Because most cichlids exhibit aggression during breeding and territorial defense, a common solution to reduce such aggression in closed systems is the introduction of sightline barriers. This can come in the form of plants, rocks, wood, decorations, or even sand piles. The basic principle is that blocking the regular view of one cichlid from another will reduce aggression between the two. However, relying solely on sightline reduction to mitigate aggression in cichlids is often futile. Why?
One reason is that cichlids, like most teleost fish, don’t depend solely on eyesight to sense predators and other threats. Chemical cues also play a vital role. Hormones are regularly excreted by cichlids in their urine. In fact, cichlids can and do control hormonal release during all kinds of interactions – friendly and otherwise. For example, cichlids can control the frequency and volume of urination, which is heavily laden with hormones. They use these hormonal variations to send signals to both friends and foes. Conversely, they use their olfactory system to sense the hormonal excretions of others and rely on them as a vital form of communication.
So next time you feel like you significantly broke up sight lines yet your fish still engage in heavy combat, it’s probably not due to your efforts.
To learn more about the sensory modalities of cichlids, the following paper is a great primer. It’s a scholarly paper so it’s quite technical.
Escobar-Camacho, D., & Carleton, K. L. (2015). Sensory modalities in cichlid fish behavior. Current opinion in behavioral sciences, 6, 115–124. https://doi.org/10.1016/j.cobeha.2015.11.002
You might also be interested in the interview I did with LSU professor Karen Maruska, who studies how sensory information affects cichlid behavior. In fact, her university research lab runs a blog, called Burt’s Blog, related to their fish research. This post from their blog a couple of years ago does a nice job describing some of what’s going on with fish and the hormonal chemical cues I discussed above. Yes, the image at the top of this post was shamelessly borrowed from her blog’s post.