Swimming activity and energetic expenditure of captive rainbow trout Oncorhynchus mykiss (Walbaum) estimated by electromyogram telemetry

Rainbow trout Oncorhynchus mykiss (Walbaum) are usually cultured at high densities to maximize production, but little is known about the physiological and behavioural consequences of high‐density fish culture. The purpose of this study was to develop quantitative correlates of activity for fish held under conditions of increasing density. Fifteen hatchery‐reared rainbow trout (mean fork length = 432.3 ± 9.2 mm) were implanted with activity (electromyogram; EMGi) transmitters and randomly assigned to each of three replicate tanks. Original tank densities (15 kg m^?3) were then increased to 30 and finally to 60 kg m^?3 at weekly intervals by adding additional fish. Remote telemetry signals indicated that activity increased with increasing stocking density. Fish were relatively inactive during the middle of the day, with diel activity patterns not differing among treatments. Fish were more active during periods of darkness, with activity increasing with increasing stocking density. Relationships between swimming speed, EMGi activity and oxygen consumption were developed using a respirometer and used to estimate oxygen consumption of the fish in the density treatments. Average oxygen consumption estimates increased with increasing density treatments as follows: low density = 75.6 mg kg^?1 h^?1; medium density = 90.0 mg kg^?1 h^?1; and high density = 102.6 mg kg^?1 h^?1. Telemetry permits quantification of the effects of increasing density on fish activity. Physiological telemetry devices may provide a useful tool for remotely monitoring animal welfare correlates under controlled conditions for fish exposed to different husbandry conditions and may prove a valuable tool for the aquaculture industry.     

Recovery from transportation by road of farmed European eel (Anguilla anguilla)

The objective of this study was to assess the effects of transportation of marketable eel (0.15 kg) in the Netherlands with respect to welfare. Eels (Anguilla anguilla) were obtained from a commercial farm and acclimatized for 7 weeks at the laboratory. Fish were transported according to regular commercial procedures. The animals were placed in water‐filled transport tanks on the trailer. Fish density increased from 72 kg m^?3 (husbandry) to 206 kg m^?3 (fasting) and was further increased to 270–290 kg m^?3 during transport. Fish transport lasted 3 h after which the eels were returned to laboratory recirculation systems to measure parameters indicative of stress load, i.e. mortality, plasma cortisol, lactate and non‐esterified fatty acids (NEFA) as well as gill morphology. Samples were taken at 0, 6, 24, 48 and 72 h after transport in transported fish and non‐transported counterparts (controls). Transportation affected water quality within known tolerable limits. No mortality during or after transport was observed. After 6 h, plasma cortisol levels had returned to baseline. However, energy metabolism had increased suggesting that transportation of eels resulted in an increased energy demand that lasted for at least 72 h in the fasted animals. Thus, it is conceivable that exposure to adverse conditions, prior to stunning/killing, in a slaughterhouse may result in allostatic overload in eel.     

Curcuma longa supplementation in the diet of Astyanax aff. bimaculatus in preparation for transport

The physiological state of fish before transportation is an important aspect to be observed when reduction in losses due to mortality is aimed. Various preparative procedures for transport are reported, but little is known about the use of additives in fish diet. In this study, we aimed to evaluate the effect of dietary turmeric (Curcuma longa) supplementation on the tolerance of juvenile Astyanax aff. bimaculatus to transportation stress. The experimental design consisted of six treatments: 0, 20, 40, 60, 80 and 100.0 g kg^?1 turmeric. Fish weighing 0.83 ± 0.04 g were distributed in 24 80‐L aquaria at a density of 0.5 fish L^?1 and were fed to satiation three times a day for 60 days. After this period, fish were transported for 24 h in plastic bags (15 fish per bag). Using a discontinuous linear response plateau (LRP) model, the lowest estimated concentration of turmeric that maximized the survival rate was 16.67 g kg^?1. Quadratic effects of turmeric on blood lactate levels were observed, and the estimated concentration of turmeric required to minimize blood lactate levels was 64.7 g kg^?1. We observed quadratic effects of turmeric on superoxide dismutase activity and the concentration of malondialdehyde in fish gills and the turmeric concentrations required to minimize the transport stress effects on these variables were 42.50 and 83.33 g kg^?1, respectively. Thus, dietary supplementation with turmeric enhanced the tolerance of juvenile A. aff. bimaculatus to transportation stress.     

