Undulatory fish swimming: from muscles to flow

Undulatory swimming is employed by many fish for routine swimming and extended sprints. In this biomechanical review, we address two questions: (i) how the fish's axial muscles power swimming; and (ii) how the fish's body and fins generate thrust. Fish have adapted the morphology of their axial musculature for high power output and efficiency. All but the superficial muscle fibres are arranged along curved trajectories, and the myomeres form nested cones. Two conflicting performance goals shape the fibre trajectories of the axial muscles. Maximum power output requires that all fibres contract uniformly. In a bending fish, uniform contraction in a single myomere can be ensured by curved fibre trajectories. However, uniform strain is only desirable if all muscle fibres have the same contractile properties. The fish needs several muscle‐fibre types that generate maximum power at different contraction speeds to ensure effective muscle power generation across a range of swimming speeds. Consequently, these different muscle‐fibre types are better served by non‐uniform contractions. High power output at a range of swimming speeds requires that muscle fibres with the same contractile properties contract uniformly. The ensuing helical fibre trajectories require cone‐shaped myomeres to reduce wasteful internal deformation of the entire muscle when it contracts. It can be shown that the cone‐shaped myomeres of fish can be explained by two design criteria: uniform contraction (uniform strain hypothesis) and minimal internal deformation (mechanical stability hypothesis). So far, only the latter hypothesis has found strong support. The contracting muscle causes the fish body to undulate. These body undulations interact with the surrounding water to generate thrust. The resulting flow behind the swimming fish forms vortex rings, whose arrangement reflects the fish's swimming performance. Anguilliform swimmers shed individual vortex rings during steady swimming. Carangiform swimmers shed a connected chain of vortex rings. The currently available sections through the total flow fields are often not an honest representation of the total momentum in the water – the wake of carangiform swimmers shows a net backward momentum without the fish accelerating – suggesting that our current picture of the generated flow is incomplete. To accelerate, undulatory swimmers decrease the angle of the vortex rings with the mean path of motion, which is consistent with an increased rate of backward momentum transfer. Carangiform swimmers also enlarge their vortex rings to accelerate and to swim at a higher speed, while eel, which are anguilliform swimmers, shed stronger vortex rings.     

Aerobic muscle function during steady swimming in fish

Axial swimming in fish varies across a range of body forms and swimming modes. Swimming by eels, tunas, mackerels, scup, rainbow trout and bass span this range from high curvature anguilliform swimmers to rigid body thunniform swimmers. Recent work on these and other species has elucidated an impressive array of solutions to the problem of how to use the red (aerobic, slow‐twitch) muscle to power steady or sustained swimming. This review will use a comparative approach to understand the generalities of aerobic muscle function during steady swimming in fish and determine possible rules for the relationships between muscle contractile kinetics, in vivo muscle activity and power output during swimming. Beyond an exploration of the diversity in muscle activity and swimming kinematics, I suggest that analysis of the molecular basis for longitudinal variations in muscle function is needed to complement morphological and physiological research on fish muscle. This will permit both a general understanding of the integrative function of the fish myotome and, perhaps, predictive tools for muscle activity and swimming performance in fish.     

Differences in swimming performance and energetic costs between an endangered native toothcarp (Aphanius iberus) and an invasive mosquitofish (Gambusia holbrooki)

Swimming performance is a key feature that mediates fitness and survival in many fish species. Using a swim tunnel respirometer, we compared prolonged swimming performance and energy use for two competing species: an endangered, endemic toothcarp (Aphanius iberus) and a worldwide invasive mosquitofish (Gambusia holbrooki). Critical (U_crit) and optimal swimming speeds, standard and maximal metabolic rates, absolute aerobic scope, as well as the minimum cost of transport were estimated and compared between species and sexes. Body streamlining and caudal peduncle depth were also measured to explain the differences in swimming performance and efficiency. Both sexes of A. iberus presented similar swimming capacity and metabolic traits, whereas males of G. holbrooki showed higher critical swimming speeds, maximal metabolic rate and absolute aerobic scope than females. We also found marked differences between species in most of the response variables examined. Aphanius iberus showed lower swimming capacity (U_crit mean <10 cm s⁻¹), higher maximal metabolic rate and absolute aerobic scope than the invasive species. By contrast, G holbrooki swam faster and had lower cost of transport at a given fish mass and speed, thereby leading to a higher swimming efficiency. The observed differences in swimming efficiency were closely related to differences in morphological characteristics and therefore to drag pressures and propulsion. Our results add a mechanistic basis to the ecological understanding of these two species and suggest that although both are poor swimmers compared to many other similarly sized species, the native species likely has more restricted water flow tolerance and dispersal capacities.     

