Frequency Of Fighting Research Articles

Aggression among finishing pigs following mixing in kennelled and unkennelled accommodation

This study examines the interactive effects of mixing and the provision of kennels to finishing pigs on agonistic behaviour. Pigs were housed either in naturally ventilated kennelled accommodation, or in an unkennelled sloping floor accommodation with automatically controlled natural ventilation (ACNV). Under each of these two housing conditions, three groups of 10 pigs were subjected to one of the following four mixing/moving treatments: no mixing (control), mixing and moving at 55 kg only, mixing and moving at 75 kg only and mixing and moving on both occasions. Groups which were not mixed at 55 kg or at 75 kg were moved to a novel pen at the time that the others were mixed. Mixing and moving pigs resulted in higher levels of aggression and skin damage compared to moving only. Levels of skin lesions were lower when mixing at 55 kg compared to mixing at 75 kg. The duration and frequency of fights in the immediate post mixing period and skin damage measured on day 1 after mixing correlated well when mixing pigs at 75 kg, but not when mixing at 55 kg. This suggests that the hierarchy takes longer to be established in younger pigs than it does in older heavier pigs, or that skin damage inflicted by heavier pigs during fights is more severe. Previous mixing at 55 kg had minimal effects on mixing at 75 kg in terms of behaviour immediately post mixing and skin lesions in the following two days. The presence of a kennel appeared to have a positive effect on the average duration of fights, but the effect on the proportion of fights which involved location changes (lying to dunging area or vice versa) was not significant. Performance data suggested that food conversion ratios were poorer in the first two weeks after mixing in the kennelled building, but not in the sloping floor building. Increased social and thermal stress after mixing in the kennelled, naturally ventilated accommodation may have been the cause of this. Over the whole of the finishing period, daily live weight gains and food conversion ratios did not differ measurably between treatments.

Conflict education in a special needs population

AbstractThis article reports on a two‐part pilot project in which a conflict education program and a peer mediation program were implemented in a special needs population to reduce students' aggressive behaviors and improve the school's climate. The participating school was an approved private school to which students (ages five through twenty‐one) with learning disability (LD), emotional disability (ED), or attention deficit‐hyperactivity disorder (ADHD) were referred from public education institutions unequipped to provide necessary services. The project is discussed in terms of needs assessment, program development and implementation, and insights for training with a special needs population. Research was conducted to ascertain the impact of conflict education training on incidents of aggressive behavior and school climate. Results indicate a significant reduction in the most serious behavioral incidents during the project period, as well as a slight increase in moderately serious incidents and a sharp increase in nonserious incidents. A decrease in the frequency of fights among younger students and a significant improvement in school climate were also apparent.

Mixing induces long-term hyperthermia in growing pigs

AbstractThe purpose of this experiment was to determine whether body temperature is a sensitive parameter to measure long-term effects of stress in pigs. Mixing of unacquainted pigs is a severe stressor that has detrimental effects on health, production and welfare. We measured deep body temperature after mixing growing pigs. Five pigs of 15 weeks of age, each individually housed with a companion pig, were mixed with two unacquainted congeners. Deep body temperature, heart rate and activity were recorded by radiotelemetry 9 days prior to until 8 days after mixing. These parameters were also recorded in five control pigs (individually housed with a companion pig) during the same time span. Behaviour during the light period was recorded on videotape on the day of mixing and on three subsequent days. Mixing induced a significant rise in body temperature that lasted for 8 h after mixing. Although heart rate and general activity level did not significantly differ between mixed and control pigs, mixing significantly increased the frequency of fighting and reduced the frequency of eating. In conclusion, the present experiment shows that mixing induces a long-lasting hyperthermia in pigs. Thus, deep body temperature may be used as a sensitive parameter to measure long-term effects of stress in pigs.

Warfare in prehistoric and early historic eastern North America

Recent criticisms of the use of historically and ethnographically recorded conflicts as models for warfare in prehistoric times force archaeologists to reexamine assumptions about the frequency, severity, and effects of intergroup fighting. In eastern North America, skeletons of victims and palisaded settlements—the only information consistently available on intergroup hostilities—indicate that the prevalence of conflicts varied greatly over time and space. Occasionally the attacks, typically ambushes of small numbers of people, cumulatively resulted in numerous casualties.Variation in palisade strength is consistent with the organizational structure and warrior mobilization potential of late prehistoric societies in different parts of the Eastern Woodlands.

