The effect of group size on space use and aggression at a concentrated food source in blue gouramis, Trichogaster trichopterus (Pisces: Belontiidae)

Synopsis We examined how spatial distribution and the use of aggressive behavior by blue gouramis, Trichogaster trichopterus (Belontiidae), in the presence of a concentrated food source were affected by group size and by the short-term presence and absence of food. Gouramis aggregated in the area of the food source, and the frequency of aggressive acts per fish was higher for fish near the food source than for fish away from it. The frequency of aggressive acts per fish near the food source decreased with group size and was about 50 times higher in groups of 2 and 4 than it was in groups of 16 and 32. In group sizes 2 and 4, the frequency of aggression was unaffected by the presence and absence of food, but in larger group sizes aggression increased during short intervals without food. The mean proportion of time spent near the food source increased from group size 2 to group size 8 and decreased from group size 8 to group size 32 and was greater during intervals of food availability than during intervals in which food was not available. We suggest that gouramis adjust their relative use of contest and scramble competition according to the costs and benefits of aggression as determined by the number of competitors and by the potential for missed feeding opportunities. The average proportion of time spent in the vicinity of the food source appears to be influenced by both the rate of aggression and by the net rate of gain available.     

The physiology of rainbow trout in social hierarchies: two ways of looking at the same data

Salmonids form dominance hierarchies in environments, where space or food are limiting. Our first objective was to investigate the physiology of individual rainbow trout in 4-fish hierarchies. Our second was to compare conclusions drawn from grouping physiological data on the basis of social rank with those based on relating individual physiology to individual aggressive behavior. To create a social hierarchy, groups of 4 juvenile trout were fed (1 % ration) using a darkened feeding container, twice daily (morning and evening). Each morning feeding was videotaped to record aggressive behavior, thereby facilitating the assignment of a social status rank to each fish. On days 5 and 10–11, physiological parameters were measured in fish fasted for 24 h. Social hierarchies formed in all tested groups. One fish would become dominant, whereas the three subordinate individuals would each assume a stable social rank. When classified according to this social rank, the three subordinate individuals all displayed similar physiology, different from the physiology of the dominant fish. The latter included higher ammonia excretion rate, greater protein utilization in aerobic metabolism, greater feeding, higher specific growth rate, greater increase in condition factor, and lower routine oxygen consumption rate. However, when individual aggression was taken into account, a continuous gradient was observed between aggression and physiology for most parameters, regardless of social status. These relationships could be improved by normalizing the aggression score to the overall level of aggression in each hierarchy. We argue that individual behavior should be considered instead of just social rank when studying the physiology of trout in social hierarchies.     

Comparison between cryoballoon double stop and single stop in patients with paroxysmal atrial fibrillation

BackgroundCurrently, cryoballoon (CB) thawing after single stop is generally performed. Previous research had reported that long thawing time using a single stop affects pulmonary veins tissue injury. However, it is uncertain whether CB thawing after single stop affects clinical outcomes.ObjectiveThis study aimed to clarify clinical significance of CB thawing in patients with paroxysmal atrial fibrillation.MethodsTwo hundred ten patients with paroxysmal atrial fibrillation who underwent CB from January 2018 to October 2019 were analyzed. We compared the clinical outcomes of patients whose CB applications were completely stopped with only the double stop technique (DS group, n = 99) and patients with single stop (SS group, n = 111). In DS group, we performed double stop technique for all CB application regardless of phrenic nerve injury or the temperature of esophagus.ResultsThe atrial arrhythmia free-survival rate at 2 years after CB was significantly lower for the DS group than the SS group (76.8% vs 87.4%; p = 0.045). Complications occurred in 2 patients from the DS group and no complications were observed in patients from the SS group (p = 0.13). Mean procedural time was shorter in the DS group than in the SS group (53.1 vs 58.1 min; p = 0.046)ConclusionDS group had higher recurrence rate than SS group. There was no significant difference regarding safety between both the groups. We found that the thawing process after single stop is very important for CB application.     

