Those Other Central American Cichlids - Part Two: Neetroplus nematopus

A pair of Neetroplus nematopus with a few of their fry. Note that the male's color pattern is less clearly defined than that of his mate. This reflects both the relatively low intensity of fry pedration under aquarium conditions and the female's more active role in the long-range deterrence od such predators. Photo by Paul V. Loiselle.

(This article was originally published in Freshwater and Marine Aquarium Magazine, jan 1983; pp. 39-44, 56-58. It is here reproduced with the permission of author Dr. Paul V. Loiselle).

(Editor note: The present article, written in 1982, lacks all the recent modifications in Central American cichlid taxonomy. In an attempt to make it current I have updated Dr. Loiselle's article to include all the curently accepted Cichlid genus. I have followed Kullander paper (Kullander 1996) on Heroines with comments for Cichlasomines systematics for this end. May-1997.).

This representative of Central America's endemic cichlid genera was described by Albert Gunther in 1869. Like many other nineteenth century cichlid genera, Neetroplus was defined on the basis of dental characteristics. The outer jaw teeth in Neetroplus are compressed and incisor-like in shape, quite different from the conical dentition characteristic of Heroines. It is something of a puzzle to me why Gunther regarded the dentition of Neetroplus sufficiently distinctive to warrant the erection of a new genus while placing Herotilapia multispinossa, a species with equally distinctive dentition, in the genus Heros. Be that as it may, he drew upon another morphological feature when coining a generic name for his new cichlid. The name of the Asian genus Etroplus refers to the heavily spined anal fin of these cichlids. Neetroplus literally means "new Etroplus ," with reference to this shared characteristic of two otherwise very different cichlids. The specific name nematopus means "thread-foot," and refers to the filamentous extensions of the ventrals of large males.

Reliance upon the shape of the jaw teeth to define the genus led to the description of a number of additional nominal Neetroplus species during the closing decades of the nineteenth and the early years of the twentieth century. As I have explained in an earlier essay (Loiselle, 1982), ichthyologists of that epoch were largely unaware of the ways in which environmental forces could operate to modify dental phenotypes. Subsequent workers (Regan, 1905; Miller & Nelson, 1961) determined that two of these nominal species, Neetroplus carpintis Jordan and Snyder 1899 and Neetroplus boucourti Vaillant and Pellegrin 1902 were properly referable to "Cichlasoma" (Now Herichthys for carpintis). The status of the remaining species of the genus was resolved in a recent paper (Rogers, 1981). Neetroplus nicaraguensis Gill and Bransford 1877 and Neetroplus fluviatilis Meek 1912 were found to be junior synonyms of N. nematopus, while Neetroplus panamensis Meek and Hildebrand 1913 proved to be another "Cichlasoma" species. The abraded jaw teeth of large specimens in the type series 'Cichlasoma' panamense led to its original misdiagnosis. As currently understood, then, Neetroplus like Herotilapia, is a monotypic genus, comprising the single valid species Neetroplus nematopus.

Given the possibility of environmental modification of tooth shape, a critical observer could hardly be faulted for suspecting the validity of the genus Neetroplus, a taxon originally defined on the basis of this characteristic. Bill Rogers, who completed his research on Neetroplus systematics during the first years of my sojourn at Berkeley, very carefully examined the ontogeny of the jaw teeth in N. nematopus and a number of Heroine species in order to gain some notion of the developmental plasticity of this diagnostic feature. He found (Rogers, 1981) that the jaw teeth of newly hatched Neetroplus are conical, but that the underlying row of replacement teeth is made up of elements that show the characteristic incisiform shape before they erupt through the gums. This is conclusive evidence that the incisor-like jaw teeth of Neetroplus do not constitute an environmentally determined phenotype. Taken with a number of other characteristics, this evidence of genetic divergence led Bill to conclude that Neetroplus as defined by Gunther ought to remain generically distinct.

If the generic validity of Neetroplus is no longer a matter of debate, its ancestry still remains something of a puzzle. This is quite unlike the situation with regard to Herotilapia, whose nearest relatives are obviously representatives of the genus Archocentrus. The combination of terete body form, enlarged head, slightly subterminal mouth and closely packed anterior jaw teeth appear to have evolved independently several times within the Heroine group of genus. This suite of characteristics appears to represent a response to the exigencies of life in rapidly flowing water. The genus Paraneetroplus has been erected to contain several Mexican and Guatemalan species that seem to have few other features in common beyond such a life style. Given what is known of the historical biogeography of the San Juan faunal province (Bussing, 1976), I would suggest that Neetroplus represents a highly specialized derivative of the genus Paratheraps. The representatives of this group of Heroines most familiar to aquarists are large, deep-bodied species such as Paratheraps synspilus.