鱼类游泳速度分类方法的探讨

游泳速度是评价鱼类游泳能力的重要指标。本文对常用的几种鱼类游泳速度概念和分类方法进行了总结。目前,以时间长度作为分类标准可将游泳速度分为巡航游泳速度(Cruising swimming speed,T200min)、长时游泳速度(Prolonged swimming speed,200minT20s)、冲刺游泳速度(Burst swimming speed,T20s)3类。但由于时间长度的选择缺乏令人信服的依据,很多学者并未遵循这一时间界定标准进行各类试验,致使游泳速度的界定出现混乱,从而使以时间长度作为分类依据的方法失去意义。作者综合多数学者的研究方法,以鱼类的游泳状态作为依据,重新对鱼类游泳速度进行分类,并在这一分类基础上拓展引申出最大探顶游泳速度这一新概念,并对其推求方法和实际意义进行了探讨。根据新的分类方法,鱼类游泳速度主要分为5大类:最优巡航速度(Optimum swimming speed)、最大续航速度(Maximum sustained swimming speed)、临界游泳速度(Critical swimming speed)、最大探顶游泳速度(Maximum domed swimming speed)、冲刺游泳速度(Burst swimming speed)。其他游泳速度概念基本可以按照上述分类进行归并。借助最大探顶游泳速度这一概念,作者进一步探讨了其与最大续航速度、临界游泳速度3者之间的联系,认为在某种程度上这3种游泳速度作为评价鱼类游泳能力的指标具有一致性。     

Effects of size and sex on swimming performance and metabolism of invasive mosquitofish Gambusia holbrooki

In freshwater ecosystems, abiotic factors such as flow regime and water quality are considered important predictors of ecosystem invasibility. The aim of this study was to investigate the critical swimming capacity and metabolism of the eastern mosquitofish, Gambusia holbrooki, focusing on sex and size effects, to evaluate the influence of water flow on its invasive success. Specimens of mosquitofish were captured from the Ter Vell lagoon (L'Estartit, north‐eastern Spain) in July 2014, and we measured the critical swimming speed (U_crit) and oxygen consumption of individual fish (30 females and 30 males) using a mini swim tunnel. The mean U_crit of this poeciliid fish was estimated at 14.11 cm·s^?1 (range = 4.85–22.26), which is lower than that of many other fishes of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alterations. However, the U_crit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same body mass, and thus probably being more resistant to strong water flows. Multiple regression models illustrate that multivariate analyses might increase the predictive power and understanding of swimming performance and metabolic traits, compared to results from conventional simple regressions.     

The effect of demand feeding on swimming speed and feeding responses in Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages

Abstract Using underwater cameras, data were collected on the feeding behaviour and swimming speeds of Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages. Comparisons were made between the behaviours of fish fed on demand using interactive feedback systems and those of fish fed under the standard feeding practice of each farm (control). In all three species, swimming speeds were similar before feeding , but they were significantly higher in the control regimes during feeding. When fed on demand, sea bass had reduced swimming speed just before and during feeding compared with that observed during the non‐feeding periods. Higher proportions of feeding fish were observed in the control regime cages than in fish fed on demand for all three species, indicating a greater feeding intensity during meals in the control regimes. This was further supported by observations of an increase in the density of sea bass in the upper water in the control cages during feeding. The results suggest decreased levels of competition between the on demand‐fed fish during feeding, which might be hypothesized to lead to improved growth and production efficiency in aquaculture.     