Effect of competitor abundance on feeding territoriality in a grazing fish,the ayuPlecoglossus altivelis

The grazing fish, ayu,Plecoglossus altivelis Temminck & Schlegel, establishes feeding territorialiry during the young stage. The population density fluctuates from year to year by more than a hundredfold, but the determinant of territory size is less well known. The feeding territoriality of ayu was examined under simulated habitat conditions where fish density was manipulated and food resources were renewable. Fish competed for algae attached to the substrata and were divided into residents with territories, and floaters without territories. By experimental alteration of fish density the number of residents increased with density and rerritory size decreased with density. Floaters intruded into territories in a school to feed on algae, which induced overt aggression of the resident and reduced the productivity of algae growing there. Both the intruding frequency of floaters over territorial areas and their feeding pressure on algae increased at higher floater density. Floaters functioned to shift cost-benefit relationships for various territory sizes. They acted as food competitors to restrict territory size below a maximum through competitive interference. Although the growth rate of residents was inversely related to fish density, residents grew faster than floaters in each group. Under a given set of competitor abundances, economic defensibility determined territory size.     

鱼类饥饿处理量化及处理因子贡献率的神经网络随机化测试

设一直投喂(SR00)、周期性饥饿2 d再投喂2 d (SR22)、饥饿7 d再投喂2 d (SR72)和饥饿7 d再投喂7 d (SR77) 4种投喂方式,将投喂方式量化为饥饿压力(SS)和循环率(CF)因子,并结合8周实验的干物质摄食量(FI)、鱼体重(BW)、温度(TE)、盐度(SA)、pH (PH)和生长时间(GT)因子,分别对花鲈增重(WG)、特定生长率(SGR)和干物质饲料转换率(FCR)构建神经网络并对其进行预测.结果表明,不同处理对WG、SGR和FCR的影响均存在显著差异(P<0.05).饥饿处理组的WG和SGR均不能达到一直投喂组水平,除SR72处理组FCR显著高于对照处理外(P<0.05),SR22和SR77组与SR00组均无显著差异(P>0.05).人工神经网络对SGR和WG具有极佳的预测效果,但对FCR无效.8个分析因子中,FI、SS、CF和GT对WG、SGR有显著贡献,且WG的大小主要取决于FI,而SGR主要取决于SS.随机化测试显示,实验处理因子(包括相关的FI因子)对WG和SGR的贡献率分别为64.9%和79.7%.     

Physiological responses to single versus double stepping pattern of ascending the stairs

The aim of this study was to compare the physiological responses and energy cost between two ascending patterns, the single-step (SS) and the double-step (DS), in climbing a public staircase. In the SS pattern, a person climbs one step at a time whilst in the double-step (DS) pattern, the individual traverses two steps in a single stride. Advocates of each stepping pattern claimed that their type of ascent is physically more taxing and expends more calories. Thirty subjects (10 males and 20 females) climbed a typical 11-storey flat (each step height of 0.15 m, a total of 180 steps and a vertical displacement of 27.0 m). The subjects climbed using either the SS pattern at a tempo of 100 steps x min(-1) or the DS pattern at 50 steps x min(-1). The prescribed stepping frequencies ensured that an equal amount of total work was performed between the SS and DS patterns. The climbing patterns were performed in random order. Physiological measures during the last 30 s of the climbs were used in the comparative analysis. The results showed that ventilation, oxygen uptake and heart rate values were significantly higher (all p < 0.01) in the SS as compared to the DS pattern. However, the caloric expenditure during the SS pattern was calculated to be only marginally higher than the DS pattern. In conclusion, ascending with the SS pattern led to significantly higher physiological responses compared to the DS pattern. The higher calorie expended with the SS compared to the DS pattern was deemed to be of little practical significance.     

Effects of kinship on aggression and RNA content in juvenile Arctic charr

The behaviour of juvenile Arctic charr Salvelinus alpinus was studied in groups of four siblings composed of familiar and unfamiliar individuals or in mixed groups of four where both siblings and unrelated individuals were present. The frequency of aggressive acts was significantly higher in the mixed groups compared to the pure sibling groups and the difference was present at all levels of the hierarchy rank order, based on a dominance index, except the lowest ranked individuals. The difference was significant after but not before feeding, implying that competition with non-kin for a food resource increased the aggression. No significant difference in weight gain was observed between sibling and mixed groups during the 6 days of the experiment, but the RNA contents of lateral musculature in dominant individuals from sibling groups were significantly higher than the corresponding fish in the mixed group, suggesting a difference in growth rate when the experiments ended. No significant difference in RNA content was observed between subordinate fish of the two treatments, i.e. siblings v . mixed.     