Health Risk Behaviors of Texas Students Attending Dropout Prevention/Recovery Schools in 1997

This study determined prevalence of health risk behaviors of 9th through 12th grade students attending dropout prevention/recovery alternative schools in Texas in 1997. Participants were 470 youth whose health risk behaviors were assessed using the Youth Risk Behavior Survey in an anonymous, self-administered format. Behaviors measured included frequency of weapon-carrying and fighting, suicide-related behaviors, substance use, and sexual behaviors. A substantial percentage of alternative school students reported participating in behaviors that placed them at acute or chronic health risk. Differences in the prevalence of risk behaviors were noted by gender, racial/ethnic, and age subgroups. In addition, alternative school students frequently engaged in multiple risk behaviors. These findings suggest a need for comprehensive school-based health education/intervention programs to reduce the prevalence of risk behaviors in populations of alternative school students.

Mechanisms underlying the absence of the pubertal shift in the playful defense of female rats

Due to the action of testicular hormones in the perinatal period, juvenile male rats engage in more play fighting than juvenile females. Also, following puberty, males, but not females, switch to using adultlike defensive tactics more frequently during play. This change in play is also due to the action of testicular hormones perinatally. In this study, two experiments were conducted to determine if the pubertal transition in defense could be induced in females. For Experiment 1, male and female cagemates were tested before and after puberty with familiar and unfamiliar partners. Even when playfully interacting with subadult males, females did not increase the use of the adultlike defensive tactics. For Experiment 2, neonatal females were either injected with testosterone propionate (TP) or ovariectomized (OVX), and again tested before and after puberty. While the TP-treated females had higher frequencies of play fighting, they did not change their pattern of defense following puberty. The OVX females exhibited the lower frequency of play fighting typical of females, but changed their pattern of defense with increased age. Thus, it appears that the pattern of pubertal change in playful defense typical of males is inhibited by ovarian hormones. The mechanisms by which ovarian hormones could exert this effect on developing females are discussed.

Mechanisms underlying the absence of the pubertal shift in the playful defense of female rats

Due to the action of testicular hormones in the perinatal period, juvenile male rats engage in more play fighting than juvenile females. Also, following puberty, males, but not females, switch to using adultlike defensive tactics more frequently during play. This change in play is also due to the action of testicular hormones perinatally. In this study, two experiments were conducted to determine if the pubertal transition in defense could be induced in females. For Experiment 1, male and female cagemates were tested before and after puberty with familiar and unfamiliar partners. Even when playfully interacting with subadult males, females did not increase the use of the adultlike defensive tactics. For Experiment 2, neonatal females were either injected with testosterone propionate (TP) or ovariectomized (OVX), and again tested before and after puberty. While the TP-treated females had higher frequencies of play fighting, they did not change their pattern of defense following puberty. The OVX females exhibited the lower frequency of play fighting typical of females, but changed their pattern of defense with increased age. Thus, it appears that the pattern of pubertal change in playful defense typical of males is inhibited by ovarian hormones. The mechanisms by which ovarian hormones could exert this effect on developing females are discussed. © 1998 John Wiley & Sons, Inc. Dev Psychobiol 33: 147–156, 1998

Fighting Tactics of Fallow Bucks (Dama dama, Cervidae): Reducing the Risks of Serious Conflict

AbstractCompetition between male fallow deer (Dama dama), during the breeding season was studied to determine if conflict strategies were consistent with the reduction of risk. Agonistic interactions between males were analysed in relation to age, dominance rank and availability of mating opportunities. The breeding season was divided into two main periods: the pre‐rut began when all males had cleaned the velvet from their antlers and ended on the last day before matings were first observed, while the rut refers to the period between the first and last matings. Overall, socially mature males (≥4yr old) were involved in more interactions than immature (≤3yr old) males. Males established dominance rank largely by non‐contact agonistic interactions during the pre‐rut and there was substantial carry‐over of rank to the rut, when it was correlated with mating success. The mating success of males was skewed; mature males achieved 99.4% of the matings and immature males accounted for 0.6%. A mature male was 13 times more likely to fight than an immature male; the mature males that fought most often did so between 0.4 and 0.5 times per hour. During the rut, the number of fights was positively correlated across days with the number of matings. The majority of agonistic interactions (79%) comprising dyads of immature males, involved antler contact. In contrast, mature males engaged antlers in only 42% of their interactions. Fights between mature males lasted more than twice as long as those between immature males and were more likely to occur between opponents with similar dominance ranks. However, towards the end of the rut formerly mismatched opponents were more likely to fight. Thus males operated conditional competitive strategies to decide when to interact and fight. The persistence of rank order from the pre‐rut period to the rut and the tendency for mature males to resolve disputes without antler contact, served to reduce the frequency of fights and therefore the risk of serious injury.