Abrasive wear of the buccal dentition in the type specimens led Herichthys carpintis to be originally described as a Neetroplus species. Its closest relative is actually the Texas Cichlid, Herichthys cyanoguttatus. Photo by Paul V. Loiselle.

A courting male 'Cichlasoma' panamense, another species originally placed in the genus Neetroplus on the basis of environmentally induced modification of its jaw teeth. The re-importation of this small, relatively unagressive species is greatly to be desired. Photo by Paul V. Loiselle.

A parental female 'Cichlasoma' panamense. As is the case in many Central American Cichlids, the color pattern of parental fish is characterized by enhanced contrast between light and dark elements, often at the expense of those features deemed aesthetically pleasing by aquarists! Photo by Paul V. Loiselle.

The similarities in overall body shape and mouth placement between this male Pseudotropheus gracilior and Neetroplus nematopus are the results of the selection pressures consequent upon a shared means of making a living. Neetroplus may be regarded as the Central American counterpart of such African of such rock-scraping cichlids as Tropheus, Pseudotropheus and Steatocranus. Photo by Paul V. Loiselle.

Neetroplus occurs in the Great Lakes of Nicaragua, in the Rio San Juan, which flows from them, and in the Atlantic slope rivers of Costa Rica. Riverine populations are typically resident in areas of vigorous current and rocky bottoms. According to Bussing (personal communication), these stream-dwelling fish are very secretive, which may account for the dearth of information on the ecology and behavior of N. nematopus in such biotopes. We are considerably better informed about these aspects of Neetroplus biology under lacustrine conditions, as populations living in Lake Jiloa, Nicaragua, have been subjected to the scrutiny of several of Dr. George Barlow's students over the past decade (Rogers and Lim, 1975; McKay, 1977a, b).

In this small crater lake, Neetroplus is a common inhabitant of rocky bottoms, occurring at all depths in considerable numbers. As might be inferred from its dental specialization, N. nematopus is adept at rasping algae from solid surfaces in much the same manner as representatives of the African genera Tropheus and Pseudotropheus. Its distinctive feeding behavior has earned it the vernacular designation of picaculo in Nicaragua. This name is both colorful and descriptive but, alas, its literal English translation is unlikely to be accepted as a suitable common name by the American Fisheries Society! Like its Malawian analogs, Neetroplus is not above exploiting other food resources when they are locally abundant. Both zooplankton and the eggs of the open-water atherinid fish Melaniris sardina are taken enthusiastically whenever they are available.

Neetroplus goes the mbuna one step further in its trophic opportunism, however. Rogers and Lim (1975) report Neetroplus successfully competing with fresh-water crabs for access to a fish carcass. Neetroplus will also attack fish entangled in a gill net. In such instances, they also observed behavior reminiscent of that cited by Fryer (1959) the Malawian Dimidiochromis compressiceps. The trapped fish's eyes are the first targets of the Neetroplus, which in some cases completes its attack by eviscerating its victim and devouring bits of the internal organs. They also report that individual N. nematopus will defend such sizeable food items against other fishes' attempts to feed from them.

Before those persons who get their kicks out of watching piranhas bisect goldfish conclude that Neetroplus is just the ticket for them, I must add that such gruesome behavior is not at all typical of this species in captivity. Such offenses as Neetroplus perpetrates against aquaristic tranquility are driven by gonadal rather than gastric enthusiasm! Indeed, the grazing behavior of this species probably underlies the appearance of a fascinating instance of facultative cleaning behavior involving Neetroplus as cleaner and a number of other Central and South American cichlids as clients.

