Barki, A., Cnaani, A., Biran, J. 2022. How does temperature affect aggression during and after dominance hierarchy formation in Nile tilapia? Applied Animal Behaviour Science 247, 105563.

Social animals commonly establish dominance relationships by means of aggressive interaction, leading to hierarchical stability and priority of access to limited resources by high-ranked individuals. In poikilothermic animals, temperature is a major abiotic factor influencing social and non-social behaviors, including aggression. Here, we investigated the effect of cold temperature on aggression in dominance hierarchies of the commercially important tropical fish Nile tilapia (Oreochromis niloticus). Aggression components were examined in fish shoals during hierarchy formation (T1) and after hierarchy establishment (T2) under optimal (26 °C) or cold (14 °C) temperatures, and 24 h afterwards (T3) following gradual temperature increase (14–26 °C, IT treatment), decrease (26–14 °C, DT treatment) or constant optimal conditions (26 °C, CT control). During dominance hierarchy formation, fish in cold water showed reduced aggressive interactions involving lower-intensity behaviors whereas fish under warm temperature exhibited high aggression involving escalated fighting. Following temperature alterations, at T3, aggression levels increased in the IT groups, decreased in the DT groups and remained similarly high in the CT groups. However, despite the drop of temperature in the DT treatment, aggression level at T3 in cold temperature in this treatment was similar to that in the IT treatment and CT control in warm temperature. Likewise, despite the increase of temperature, aggression level in the IT treatment at T3 was lower than that observed under the same warm temperature conditions in the DT and CT groups. Our results demonstrate that in addition to the acute effect of the current temperature on aggression in dominance hierarchies, there is a significant carryover effect of prior thermal conditions under which dominance hierarchy has been formed. Thus, cold temperature can possibly be applied during hierarchy formation for mitigating adverse social effects arising from fish grouping under captive conditions.