5% may be meaningful over the life of a fish. Also, finlets may improve performance at high sustained speeds in rapid accelerations and turns.     

Hydrodynamic Analysis of C-start in Crucian Carp

The kinematics of turning maneuvers of startled Crucian Carp (Carassius auratus) are presented. All escape response observed are C-type fast-starts. The position of the center of mass and the me,merit of inertia of the fish are calculated. The results show that the position of the center of mass is always at 35% of the length of the fish from the head and the position of the center of mass and rroment of inertia can be considered unchanged during C-start of Crucian Carp. Hydro-dynamic analysis of the C-start is given based on the kinematics data from our experiments. The C-start consists of three stages. In stage 1, the tail fin of fish rapidly flaps in one direction, and a large moment acts on the fish‘s body, which rotates around the center of mass with an angular acceleration. In stage 2, the tail fin flaps more slowly in the opposite direction at slower speed, the fish‘s body rotates around the center of mass with angular deceleration and the center of mass of the fish moves along an are. In stage 3, the moment approximately equals zero, the fish‘s body stops rotating and the center of mass the moves along a straight line.     

Ontogenetic changes in temperature preference of Atlantic cod

Final thermal preferendum ( T ) experiments were conducted in a horizontal thermal gradient tank from the beginning of August 2001 to mid‐November 2001 using Atlantic cod Gadus morhua from 6·5 to 79·0 cm fork length ( L _F). The value of T varied significantly ( P  < 0·005) with L _F( T  = 7·23–0·054 L _F), with smaller (younger) fish choosing higher temperatures than larger (older) fish. The preferendum varied from 6·9° C for fish of 6·5 cm to 3·0° C for those of 79·0 cm. Experiments comparing fish positions in the gradient tank between thermal gradients of 0·5–11·0 and 4·5–14·5° C demonstrated that fish positions were determined by temperature selection instead of undesirable tank effects. This study is the first to demonstrate the effect of ontogeny on temperature preferences of a marine fish species.     

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.