The fish in question were housed in a very large Neotropical cichlid community display at Steinhart Aquarium in San Francisco. According to Alfred D. Castro, who first observed this behavior, the client fish solicited the attentions of the Neetroplus with a combination of motor patterns and color changes comparable to those employed by coral reef fishes to communicate readiness to be groomed to such "traditional" cleaners as Labroides dimidiatus. Though much smaller than many of his clients, this enterprising Neetroplus was quite uninhibited in his behavior, grooming even large specimens of Vieja maculicauda and Parachromis managuense. This remarkable example of behavioral flexibility came to an abrupt halt when the successful innovator solicited a newly introduced specimen of Parachromis dovii. El lagunero is a major predator of Neetroplus in the Nicaraguan lakes (McKaye, 1977a), a significant fact apparently unknown to this American-born picaculo. In keeping with such established behavior, the prospective client's response to the displaying cleaner was swift, unambiguous and irreversible! The occurrence of comparable cleaning behavior in nature must remain an open question in the absence of confirmatory observations from the field. The unfortunate conclusion of the Steinhart episode underlines some of the obstacles that hinder the evolution of such symbiotic interactions.

As might be inferred from the foregoing, Neetroplus is not overly picky at mealtimes. Flakes or pellets, any of the usual live or frozen foods and fresh greens are all attacked with gusto. Like its Malawian analogs, Neetroplus much prefers feeding at the surface to scraping algae from solid surfaces. It usually requires several days without access to other sources of nourishment before individuals will revert to their typical feeding behavior in captivity. When I maintained this species at Berkeley, I could invariably anticipate finding "Neetroplus tracks" on the back and sides of their tank upon my return from a long weekend.

The other aspects of Neetroplus maintenance pose few problems. The lakes of Nicaragua have very hard, alkaline water (Barlow et al., 1976). Such conditions, albeit to a lesser degree, characterize riverine biotopes elsewhere in Central America as well. Like all Mesoamerican cichlids, Neetroplus prefers such water conditions in captivity, but will do well enough in moderately soft, neutral to slightly acid water. In contrast to Herotilapia, this species is probably the least tolerant of nitrogen cycle mismanagement of any Central American cichlid. Stressed individuals become abnormally dark and manifest a greatly accelerated rate of respiration in conjunction with severely inflamed gill filaments. They will dash frantically about their tank at the slightest disturbance and often attempt to escape their polluted surroundings by jumping out. Regular partial water changes are an indispensable adjunct to the successful maintenance of N. nematopus. So is an easily cleaned outside power filter, which will also provide the water movement this species appears to relish.

Rogers and Lim (1975) comment upon the vulnerability of Neetroplus to low oxygen tension. This susceptibility complicated the initial efforts to import this species and slowed its subsequent dispersal into the hobby. The use of supplementary aeration is dictated by this fact of Neetroplus physiology if the fish are maintained under even slightly crowded conditions. It is particularly prudent to supply supplementary aeration if the fish are housed in tanks filtered by units that rely upon siphon intakes. Accidents interrupting normal water flow through such filters can, and often do, occur in cichlid tanks. Given the probable consequences, it is far better to be safe than sorry. By way of partial compensation, Neetroplus can tolerate temperatures as low as 13° C. for up to twelve hours without coming to harm though a range of 21°- 30° C. is recommended for normal maintenance.

The behavior of Neetroplus, whether towards conspecifics or fishes of other species, is not easily summarized. It is strongly influenced by such external considerations as population density as well as by the internal state of the fish themselves. One can assert with minimal risk of contradiction that Neetroplus is not an efficient piscivore and poses minimal risk to free swimming companions too large to be easily swallowed. As is the case with many cichlids, N. nematopus behaves much more aggressively towards others of its species than it does towards heterospecifics. The consequences of this behavior depend in large measure upon the density at which the fish are housed.

At very low densities, on the order of six fish per 400 l of tank volume, relatively little aggression will occur outside periods of sexual activity. Assuming a modicum of cover, even at such times, non-breeding fish have little difficulty in avoiding the spawning pair. At the other extreme, as exemplified by holding tanks in Barlow's lab where stocking rates of close to 100 adult and sub-adult fish per 160 l aquarium were sometimes the rule, aggressive interactions occur frequently but rarely result in injury to the contestants. This is due to the nature of these encounters. Under such crowded conditions, ritualized aggression is the rule, real combat virtually non-existent. It is a measure of this species' behavioral flexibility that even under such crowded conditions, pairs required only a minimum of shelter to spawn successfully and bring fry to independence. In reality, it is at intermediate population densities, on the order of a dozen adults per 160 l of tank volume, that damaging or even lethal manifestations of aggression are most apt to occur. Such a U-shaped response curve is characteristic of many cichlids and of other notably bellicose fishes such as Betta splendens also.

