The Latin name for the genus Retroculus is derived from its rather posteriorly placed eyes. Its name could also be Robustorpedus, as fish of this genus are very strong and muscular, yet their overall profile is sleek.
The type species, R. lapidifer, has the peculiar habit of resting on the bottom in a pose reminiscent of performing push-ups, only the supporting arms are replaced by erect ventral fins. Their swimming style appears clumsy at first glance, due to the reduced swim bladder the fish needs to overcome the constant “overweight”. However, all this clumsiness disappears as soon as something interesting gets its attention and the fish takes off at lightning speed. This and everything else about retroculus seems to be perfectly suited to their rheophilic (= current-loving) lifestyle, starting with the way they behave and their strong fins and ending with their extremely sticky roe.
The phylogenetic relationship of the genus Retroculus to other Neotropical cichlids has been much studied until recently. Kullander separated the genus Retroculus, which was part of the subfamily Geophaginae, and created their own group Retroculinae. This position was later confirmed by two studies based on mitochondrial and nuclear DNA by Farias et al. which proved the basic placement of the genus Retroculus within all Neotropical cichlids. In other words, although Retroculus may remind some of elongate satanoptera, there is no closer relationship between the two than between Retroculus and, for example, discus.
Spawning
I got my first four specimens of R. lapidifer in 2002, when the 3-4 cm juveniles (they were the very first in Finland) moved into a 160-litre aquarium. The little retrovia ate anything with great gusto, and after they grew to twice their size, I moved them to a 530-litre aquarium. In the larger tank, the fish took off growing even more and after a year of keeping them, the largest one measured 15 cm.
At this point a pair formed out of nowhere and both male and female (this was obvious due to the larger size and more massive appearance of the male) started digging a large hole in the sand. For a few weeks there was a distinct excitement in the aquarium, but eventually nothing happened.
After a week, I was lucky enough to meet Thomas Weidner, who was attending a sequence of seminars of our national club (Ciklidistit) in Helsinki. I asked for his opinion on my chances of breeding. Thomas was quite measured and replied that the fish were still too small and young and maybe when they were 20 cm old…
As Thomas predicted, the courting stopped and it took one full year before it started again. This time it was really wild. The pair began a display of outstretched gills and side display, unmatched by any cichlid I’ve had the opportunity to see spawning. They also exhibited a strange habit, pointing their heads at a certain point next to the rocks and began aggressively shaking their heads.
After almost two weeks of courting, the pair dug a hole in the spot they had previously pointed to. The digging went on for a few days until one day when I returned from work, it seemed like it was all over. The hole was half covered and the couple showed less interest in each other. The next day it was obvious that something had gone wrong. They had lost interest in their pit altogether and allowed other ground eaters (Geophagus, Satanoperca and similar species, ed. note) to hang around across where the pit had been. Water parameters during spawning were as follows: 28.4 °C, pH 6.3, NO3 10 mg/l, NO2 <0.1 mg/l and 2.5 °dKH.
A month later the courtship started again and was, if possible, even more extravagant. This time, I relocated the Satanoperca daemon, which also got overexcited on the last attempt. After this, all the other fish hid in their hiding places and a couple of retroves started to dig. They made a 25 cm wide and 10 cm deep hole next to a pile of stones the size of a man’s fist, aligned with a nice pile of sand.
Three days later, the spawning began. This time I was lucky enough to be at home when the courtship turned into a synchronized swim by both partners. The female deposited about 10-20 eggs per turn, the male waiting right next to the female’s tail fin immediately followed her to fertilize the eggs and mix the milt with the eggs and sand. After a few rounds, both parents began bringing one to three mouthfuls of coarser sand and gravel to the top of the egg-laying site, which they had previously separated from the otherwise fine sand and dumped next to the spawning site.
At this point it was clear that the eggs were very sticky. This no doubt reflects the fast-flowing home rivers of species of the Retroculinae group. The already heavy eggs gain extra weight by attaching to grains of sand, so they are able to avoid being washed away by the strong current of the river. The wild R. lapidifer use even quite large pebbles to cover their eggs, but apart from fine “earthy” sand of 1 mm grain size, the only pebbles I have been able to offer them are of 5-10 mm grain size. Apparently, by using larger grains of gravel or pebbles, the retrovia will provide an oxygen supply even for the deeply buried eggs, thanks to the easier water flow.
After about ten rounds of egg deposition, the pair took a break to rest. I ventured out to suck up about a third of the sand with the eggs with a hose and moved them to the brood box, which was positioned directly in front of the filter outlet that provided additional flow in a separate 60-gallon aquarium. The male was quite aggressive towards me while I was sucking out the eggs, but both parents calmed down after I finished.
At that point, another task began for them, which they will continue to attend to 24 hours a day. The pair moved the egg layers along with coarse gravel into the newly dug pits, which they did about 4 times a day. The fish did not rest at all, even during the night as they continued to work with the help of the night light that was on in the next room. This effort exhausted them, as they are used to oxygen-rich water in their native habitat. So, in the sub-optimal conditions of my aquarium, their hyperactive actions caused them to breathe very heavily at all times. Regardless, the pair also found plenty of energy and time to strengthen their bonds with the usual extravagances of side-showing, amidst all the digging and moving around.
The eggs I separated started hatching 72 hours after spawning, but despite a small precautionary dose of methylene blue, 80% of the eggs molted and did not hatch. The large mass of eggs seemed to have persisted and hatching was really just the addition of a thin, fast moving tail to the eggs as a hair.
Meanwhile the parents in the larger tank continued their all-too-active migrations, which, especially now that the brood had hatched, seemed so rough that it was a small miracle that the brood was not injured by the ever-accompanying gravel.
After a week, I also sucked the rest of the brood with the sand into the same smaller aquarium, as the parents looked really exhausted. Although the broodstock was hard to distinguish from the sand, it was later clear that the hatching success rate was far better with the parents than in a separate tank. It is likely that the harsh-looking handling and constant handling of the eggs is beneficial due to the abrasion of harmful substances or even the loss of some of the outer shell that protects the eggs in the early days after fertilization.
The following day (eight days after spawning) the fry floated away and the very next day began feeding on freshly hatched Artemia nauplii. Later, the little retrovia switched to bosminia and then to snappers. It seems that the patentinae are the food they most prefer, which is not at all surprising since Moreira et al. have published that 50-99% of the stomach contents of retroculus are just the larvae of tadpoles.
Despite their appetite, R. lapidifer are rather slower in growth, at least compared to the Satanoperca jurupari broodstock that I keep in the same 240-litre tank. While S. jurupari peacefully and incessantly graze the bottom, the young R. lapidifer concentrate on the people in the room and rush to the feeding site at the slightest movement many metres away from the tank. They also seem to consume a lot more in their active life style, and at four months, when they are 3cm, they are beginning to show something of their parents’ temperament as well. What a stunning fish!