Weapon-carrying, physical fighting, and fight-related injury among U.S. adolescents

Introduction: Access to firearms and other weapons has been cited as an important factor contributing to the rise in violence-related injury among adolescents in the United States. Methods: Data from the Youth Risk Behavior Survey supplement to the 1992 National Health Interview Survey were analyzed to examine relationships among weapon-carrying, physical fighting, and fight-related injury among U.S. adolescents aged 12–21 years ( N = 10,269). Adjusted odds ratios (OR) were used to describe the association of weapon-carrying during the past 30 days with physical fighting and fight-related injury during the past 12 months. Results: Weapon-carrying (15%) and physical fighting (39%) were common among adolescents. One out of 30 (3.3%) adolescents reported receiving medical care for fight-related injuries. Controlling for demographic characteristics, youth who carried weapons were more likely than those who did not to have been in a physical fight (OR = 3.3). The association between weapon-carrying and physical fighting was stronger among females (OR = 5.0) than among males (OR = 2.9), but did not vary significantly by age, race/ethnicity, or place of residence (urban, suburban, rural). Controlling for frequency of physical fighting and demographics, adolescents who carried a handgun (OR = 2.6) or other weapon (OR = 1.6) were more likely than those who did not carry a weapon to have had medical care for fight-related injuries. Conclusions: Among adolescents, weapon-carrying is associated with increased involvement in physical fighting and a greater likelihood of injury among those who do fight. Efforts to reduce fight-related injuries among youth should stress avoidance of weapon-carrying.

The association of weapon carrying and fighting on school property and other health risk and problem behaviors among high school students.

To examine the association between weapon carrying on school property and engaging in health risk and problem behaviors such as fighting and substance use on school property, fear of attending school, and victimization at school. A complex 2-stage probability survey (Massachusetts Youth Risk Behavior Survey). High schools in Massachusetts. Three thousand fifty-four high school students. Number of days a weapon was carried on school property during the 30 days prior to the survey. The prevalence of self-reported weapon carrying on school property was 15% among male students and 5% among female students (P < .001). Weapon carrying on school property was significantly (P < .001) associated with frequency of physical fights on school property (r = 0.26), being a victim of threat or injury with a weapon on school property (r = 0.27), being a victim of stolen or damaged goods on school property (r = 0.14), not attending school owing to fear (r = 0.15), and substance use while at school, including smoking cigarettes (r = 0.20), using chewing tobacco (r = 0.18), smoking marijuana (r = 0.24), and using alcohol (r = 0.29). The association between weapon carrying and alcohol use in school was higher among students who were afraid to come to school (r = 0.49) than among students who were not afraid (r = 0.28). Students who had engaged in same-sex sexual activity (P < .001) or had been offered, given, or sold illicit drugs at school (P < .001) were more likely to carry a weapon at school. Multiple regression analysis showed that male sex and the frequencies of physical fighting, being a victim of a threat or injury, drinking alcohol, smoking cigarettes, and being offered or sold an illicit drug while on school property accounted for 21% of the variance in weapon carrying in school. When weapon carrying was dichotomized and analyzed with logistic regression, a model containing age, male sex, lower academic achievement, days not attending school owing to fear, times threatened or injured with a weapon at school, frequency of fighting at school, cigarette smoking, alcohol use, and being offered or sold illicit drugs on school property correctly classified 91.83% of the students who did or did not carry weapons. Weapon carrying at school was more strongly associated more with use of violence and the use of substances at school than with previous victimization and fear of attending school. However, there is a subgroup of students that seems to have been victimized at school, is afraid to come to school, is using alcohol at school, and is carrying weapons at school.

