Observations on agonistic behaviour of Clarias gariepinus larvae and juveniles under different densities and feeding frequencies in a controlled environment

Ten-day-old African catfish larvae, Clarias gariepinus , were stocked in aquaria at 5, 13, 22, and 30 larvae per liter with fish at each density being fed three and six times per day over 35 days. Fish were fed with an artificial diet in excess of their satiation requirements at each feeding. Every week total length was determined for samples of 25 fish per tank and all fish were counted at weekly intervals. Behaviour patterns were categorized into timed behaviour (i.e. resting, swimming and browsing), and frequency events e.g. number of contacts, aggressive contacts and number of head or body attacks. Fish at the lowest density grew faster than fish at the other densities. Feeding frequency had no effect on growth. With increasing densities fish less frequently changed timed behaviour patterns while spending a greater percentage of the time swimming. Aggressive behaviour was highest at the lowest density but remained uninfluenced at densities greater than five fish per litre. The high feeding frequency provoked a higher rate of aggressive contacts than the low feeding frequency. A suggested explanation was that these fish were more often in anticipation of food and consequently more active between feedings. In summary, it was shown that density had an effect on duration behaviour patterns such as resting and swimming, while feeding frequency significantly influenced frequency events, in particular the rate of aggressive behaviour. The study contributes to an understanding of factors influencing C. gariepinus juvenile behaviour and suggestions for follow-up experiments are discussed.     

The Effect of Habitat Structure and Density of Nests on Territory Size and Territorial Behaviour in the Black-headed Gull (Larus ridibundus L.)

We studied the effects of vegetation structure and nest density on territory size and aggression in the black-headed gull (Larus ridibundus). Vegetation structure influenced the types of aggressive behaviour, but not territory size. The proportion of overt aggression (attacks, fights) was highest in barren areas or those with short, sparse vegetation, and lowest in plots covered with dense, tall grass. We explain this by decreased visibility of conspecifics in habitats isolated by vegetation. In such areas, total aggression did not decrease, because the low proportion of attacks and fights was offset by an increase of more moderate (“upright”) displays. Only when nest density was high did the vegetation reduce the frequency of agonistic behaviour — but then it comprised almost exclusively attacks and fights. As expected, greater nest density was related to reduced territory size and an increased proportion of overt aggression. A high proportion of attacks and fights occurred in the plot with the lowest nest density, where at the same time there were also numerous first-year breeders. We conclude that, when analyzing the effects of habitat conditions on aggressive behaviour, it is important to consider the structure of behaviour, and not only the total frequency of all types of agonistic interactions.     

A brief report on intra-species aggressive biting in a goat herd

This study aimed at analysing the effects of age, horn and places on biting and butting as intra-species aggressive activities. Seventy-two Turkish Saanen goats were used as animal material and 22,686 aggressive behaviours were recorded in different places from a total of 118 h direct observation. Of the observations of aggressive behaviours, 32.7% was biting behaviour and the rest was butting behaviour. The frequency of biting behaviour in 3 or more years old goats was significantly higher than that of biting behaviour in 1 and 2 years old animals (P ≤ 0.01). The observations revealed that horned or hornless goats exhibited biting behaviour; however the frequency of biting behaviour in hornless goats was 2.38 times higher than in horned goats (P ≤ 0.01). Biting and butting behaviours were found to be well correlated with the area of places (P ≤ 0.01). As the area of places got narrowed, the frequency of biting increased. However, such a trend was not observed in butting behaviour. The frequency of butting behaviour again increased with the increase in social hierarchy (P ≤ 0.01), whereas the frequency of biting behaviour was not affected by social hierarchy (P = 0.30). In conclusion, intra-species biting behaviour, which is thought to have developed as a result of horn absence, should be questioned whether this is unique to the herd or to the genotype.     