Unless one is inordinately fond of the beasts, it is difficult to imagine anyone but a wholesaler maintaining Neetroplus in sufficient numbers to dampen intraspecific aggression by sheer weight of numbers. Most aquarists find a single pair of N. nematopus around the premises to be more than sufficient! However, the usual technique of arriving at that point by allowing six to eight juveniles to grow to maturity together does run a greater risk of generating battered corpses in this instance than is usual among Neotropical cichlids. The best way to keep this sort of battery at acceptable levels is to dilute the Neetroplus in a community assemblage of somewhat larger cichlids. This seems to have much the same effect upon the expression of aggressive behavior as extreme crowding of conspecifics. If one houses a group of young Neetroplus in this manner, the odds are excellent that all will attain adulthood without mishap.

Until it attains sexual maturity, N. nematopus is a satisfactory resident in a cichlid community tank. Apart from asserting themselves at feeding time, individuals so housed make very few waves. With the onset of reproductive activity, which arrives with alarming precocity and manifests itself on a continuous basis thereafter, the situation undergoes a complete reversal. I will concede the existence of cichlids equally aggressive when breeding, but I challenge anyone to come up with a species that is more aggressive than Neetroplus at this time! Because paring tends to occur quickly and in the absence of elaborate courtship behavior, the first indication of impending spawning under community conditions is usually the vigorous defense of a spawning territory by the newly formed pair. Such behavior is hardly unique to Neetroplus. What does set this species apart from any other Neotropical cichlid I have ever kept are the size of the area sequestered relative to that of its defenders and the speed with which its limits are established. A 5.0 cm SL male and his slightly smaller mate can clear every other fish in their tank out of an area 60 cm square within 48 hours of the onset of territorial behavior. There are Heroine species that can match this performance, e.g., 'Cichlasoma' salvini, but all are much larger than Neetroplus.

A parental female Neetroplus in all her glory! Her color pattern at this time is reminiscent of that of adult Tropheus duboisi. The color change this little cichlid undergoes when breeding is one of the most dramatic in the entire family Cichlidae. Photo by Paul V. Loiselle.

Having watched many pairs of N. nematopus stake out their territories, I suggest the secret of their success lies in a combination of agility, teamwork and tenacity. Intruders are attacked so persistently that they learn very quickly to avoid the pair's demesne, while the speed with which attacks are delivered barely gives victims time to react. Any fish that does attempt to slug it out with its tormenters must contend with an opponent whose smaller size allows him a shorter turning radius than most Neotropical cichlids can boast. If the added edge in maneuverability this feature confers were not enough, both sexes collaborate in the expulsion of intruders. Usually the male distracts the pair's target with a frontal threat while the female swings around to attack its flanks or rear. Is it any wonder that even much larger fish are more than willing to cede the field to such determined and skillful antagonists?

The focus of territorial defense is a suitable spawning site. Neetroplus is a cave or hole spawning cichlid. Such sites are often limiting in nature (McKaye, 1977a,b). Indeed, it is probable that the remarkable bellicosity of this species has evolved specifically in response to the necessity of securing access to suitable spawning sites. According to McKaye (pers. comm.), the only cave-spawning cichlid in Lake Jiloa that can resist the attentions of a pair of ripe Neetroplus is the much larger Amphilophus citrinelus. The preference of that species for larger holes no less than its somewhat later breeding season in any case serve to minimize the likelihood of confrontation between the two. Under aquarium conditions, a pair of N. nematopus can ­ and will ­ roust any and all competitors out of the desired shelter. Parental cichlids with similar requirements, such as the various Archocentrus species, are supplanted as a matter of course. Other bottom-living fishes, such as loaches and catfishes are harassed until they vacate the premises in contention. Not even large loricariids or Synodontis are immune to such attentions. If the pair's targets have enough space to escape beyond the limits if the defended area, no further violence need be anticipated. If they do not, their lives will be brief, brutish and nasty. This is the main reason I would advise against allowing Neetroplus to spawn under community conditions in any aquarium under 160 I capacity.