Salt as a stress response mitigator of matrinxã, Brycon cephalus (Günther), during transport

The present study evaluated the physiological responses of matrinxã, Brycon cephalus (Günther) submitted to transport stress under the influence of sodium chloride. Different salt concentrations (0.0%, 0.1%, 0.3% and 0.6%) were added to four 200-L plastic tanks. Each tank was stocked with 30 fish (mean weight 1.0 ± 0.2 kg) and transported for 4 h. Blood was sampled prior to transport and immediately after and 24 and 96 h after transport. Plasma cortisol and glucose and serum sodium and potassium, plasma chloride and ammonia were analysed. Changes in plasma cortisol were observed immediately after transportation, except in fish transported in 0.3% and 0.6% salt. Twenty-four hours later, this hormone had returned to its initial level in all fish. Blood glucose was not changed in fish treated with 0.6% salt immediately after transport, and returned to the initial level within 96 h after the other treatments. All treatments resulted in lower levels of plasma chloride after transport, except for fish treated with 0.6% salt, with fish treated with 0.0% and 0.3% salt recovering 24 h later. Serum sodium decreased immediately after transport only in the control fish, returning to the initial level 24 h later. The results indicate that treatment with 0.6% NaCl reduces most of the physiological responses of matrinxã to the stress of transport.     

鲢顶流游泳速度与摆尾行为相关性分析

鱼类的顶流游泳行为是过鱼设施水力学设计的关键问题之一,获取鱼类在顶流游泳过程中的运动学参数将有助于研究目标鱼类的生理特性、游泳能力及其与水力环境因子的响应关系。本研究以鲢为对象,通过行为学分析软件对鲢在顶流游泳状态下顶流静止和顶流前进的行为中,水流速度U、摆尾频率f、相对摆尾振幅A、绝对游泳速度V和游泳加速度a之间进行了相关性分析。结果显示,鲢在顶流静止状态下,摆尾频率f与水流速度U呈现正相关性;相对摆尾振幅A为(0.0876±0.0098)BL,但与摆尾频率f之间没有明显的相关性;鲢在顶流前进状态下,不同水流速度U中摆尾频率f都要大于顶流静止状态下的摆尾频率,相对摆尾振幅A反而相差不大;摆尾频率f与绝对游泳速度V之间有显著的正相关性,但摆尾频率f与相对摆尾振幅A之间却没有明显的相关性;鲢在顶流前进的过程中,游泳加速度a会随着时间的变化而变化,大多数的游泳加速度为0.02 ga≤0.06 g(55.84%)。本研究主要在水槽中进行,流场环境比较单一,自然的流场环境相对复杂,复杂流场条件下鱼类行为与流场中水力因子之间的关系还需进一步研究。     

Effects of Temperature Reduction and MS‐222 on Water Quality and Blood Biochemistry in Simulated Transport Experiment of Largemouth Bronze Gudgeon,Coreius guichenoti

The effects of temperature reduction, MS‐222 (3‐aminobenzoic acid ethyl ester methanesulfonate) anesthesia and the combination of these factors on water quality and the blood biochemistry of the largemouth bronze gudgeon, Coreius guichenoti, a rare, endangered, and valuable fish in the upper Yangtze River, were investigated before and after simulated long‐term transport. The results showed that transport caused deterioration of water quality and elevated the concentrations of plasma cortisol (2–3.5 times) and plasma lactate (1.33–2.5 times) in C. guichenoti. Temperature reduction was found to play a major role in improving the water quality by reducing total ammonia nitrogen and oxygen consumption, while MS‐222 anesthesia mainly inhibited the activity of transported C. guichenoti and suppressed the increases in plasma lactate and alanine aminotransferase. Some interactions were observed between anesthesia and temperature reduction during C. guichenoti transportation regarding improving the water quality and reducing the physiological stress. The results suggest that during the long‐term transportation of C. guichenoti, the combined use of temperature reduction and MS‐222 is most preferable, followed by the use of temperature reduction alone or MS‐222 at a relatively high temperature. These data provide useful information regarding the transport and physiological response of C. guichenoti as well as other related stresses in this fish.     