The effects of competitor density on aggressive behaviour and resource defence in a Poeciliid fish

To test the hypothesis that competitor density and time spent at a food resource influences aggressive behaviour in male swordtail, Xiphophorus sp., fish were kept at two densities (low: 18 fish m^?3; high: 54 fish m^?3) and aggressive behaviour was recorded with the time at the food resource used as a covariate. Competitor density is likely to affect the cost:benefit ratio of food defence. When density is low, there should be sufficient food for all individuals and intra‐specific interactions are expected to be rare, while at high densities, increased intra‐specific encounter rates mean that individuals may spend more time defending a resource than utilising it. Food resource defence should occur at intermediate densities. The frequency of aggression, i.e. bites, chases, and display behaviour was significantly positively influenced by time spent at the food resource (Bites: F_1,31 = 8.186, P = 0.007; Chases: F_1,31 = 6.439, P = 0.016; Displays: F_1,31 = 4.435, P = 0.043) suggesting that food resource defence occurred. Competitor density had no effect on food resource defence and minimal effect on the frequency of aggression with only one type of aggressive behaviour, male–male displays, showing a difference between densities (F_1,31 = 6.975, P = 0.013). This finding is suggested to be a result of the formation of dominance hierarchies in this species. Aggression from the dominant individual may be directed at only subordinates of the next dominance rank and subordinate behaviour may be restricted by status rather than immediate threat. In such a situation, aggression may be independent of competitor density.     

Reduced resource defence in an uncertain world: an experimental test using captive nutmeg mannikins

Recent models of economic defence in a group-foraging context predict that the frequency of aggressive interactions should decline as resource density increases, but empirical studies have provided only equivocal support for this prediction. We suggest that whether or not foragers have information concerning the location of patches will influence both the intensity of aggressive encounters and the effect that changes in food density will have on aggression. The intensity of aggression should be greatest when patch locations are known to all, making resources spatially predictable and the availability of alternatives more certain. When food is hidden, increasing the density of patches should have little effect on aggression levels, mostly as a result of the greater uncertainty about the availability of replacement food patches. To test these predictions, we investigated the effect of patch density on the use of aggressive behaviour in nutmeg mannikins, Lonchura punctulata, when food patches were either visible (signalled patch location) or hidden (unsignalled patch location) to all foragers. As predicted, we found that the intensity of aggressive encounters was higher when patch location was signalled than when it was not. Moreover, the effect of patch density on aggression depended on whether patch location was signalled or not. When patch location was unknown, the number of aggressive encounters was unaffected by changes in patch density, but when food location was signalled, increasing patch density resulted in the expected decline in the frequency of aggression.     

Aggressive behaviour of underyearling rainbow trout in simulated winter concealment habitat

The behaviour of wild underyearling rainbow trout Oncorhynchus mykiss in concealment habitat in a laboratory stream aquarium at 2 and 6°C was recorded daily with an infrared video camera for 90 min over dawn. Aggressive behaviours (threat nips, nips and chases) were frequent during this time as fish entered concealment habitat. Aggressiveness varied widely among fish groups, with a range of 1 to 45 aggressive acts being initiated during a 90-min filming period. Larger fish initiated most of the encounters and removed a higher proportion of fish from concealment than did smaller aggressors. Thirteen per cent of the aggressive acts resulted in the recipient being completely removed from concealment habitat. The highest combined frequency of aggressive acts was 0.64 per visible fish per 10 min period and occurred at relatively low light levels (300 lx). The data suggest that when fish density is high, such as when habitat is limited, aggressive behaviour in winter may cause some underyearling salmonids to be excluded from concealment.     

Aggressive behaviour of male Microtus breweri and its demographic implications

Patterns of laboratory-determined aggressive behaviour and exploratory activity were examined in wild-caught male beach voles (Microtus breweri), an island-endemic species. This species is ecologically interesting because it has been found not to exhibit the super-annual population cycles typical of other rodents in the subfamily Microtinae. We found that body weight and reproductive condition were good predictors of aggressive behaviour, with heavier and reproductively active voles showing higher incidences of several stereotyped aggressive acts. Aggression also increased as the percentage of males and females who were reproductively active in the control population increased. Aggression was negatively correlated with population density, and more or less independent of dispersal rate. Dispersers and residents exhibited similar aggressive behaviour patterns. These observations are consistent with models which have proposed that population cycles in other vole species are controlled through the social interactions of individuals.     

A quantitative analysis of social interaction of the guppy, Poecilia reticulata (pisces: Poeciliidae) as a function of population density

Various controlled densities of guppies, Poecilia reticulata, wer observed in order to determine the effects of population density on frequency of courtship and agonistic interactions. Populations with single male exhibit a low level of courtship activity; the presence of a second male increases this level of activity markedly. Populations with a 1:1 sex ratio in densities greater than one pair exhibit a constant mean number of courtship interactions but, with increased crowding, an increasing variance in level of courtship activity. This results in a frequency profile of courtship interaction characteristic of each observed density. Each population density exhibits a density-dependent pattern of social interaction defined quantitatively by frequencies of courtship aggressive interactions at the population level. The contribution of the behaviour of individual males and to this patterning of social interaction in each population was partially determined.     