Developing a Code of Conduct for whale shark interactions in Mozambique

• 1. The whale shark (Rhincodon typus) is a popular focal species within the global marine tourism industry. Although this has contributed to increased protection being granted to the species in several countries, tourism itself can be detrimental to the sharks in the absence of appropriate management. Potential impacts can be mitigated, at least in the short term, by adherence to well‐designed interaction guidelines.
• 2. A burgeoning marine tourism industry based on swimming with whale sharks has developed at Tofo Beach in Mozambique. However, no formal management is currently in place at this site.
• 3. The behaviour of whale sharks during interactions with boats and swimmers were recorded during 137 commercial snorkelling trips run from Tofo Beach over a 20 month period. Whale sharks were encountered on 87% of trips, which operated year‐round.
• 4. Boat proximity and shark size were significant predictors of avoidance behaviour. No avoidance responses were recorded at >20 m boat distance.
• 5. The mean in‐water interaction time between sharks and swimmers was 8 min 48 s overall. There was a significant decrease in interaction times during encounters where sharks expressed avoidance behaviours, and also in cases where sharks had expressed boat avoidance behaviour before swimmers entered the water.
• 6. It is suggested that mean encounter times can be extended through adherence to a basic Code of Conduct for operators and swimmers that enforces minimum distances between the sharks, boats and swimmers. Using encounter time as a measure of the ‘success’ of interactions holds promise, as longer encounters appear to be indicative of lower impacts on sharks while also providing higher customer satisfaction for swimmers. Copyright © 2010 John Wiley & Sons, Ltd.

     

Classification of sound-scattering layers using swimming speed estimated by acoustic Doppler current profiler

There are various techniques for identifying fish species, including the multi-frequency method, in situ target strength characteristics, and digital image processing methods. Acoustic Doppler current profilers (ADCPs) are able to determine multiple current fields simultaneously and have been used to observe the swimming speed and behavior patterns of shoals of pelagic fish under natural conditions. In this study, we evaluated a classification method that can be used to determine the swimming velocity of both the sound-scattering layer and pelagic fish shoals using an ADCP (153.6 kHz) and a scientific echosounder (38, 200 kHz). To calculate the actual swimming speed of the fish shoals, the mean swimming velocity vectors of each stratified bin must be compared with the mean surrounding three-dimensional (3D) current velocity vectors. We found the average 3D swimming velocity of the sound-scattering layer to be characterized by a deviation of >5.3 cm/s from the surrounding current field. The average 3D swimming velocity of Pacific saury Cololabis saira was calculated to be 91.3 cm/s, while that of lanternfish Diaphus theta was 28.1 cm/s. These swimming speeds correspond to 4.19- and 4.26-fold the body length, respectively. Thus, the use of ADCP swimming velocity data can be expected to be a valuable species identification method for various fishes distributed in a given survey area.     

Do swimming fish always grow fast? Investigating the magnitude and physiological basis of exercise-induced growth in juvenile New Zealand yellowtail kingfish, <Emphasis Type="Italic">Seriola lalandi</Emphasis>

There is a wealth of evidence showing that a moderate level of non-stop exercise improves the growth and feed conversion of many active fishes. A diverse number of active fish are currently being farmed, and an optimal level of exercise may feasibly improve the production efficiency of these species in intensive culture systems. Our experiments have set out to resolve the growth benefits of juvenile New Zealand yellowtail kingfish (Seriola lalandi) enforced to swim in currents at various speeds over two temperatures (14.9 and 21.1°C). We also probed potential sources of physiological efficiency in an attempt to resolve how growth is enhanced at a time of high energetic expenditure. Results show that long-term exercise yields a 10% increase in growth but this occurs in surprisingly low flows (0.75 BL s⁻¹) and only under favourable environmental temperatures (21.1°C). Experiments using a swim flume respirometer indicate that exercise training has no effect on metabolic scope or critical swimming speeds but it does improve swimming efficiency (lower gross costs of transport, GCOT). Such efficiency may potentially help reconcile the costs of growth and exercise within the range of available metabolic energy (scope). With growth boosted in surprisingly low flows and elevated water temperatures only, further investigations are required to understand the bioenergetics and partitioning of costs in the New Zealand yellowtail kingfish.     

Geolocation of Atlantic cod (Gadus morhua) movements in the Gulf of Maine using tidal information

Information derived from archival tags (digital storage tags, DSTs) were used to backtrack the migration of 11 tagged Atlantic cod (Gadus morhua) during 2001 in Massachusetts Bay, the Gulf of Maine, and Georges Bank. The DST tags continuously recorded time, temperature and depth. To geolocate fish positions during its time at large, we first extracted the tidal signal from the pressure recordings on the DST tags, and then compared the resulting data to data predicted with a Massachusetts Bay tidal model that provided us with geographical coordinates at a given date and time. Using least‐squares criteria within an estimated geographical region of confidence that was constrained by biological and statistical information (e.g. swimming speed, known release and recapture location, and bottom depth) we were able to geolocate the fish. The resultant geolocated migration tracks indicate a large degree of movement of Atlantic cod in the region and an elevated importance of the Great South Channel (GSC) migration corridor between Massachusetts Bay and the western Georges Bank and Nantucket Shoals region. This observation contrasts strongly with inferences of limited movements by Atlantic cod based on conventional tag recapture methods (mean of 1200 km traveled versus 44 km traveled as measured by conventional tagging and geolocation, respectively). This study demonstrates that geolocation methodologies applied to archival tag studies hold great promise of becoming an important new tool for fisheries managers to quantify the movements of fishes. It also points out the need for greater collaboration between fisheries scientists and oceanographers, and particularly for the development of improved tidal models to cover stock regions more accurately and with higher precision.     

