The Cichlid Diversity of a Volcanic Nicaraguan IslandAuthor: Shannon Loughnan
Located in the Central American heart of volcanic activity, Nicaragua is a majestic country that bears an array of aquatic attractions. Well known by many aquarists and travelers alike is the great Lake of Nicaragua, which is fed by 45 rivers and has an average depth of 70 meters (230 feet). Outside of Africa, this lacustrine ecosystem houses the largest tropical lake on the planet, which not only exhibits an array of freshwater fish, but also visiting Caribbean bull sharks Carcharhinus leucas, sawfish Pristis pristis, and tarpon Megalops atlanticus (McKaye et al., 1995). Due to these reasons and the exposure of sports fishermen hunting large guapote like Parachromis dovii and P. managuensis, I have held an interest in the lake for many years. It wasn’t until I visited the region in late August of 2006, however, that I became aware of an even more delectable secret.
The island of Ometepe is a popular retreat for backpackers and a home to many resident organic farmers. It is the biggest of 400 islands in Lake Nicaragua and the largest freshwater island in the world (McCrary et al., 2005). This sweltering island paradise provides a multitude of activities for tourists, from hiking one of its two volcanoes to horseback riding through the jungle in the search of howler monkeys or wild green parrots. Although these were all intriguing options, my purpose was to investigate the aquatic life of the Buen Suceso River, which lies in the valley created by the awesome spectacles of the volcanoes Concepción and Maderas.
Eventually flowing into the dusty waters of Lake Nicaragua, the Buen Suceso River is a haven for a variety of cichlids that are either permanent residents or visiting briefly to reproduce, feed, or seek protection from the expanses of the lake. Naturally, the river provides a remarkable contrast in habitat when compared to lake conditions, principally due to its spring-fed origin. My goal was to snorkel approximately one kilometer downriver, photographing and observing as many cichlid species as possible.
Traveling can be tough on Ometepe; roads are corrugated and potholed, and buses are slow and crowded. It was late in the afternoon when I finally arrived at my place of accommodation, the bus driver alerted me as we crossed the Buen Suceso River via a narrow concrete bridge. I was excited at seeing the water course I had learned so much about. I was eager to explore it immediately, but I thought it would be best to find my place of rest first.
When I arrive at a potential study site I like to pre-assess the location the day before—it leaves me feeling more confident and better planned for the following day’s activities. That evening I did just this, exploring the area close to the bridge and approximately 50 meters (164 feet) downstream. I felt more prepared for beginning my investigation the next morning, plus I was unsure how much time was needed to wade downstream and the sun was rapidly setting.
In this region the river was narrow, between 2 and 4 meters (6 ½ and 13 feet), and the depth ranged from 20 centimeters to one meter (½ foot to 3 feet). The riparian zone was well vegetated and 5 meters (16 feet) thick in sections, with established trees; but smaller shrubs, creepers, and juvenile saplings dominated. Many large trees grew partly submerged, their root systems providing great aquatic habitat and bank stabilization. A multitude of branches provided a canopy that shaded overhead, a factor that would have contributed to the absence of submerged macrophytes.
Water velocity was consistent but not overpowering, and the gradient of the land was only slight, producing immature meanders. The river edges were rocky, containing smooth boulders up to a meter in diameter, and the substrate was coarse and colorful, displaying reds, browns, and blacks of a volcanic nature and thus providing the water with excellent clarity. In some places green filamentous algae covered rocks; when absent it was replaced with a brown, less attractive species.
A multitude of insects danced on the surface of the water, indicative of the late afternoon. Visible were fast Astyanax sp., high in density, demolishing any organic matter that flowed downstream, including soap residue from an elderly man washing his trousers close to the bridge. The act of domestic washing in natural bodies of water continues to be a problem across the expanse of Latin America. Locals are either uneducated about the detrimental effects of detergents, or simply do not have the opportunity to change their habits
Upriver from the bridge the water had expanded into what appeared to be a mini floodplain. It was difficult to ascertain the main flow amongst the thick vegetation and the hoard of human construction, not only houses but stockyards and the rubble of waste that frequently accompanies it. There were some deeper pools, but water here was mostly shallow and a clear passage upriver was difficult to find. Downriver a clearly marked path lined with large boulders and established trees accompanied the direction of the flow. Shade would be a pleasant relief the following day from the draining Nicaraguan sun.