Factors affecting aggressive behaviour of spawning migratory males towards mature male parr in masu salmon Oncorhynchus masou

This study examined whether dominant migratory males (adopting fighter tactics) of the masu salmon Oncorhynchus masou would more aggressively attack large mature male parr (adopting sneaker tactics) as large mature male parr are expected to have the potential to cause a greater decrease in fertilization success. The frequency of aggressive behaviour was not related to the body size of males, and it increased with the frequency of interactions with mature male parr. The fertilization success of mature male parr was much lower than migratory males, and no relationship was observed between fertilization success and aggressive behaviour. The low fertilization success of mature male parr, despite infrequent aggressive behaviour by migratory males, indicates that there might be little benefit for migratory males to attack mature male parr more aggressively according to their body size.     

The social interaction between mother and offspring during weaning in German Shepherd dogs: Individual differences between mothers and their effects on offspring

Seventeen litters of German Shepherd dogs were observed for 5–7 days per week between 3 and 8 weeks post-partum. Social behaviour patterns, aggressive signals towards the puppies and nursing were quantified. Mothers were found to differ in the frequency of both social and aggressive behaviour. Nursing declined during the period, while both agonistic and grooming behaviour towards puppies increased until the 7th week. During Week 7, agonistic behaviour patterns were found to be significantly correlated to grooming behaviour patterns. Some of these behaviour traits were significantly correlated to the puppies performance on a puppy test given at the age of 8 weeks. It is suggested that the interaction between mother and offspring may facilitate the appearance of submission, and the effects on later trainability are discussed.     

Entire male pigs in farrow-to-finish pens—Effects on animal welfare

Aggressive and sexual behaviour can hamper animal welfare in entire male pig production. The aim of the present study was to investigate if rearing entire male pigs in sibling groups (in farrow-to-finish pens) could reduce aggressive and sexual behaviour and thereby improve animal welfare in entire male pig production. Frequencies of aggressive and sexual behaviour among finishing pigs were recorded in three different groups in one herd; FTF-group (entires + gilts, siblings), mix-group (entires + gilts, mixed) and castrate-group (castrates + gilts, siblings). Frequencies of skin wounds were recorded in this herd and in an additional herd (only FTF-group and mix-group) shortly before the animals were sent to slaughter. Higher skin lesion scores in the entire male pig groups were in accordance with the behaviour data. Rearing entire male pigs in sibling groups reduces aggressive behaviour, though the frequency of the aggressive behaviour bouts was still higher than it was in the castrate-group. The frequency of skin wounds in the FTF-group was reduced to similar levels as in the castrate-group. The findings suggest that rearing entire males in sibling groups may be an appropriate management strategy for improving animal welfare in entire male pig production.     

The social interactions of young bulls and steers after re-grouping

A study was conducted to determine the behavioural responses of bulls and steers to social re-grouping. Thirty-two bulls and 32 steers kept in pens of 8 (bulls and steers penned separately) were re-grouped in January, April and July, when the cattle were about 9, 12 and 15 months old. This was done in such a way that each animal was penned with 6 strangers and 1 aquaintance. For 10 days after mixing, each of the 8 pens of cattle was observed for 22.5 min, 3 times per day. The occurrence of various activities was recorded. In both genders, mixing led to high rates of overt aggressive behaviour. Although, initially much higher in bulls than steers, the frequency of this activity decreased quickly, and by 10 days post-mixing, both bulls and steers showed very little aggressive behaviour. Mounting and other “sexual” behaviour followed a similar pattern of very high levels immediately after re-grouping followed by a decline in activity. However, the rates of these behaviours remained higher among bulls than among steers. The influence of stocking density and group size is discussed. It is concluded that the differences between the bulls and steers increased with age, and it is suggested that steers are behaviourly less mature than bulls.     

Changes in the structure of group behavior in callosotomized rhesus monkeys

The studies were performed on 4 intact and 3 callosotomized adult male rhesus monkeys that comprised one social group. Group behaviour of all the monkeys was investigated by the frequency method of social contacts registration. Both aggressive and friendly contacts were registered. The results obtained have shown a considerable decrease in social contacts of callosotomized rhesus monkeys, as compared to normal animals. The aggressive contacts prevailed in the behaviour of the operated monkeys. The data suggest that callosotomy does not only significantly decrease the frequency, but also alters the structure of social contacts in the rhesus monkeys.     

