Fighting and Aggression

Abstract

Aggression (behaviour that actually or potentially causes harm to another animal) is widespread among fishes, often taking the form of territoriality or dominance. The mechanisms that control aggression in fish are described, including the effects of stimuli from opponents, the importance of the context in which an aggressive encounter occurs and the effects of nutritional condition, endocrine status and brain biochemistry. The way aggression changes during development is then considered, evidence given for inherited differences in aggressiveness and an account presented of the environmental factors that influence the way aggression develops. The benefits that fish gain from winning fights, the costs that they incur from fighting and how they balance costs against benefits to promote their individual fitness are described. Data are then given on the incidence of aggression among cultured fish, on some resulting problems for production, welfare and environmental protection and on the effects of domestication and captive rearing of aggressiveness. Possible solutions to such problems are discussed, based on selecting appropriate fish for culture and the design of husbandry systems that minimise aggression. Finally, some systems for mitigating the effects of domestication and captive rearing on the aggressive behaviour of cultured fish are described.

The effects of rearing density on growth, size heterogeneity and inter-individual variation of feed intake in monosex male Nile tilapia Oreochromis niloticus L.

“…It has been shown that feeding intervals are strongly correlated with hunger and return of appetite (Riche et al, 2004). Low feeding frequency may lead to increased hunger, intraspecific competition and interindividual FI (Damsgå rd and Huntingford, 2012). When feed availability and accessibility are reduced, the agonistic behaviour tends to increase and feed monopolization tends to be more intense, which may result in disproportional feed acquisition, considerable variation in feed consumption and this ultimately gives rise to differential growth.…”

Social Behavior and Welfare in Nile Tilapia

“…Indeed, the number of animals clearly hinders the aggressive behavior quantification for most of those conditions. Furthermore, there are differences in the experimental protocol between those studies that make it difficult to conclude only in terms of high or low density if social hierarchy can be affected by the number of animals in the group, without considering the amount of available food, shelter, and space [5]. Nevertheless, studies combining the effect of stocking density and social aggressive interactions should be conducted in order to allow us a better understanding of its impact on Nile tilapia's welfare.…”

“…Social behavior is defined as any kind of interaction between conspecifics, in such a way that it influences their immediate or future behavior [1]. In this conceptual framework, fish social behavior includes reproductive behavior, such as mating and courtship, cooperative interactions [2,3], shoaling [4], and social hierarchy, which is marked by aggressive interactions to reach a certain social rank and to defend territory, as well as environmental resources [5]. Social interaction, however, is not limited to conspecifics, but it can also occur among heterospecifics, such as in client-cleaner coral reef fishes, wherein a species cooperates by cleaning parasites off of another species, thus interacting between them [6,7].…”

“…Although aggressive interactions are part of their natural behavior, some of the common practices in aquaculture, such as classifying individuals by matching their size, water renewal, stock density, and environment lighting can affect social interactions in a way that shrinks the natural adaptive value of social behavior. As a consequence, there will be reduced welfare in social fish species, as well as an impact on fish production [5]. In this paper, we present a synthesis on social impairment and welfare of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), an African cichlid fish widely used both in fish farms and as a research model due to its physiology and behavior.…”

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“…In their study, researchers have confirmed that, in certain ontogenetic stages, the environment background color could indirectly influence the increase or decrease of aggression levels in the fish species. Therefore, for rearing in closed systems, changing the color could represent a simple, but an efficient way to ethologically manipulate the fish (Damsgård and Huntingford, 2012).…”