Effects of habitat complexity,dominance and personality on habitat selection: Ideal despotic cichlids

Habitat structure can impede visibility and movement, resulting in lower resource monopolization and aggression. Consequently, dominant individuals may prefer open habitats to maximize resource gain, or complex habitats to minimize predation risk. We explored the role of dominance on foraging, aggression and habitat choice using convict cichlids (Amatitlania nigrofasciata) in a two‐patch ideal free distribution experiment. Groups of six fish of four distinct sizes first competed for shrimp in one‐patch trials in both an open and complex habitat; half the groups experienced each habitat type first. Following these one‐patch trials, each group then chose between habitat types in a two‐patch trial while competing for food. Finally, each fish underwent an individual behavioural assessment using a battery of “personality” tests to determine if behaviour when alone accurately reflected behaviour within a social context. In the one‐patch trials, dominant fish showed similar food consumption between habitats, but chased more in the complex habitat. In the two‐patch choice trials, dominants preferred and defended the complex habitat, forming an ideal despotic distribution with more than half the fish and competitive weight in the open habitat. Within the groups, individual fish differed in foraging and chasing, with repeatabilities of 0.45 and 0.23 across all treatments. Although a higher foraging rate during the individual assessment predicted foraging rate and use of the complex habitat during the group trials, aggression and boldness tests were not reflective of group behaviour. Across groups, heavier dominants and those with higher foraging rate in the open habitat used the open habitat more, suggesting that both risk and energetic state affect habitat preference in dominant convict cichlids.     

Agonistic behaviour and control of access to hiding places in two intertidal blennies, Lipophrys pholis and Coryphoblennius galerita (Pisces: Blenniidae)

In this study we investigated the relationships between dominance rank and access to shelters in captive groups of Lipophrys pholis and Coryphoblennius galerita, as well as the effects of group size and shelter availability. Dominance rank was strongly correlated with size in juvenile L. pholis and with sex and size in adult C. galerita, males being dominant over females of similar size. Access to shelters was significantly correlated with dominance rank. For both species, most interactions occurred out of shelters. Direct disputes over shelters were always initiated by the dominant fish and the initiator was always the winner. The rate of aggression per fish per unit time decreased with an increase in the number of fish in L. pholis but not in C. galerita. No significant differences were found in groups differing in the number of shelters. C. galerita showed a higher rate of agonistic interactions and a higher proportion of overt aggression than L. pholis. It is suggested that one of the functions of agonistic interactions in these fishes is the control of a set of shelters, in the network of pathways used by each individual within its home range, minimising the time required to hide in case of danger. Received in revised form: 29 January 2001 Electronic Publication     

Effect of Group Size on Feeding Rate when Patches are Exhaustible

One benefit of group foraging is that individual foragers can join the food discoveries of companions and thus increase encounter rate with food patches. When food patches are exhaustible, however, individual shares of each patch will decrease with group size negating the effect of increased encounter rate. Mean feeding rate may actually decrease with group size as a result of aggression or time wasted joining already depleted patches, or when searching to join the food discoveries of others, which is referred to as scrounging, precludes finding food. I examined the relationship between mean feeding rate and group size in captive flocks of zebra finches (Taenopygia guttata) foraging for small clumps of seeds. Finches in groups of two or four fared better than solitary birds in terms of mean feeding rate despite the fact that birds in groups scrounged a large proportion of their food. Solitary birds initiated feeding activity after a longer delay, which led to their lower success. Early departures by food finders from food patches joined by others may have lessened the impact of scrounging on mean feeding rate. As a result of benefits from the presence of companions, group foraging in zebra finches appears a viable alternative to foraging alone despite the cost of sharing resources.     

Effects of Familiarity and Population Density on Competitive Interactions and Growth: An Experimental Study on a Territorial Salmonid Fish

The deleterious effect of competition for space and food in animals increases with increasing population density. In contrast, familiarity towards conspecifics can relax the intensity of interference competition. Here, we hypothesized that familiarity towards conspecifics mitigates the effect of density‐dependent growth and dispersal behaviour in territorial animals. To test this, wild‐captured juvenile brown trout were subjected to two consecutive laboratory experiments. First, growth and fin erosion were measured for 40 d in a 2 × 2 factorial design manipulating density and familiarity. The density was manipulated via size of experimental tanks, while per capita food abundance and fish number was constant. All fish were subsequently exposed to an emergence test, giving them the option to leave their group and disperse to a novel unoccupied environment. The results show that familiarity increases growth and decreases the level of fin erosion (i.e. proxy of intensity of aggressive interactions). We found no significant effect of population density on growth rate. However, there was a tendency towards higher fin erosion in fish kept under high density. The growth of individuals was also affected by their size rank within the group, with the largest individuals in each group growing disproportionally faster than the rest of the group, probably due to their high social rank. However, the second and third fish in the size rank did not grow significantly faster and tended to suffer higher mortality than the rest of the group. During the emergence test, the largest individuals in the familiar groups left the shelter either as the first (six of 12 groups) or last (five of 12 groups) individual in the group, while no such pattern was observed in unfamiliar groups. Our results suggest that individuals in familiar groups receive less aggression and stress (i.e. fin damage) and grow faster than fish in unfamiliar groups. The mechanisms indicated in this laboratory study may be especially important in highly fecund organisms like fish which undergo density‐dependent bottlenecks during early life.     