Effect of density on the reproductive behaviour of the territorial male demoiselle Chromis dispilus (Pisces: Pomacentridae)

Synopsis Characteristics of nest sites and reproductive behaviour of territorial male demoiselles Chromis dispilus were examined at sites of low, medium and high population density in northeastern New Zealand, by use of SCUBA diving and a remote underwater video system. Nest territories were closer together at high density (relative to areas of low population density) and this was accompanied by an increase in the frequency of spawning sequences and territorial defence against conspecifics. Territorial males were more aggressive during periods of display and spawning than during egg guarding. Fish from areas of low density spent more time on courtship display (signal jumps) and territorial defence against fish of other species, than demoiselles from areas of high population density. Territories and nest sizes tended to be largest in areas of medium population density. As in other damselfishes, population density is a major determinant of the frequency and intensity of reproductive behaviours.     

The relationships between stocking density and welfare in farmed rainbow trout

There is increasing public, governmental and commercial interest in the welfare of intensively farmed fish and stocking density has been highlighted as an area of particular concern. Here we draw scientific attention and debate to this emerging research field by reviewing the evidence for effects of density on rainbow trout. Although no explicit reference to ‘welfare’ has been made, there are 43 studies which have examined the effects of density on production and physiological parameters of rainbow trout. Increasing stocking density does not appear to cause prolonged crowding stress in rainbow trout. However, commonly reported effects of increasing density are reductions in food conversion efficiency, nutritional condition and growth, and an increase in fin erosion. Such changes are indicative of a reduced welfare status—although the magnitude of the effects has tended to be dependent upon study‐specific conditions. Systematic observations on large scale commercial farms are therefore required, rather than extrapolation of these mainly small‐scale experimental findings. There is dispute as to the cause of the observed effects of increasing density, with water quality deterioration and/or an increase in aggressive behaviour being variously proposed. Both causes can theoretically generate the observed effects of increasing density, and the relative contribution of the two causes may depend upon the specific conditions. However, documentation of the relationship between density and the effects of aggressive behaviour at relevant commercial densities is lacking. Consequently only inferential evidence exists that aggressive behaviour generates the observed effects of increasing density, whereas there is direct experimental evidence that water quality degradation is responsible. Nevertheless, there are contradictory recommendations in the literature for key water quality parameters to ensure adequate welfare status. The potential for welfare to be detrimentally affected by non‐aggressive behavioural interactions (abrasion, collision, obstruction) and low densities (due to excessive aggressive behaviour and a poor feeding response) have been largely overlooked. Legislation directly limiting stocking density is likely to be unworkable, and a more practical option might be to prescribe acceptable levels of water quality, health, nutritional condition and behavioural indicators.     

Revisiting the influence of aggressive interactions on the survival of the first‐laid egg in crested penguins (genus Eudyptes)

Crested penguins Eudyptes spp. have evolved a unique form of breeding in which the first of two eggs laid is much smaller than the second and has a higher likelihood of being lost during egg laying and incubation. In this study, we quantified aggressive behaviour in nesting Snares penguins and undertook an egg survival analysis to examine which factors influence egg loss. During 120 h of observation of 50 nests, we recorded a total of 300 aggressive events in which females were repeatedly pecked, bitten and beaten. Aggressive events lasted from less than a minute to up to 55 min (mean 4.6 ± 7.4 min). Single males were the aggressor in 75% of aggressive events and in 50.7% of aggressive events the aggressor was identified as a neighbouring, breeding male. A greater percentage of the small first eggs (34%) were lost than the large second eggs (4%). We found that egg mortality was influenced by 1) whether the other egg within a nest had hatched, 2) who was present at the nest (father, mother or both) and 3) the average duration of aggressive events on the nest. When one egg within a nest had hatched, the other egg had a vastly increased mortality risk irrespective of aggression. However, long, aggressive events directed towards females after their partners had gone foraging, also increased the probability of egg loss. We suggest that the prolonged nest attendance by breeding males well beyond egg laying is in response to the high frequency of aggressive behaviour during this time. Our data show that A‐egg losses occur due to intraspecific aggression in this species. Further research is needed to clarify whether aggressive behaviour in breeding crested penguins is modulated by elevated testosterone levels in the males and whether any reproductive benefits accrue to the aggressors.     