Captive Breeding of Threatened African Carp,Labeo victorianus,of Lake Victoria

African carp, Labeo victorianus, is one of the threatened endemic fishes of Lake Victoria which requires conservation and has potential for aquaculture. We conducted a series of experiments on L. victorianus aiming at producing juveniles for both human consumption and stock enhancement. A total of 79 broodstock (mean body weight = 227.06 g) were collected from the wild; packed at 200, 300, and 500 g/L; and transported by road for 7 h. All fish survived during transportation whereas dissolved oxygen decreased and total ammonia nitrogen increased significantly after transport. Females produced 46,702–86,712 eggs (mean = 68,189 ± 2397) and fecundity was highly correlated with the fish body size (R² = 0.96). Only males re‐spawned in captivity while females did not. At 28 C, females spawned 11–12 h after pairing with males. Larvae can either be fed with formulated diet or natural zooplankton. Juveniles (mean length = 36.7 mm; mean body weight = 0.46 g) can be packed as high as 60 fish/L and transported by road for 12 h with low mortality (2.7–10.3%). These results show that captive breeding of L. victorianus can be a good strategy to produce juveniles to boost wild population as well as a source of seeds for culture.     

Measuring cultured fish swimming behaviour: first results on rainbow trout using acoustic telemetry in tanks

An experiment was conducted to measure swimming activity of rainbow trout (254.0±33.7 g) held in outdoor tanks under three culture conditions with stocking density used to generate differences: 27 (Culture Density 1, CD1), 80 (CD2) and 136 kg m⁻³ (CD3). Fish were fed dry pellets at 1% of tank biomass from 9h00 to 13h00 with automatic feeders. Using acoustic telemetry, fish positions were monitored every 5 s during 48 h for nine fish (three in each treatment). Swimming behaviour was analysed in terms of trajectories: they varied between (i) holding position (high turning angles), (ii) chaotic trajectories (equal use of all turning angles) and (iii) circular swimming (average turning angle of 60°). Space utilisation differed for each culture condition: CD3 conditions induced a prolonged residence time in the central zone of the tank. Rainbow trout swimming activity patterns and levels differed depending on both day–night alternation and culture conditions. All fish reared at CD1 and one reared at CD2 were day-active. All the other fish showed high activity pattern variability and a higher swimming level was observed under CD3. These results illustrate that monitoring fish swimming activity is feasible even under high densities and provide relevant insights on fish activity which can lead to behavioural welfare indices in relation to constraints imposed by culture conditions.     

The use of acoustic acceleration transmitter tags for monitoring of Atlantic salmon swimming activity in recirculating aquaculture systems (RAS)

Successful operation of recirculating aquaculture systems is dependent on frequent monitoring of the optimal function of water treatment processes in order to maintain environmental conditions for optimal growth and welfare of the fish. Real time monitoring of fish status is however usually not an integrated part of automatized systems within RAS. The aim of this study was to evaluate the use of implanted acoustic acceleration transmitters to monitor Atlantic salmon swimming activity. Twelve salmon post-smolts were individually tagged and distributed in three tanks containing salmon at start density of 50 kg m⁻³. The tagging did not cause any mortality and all individuals increased their body weight during this study. Following initial recovery, acceleration data were continuously logged for one month, including treatment periods with exposure to hyperoxic (170% O₂ saturation) and hypoxic (60% O₂ saturation) conditions, and different tank hydraulic retention times (HRT; 23 and 58 min). Changes in-tank dissolved oxygen levels to hyperoxic and hypoxic conditions reduced the total activity of Atlantic salmon in this study. On the contrary, increased and reduced tank HRT increased the total activity levels. Feeding periods induced a sharp increase in the Atlantic salmon swimming activity, while irregular feeding caused larger oscillations in activity and also lead to increased swimming activity of the tagged fish. Atlantic salmon responded with a maximum recorded total activity to stress caused by technical problems within the system and consequent changes in the RAS environment. The results of this study indicate that Atlantic salmon respond quickly with changed swimming activity to changes in the water quality and acute stress caused by normal management routines within RAS. The use of acoustic acceleration transmitters for real time monitoring of swimming activity within aquaculture production systems may allow for rapid detection of changes in species-specific behavioural welfare indicators and assist in the refinement of best management practices. In addition, acceleration tag could potentially serve as a valuable research tool for behavioural studies, studies on stress and welfare and could allow for better understanding of interaction between fish and RAS environment.     