Relationships between release season and feeding performance of hatchery-reared Japanese flounder Paralichthys olivaceus: In situ release experiment in coastal area of Wakasa Bay, Sea of Japan

Two groups of hatchery-reared juveniles of Japanese flounder Paralichthys olivaceus (Temminck and Shlegel) were experimentally released in Wada Beach, Fukui Prefecture, Japan and their feeding state examined in comparison to wild juveniles to investigate the optimal release season and the relationship between food availability and feeding performance of juveniles. We released two groups of 40,000 juveniles of ca. 50 mm size, one group in the early (29 May) and the other in late (2 July) seasons, periods with predicted high and low densities of prey mysids, respectively, although the abundance of mysids fluctuated markedly during the season. Food availability was higher for the early release group than the late release group. Although the main stomach contents of released and wild juveniles were mainly mysids and fish, the feeding state differed between the early and late release groups. The early release group had a stomach content index (SI) similar to that of the wild juveniles, but the SI of the late group was significantly less than that of the early release group and wild juveniles. The percentage of fish with empty stomachs was much higher in the late release group than in the other two groups. In addition, the density decrease rate was significantly more rapid for the late release group than the early release group. Clear correspondence between the food availability and feeding state of the released flounder juveniles indicates that the release of juveniles in an appropriate season when mysids are abundant is crucial for successful stocking.     

Feeding and Growth Response of Roach, Rutilus rutilus, to Alarm Substance

Feeding and growth responses of roach from three size classes to alarm substance (Schreckstoff) were quantified in laboratory experiments. Larger fish (60.0–80.0 mm in length) reacted stronger to treatment than two smaller sized groups (35.0–45.0 and 46.0–55.0 mm) lowering feeding rate by 80 and 40 and 50%, respectively. The reduction in feeding rate of larger fish caused decrease in growth rate in length and weight, while the lowered consumption of smaller fish caused only reduction in growth rate in weight. Condition factor of exposed to alarm substance small sized roach was lower than that of the control individuals and roach from other two size classes, both, treated and untreated. The difference in growth response to a danger of predation has its roots probably in different metabolism and growth rates of small and large fish. Small fish have higher metabolic rate and less lipid reserves than larger ones, therefore they are probably forced to feed to be able to grow. Also, small sized roach is more vulnerable to predation than large sized fish, thus growing fast seem to be crucial for survival in a risky environment. Study shows that small roach trade off their safety against food, feeding in risky environment to sustain fast growth. This ability of fast outgrowing of a dangerous, vulnerable to predators, size increases survival of juveniles in dangerous environment.     

The effect of acute stretching on agility performance

Static stretching (SS) has shown decreases in many areas including strength, anaerobic power, and sprinting time. Dynamic stretching (DS) has shown increases in anaerobic power and decreases in sprinting time. Research on the effects of stretching on agility performance is limited. The purpose of this study was to determine the effect of SS and DS on performance time of a sport agility test. Sixty male subjects consisting of collegiate (n = 18) and recreational (n = 42) basketball athletes volunteered for the study. Subjects were randomly assigned to 1 of 3 intervention groups: SS, DS, or no stretching (NS). All groups completed a 10-minute warm-up jog followed by a 3-minute rest. The SS and DS groups then completed an 8.5-minute stretching intervention. Next, all subjects completed 3 trials of the 505 agility test with 2-5 minutes of rest between trials. A 2-way repeated-measure analysis of variance (Stretch group, athlete category, group × athlete interaction) was used to determine statistical significance (p < 0.05). A Tukey post hoc test was performed to determine differences between groups. For all athletes, the DS group produced significantly faster times on the agility test (2.22 ± 0.12 seconds, mean ± SD) in comparison to both the SS group (2.33 ± 0.15 seconds, p = 0.013) and NS group (2.32 ± 0.12 seconds, p = 0.026). Differences between the SS and NS groups revealed no significance (p = 0.962). There was a significant difference in mean times for the type of athlete (p = 0.002); however, interaction between the type of athlete and stretching group was not significant (p = 0.520). These results indicate that in comparison to SS or NS, DS significantly improves performance on closed agility skills involving a 180° change of direction.     

