Can Living with an Alien Invasive Fish, Tilapia, Influence the Shoaling Decision-Making and Exploratory Behaviour of an Air-Breathing Freshwater Fish, the Climbing Perch?

The biodiversity of freshwater aquatic ecosystems is threatened by invasive alien species across the world. We studied the impact of the presence of an invasive piscine species, the tilapia Oreochromis mossambicus and acquisition of familiarity with it on the social decision-making and exploratory behaviour of a native, air-breathing, freshwater fish, the climbing perch Anabas testudineus. Our results reveal that the climbing perch did not show any significant preference or aversion to any of the stimulus shoals when unfamiliar monospecific shoals of tilapia, mixed-species shoals of tilapia and climbing perch that were divergent in the composition, or groups comprising only tilapia familiar to the subject fish for a duration of 30, 60, 90 or 120 days, were presented in opposition to a shoal with an equal number of unfamiliar conspecific individuals. No preference for isolated familiar individual tilapia was also observed against its unfamiliar counterpart or a conspecific individual. It is also noteworthy that the propensity of subject climbing perch to initiate exploration of a novel area (a measure of boldness) or exploratory activity and its sociability remained unchanged under different social conditions, including presence of unfamiliar conspecific, familiar conspecific, unfamiliar heterospecific or familiar heterospecific individuals. These results are discussed in the light of ever-increasing levels of invasion by alien fish species and the struggle for survival that currently confront native piscine species in most tropical freshwater ecosystems globally.