A review of temperature and oxygen tolerance studies of tunas pertinent to fisheries oceanography, movement models and stock assessments

Detailed data on the physiological abilities and habitat requirements of some tuna species have now been collected. Laboratory and field studies show tunas are not strictly prisoners of their own thermoconserving mechanisms, but have rapid and extensive control over the efficacy of their vascular countercurrent heat exchangers. Skipjack tuna (Katsuwonus pelamis) are, therefore, probably not forced out of formerly suitable habitats as they grow because of the potential for overheating, as formerly thought. Because of their thermoregulatory abilities, bigeye tuna (Thunnus obe-sus) apparently can exploit food resources well below the thermocline by minimizing rates of heat loss when in cold water, and then maximizing rates of heat gain from the environment during brief upward excursions into the warmer mixed layer. Widely cited estimates of limiting oxygen levels, based on estimated metabolic rates at minimum hydrostatic equilibrium swimming speeds, are not accurate because tunas have exceptionally high oxygen demands even at slow speeds. High metabolic rates, even at slow swimming speeds, most likely result from the high osmoregulatory costs engendered by tunas' large thin gills and/or their other adaptations for achieving exceptionally high maximum metabolic rates. Recent laboratory research and modelling efforts suggest the capacity of tunas' cardiorespiratory systems to deliver oxygen at extraordinarily high rates was evolved to allow rapid recovery from strenuous exercise, rapid digestion, and high rates of gonadal and somatic growth, not high sustained cruising speeds. The rate at which reduced ambient oxygen levels prolong the time required for tunas to recover from strenuous exercise appears to be a good index of habitat suitability, with respect to oxy-een.     

The Behavioural Response of Coral Reef Fish Following Introduction to a Novel Aquarium Environment.

Following the construction of a large-scale public aquarium, we were presented with an opportunity to investigate how wild caught Caribbean reef fish respond to their first encounter with a novel environment. Within the constraints of this opportunity, we designed a behavioural study to determine the reef fishes' response to a new habitat in relation to their locomotory mode. Nine species of fish representing three locomotory modes: carangiform, sub-carangiform and labriform/sub-carangiform were observed over a four-week period following their first introduction to the aquarium. Fish activity levels and spatial distribution were quantified in relation to time since their first encounter with the novel environment. The most important result was that, regardless of locomotory mode or ecology, all of the species extensively explored the novel environment rather than settle on the first habitat that they encountered. This is a particularly interesting result for territorial species. More specifically, however, there were significant differences between species in activity through time. Carangiform activity level was lowest in the initial phases of an encounter with the novel environment subsequently rising to a stable level. The other species had variable activity throughout the study, but all of them exhibited a phase of low activity at some stage during the study. In terms of the fishes' use of the 2.5 million litres of water, six species utilised the whole of the aquarium based on a predefined zoning scheme. Although the initial activity level was low, carangiform swimmers used at least 90% of the zones in the early phases of an encounter with the novel environment and subsequently used all of the zones. Sub-carangiform species also used 100% of the zones by the end of the study. Three of the four labriform/sub-carangiform swimmers used a maximum of 90% of the zones. There was no significant difference between species in their use of the zones. However, each individual zone was subject to differential use by the fish. Owing to the extensive scale of the aquarium, we discuss the applicability of the behavioural results obtained to the natural environment in the context of the ecology of the species of fish studied. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fine‐scale swimming movement and behaviour of female silver eels,Anguilla dieffenbachii,within a lake affected by hydro‐power generation

Lake Manapouri (South Island, New Zealand) maintains the country’s largest hydroelectric scheme (700 MW). During their seaward migration, silver eel Anguilla dieffenbachii Gray in this lake are attracted to the power station intake, as well as the natural outlet. To understand the behaviour of such eels, 210 female eels were tagged with acoustic transmitters between 2005 and 2010. Swimming speeds of tagged eels averaged 2.0 km/hr, and swimming depths were deeper during daytime than at night. Silver eels from sites upstream of Lake Manapouri tended to spend more time exploring Lake Manapouri than locally caught eels, and a higher proportion entered the power station intake. Almost 20% of tagged eels did not leave the lake during the year they were tagged. Eels typically showed extensive and complex patterns of movement before emigrating, including multiple passes across the power station intake or the natural outlet.     