Diagnostic Accuracy of Dermoscopy for Scabies

The diagnostic accuracy of dermoscopy (DS) for scabies, a highly contagious parasitic disease, remains disputed. This study aimed to assess the diagnostic accuracy of DS in scabies, analyze the factors influencing DS, and explore its role in post-treatment evaluation. Patients with suspected scabies were randomly divided into 2 groups: 71 patients in the skin scraping (SS) group and 73 patients in the DS group. The diagnostic efficiencies of SS and DS in these groups were calculated. We also analyzed the influence of body part and investigator competence on the accuracy of DS. Then 16 body parts with typical signs of scabies were monitored by DS 2 and 4 day after sulfur ointment treatment. The sensitivity and specificity of DS were 98.3% and 88.5%, respectively. Hands, arms, and the abdomen had higher positivity rates than other body parts (P<0.001). The accuracy of dermatologists’ interpretations of images negative for scabies in the intermediate- and high-level groups was higher than that in the low-level group (P<0.001). At follow-up, the mites were still visible on 43.8% to 62.5% of the skin lesions 2 and 4 day after sulfur ointment treatment. These results showed that DS could significantly increase the accuracy of diagnosing scabies owing to its high sensitivity and specificity. Therefore, it may be useful for monitoring clinical responses to anti-parasitic treatment.     

Growth depensation and group behaviour in juvenile hybrid striped bass Morone chrysops×Morone saxatilis: effects of group membership, feeding method, ration size and size disparity

The effects of group membership (three group sizes), feeding method (single site v. scattered), variation in ration size (low v. high) and starting size disparity (range of starting sizes) on growth, growth depensation and group behaviour of juvenile hybrid striped bass (HSB) Morone chrysops female × Morone saxatilis male were tested. Group membership, starting size disparity and ration size affected the growth, growth depensation and behaviour of juvenile HSB. Growth was higher in fish held within large group memberships and high ration treatments. Growth depensation (size variation among individuals of the same age) in group memberships of three and 12 fish per tank was minimal when compared to intermediate memberships (six fish per tank). In addition, small fish held in tanks with fish of intermediate sizes demonstrated higher growth when compared to small fish housed with large individuals. Some behaviours, specifically activity and scramble feeding, were more elevated in large group memberships when compared to groups with fewer members. Activity was also found to increase over time during size disparity testing. Results suggest that HSB are ideally suited for high-density, intensive aquaculture since they appear to thrive in high group memberships of similar starting sizes and when a sufficient amount of feed in administered.     

Effects of Quillaja saponins on growth,metabolism, egg production and muscle cholesterol in individually reared Nile tilapia (Oreochromis niloticus)

The effects of supplementation of a Quillaja saponin (QS) mixture in the diets of tilapia have been studied using a respirometer system that allowed feeding and continuous measurement of oxygen consumption of individual fish. Five fish each were given control diet (C group) and control diet supplemented with 150 mg kg^?1 (S150 group) or 300 mg kg^?1 (S300 group) QS. At the end of 14 weeks the weight gain of the S300 group was significantly higher than control (P<0.05) whereas that of the S150 group had an intermediate value. The S150 group had a higher growth rate (P=0.05) after the first 3 weeks of feeding with the experimental diets, compared to the other two groups. At the end of the experiment the S300 group had significantly higher (P<0.05) average values for energy retention, apparent lipid conversion, carcass fat, energy and significantly lower (P<0.05) average values for apparently unutilised energy and carcass ash content compared to the C group. The corresponding values of the S150 group were intermediate between the C and S300 groups. One out of two female fish in the S150 group and both female fish in the S300 group never produced eggs during the entire 14-week experimental period. Contrarily, all three female fish in the control group and one out of the two female fish in the S150 group regularly produced eggs, at a rate of approximately once in every 14 days. The muscle cholesterol level in the S300 group was significantly higher than that of the C group. Possible mechanisms of action of the dietary saponins are discussed.     

