Bile acids as putative social signals in Mozambique tilapia (Oreochromis mossambicus)

Chemical cues provide potential mates with information about reproductive status and resource-holding potential. In the Mozambique tilapia (Oreochromis mossambicus), males can distinguish female reproductive status through chemical cues, and accessibility of males to females depends on their position in the hierarchy, determined in part by chemical cues. Here, we hypothesized that tilapia faecal cues are attractive to conspecifics once released into the water. C18 solid-phase extracts of faeces from dominant males and pre-ovulatory females evoked stronger olfactory epithelium electrical responses (EOG) than, respectively, subordinate males and post-spawning females. Mass spectrometry of the reverse-phase C18 high-performance liquid chromatography fractions of these extracts with highest EOG, identified by amino acids and bile acids. Faeces from pre-ovulatory females contain significantly higher concentrations of cholic acid (CA) and taurocholic acid (TCH) than both post-spawning females and males. A pool of amino acids had no effect on aggression or attraction in males. However, males were attracted to the scent of pre-ovulatory female faeces, as well as CA and TCH, when applied separately. This attraction was accompanied by increased digging behaviour compared to the odour of post-spawning females. CA and TCH exert their action through separate receptor mechanisms. These findings are consistent with a role for faeces - and bile acids therein - in chemical communication in this species, acting as an attractant for males to reproductive females.