Combining Analysis and Action to Solve the Problem of Youth Violence

Purpose: To evaluate a Social Cognitive Theory–based violence prevention curriculum among sixth-grade students.Methods: The evaluation was conducted using a quasi-experimental pretest–posttest control group design. Students were pretested 2 weeks before the intervention started and were posttested 2 weeks after it ended. The study was conducted in four middle schools serving children and adolescents living in or around public housing in a southeastern city. The participants included all sixth-grade students who were predominantly African-American (88.7%), 41% lived in public housing, and 80% lived in homes with an employed head of household. The intervention schools had 292 students, and the control schools 412 students. The Peaceful Conflict Resolution and Violence Prevention Curriculum is a 13-module skills-building curriculum based on Social Cognitive Theory. It taught identification of situations that could result in violence; avoidance, confrontation, problem-solving, and communication skills; conflict resolution skills; the conflict cycle; the dynamics of a fight; and how to express anger without fighting.Main Measures: The primary outcome variable was a five-item scale assessing the frequency of fighting and weapon carrying behaviors (α = .72) and a scale measuring intentions to use violence in 11 hypothetical situations (α = .81). Levels of exposure to violence and victimization (α = .82) and depression (α = .86) were also assessed. The data were analyzed with general linear modeling with repeated measures.Results: At pretest, the intervention and control groups did not differ in gender, age, depression, exposure to violence, or any other demographic variable. A group × time interaction effect (p = .029) was found in the use of violence scale. From pretest to posttest there was a decrease in the use of violence by students in the intervention group and an increase in the use of violence in the control group. Most of the changes were accounted for by changes in the frequencies of carrying concealed guns and fighting resulting in injuries requiring medical treatment. A group × time interaction effect (p = .002) was also found for the intention to use violence scale. Students in the intervention group did not change their mean scores from pretest to posttest, whereas students in the control group increased in their mean intention to use violence scale scores. Neither interaction effect was influenced by gender, exposure to violence, or level of depression.Conclusion: The Peaceful Conflict Resolution and Violence Prevention curriculum appears to have positive short-term effects on self-reported use of violence and intentions to use violence by these middle-school students.

Comparison of two violence prevention curricula for middle school adolescents

To compare the effectiveness of the Violence Prevention Curriculum for Adolescents to the Conflict Resolution: A Curriculum for Youth Providers among middle school students. A sample (N = 225) of adolescents (males = 48%) representing 20% of the student population in two middle schools were administered a pretest questionnaire. Of these students, 89% were African-American, 10% were white, and 1% were Native-American and lived in public housing (40%) or in neighborhoods adjacent to public housing (60%). Each school was randomly assigned to one of the curricula. Each curriculum was administered during 10 50-min sessions held twice a week over 5 weeks. One week later, 209 students who completed the 10 sessions were tested with the same questionnaire. The data were analyzed with a repeated-measures analysis of variance. Students who received either curriculum reported significant decreases in their self-reported use of violence in hypothetical conflict situations, frequency of use of violence in the previous 30 days, and frequency of physical fights in the previous 30 days. The conflict resolution curriculum was more effective in reducing the frequency of fights resulting in an injury requiring medical treatment in the previous 30 days. Both curricula were successful in reducing three indicators of violence. However, the conflict resolution approach was more successful in reducing the frequency of more severe physical fights requiring medical treatment. The latter finding is of particular importance, because that physical fighting is the form of violence behavior in which young adolescents most often engage.

The expression of anger and its consequences

Cluster analysis, using TRYSYS key cluster variable analyses, on 59 anger expression items replicated Spielberger's Anger-In and Anger-Control dimensions and revealed seven additional forms of anger expression: Noisy Arguing, Verbal Assault, Physical Assault-People, Physical Assault-Objects, Reciprocal Communication, Time Out, and Direct Expression. Aggressive dimensions (Noisy Arguing, Verbal Assault, Physical Assault-People and -Objects) correlated positively with each other and with trait anger and negatively with non-aggressive forms of expression (Control, Reciprocal Communication, and Time Out). The latter were positively correlated with each other and negatively with trait anger. Forms of expression correlated logically with the frequency of eight types of anger consequences, and there was evidence of distinct relationships between anger expression and anger consequences; e.g. Physical Assault-People correlated most with frequency of physical altercations, and Noisy Arguing and Verbal Assault with the frequency of verbal fights. Males were more likely to utilize aggressive forms of expression and to suffer consequences involving physical and verbal fights and property damage. Results are discussed in terms of convergent and discriminant validity, and in terms of their implications for assessment, treatment, and future research.