Dominance and effects of strange conspecifics on aggressive interactions in the hermit crab Pagurus longicarpus (say)

Dominance orders in the hermit crab Pagurus longicarpus were observed in the laboratory. Groups of four crabs formed loose dominance hierarchies as determined by repeated display and retreat behaviour. Stronger dominance orders were inversely correlated with the frequency of aggressive interactions. Recognition of individuals, as measured by frequency and intensity of aggressive encounters between familiar crabs and introduced strangers, was not important in maintaining dominance orders. Rather, P. longicarpus recognized the aggressive state of conspecifics, as shown by frequencies of aggressive encounters after individuals of different dominance rankings were exchanged between established hierarchies.     

Roles of brain monoamine neurotransmitters in agonistic behaviour and stress reactions,with particular reference to fish

1. Experimental results on the involvement of brain monoamines in agonistic behaviour and stress in fish are reviewed and discussed in relation to available data from other vertebrates.2. In fish as well as mammals, stress induces increased brain serotonergic activity, and a similar increase in serotonergic activity is seen in subordinate individuals in a dominance hierarchy.3. The brain serotonergic system appears to inhibit aggression and spontaneous locomotor activity in both fish and mammals.4. Subordinate fish show several behavioural characteristics, notably inhibition of aggressive behaviour, low spontaneous locomotor activity and decreased food intake, that are likely to be related to their increased brain serotonergic activity.5. By contrast, the brain dopaminergic system appears to stimulate aggressive behaviour in both fish and mammals, and dominant fish show signs of elevated dopaminergic activity in telencephalon.6. The similarities between fish and mammalian monoaminergic functions suggest that these are phylogenetically very old mechanisms that have been conserved during the last 400 million years of vertebrate evolution.     

Comparison of social ranks based on worm-running and aggressive behaviour in young domestic fowl

Worm-running is behaviour in which a chick runs carrying a worm-like object while flock mates follow and attempt to grab the object from its beak. We hypothesised that social ranks based on worm-running frequency are stable over time and are positively correlated with social ranks based on success in aggressive interactions when older. At 8-12 days of age, we scored worm-running in 17 groups of 12 female White Leghorn chicks during three 10-min tests. Based on instantaneous scans at 5-s intervals, the bird carrying the 'worm' most often was placed in rank one and so on down the rank order. These tests were repeated at 68-70 days of age. An aggression index for each bird was calculated as the number of aggressive acts given, divided by the number given and received, during three 1-h observation periods when the birds were 68-70 days. Ranks obtained in worm-running tests were positively correlated over the two age periods (P < 0.05) but were not correlated with ranks based on the aggression index (P > 0.05). Our results indicate that worm-running ranks are not predictive of success in aggressive interactions. Instead, worm-running fits some criteria for play.     

Ontogeny of Acoustic and Feeding Behaviour in the Grey Gurnard, Eutrigla gurnardus

Although sound production in teleost fish is often associated with territorial behaviour, little is known of fish acoustic behaviour in other agonistic contexts such as competitive feeding and how it changes during ontogeny. The grey gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during competitive feeding and seems to adopt both contest and scramble tactics under defensible resource conditions. Here we examine, for the first time, the effect of fish size on sound production and agonistic behaviour during competitive feeding. We have made sound (alone) and video (synchronized image and sound) recordings of grey gurnards during competitive feeding interactions. Experimental fish ranged from small juveniles to large adults and were grouped in four size classes: 10–15, 15–20, 25–30 and 30–40 cm in total length. We show that, in this species, both sound production and feeding behaviour change with fish size. Sound production rate decreased in larger fish. Sound duration, pulse duration and the number of pulses increased whereas the peak frequency decreased with fish size, in both sound types (knocks and grunts). Interaction rate and the frequency of agonistic behaviour decreased with increasing fish size during competitive feeding sessions. The proportion of feeding interactions accompanied by sound production was similar in all size classes. However, the proportion of interactions accompanied by knocks (less aggressive sounds) and by grunts (more aggressive) increased and decreased with fish size, respectively. Taken together, these results suggest that smaller grey gurnards compete for food by contest tactics whereas larger specimens predominantly scramble for food, probably because body size gives an advantage in locating, capturing and handling prey. We further suggest that sounds emitted during feeding may potentially give information on the motivation and ability of the individual to compete for food resources.