LAUSR

Abstract Nile tilapia Oreochromis niloticus (NT) and Black-chinned tilapia Sarotherodon melanotheron (BCT) are respectively characterized by fast growth and water salinity tolerance which attract the farmers who could take advantage of both species characteristics by producing hybrids reared in brackish or marine waters. Little information is however available about social interactions between the two species which are distinct by their mode of parental care (oral incubation). The objective of this study was to determine the behaviour of the two species, NT and BCT placed in freshwater intraspecific and interspecific pairing contexts. Females of both species (n = 20 per species) were first isolated for 90 days in a 60 L aquarium to determine the average duration between spawning in the absence of males. With the approach of 4th spawning or after 90 days of isolation, intra and interspecific pairing (fish average weight 200.4 ± 5.1 g) were made 10 times by pairing mode in a 350 L aquarium. The day after fish pairing, 15 min videos were recorded at one hour intervals from 8:00 h to 17:00 h, and courtship and aggressiveness behaviour were quantified. The results showed that isolated NT females had an average duration between two spawning of 15.9 days. No spawning was observed in BCT females. Spawning events were observed in the NT intraspecific pairs, with strictly maternal oral egg incubations. Behavioural differences and some similarities were noted between the two species. NT male was the most dominant in front of females of both species and NT females showed dominance on BCT males. No clear hierarchy was observed in BCT pairs. Courtship behaviours were observed in all pairings with longer durations in NT pairs. Nest building was observed from 8:00 h to 17:00 h in both sexes of BCT and male NT. NT females built nests from 11:00 h with longer durations when paired with males BCT than when paired with their conspecific males. These first results, reflecting behavioural plasticity in both species suggested that other breeding conditions favouring less aggressive behaviour could lead to a natural interspecific hybridization between NT and BCT.