Testing hypotheses about fecundity, body size and maternal condition in fishes

Recent research suggests that maternal condition positively influences the number of eggs spawned in fishes. These studies commonly choose a priori to use body length rather than weight as an explanatory variable of offspring production, even though weight is usually the better predictor of fecundity. We are concerned that consistent exclusion of body weight as a predictor of egg production inflates the variance in fecundity attributable to maternal condition. By analysing data on three populations of Atlantic cod (Gadus morhua, Gadidae) and 10 populations of brook trout (Salvelinus fontinalis, Salmonidae), we illustrate the need for a statistically defensible method of model selection to distinguish the effects of maternal condition on egg production from the effects of body size alone. Forward stepwise regression and null model analyses reveal how length‐based regressions can significantly over‐estimate correlations between condition and fecundity, leading us to conclude that the effect of condition on egg productivity may not be as ubiquitous or as biologically important as previously thought. Our work underscores the need for greater statistical clarity in analyses of the effects of maternal condition on reproductive productivity in fishes.     

The swimming capacity of juvenile Murray cod (Maccullochella peelii): an ambush predator endemic to the Murray‐Darling Basin,Australia

This study documented the swimming capacity of a large ambush predator, Murray cod Maccullochella peelii, endemic to the Murray‐Darling Basin, Australia. It was evident that the species is a swimming generalist, maintaining moderate ability across all aspects of the swimming capacity parameters that were investigated. For instance, the species was capable of prolonged swimming performance (critical swimming speed, U_crit: absolute, 0.26–0.60 m·s^?1, relative, 1.15–2.20 BL s^?1) that was inferior to active fish species, but comparable with other ambush predators. The species had low energetic demands, maintaining a low mass‐specific standard (21.3–140.3 mg·h^?1 kg^?1) and maximum active metabolic rate (75.5–563.8 mg·h^?1 kg^?1), which lead to a small scope for activity (maximum active metabolic rate–standard metabolic rate; 1.4–5.9). They were reasonably efficient swimmers (absolute and relative optimal swimming speed, 0.17–0.61 m·s^?1 and 0.77–1.93 BL·s^?1, respectively) and capable of repeat bouts of prolonged performance (recovery ratio = 0.99). Allometric changes in aspects of swimming capacity were realised with body mass, whereas broad swimming capacity was maintained across a wide range of temperatures. The swimming capacity demonstrated by M. peelii reflects a sit‐and‐wait foraging strategy that seeks to conserve energy characteristic of ambush predators, but with distinct features (e.g., lack of fast‐start ability) that may reflect their evolution in some of the world's most hydrologically and thermally variable rivers.     

EMG telemetry studies on upstream migration of chum salmon in the Toyohira river,Hokkaido, Japan

The movements of 28 adult chum salmon, Oncorhynchus keta (Walbaum) tagged with electromyogram (EMG) transmitters were tracked along the Toyohira river, Hokkaido, Japan, in October of 2007 and 2008 to investigate and evaluate the upstream migratory behavior through the protection bed and fishway of ground sills. The approach time of fish that ascended successfully through the protection bed and fishway was shorter than that of unsuccessful fish. The unsuccessful fish were observed to swim in currents with high water velocity and shallow water depth at swimming speeds that exceeded their critical swimming speed (U _crit) during the approach to these structures. In consequence, unsuccessful fish frequently alternated between burst and maximum sustained speeds without ever ascending the fishway, and eventually became exhausted. It is important that fishway are constructed to enable chum salmon to find a passage way easily, so that they can migrate upstream rapidly without wasting excessive energy.     

