If you keep Julidochromis species (Julies), you probably have a considerable amount of rock work in your tank. Here’s the scenario. You started off with a small group of sub-adults or juveniles, maybe five or so. You haven’t vented them and they’re all the same size, so you have no idea what sex ratio you have. You end up with some fry, you can’t tell who the parents are, and you want to know. What do you do?
Well, the short answer is you don’t have to do anything unless your tank is too small. In that case, you might end up with some of your original group dead from aggression. If your tank is reasonable in size (~48 inches long), you’ll be fine. That is until you end up with multiple broods, and some of them reach adulthood or the same size as your original group. At this point, you may not know who the parents are but you want to reduce the size of your colony. How do you do that if you can’t identify the parents and don’t want to remove them (i.e., keep the parent for more breeding)?
There are visual cues you can look for to identify the parents among a set of equal size, mixed adults.
First, if you read up on your species, you can usually tell by size which sex they are. For example, female regani are larger than males whereas male dickfeldi are typically larger than females. Once you actually know the sex of your Julies, it will make it much easier to tell who the parents are, which leads to the second cue.
Second, look for a particular fish that doesn’t venture out into the open much, but rather stays hidden most of the time. This one is a bit tricky because the particular fish could be avoiding a dominant fish of the same sex. For example, males will often be intolerant of other males and may keep other males pinned behind a filter, a heater, or near the surface around either one. However, a female guarding eggs or fry will generally stay near the spawning site. She’ll chase off immediate threats but will go right back to her site. Males in some Julie species will guard the perimeter of the spawn site, openly chasing intruders that get anywhere close to the site. Julies, like most other cichlids, are highly protective of their offspring.
Third, look for the most aggressive. This means that Julies that have spawned will typically become more aggressive than normal towards both conspecifics and other species. You will need to learn, through observation, what is typical protective aggression versus territorial aggression. You will be able to tell the difference with experience.
In aggregate, these cues will help determine the parents of all of the fry you keep seeing, especially if the parents are spawning somewhere you can’t visually locate (e.g., deep in the rocks) and you grow them out to adulthood.