Approximately 50 meters (165 feet) downriver from the road crossing, before a barbed-wire fence separating livestock, was a small pool 3 meters (10 feet) in diameter to the left of the main flow. It was partly enclosed by a barrier of large rocks. Without entering the water, convict cichlids Cryptoheros nigrofasciatus could be clearly seen. The larger males were tussling with other conspecifics over territory and feeding rights. In amongst them were the ever present Astyanax sp. and attractive livebearers Poecilia mexicana, taking advantage of the slow water as potential food entered from the main current. This was a perfect spot to start my investigations the next morning.
Feeling like an eager explorer, I awoke at dawn and made my way to the concrete bridge to commence my journey. Unfortunately I had to virtually climb over an influx of clothes washers to head downriver (they were obviously taking advantage of the cooler morning conditions in which to conduct their work). Boulders were coated in soap scum and plastic detergent wrappers were thoughtlessly strewn across the ground and in the water.
Surely enough, Cryptoheros nigrofasciatus was the first cichlid species that I discovered in the Buen Suceso River. In the same pool that I investigated the preceding evening, three convict pairs were clearly observed, defending territory neatly spaced around the pool. No fry were present, but the constant activity and body colors suggested that families were planned in the near future.
These convicts displayed colors that I had never before witnessed in captivity, possibly due to the limited bloodline available in the aquarium trade in my home country. Clean horizontal bands of charcoal dressed the flanks of larger males, while pelvic fins were dipped in yellow for some individuals. Females possessed brilliant shades of gold in the dorsal and turquoise in the anal fins. Their plump bellies were touched with rose, an indication of their ripeness. Freshwater crabs inhabited the same pool; crouching beneath a ledge, I could see their red carapaces the size of my palm.
Still upriver, and frequently in the company of C. nigrofasciatus, were some Amphilophus longimanus enjoying the rocky habitat and seeking refuge between smooth rocks that would provide a perfect substrate for adhesive eggs. A pink hue engulfed the throat and breast. Larger specimens displayed a gold arc surrounding a dark pupil, with an additional wisp of copper painted upon the operculum. Also in the area was Gobiomorus dormitor, a sly benthic carnivore lazing camouflaged among the leaf litter that had accumulated between rocks.
After my initial excitement had subsided, I continued my venture downriver, snorkeling where possible, wading where shallow, or walking along the bank-side track. Walking the bank-side track was preferred when sections of the river became choked with fallen logs and boulders, although walking along this method of travel also provided some unexpected difficulties. Small black soldier ants attacked my feet and legs, and they bit my hands as I attempted to brush them off. In some places the spiderwebs were so thick that I didn’t dare attempt to pass; in one section a multitude of webs crossed the path where I counted over 50 spiders of various species. I was also paranoid about the deadly coral snake Micrurus sp., a small but venomous species that is all too common on Ometepe Island.
Underwater I investigated every section of the river that was deep enough for me to place my facemask, including beneath a concrete wash trough. Below this structure I found a resting Parachromis dovii shaded from the sun and ready to snap a meal moving downstream. At approximately 22 centimeters (8½ inches) in length, this piscivore was still considerably young, and while appearing harmless and shy, fine teeth were slightly exposed from its partly agape jaw, always at the ready. With care and little movement, I was able to photograph at will while my subject observed me.
As submerged timber increased in density and smaller branches and leaves accumulated within the river, I discovered Neetroplus nematopus, a small but aggressive cichlid species that was scrounging among branches for filamentous algae and plant detritus. With amazement I watched a mature male suspend himself upside-down beneath a log. Pushing his characteristic curved snout and mouth toward the base of the structure, he extended his jaw. His body shimmered rapidly and fins stood erect in order to increase the force of his search, and he obsessively tore away rotting timber. He made frequent bursts from inside the log where his female lay, spying on me through a window from within the woodwork.
The male was annoyed at the presence of a persistent Amphilophus rostratus that was determined to make the same log its shelter. No eggs or fry were witnessed from N. nematopus, and the female did not display her typical dark brooding colors—although this could not be discounted due to her stationary position and the ever present A. rostratus. Although normally a forager among detritus and feeder of insects, A. rostratus is an opportunistic feeder all the same (Alonzo et al. 2001).