Metabolic measurements and parameter estimations for bioenergetics modelling of Pacific Chub Mackerel Scomber japonicus

As a crucial step in developing a bioenergetics model for Pacific Chub Mackerel Scomber japonicus (hereafter chub mackerel), parameters related to metabolism, the largest dissipation term in bioenergetics modelling, were estimated. Swimming energetics and metabolic data for nine chub mackerel were collected at 14°C, a low temperature within the typical thermal range of this species, using variable‐speed swim‐tunnel respirometry. These new data were combined with previous speed‐dependent metabolic data at 18 and 24°C and single‐speed (1 fork length per second: FL/s) metabolic data at 15 and 20°C to estimate respiration parameters for model development. Based on the combined data, the optimal swimming speed (the swimming speed with the minimum cost of transport, U_opt) was 42.5 cm/s (1.5–3.0 FL/s or 2.1 ± 0.4 FL/s) and showed no significant dependence on temperature or fish size. The daily mass‐specific oxygen consumption rate (R, g O₂ g fish^?1 day^?1) was expressed as a function of fish mass (W), temperature (T) and swimming speed (U): R = 0.0103W^?0.490 e^(0.0457T) e^(0.0235U). Compared to other small pelagic fishes such as Pacific Herring Clupea harengus pallasii, Pacific Sardine Sardinops sagax and various anchovy species, chub mackerel respiration showed a lower dependence on fish mass, temperature and swimming speed, suggesting a greater swimming ability and lower sensitivity to environmental temperature variation.     

Influence of disc content on zone sizes obtained in standard disc diffusion antimicrobial susceptibility tests

The influence of disc content on the zone sizes produced was investigated using standard disc diffusion antimicrobial agent susceptibility test protocols. Replicate measurements were made of the zones of inhibition produced by discs containing 2-64 μg of oxytetracycline and oxolinic acid against Escherichia coli, Aeromonas salmonicida and Vibrio parahaemolyticus. Five replicate data sets were obtained for each of the six organism-agent combinations. Analysis of these 30 data sets demonstrated that they all showed a very high correlation (mean r² = 0.98 ± 0.009) with the predictions of best-fit equations specifying a linear relationship between log₁₀ of the disc content (μg) and the resultant zone sizes (mm). The mean value of the slopes of the best-fit straight-line equations was 9.8 ± 1.8. The overall similarity of these values for the slopes suggested that the quantitative relationship between disc content and zone size was, at least to a first approximation, independent of the organism or the agent involved in the test.     

Elasmobranch pericardial function. 3. The pericardioperitoneal canal in the horn sharkHeterodontus francisci

The pericardial and peritoneal spaces of elasmobranch fishes are connected by the pericardioperitoneal canal (PPC), which allows pericardial fluid to escape when pressures exceed 0.1–0.3 kPA. Using the horn shark (Heterodontus francisci), we tested the hypothesis that the PPC functions to increase cardiac stroke volume by lowering pericardial pressure during activity. We also assessed the role of the PPC during coughing, feeding, or burst swimming and examined the effects of PPC occlusion. Increases in heart size were not prevented following augmented venous return in sharks with undisturbed or occluded PCP, evidence that argues that pericardial fluid loss through the PPC is a cause of increased cardiac stroke volume and not the result. Coughs, feeding, and burst swimming led to discharge of pericardial fluid. Chronic PPC occlusion resulted in an increased pericardial pressure, fluid volume, and frequency of coughing, and a decreased survival time compared to shams. Thus, in the horn shark the PPC likely compensates for constraints that may be imposed by the pericardium, provides a route for pericardial drainage, and regulates cardiac stroke volume during periods of activity.     

长江口横沙浅滩及邻近水域夏季游泳动物群落结构分析

为了解长江口横沙浅滩及邻近水域游泳动物群落结构状况,分析其是否受河口工程建设的影响,本研究于2019年6月对该水域展开底拖网数据调查,通过分析其优势种、物种多样性、群落结构特征来了解群落结构现状。结果显示,夏季该水域共出现游泳动物68种,种类组成主要以节肢动物和鱼类为主。优势种分别为安氏白虾（Exopalaemon annandalei）、葛氏长臂虾（Palaemon gravieri）和矛尾虾虎鱼（Chaeturichthys stigmatias）,主要为小型、低营养层次和短生命周期的物种。调查水域游泳动物生物多样性指数偏低,群落结构总体不稳定,受环境扰动较大。聚类和排序分析显示调查水域站位大致可分为两组,并且两组组间物种群落结构差异极显著（R=0.825,P<0.01）,主要是受到盐度和水温的影响。总体上看,近年来长江口深水航道和滩涂围垦等工程的建设可能对横沙浅滩及邻近水域游泳动物群落结构造成了一定程度的影响。