You are Not Welcome: Social Exchanges between Female Spider Monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>)

Group living leads to competition for food between group members. Two types of intragroup food competition may occur: scramble competition, in which all group members use the same resource, such that feeding opportunities are equal for everyone; and contest competition, in which some group members monopolize resources through aggression and dominance. In species in which females disperse from the natal group and immigrate into other groups, immigrant females increase group size and thus possibly food competition. Under these circumstances, other females may use aggression to discourage new females from joining the group. We assessed the distribution of aggression, embraces, and kisses among female spider monkeys (Ateles geoffroyi) in relation to group tenure. We recorded social interactions during 1688 10-min focal animal samples on 11 females in Santa Rosa, Costa Rica. We found that aggression was rare between long-term resident females and aggression rates were not higher during feeding than in other contexts, suggesting there was little contest competition. Long-term residents and less recently immigrant females showed higher aggression rates toward the most recent immigrants than toward other females, especially during the first months after a female immigrated, which coincided with the dry season. We did not find similar patterns for embrace and kiss. These results suggest that other females target aggression toward the most recent immigrants to reduce scramble competition. This finding suggests that group tenure should be included in socioecological models for species with female dispersal.     

锦鲫幼鱼的社群等级地位及其与标准代谢率、血糖和临界游泳能力的关系

在(25.0±0.5)℃实验室条件下,考查标记后体重相近的30尾锦鲫幼鱼(3.5±0.1g)的标准代谢(standard metabolic rate,SMR),然后将实验鱼分为10个组(每组3尾);分别以好斗行为和摄食成功率两个指标将各组实验鱼评估为3个不同的社群等级;再分别测定各等级地位实验鱼的SMR、血糖浓度和临界游泳速度(critical swimming speed,Ucrit)。结果显示:锦鲫幼鱼3个等级地位由高到低的摄食成功率分别为(51.2±1.61)%、(29.3±1.87)%、(19.5±0.73)%;好斗行为指标得分分别为(8.1±0.30)、(1.9±0.30)、0.0,两个评估指标均存在显著性差异(P0.05);Ucrit分别为(35.5±0.22)、(33.7±0.66)、(29.8±1.02)cm/s,血糖浓度分别为(3.4±0.22)、(4.2±0.30)、(4.5±0.33)mmol/L(P0.05);而评估前、后各等级之间实验鱼的SMR均没有显著差异(P0.05)。结果表明:锦鲫幼鱼存在着明显社群等级分化的现象;好斗行为和摄食成功率两个指标分别对社群等级地位的评估结果具有显著的一致性;实验鱼等级地位越高其游泳能力越强,血糖浓度越低;这一现象提示,高等级地位的鱼受到较低的社群胁迫且具有较高的生理适合度。     

Surface feeding and aggressive behaviour of diploid and triploid brown trout Salmo trutta during allopatric pair‐wise matchings

Diploid and triploid brown trout Salmo trutta were acclimated for 6 weeks on two feeding regimes (floating and sinking). Thereafter, aggression and surface feeding response were compared between pairs of all diploid, all triploid and diploid and triploid S. trutta in an experimental stream. In each pair‐wise matching, fish of similar size were placed in allopatry and rank was determined by the total number of aggressive interactions recorded. Dominant individuals initiated more aggression than subordinates, spent more time defending a territory and positioned themselves closer to the surface food source (Gammarus pulex), whereas subordinates occupied the peripheries. In cross ploidy trials, diploid S. trutta were more aggressive than triploid, and dominated their sibling when placed in pair‐wise matchings. Surface feeding, however, did not differ statistically between ploidy irrespective of feeding regime. Triploids adopted a sneak feeding strategy while diploids expended more time defending a territory. In addition, we also tested whether triploids exhibit a similar social dominance to diploids when placed in allopatry. Although aggression was lower in triploid pairs than in the diploid and triploid pairs, a dominance hierarchy was also observed between individuals of the same ploidy. Dominant triploid fish were more aggressive and consumed more feed items than subordinate individuals. Subordinate fish displayed a darker colour index than dominant fish suggesting increased stress levels. Dominant triploid fish, however, appeared to be more tolerant of subordinate individuals and did not display the same degree of invasive aggression as seen in the diploid and diploid or diploid and triploid matchings. These novel findings suggest that sterile triploid S. trutta feed similarly but are less aggressive than diploid trout. Future studies should determine the habitat choice of triploid S. trutta after release and the interaction between wild fish and triploids during the breeding season prior to utilization of triploids as an alternative management strategy within freshwater fisheries.