Swimming performance of brown trout and grayling show species‐specific responses to changes in temperature

Fishways have historically been constructed to restore and preserve the ecological connectivity for fish in fragmented rivers. However, the fishways are often selective on species due to different size and swimming capacity. As the proportion of dammed rivers is still increasing, there is a growing need for more information on wild fish and their migration potential. In this study, we compared the swimming capacity of wild caught brown trout (Salmo trutta) and European grayling (Thymallus thymallus) until the fish were exhausted in a critical swimming speed (U_crit) test, under three different naturally occurring stream temperatures in Norway: 1.7, 5.5 and 10°C. The results indicated that trout swim better at the warmer temperatures than at colder temperatures. The grayling showed consistent swimming patterns with little variation across all tested temperatures. The results therefore signify the need to have operational fishways already early in the spring when the grayling migration starts and highlight the need for more studies on fish migration abilities across a wider range of species and seasons.     

Stress in African catfish (Clarias gariepinus) following overland transportation

Of the many stressors in aquaculture, transportation of fish has remained poorly studied. The objective of this study was therefore to assess the effects of a (simulated) commercial transportation on stress physiology of market-size African catfish (Clarias gariepinus). Catfish weighing approximately 1.25 kg were returned to the farm after 3 h of truck-transportation, and stress-related parameters were measured for up to 72 h following return. Recovery from transportation was assessed through blood samples measuring plasma cortisol, glucose and non-esterified fatty acids (NEFA) and gill histology. Also, the number of skin lesions was compared before and after transport. Pre-transport handling and sorting elevated plasma cortisol levels compared to unhandled animals (before fasting). Plasma cortisol levels were further increased due to transportation. In control fish, plasma cortisol levels returned to baseline values within 6 h, whereas it took 48 h to reach baseline values in transported catfish. Plasma glucose and NEFA levels remained stable and were similar across all groups. Transported catfish did not, on average, have more skin lesions than the handling group, but the number of skin lesions had increased compared to unhandled animals. The macroscopic condition of the gills was similar in control, transported and unhandled catfish; however, light microscopy and immunohistochemistry revealed atypical morphology and chloride cell migration normally associated with adverse water conditions. From our data, we conclude that transportation may be considered a strong stressor to catfish that may add to other stressors and thus inflict upon the welfare of the fish.     

Temperature and size range for the transport of juvenile donkey's ear abalone Haliotis asinina Linne

Live transport of hatchery‐produced juvenile donkey's ear abalone Haliotis asinina Linne was examined to evaluate the effect of transportation on the survival of juvenile abalone. Simulated transport experiments were conducted to determine the appropriate temperature using 5, 10 and 20 g L^?1 of ice to air volume for 8 h and the appropriate size using two size groups (Size A, 15–20 mm, 0.5–1.3 g, and Size B, 30–35 mm, 5.3–8.5 g) up to 24‐h out‐of‐water live transport. Survival was significantly higher (P<0.001) when 10 g L^?1 of ice was used to decrease the temperature to the range of 17–23 °C. At this temperature, both size groups subjected to simulated transport for 8 and 10 h had 100% survival after 48 h, while mortality occurred in abalones subjected to 16 and 24 h of simulated transport. The Size B abalone subjected to 24 h of transport had significantly higher survival (64.4 ± 2.9%) (P<0.001) than the Size A abalone (5.5 ± 1.6%) after 48 h. Live juvenile abalone were successfully transported to the field applying the protocols developed in the lab experiment. This study serves as a guide for handling and shipping live juvenile abalone.     