The influence of size differntial on agonistic behaviour in the freshwater crayfish, Cherax cuspidatus (Decapoda: Parastacidae)

The agonistic behaviour of juvenile pairs of intermoult freshwater crayfish Cherax cuspidatus, interacting over space in experimental containers, was examined. The study investigated the effects of differences in Resource Holding Potential (RHP) on social rank, patterns of interaction initiation, and the importance of fighting during encounters between pairs of crayfish. Crayfish were paired with unfamiliar opponents at size classes of 1 : 1, 1 : 0.9, 1 : 0.8, I : 0.7 and 1 : 0.6 using standard carapace length as the RHP index.Larger animals were dominant during significantly more than 50% of replicates at all size classes. Larger animals were dominant at all size ratios lower than 1 : 0.89. Seven smaller animals were dominant at size ratios between 1 : 0.89 and 1 : 0.99. The dominance of smaller animals could not be explained on the basis of morphological measures or age. The influence of prior experience as dominants or subordinates on the behaviour of contestants during these encounters appeared the most likely explanation.Carapace length, body length, and weight were equally reliable RHP indices. Age, number of injuries, and sex were not reliable RHP indices.The probability of initiating the first agonistic bout was independent of relative size for three of the five size classes. Larger initiators of the first bout invariably were successful, while smaller initiators rarely won. The winner of the first bout was the overall dominant during significantly more than 50% of replicates at each size class. The dominant individuals initiated the majority of bouts at all size classes, including the seven replicates where the smaller crayfish was dominant.Fighting (fight time, fight frequency, average bout length), a high intensity behaviour, was an important component of contests at the 1 : 1, 1 : 0.9, and 1 : 0.8 size classes. The significance of fighting was greatly reduced at the 1 :0.7 and 1 : 0.6 classes, indicating that fighting was correlated with the relative size of opponents.

The association between weapon carrying and the use of violence among adolescents living in and around public housing

To test the hypothesis that adolescents who carry lethal weapons are more likely to engage in violent behavior than adolescents who do not carry weapons. Cross-sectional Survey. Black adolescents (N = 225) from a lower socioeconomic (SES) background living in or around nine Housing and Urban Development housing projects. An anonymous questionnaire containing scales from the CDC Youth Risk Behavior Survey and Self-Reported Delinquency Questionnaire was administered. Data were analyzed with Spearman rho correlation coefficients (r), followed by partial correlation coefficients controlling for age and gender. Thirty-five percent of males and 16% of females reported carrying a weapon during the previous 30 days. Frequency of weapon-carrying was correlated (r = .33, p < or = 0.0001). with the frequency of physical fights in the last month, but the relationship was stronger among males than females. Weapon-carrying was also associated (r = .20, p < or = 0.003) with frequency of receiving a serious injury during a fight and the frequency of attacking someone with a weapon with the idea of seriously hurting or killing them (r = .48, p < or = 0.0001). Although males were more likely to carry a hidden weapon than females, the frequency of weapon-carrying was more highly correlated with the frequency of carrying a hidden weapon by females (r = .63, p < or = 0.0001) than males (r = .49, p < or = 0.0001). Females who carried weapons were more likely than males to be involved in gang fights. Among males (r = .27, p < or = 0.008), frequency of weapon-carrying was correlated with frequency of attacking someone with whom they lived. This was not so among females (r = .02). These data support the hypothesis that the lower SES black adolescents in this sample who carried weapons were more likely to engage in violent behaviors than those who did not carry weapons.

Exposure to violence and victimization and fighting behavior by urban black adolescents

Purpose: We hypothesize that adolescents' exposure to violence and personal victimization will be associated with the frequency with which they engage in fighting behaviors. However, adolescents who are future-oriented and goal-directed and from more secure families are hypothesized to report less fighting behavior. Methods: A cross-sectional, anonymous survey was administered to 225 youths (males = 44%) aged 11–19 years, living in or around nine Housing and Urban Development housing projects in an urban area. The questionnaire contained multiple standardized scales. The dependent variables were the frequency of physical fights, hitting someone with whom the subject lived, and gang fighting during the last year. Results: Previous exposure to violence and victimization, school grade, and number of sexual partners accounted for 16.2% of the variation in frequency of fighting during the last year (based on multiple regression analysis). Exposure to violence and victimization and a family with an unemployed head of household accounted for 11% of the variation in domestic fighting. Exposure to violence and victimization, hopelessness, and anticipated socioeconomic status accounted for 15% of the variation in the frequency of gang fighting. Conclusions: These data support the hypothesis that exposure to, and being a victim of, violence is associated with the frequency of fighting by adolescents.

