Territorial fish distinguish familiar neighbours individually

Abstract

True individual recognition (TIR), the ability to distinguish multiple familiar members individually, is more elaborate than class-level recognition, and evidence for the ability to perform TIR is reported from primates, some other social mammals, birds and lizard in vertebrates. These animals exhibit a highly social structure, wherein TIR is essential for their social interactions. Such high sociality has been documented in fish, but clear evidence of TIR has been limited. The cichlid,Neolamprologus pulcher, a cooperative breeder that guards a territory, exhibits the dear enemy relationship. Here, we show that this fish distinguishes two familiar neighbours individually, i.e., TIR ability, using one-way mirrors in experimental tanks. Focal fish established the dear enemy relationship with two neighbours, NAand NB, and displayed limited aggression towards these familiar neighbours. However, their aggressiveness towards neighbour NBincreased when they were shifted from the original side of the tank after NAwas removed, suggesting that they distinguished NBfrom NAor regarded NBas a stranger. Interestingly, this aggression level against the shifted neighbour NBlargely decreased within 1 min. This decrease contrasted with the longer and more frequent aggressiveness towards unfamiliar strangers. These results suggest that focal fish recognised neighbour NBas a familiar stranger but probably punished NBthat moved beyond its territory, that is, betrayed the dear enemy relationship. We prevented the effects of the behavioural reactions of exposed individuals using a one-way mirror. Thus, we conclude that this fish species displays TIR and discuss that TIR is prevalent in territorial animals in which the dear enemy effect is common.

Social buffering of stress in a group-living fish

“…During the recovery period, focal individuals occupied one-quarter of the tank, and were separated by a non-perforated, clear barrier from the other three-quarters of the tank containing either their own social group or a novel social group. Neolamprologus pulcher are a highly visual species and are capable of individual recognition using only visual information [57][58][59]. Novel social groups were matched in number and composition of individuals to each individual's own social group and were exchanged with the original social groups during the air exposure of the focal individual.…”

Agonistic Behavior Is Affected by Memory in the Dusky Damselfish Stegastes fuscus

“…In addition, the dear enemy effect can be established, where the frequency and intensity of aggression are reduced in interactions with familiar animals (Fisher, 1954;Briefer et al, 2008). This phenomenon has been confirmed in territorial fish by the lower number of displays (Earley et al, 2003;Sogawa et al, 2016;Silveira et al, 2020) and changes in the use of space (Frostman and Sherman, 2004;Saeki et al, 2018) between neighbors. As a consequence, these agonistic interactions may have community-level impacts (Fontoura et al, 2020), and could provide useful information for the individual's recognition process (Miklósi et al, 1992).…”

Social Recognition and Social Attraction in Group-Living Fishes

“…Under threat of predation, performing predator inspection alongside a co-operative individual may yield benefits (Mesterton-Gibbons and Dugatkin, 1992). In territorial contexts, remembering the outcome of previous interactions may reduce future levels of aggression with the same individuals [i.e., the 'dear enemy' effect, Jaeger, 1981 (on salamanders); Saeki et al, 2018], although this may result through time-place learning rather than necessarily being individual recognition. Given the higher memory costs associated with learned individual recognition, it may be adaptive to adjust the specificity of recognition based on the context.…”