Have you ever wondered if bi-parental cichlids actually distinguish threats to their brood based on the threat agent? In other words, are cichlid parents able to determine and rank the threat level of other fish (conspecific or not) to the brood their protecting? The short answer is Hypsophrys nematopus (formally Neetroplus nematopus) can. It’s not out of the realm of comprehension that other cichlid species can do the same.
Conducting an experiment in-situ at Lake Xiloá in Nicauragua, a group of scientists exposed 23 breeding pairs of H. nematopus to territorial threats of equal-sized agents from three species: bigmouth sleepers (Gobiomorus dormitor), convict cichlids (Amatitlania siquia), and a species of molly (Poecilia sp.). The nematopus level of aggression exhibited toward these fish in the experiment varied but was conclusive for each species of interloper, suggesting that nematopus can distinguish levels of threats based on the threatening species and vary their own aggression accordingly. However, the aggression you see in your own tank from breeding pairs of cichlids may or may not be similar. While many cichlid behaviors in closed systems (e.g., fish tanks) may mimic natural behavior in the wild, that is not a given for every cichlid species. Remember, this experiment was conducted in a natural setting, not an artificial one like an aquarium.
For more information on the experiment and its results, you can read the paper from Behavioral Ecology here.
Citation: Sowersby, W., Lehtonen, T. P., Wong, B. B. M. “Threat sensitive adjustment of aggression by males and females in a biparental cichlid.” Behavioral Ecology, ary037. 2018. https://doi.org/10.1093/beheco/ary037.