Chemical recognition and fish shoaling

James Herbert-Read (Supervisors: Associate Professor Ashley Ward, Professor Tony Underwood and Dr Angus Jackson)


In nature, a variety of aggregations are observed such as swarms, flocks, herds and shoals. The vast majority of these aggregations are comprised solely from individuals of the same species (conspecifics). For these well ordered groups to form, lone individuals must recognise individuals of their own species if they are to join a group of conspecifics. Senses allow this recognition, for example vision, sound and smell. Many animals can recognise the presence of conspecifics through smell and the use of chemical signals.

In the aquatic world, chemical signals are used by a wide variety of animals including fishes. It has been shown that in freshwater, shoaling fish species can detect the presence of conspecifics through these chemical signals. In freshwater, therefore, these chemical signals may aid individuals in moving towards the direction conspecific shoals by providing information on the position of others. It is has yet to be tested, however, whether in saltwater, shoaling fishes use chemical signals to detect the presence of conspecifics.


My research will concentrate on one species of fish, the Pacific Blue-eye. This species is found along the East Australian Coast living in both fresh and saltwater environments. I aim to determine whether the Pacific Blue-eye uses chemical signals to detect the presence of conspecifics in both fresh and saltwater. Furthermore, I will determine whether it takes individual fish longer to find a conspecific shoal when chemical cues from the shoal are either present of absent. I will also test whether this species responds to not only the chemical signals of conspecifics, but also to the chemical signals from other species of fish (heterospecifics).


Researchers studying the use of chemical signals in fishes have concentrated on the role of these signals in courtship and reproduction, and less has been investigated on the involvement of chemical signals in freshwater and marine shoaling species. This study will increase our understanding of the behavioural ecology of shoaling fish species and will determine whether shoaling behaviours differs between marine and freshwater environments. This will be of key interest to other behavioural ecologists studying chemical communication.


I have demonstrated that in freshwater, the Pacific Blue-eye responds to water that has contained conspecifics, whereas in saltwater, it does not. Water that had contained conspecifics presumably contained chemical signals from the conspecific fish. This then led me to determine whether individuals took longer to find a conspecific shoal in saltwater compared to in freshwater. This was based on the idea that in freshwater, fish use chemical cues to detect the presence of conspecifics whereas in saltwater they do not. When chemical signals from a conspecific shoal were present, it took individuals a shorter period of time to find a conspecific shoal in freshwater compared to in saltwater. I also determined that the Pacific Blue-eye did respond to water that had contained heterospecifics; however this response was reduced compared to when individuals responded to water that had contained conspecifics.

In summary, the ability of the Pacific Blue-eye to detect chemical signals from conspecifics may greatly aid individuals in locating the whereabouts of conspecific shoals.