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.     

Effect of lordosis on the swimming performance of juvenile sea bass (Dicentrarchus labrax L.)

The critical swimming speed (U_crit, cm s⁻¹) value of normal juvenile sea bass (Dicentrarchus labrax) (64.7±6.33) was significantly higher than that of fish with lordosis (60.3±6.66) (P<0.05). Both normal fish and those with lordosis showed increased endurance with increasing length during exercise at a fixed water velocity of 50 cm s⁻¹. This speed was used to investigate the separation possibility of deformed specimen from the normal developed fish based on their swimming performance, and 28% separation was achieved without losing any normal fish by the end of the 10th minute. To achieve a better separation of the deformities from the normal, first grading of the juveniles and then a swimming endurance test is advised.     

Red drum,Sciaenops ocellatus L., stock enhancement in Biscayne Bay,FL, USA: assessment of releasing unmarked early juveniles

The State of Florida’s practice of releasing unmarked early juvenile red drum Sciaenops ocellatus L. to create a recreational fishery in Biscayne Bay, FL, USA, was assessed. Cohorts were reared in ponds to an early juvenile size of ≈ 50 mm total length. Fish were then harvested and transported immediately to release locations within 24 h. Substantial mortality often resulted after harvesting and immediate transport of early juveniles. Weak correlations between post-transport mortality, transport conditions and fish characteristics (i.e. age, size and condition) suggested that stressors operating before or during pond harvest were predetermining toleration of transport. Seine sampling 1–6 days after cohorts were released indicated that fish ‘disappeared’ from release sites faster than the rates of mortality observed for their siblings monitored in food-rich, predator-free tanks. Visual and immunological analyses of gut contents suggested that juvenile great barracuda Sphyraena barracuda (Walbaum) and adult redfin needlefish Strongylura notata (Poey) were the major predators. Strategies for reducing pre- and post-release mortality and directions for future research are suggested. Discontinuing the release of unmarked organisms of any type is strongly recommended.     

Transport stress in Atlantic salmon (Salmo salar L.): anaesthesia and recovery

The effects of metomidate anaesthesia on levels of plasma cortisol, glucose, haematocrit and chloride in Atlantic salmon (1⁺) (Salmo salar L.), after a 2‐h transport and during a 48‐h recovery period were investigated. The use of metomidate anaesthesia during transport led to a reduced release of cortisol and significantly lower levels of plasma cortisol after a 48‐h recovery period. Plasma glucose did not return to basal level after a 48‐h recovery period, indicating that even longer recovery may be needed for the fish to return to a pre‐stress state. The results show that metomidate anaesthesia combined with a recovery period lessens the stress burden imposed by hauling and transport.     

盐度对条石鲷幼鱼Na+/K+-ATP酶活力的影响

研究了盐度变化对条石鲷幼鱼鳃、肾脏和肝脏中Na⁺/K⁺-ATP酶活力的影响。经不同盐度(8、18、28、38、48)的处理,条石鲷幼鱼3种组织Na⁺/K⁺-ATP酶活力均受到不同程度的影响。经低盐度(8和18)处理的幼鱼鳃Na⁺/K⁺-ATP酶活力在前6 h略微增加,然后逐渐降低,在处理24 h时下降到最低,之后又开始增加。经高盐度(38和48)处理时,鳃中Na⁺/K⁺-ATP酶活力在前6 h有所降低,然后迅速升高,并在处理24 h时达到最大,之后酶活力逐渐降低,并在处理96 h后与对照组无显著性差异(P>0.05)。所有盐度处理组幼鱼肾脏Na⁺/K⁺-ATP酶活力在处理开始6 h均稍有增加,而从处理6 h开始降低,在处理24 h下降到最低,此后酶活力又呈现增加的趋势。在盐度为8的处理组中,肝脏Na⁺/K⁺-ATP酶活力与肾脏中变化趋势相似,而其它3组则逐渐降低,在处理24 h时达到最低,之后又逐渐增加。结果表明,条石鲷幼鱼适盐范围广,具有较强的渗透压调节能力。3种组织的Na⁺/K⁺-ATP酶活力酶活性在盐度为18～38的范围内变化不明显,而在8和48的盐度下变化较大,最终酶活力均高于对照组。与肾脏相比,盐度变化对鳃和肝脏Na⁺/K⁺-ATP酶活力的影响较大。     

