What drives mixed-species shoaling among wild zebrafish? Role of predators, food access, abundance of conspecifics, and kin familiarity

Abstract

Mixed-species groups commonly occur across a wide range of faunal communities and are known to provide several benefits to members. While zebrafish have often been observed to form mixed-species shoals with coexisting species, the factors determining their occurrence is not yet understood. Using laboratory-based experiments, we decipher the main ecological drivers of mixed-species shoaling in these tropical fish communities. Shoals comprising zebrafish (Danio rerio), flying barbs (Esomus danricus) and whitespots (Aplocheilus panchax) were collected from a stagnant canal at Haringhata (West Bengal, India). Experiments to assess foraging efficiency were conducted where single or mixed-species shoals (comprising 5 individuals) were given low or high amounts of food. Shoal choice experiments were also conducted to assess the preferences of test subjects (zebrafish individuals) for forming associations based on shoal composition and familiarity. Results from experiments on feeding efficiency revealed that foraging time varied substantially among the shoal types (i.e., single or mixed-species), and was dependent on the quantity of food available, but not linked to the body size of species composing the shoal. The choice experiments to examine preference for associations revealed that under predator risk, zebrafish associate more with mixed shoals, and showed comparable associations to shoals differing in the abundance of conspecifics. Furthermore, we found that zebrafish preferred to associate with familiar conspecific over unfamiliar mixed and unfamiliar conspecific shoals. Therefore, equitable food consumption in mixed shoals, greater association to mixed shoals in presence of predator and familiarity were found to be important drivers for choosing mixed-species shoaling by zebrafish.