Antler growth and morphology in a feral sika deer (Cervus nippon) population in Killarney, Ireland

Antler growth and form was examined for a sample of 303 sika stags (Cervus nippon) culled over an eight‐year period from a feral population in Killarney National Park, County Kerry, Ireland. Most antler measurements taken were highly correlated with each other and growth was complete after the sixth year. Few abnormalities were recorded and the degree of asymmetry in structure was less than previously reported for other sika populations. Variability in structure decreased with age and there was no effect of year of birth or cull on antler size for either adult or yearling stags. The growth pattern was similar to that of other populations except that the proportion of ‘eight pointers’ was low. An examination of antler damage was used to estimate fighting frequency across age classes. The results are discussed in relation to the genetic history of the herd and the use of antlers as weapons for intra‐specific combat.

A reanalysis of patas monkeys' “grimace and gecker” display and a discussion of their lack of formal dominance

In a captive group of subjects, we tested the claim (Jacobus and Loy, 1981) that patas monkeys possess a “grimace and gecker” display that functions as a signal of submission/appeasement. The results show the grimace and gecker to be an ineffective preventive both for supplantation and for the continuation of aggression by dominant animals, which suggests that it is not an important display for patas monkeys. Without the grimace and gecker, it appears that patas monkeys lack “formal dominance.” Therefore, we investigated the effects of such a deficency via interspecific comparisons. They suggest that patas monkeys do not differ from cercopithecine species that possess formal dominance with regard to frequency of fighting, intensity of fighting, or rates of postfight reconciliation. Patas show lower rates of allogrooming and higher fight:groom ratios than formal dominance species do. These results support the view that a lack of formal dominance is likely to be correlated with reduced social cohesion.

Male distribution and interactions at female oviposition sites as factors affecting mating success in the flyDryomyza anilis (Dryomyzidae)

Dryomyza anilis males gather around carcasses where females arrive to lay their eggs and mate with them before oviposition. Distribution and mating success of males of different size at these sites were studied. The position of males of different size on the carcass and in ten circular zones around it was recorded every 10 min during 2–3 h observation periods. The position of mating pairs, mating initiations and the number of take-overs in different zones were also recorded. It was expected that males would distribute themselves according to the ideal free distribution, i.e. their gain rate in different zones in terms of number of mating initiations would be equalized. Males in different zones reached a stable distribution after 30 min from the beginning of observations. Although males, females and mating pairs were distributed over several zones, most matings were started and take-overs took place on the carcass or in the first zone (C+Z1) because arriving females usually reached the centre before being intercepted by a male. Therefore, males in C+Z1 attained a much higher mating rate than males further away: the percentage of matings started there was significantly higher than the percentage of males present there at the same time. The frequency of male-male fights was highest in C+Z1 which is likely to prevent more males from entering the central area. In this respect the observed male distribution bears resemblance to the ideal despotic distribution. However, the distribution of males of different size did not differ, and there were many small males in C+Z1. Small males in C+Z1 had a higher likelihood of starting a mating than small males further away but suffered from frequent take-overs like small males in all zones. For example, small males started 38% of all matings but there were only 8% of them among males guarding an ovipositing female. The corresponding figures for large males were 35% and 77%, respectively, suggesting that kleptoparasitic interactions and not aggressions between males were the main reason for differences in mating success between males of different size. Since small males do not have any alternative mating sites where large males would be absent, being the second last male to mate with a female is the best small males can achieve. Large males may even benefit from the presence of small males in the centre: they intercept females which large males can then easily take over.

Interspecific dominance relationship and aggressive interactions in the freshwater crayfishes Astacus astacus (L.) and Pacifastacus leniusculus (Dana)

Interspecific and intraspecific aggressive interactions in the coexisting crayfish species Astacus astacus and Pacifastacus leniusculus were experimentally studied in the laboratory. Pacifastacus leniusculus strongly dominated aggressive interactions with similar-sized A. astacus in heterospecific pairs of juveniles and adults. Pairs of young-of-the-year were considerably less aggressive than the larger body-size groups, and in this size group neither species was aggressively dominant. The two species showed substantial differences in patterns of aggressive behaviour. A higher frequency of unilateral aggressive acts and much lower frequency and shorter duration of fights in P. leniusculus pairs indicate that this species is more inclined to establish a dominance order than A. astacus. The aggressive dominance of P. leniusculus over A. astacus indicates that P. leniusculus might be able to competitively exclude A. astacus when the species are competing for a limited resource.