Effects of azithromycin on tilapia (Oreochromis niloticus): health status evaluation using biochemical,physiological and morphological biomarkers

Bacterial diseases cause tilapia's high‐mortality outbreak. This study investigated the toxicity of azithromycin (AZT), a macrolide antibiotic that has been considered a possible therapeutic drug for tilapia aquacultural use. The 48‐h acute toxicity (50% lethal concentration, LC50; 48 h) of AZT was determined for Oreochromis niloticus. Thereafter, fish were exposed to 0, 1, 50 and 100 mg L^?1 AZT during 14 days (chronic exposure) and measured the haematological variables, the activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione‐S‐transferase (GST) and the concentration of glutathione (GSH), protein carbonyl and lipid peroxidation in the liver; histopathology was analysed the liver, gills and kidneys. The LC50; 48 h was >100 mg L^?1. No fish died during chronic exposure. Haematocrit and haemoglobin concentration increased in fish exposed to 50 and 100 mg L^?1, and the total number of leucocyte and thrombocyte increased after exposure to 100 mg L^?1 AZT, suggesting a stimulation of defence cell production. In the liver, the antioxidant enzyme activities did not change, but GST activity and the GSH level increased in fish exposed to 100 mg L^?1 AZT. Oxidative stress did not occur. Histopathological index (HI_L) indicates moderate liver damage; minor histological changes in the gill and no change in the kidneys. AZT was considered non‐toxic for O. niloticus after acute exposure and, although it causes moderated histopathology in the liver after chronic exposure, this antibiotic may be an alternative against bacterial infections, depending on its efficacy to control bacterial disease in fish.     

Feeding behaviour of fast- and slow-growing strains of rainbow trout, Oncorhynchus mykiss (Walbaum), during first feeding

The development of feeding behaviour in two rainbow trout strains and their hybrid was compared at the transition from endogenous nutrition to exogenous feeding. After 60 min of acclimatization, the swimming pattern, spatial distribution, agonistic behaviour and snapping of fish were quantified by making 5-min observations on groups of five fish. Behavioural patterns were recorded in four replicate groups per treatment, before and after the introduction of dry trout feed or Artemia nauplii (actometric tests) or extracts of these (olfactometric tests). Fish of the slow growing strain were less active than those of the other two strains. Greater swimming activity observed in the fish of the fast growing strain was associated with more rapid feeding and a higher number of snapping responses. Such behavioural precocity is of interest because it could provide the basis for the growth differences between the fast and slow growing strains.     

Diet and fish choice of Eurasian otters (<Emphasis Type="Italic">Lutra lutra</Emphasis> L.) in fish wintering ponds in Hungary

The diet composition and fish preference of piscivorous Eurasian otters (Lutra lutra) were studied in two fish farm systems in Hungary using spraint (otter faeces) analysis during two wintering periods. The primary food source of otters in both fish farms was fish (97–99% of biomass). The main fish prey was small-sized, below 100 g in weight (96% in both areas), while fish prey above 500 g comprised only 0.1–0.4% of the diet. The bulk of the otters’ diet consisted of less-valued species, especially non-native Prussian carp (Carassius auratus gibelio). Consumption of commercial fish species ranged between 15 and 31% of the total diet. Otters preferred fish below 100 g in weight (Ivlev’s electivity index, E _i = 0.65–0.70), and showed a lesser preference for (or avoided) fish above 100 g in weight (E _i = −0.37–1.00). With regard to species distribution, otters preferred small (below 100 g) grass carp (Ctenopharyngodon idella), zander (Sander lucioperca), pike (Esox lucius), Prussian carp, topmouth gudgeon (Pseudorasbora parva), while they consumed common carp (Cyprinus carpio), the most important commercial species, proportionally to its abundance in the environment (E _i = −0.18–0.29).