One of my favorite species, A. rostratus displays the familiar head design and large mouth of a South American eartheater, although it is not known to employ its snout to filter soft sections of substrate for burrowing crustaceans (Bussing, 2002). Characterized by a large lateral blotch on its flank, this peaceful species also exhibited iridescent blue to green specks on its head, as well as on the dorsal and anal fins.
In close vicinity were some convict cichlids with an ugly skin disorder. Having the appearance of body fungus (Saprolegnia sp.), the small cotton-like tufts engulfed a third of their body but they were happily mingling with conspecifics and feeding. This could certainly be a naturally occurring bacterial infection, possibly inflicted from injury but I suspect that the input of pesticides from agricultural practices and phosphates from detergents have contributed to its presence.
Archocentrus and Amphilophus
As I proceeded further towards the mouth of the river and the grand Lake of Nicaragua, the water velocity slowed and sections of deeper water of up to 2 meters (6½ feet) were more common. Pools were a pleasure to snorkel, as they provided me with more leg room as I held onto submerged tree roots to steady myself for a multitude of photos. Vegetation overhung the edges, and it threatened to choke the river in sections but provided excellent cover for juvenile Archocentrus centrarchus and Amphilophus rostratus, both of which would prefer to avoid larger piscivores. Archocentrus centrarchus is a beautiful species; its deep body is gifted with charcoal mottled bars across a background of pale green, with an overall metallic silver sheen to it. Some individuals also displayed minor highlights of blue and orange in the dorsal and anal fins.
In the corner of my mask I caught a fleeting glimpse of a school of up to 12 Amphilophus rostratus adults moving upriver, sticking close to the substrate and bank edges. Unfortunately they did not allow me any time to view them, as they were obviously shocked at my presence. As they rounded a meander, they moved rapidly forward into the oncoming current. Water clarity began to deteriorate slightly as the water began to deepen. An excess of silt, vegetation, and other inorganic material that flowed from high upriver began to settle in the slower-moving waters, altering the substrate to a finer consistency.
Rarely Seen Herotilapia
Preferring submerged vegetation bordering the turbid waters of Lake Nicaragua, Herotilapia multispinosa is normally a difficult species to observe in this region, and it’s generally small enough to evade the nets of fishermen. I was fortunate enough to spot two males scraping filamentous algae from the rocks in the lower stretches of the river. In captivity this cichlid is known for its ease of spawning and high fecundity, but no fry were observed in its natural habitat.
Both males were approximately 8 cm (3 inches) in length and were well-fed, healthy individuals. Pale-colored females were also in the vicinity, but the males showed no interest in them. They displayed an aura of colors, such as a pale blue and dark orange smeared through the dorsal fin, and the anal fin exhibited a lusty gold. A dark lateral stripe commenced from the eye but halted at a large lateral blotch, only to continue on to the caudal peduncle.
While observing another P. dovii on the edge of some wooded habitat, I spotted a species in the background of my shot that I was determined to find in the Buen Suceso River. A Tomocichla tuba of approximately 20 cm (8 inches) in length was lying within the shaded edges of the overhanging bank among some leaf litter. It was well protected by some fallen branches. It was interesting to see this cichlid in this location; its arrival to the river has been suspected via rafts of vegetation from San Juan River populations (McCrary et al. 2005). Not preferring the still, murky lake waters, T. tuba has acclimated to lotic conditions as it has done in other regions of Nicaragua, Costa Rica, and Panama.
The powder-white belly captured my eye, and as I moved in closer the fish scattered into the nearby wooded area. Repeatedly, the same individual returned to the exact location where it was first spotted. I became suspicious of the fish’s obsession with guarding this identical spot, and upon one rapid flee I carefully parted the leaf litter. I was optimistic about my chances of finding some fry, but unfortunately there were none, and I did not want to disturb the area too much.
With some patience the cichlid returned permanently to its location, trusting its photographer. Its elongated body contained large, dappled black paint marks from the operculum to the caudal fin, and its white breast faded into coffee and olive-green tones toward the dorsal. Surrounding the dark pupil was a fiery red with intermittent lines of black. T. tuba possesses lips of sort, not as pronounced as those exhibited on Amphilophus species found in Lake Nicaragua and surrounding volcanic crater lakes (McKaye et al. 2002), but more delicate, with yellow to olive colors in the upper lip and white in the lower. Pleased with discovering another T. tuba nearby—although it was smaller and its colors were still immature—I was satisfied with the cichlids I had so far discovered, and any more would be a bonus.
