Eretmodus cyanostictus (pronounced sigh–an–o–stik–tus) is among the group of cichlids called gobies. Other gobies include all fishes from the three genera: Eretmodus, Spathodus, and Tanganicodus. Like all gobies, E. cyanostictus is an algae-scraping cichlid that has a uniquely interesting spawning behavior - it's a bi-parental mouthbrooder.
Gobies only occur naturally in the surge habitat of the lake, which is the upper 3 feet of the water at the shoreline. This habitat is called surge because of the strong currents and rough waves that break in this zone. Gobies are able to combat the strong currents through their compressed bodies and long dorsal fin, just like Labeotropheus trewavasae, who inhabits a similar niche in Lake Malawi. Using their ventral and pectoral fins, gobies affix themselves between the rocks. They are also unique in that their swim bladder is non-functional, meaning that when they're not swimming, they drop to the bottom like a rock. This too helps to keep them from getting tossed around by the waves.
Eretmodus cyanostictus is a monomorphic species, however, fry show a slight dimorphism for the first couple of days following release - males are a dark brown while females are a light brown. But this minor difference lasts only a few days. Adults are "sand-colored" with nine dark, vertical bars along their sides. The cyanostictus pictured here is the race from Kigoma, which has a little more red and orange in its fins than do the northern race. E. cyanostictus grows to 3-inches (8 cm), but females stay about 1/5 smaller than males.
Eretmodus cyanostictus lives on a diet of algae that are scraped off the rocks. It has has red, spatula-shaped teeth, which aid in removing the algae, often leaving behind long rows of teeth marks. Their mouth is "underslung," similar to the mouth of Labeotropheus trewavasae, but even more so. This allows them to eat at more of a horizontal position, providing two advantages. First, they can scrape the algae from rocks that are submerged by only an inch of water! Second, the shape of their mouth permits them to hug the rocks when eating instead of having to approach the rocks from a vertical position, where their whole body would be exposed to the current.
The aquarium should be decorated with lots of rocks to create nooks and crannies. This fish will dine on any algae allowed to grow on these rocks. Algal growth can be stimulated with a strong lamp (bulb) and will grow best on the rocks nearest the surface. In the tank, E. cyanostictus is found in the middle and upper parts of the rockwork, perhaps because this is where the algae grow best.
Sand should be used for substrate. The reasoning behind this is that most wild specimens were found to have sand grains in their intestines along with algal matter. While it has not been proven, it has been hypothesized that these sand grains may help to grind the difficult-to-digest algae just as birds swallow pebbles to help grind their food. To further substantiate this hypothesis, those Eretmodus populations found in surge habitats without sand are always small in number.
The surge habitat has a slightly higher pH because the agitated water quickly releases the CO2 in the water. Conversely, the water is well-oxygenated. Gobies have adapted themselves to the these conditions and therefore need their water to have a high oxygenation value. A good trickle filter and one or a few air stones will help to keep the water sufficiently oxygenated.
Gobies are best kept as pairs. It's possible to keep more than one pair in the same tank, but realize they can be quite pugnacious to one another. A single pair can be kept in a tank as small as 40 gallons, but two pairs should be housed in a tank no smaller than 75 gallons. Gobies in general can be quite nasty to each other, but once pairs form, "the fight is over." Males and females will form a pair-bond that lasts for life.
E. cyanostictus does not maintain a permanent territory, but when they prepare to spawn and an area has been selected (usually a flat rock), this area will be defended by both the male and the female. Any onlookers that get too close are vigrously chased away. Spawning E. cyanostictus do not assume the typical "T position" commonly seen in other cichlid species. Instead, they swim alongside each other, with their heads close together. The female will shake as she lays her eggs and then quickly turns around to pick them up. The male then shakes as he fertilizes the eggs, right at the moment the female scoops them up
As already mentioned above, E. cyanostictus is a bi-parental mouthbrooder. After 10 - 12 days, the female will make a great effort to get the male's attention. Just when it seems that they're going to spawn again, the female slowly and methodically passes each larva to the male, who catches them in his mouth. He will finish up the incubation period, holding the young for another 7-10 days.
Clutch size is 10 - 30 eggs. Once fry are released by the male, they are ignored by the parents. The male can be removed (at night) to a nursery tank where he can release the fry before being returned. Alternatively, a balcony/shelf submerged by just a few inches of water could be installed in the main tank. The male will release the fry in this area where they will be safe from predation due to its shallow depth.
The food of choice for E. cyanostictus is a good Spirulina flake. Mysis and Cyclops make good supplementary foods, but avoid Brine Shrimp at all costs. Suitable tankmates include other algae-eating tanganyikans, such as Tropheus and Simochromis species. □