Colorful Hypsophrys nicaraguensis
Still moving closer to the mouth, the river was forcefully channeled through a gap of only one meter, where it rapidly gained velocity over a rocky step. A concrete barrier nearly 2 meters (6½ feet) in height had been constructed to keep cattle separated, as the river’s riparian vegetation began to deteriorate. The river’s substrate was now completely fine, and before the water depth grew no higher than my ankles I found a young female Hypsophrys nicaraguensis seeking camouflage amongst a congregation of fallen branches and coconut husks. As with the color comparisons of Cryptoheros nigrofasciatus between wild and captive stocks, I was intrigued with the colors of H. nicaraguensis. Shades of red streaked through her dorsal fin as blue tipped the edges of the dorsal spines, and she displayed a dark and evident lateral blotch and stripe.
In these lower stretches of the river I came across a large school of fry. Ranging from 1½ to 2 cm (½ to ¾ inch) in length, they were busily foraging amongst the substrate and picking at matter in the water column. No parents were in the vicinity; the fry were left to fend for themselves, but they were strong, fast, and vastly independent. I was unsure of their identification but due to the quantity and size of the fry, I suspected a species of guapote to be responsible. The young displayed a snout that eventually tapered off at the jaw, and two dark stripes were evident: one from the mouth to the caudal peduncle following the lateral line, and the other along the base of the dorsal fin. Their bellies had a white coloration that faded into a light tinge of yellow. Pleased to see the evidence of a recent spawning, I was truly satisfied with the day’s exploration.
Around the very next bend I glimpsed the expanse of Lake Nicaragua as waves lapped at the shore like a seaport possessing a tide. The substrate of the river had turned to powdery sand and the mouth was shallow, no more than 30 cm (12 inches), while in sections ground vegetation crept into the water. Here I came across a floating plant Pistia stratiotes. It had thick green leaves that formed a rosette of up to 10 cm (4 inches). This aquatic plant species reproduces rapidly and can develop into an invasive pest in some habitats. I was surprised at finally discovering some aquatic vegetation, but due to its floating nature the plant may have originated from another region within the lake, arriving to the river mouth in similar ways as the floating rafts and T. tuba. The river now lacked the power to cut a deep channel and was approximately 8 meters (26 feet) in width at its entrance into the lake, enabling white long-necked water birds a greater surface area in which to forage.
Not far up the beach I could see clothes drying on the branches of a fallen tree; two fishermen were splaying fishing poles in a small dugout canoe nearby. I was relieved to be able to return along the coast line of the lake, a relaxing way to complete a satisfying day. As I walked along the beach toward my base, I admired the sparsely vegetated jagged rock islands offshore and recounted the day’s adventures.
In all, I had found and photographed nine species of cichlids. As I moved downriver the number of species increased, but Cryptoheros nigrofasciatus and Amphilophus rostratuswere the only cichlids I witnessed along the whole section of the river. I learned that C. nigrofasciatus is not only prevalent in the aquarium trade, but also in its native habitat. Amphilophus longimanus was solely present in the upper reaches, while Parachromis dovii, Archocentrus centrarchus, and Neetroplus nematopus were located in the middle and lower sections. Herotilapia multispinosa, Hypsophrys nicaraguensis,and Tomocichla tuba were only found in the lower regions of the river. In addition, McCrary et. al (2005) also reported sightings of Parachromis managuensis, Parachromis loisellei, two forms of Amphilophus citrinellus, and the introduced Oreochromis niloticus niloticus in the same stretch of river. Cichlid fry were limited, but as in other Nicaraguan freshwater systems, a selection of these species may spawn seasonally (McKaye et al., 2002).
Although restricted by its small dimensions, I have demonstrated that the Buen Suceso River provides an array of aquatic diversity. Obviously it is sustained by Lake Nicaragua, but the river provides an alternative habitat for species that have discovered their niche. Overall the river and its surroundings were in good condition. Advantageous was the constant renewal of fresh water from the upper reaches, which kept the water well oxygenated and clarity consistent. Unfortunately such a small river system is highly susceptible to human practices, such as construction and agriculture. These threats cannot be disregarded.