Preferred spawning sites combine a narrow entrance with a height not greatly in excess of the maximum body depth of the male of the pair in question. Four inch flowerpots sliced in half lengthwise are enthusiastically accepted. So are inverted matching clay saucers for such pots if a suitably sized opening is cut out of the rim. In the absence of a prefabricated shelter of this sort, a pair will excavate a cave to their specifications. Though a small cichlid, N. nematopus is an accomplished and highly efficient digger. It is, therefore, essential that any rockwork in its quarters rest securely upon the bottom of the aquarium, rather than on the surface of the gravel. Otherwise, the pair's energetic excavation is apt to provoke spectacular underwater avalanches as the rockwork's foundations are systematically undercut. While this poses some risk to the excavators, the real danger from such rockfalls is the inadvertent rupture of a glass pane, with dystrophic consequences for all parties concerned.

A sexually quiescent male Neetroplus. The coloration of this species, while attractive enough, is certainly not its strongest selling point as an aquarium resident! Photo by Dr. Jeffrey R. Baylis.

The appearance of a conspicuous ovipositor is a certain sign that a spawning can be expected within a day's time. There is absolutely no problem in ascertaining whether spawning has actually occurred in this species. A parental female undergoes a dramatic color pattern change as soon as the eggs have been deposited, becoming, in effect, a photographic negative of herself! Division of post-spawning responsibilities follows the usual Heroine pattern. The male carries out the bulk of territorial defense, while the female tends the clutch of ovoid, reddish-brown to burgundy colored eggs. Spawns tend to be small, rarely exceeding a hundred eggs, with the mode closer to forty. In compensation, the eggs are quite large, measuring 2.25 mm along the major axis. This makes them almost half again the size of those of cave-spawning Archocentrus species such as Archocentrus nigrofasciatus.

The eggs hatch in just over 24 hours at 28°-30° , and the mobile fry emerge from the spawning shelter five days later. At this juncture, the male's color pattern also undergoes a "positive-negative" transformation, though in my experience, the contrast between the white median bar and the dusky background color is never as marked in parental males as it is in their consorts. Neetroplus pairs are superb parents, capable of rearing young to independence even under highly crowded conditions in captivity. Indeed, the only reason I can think of for removing a pair's fry for separate rearing is the essentially humane one of sparing any other fish present eight to ten weeks of concerted parental attention!

This period is particularly wearing for other fish because of the strong commitment Neetroplus makes to the "search and destroy" doctrine of fry defense. Most Heroine species remain closely tied to the vicinity of their schooling fry, venturing to attack only those predators that move into striking range of their progeny. This approach I refer to as the "convoy" doctrine, because of its similarity to the convoy system of defending cargo vessels against submarine attack. The behavior of Neetroplus parallels more closely that of highly mobile, hunter-killer groups of anti-submarine units. These seek out and destroy enemy submarines before they come close enough to pose a threat to a merchant convoy.

Typically, the female of a parental pair of Neetroplus will swim a wide circle away from her mate and young, deviating from the course only to energetically attack any fish she encounters, regardless of size. A female may swim as far as a meter from her family on such sorties. In most instances, the disparity in size between attacker and victim make it improbable that any serious damage will arise from her attacks. However, the intensity with which they are mounted does little to encourage any latent tendencies their victims might nurse to remain in the immediate vicinity of the dramatically colored attacker.

The behavior of Neetroplus simply represents a further refinement of the strategy of long-range deterrence of fry predation discussed in the initial essay of this series. Like Herotilapia multispinossa, Neetroplus in effect carries out the Pavlovian conditioning of potential fry predators. As in Herotilapia, the contrast-rich color pattern of parental fish transmits an unambiguous signal to potential fry predators: "Avoid me ­ I'm pure trouble!" Training other fish to avoid the vicinity of parental Neetroplus automatically keeps them out of striking range for attacks on fry. How well these tactics work in nature remains to be precisely determined. In captivity, some indication of their efficiency comes from the repeated observation that a pair of Neetroplus will commonly rear an entire brood to independence in a community tank containing larger cichlids and catfishes. In my experience, the only meaningful sources of fry mortality under such conditions are power filter intakes, which are not notably responsive to parental conditioning!

The fry are easily reared. They are large enough to take Artemia nauplii and finely powdered prepared foods immediately. Given ample food and frequent partial water changes, the fry grow rapidly. It is not uncommon for the larger individuals in a brood to have grown to 1.5 cm TL by their fourth week free-swimming. Parental care in Neetroplus is typically prolonged. I have, on several occasions, seen fry half the length of their 23.0 cm SL mother still being vigorously defended by their parents. Like the rainbow cichlid, Neetroplus is very tolerant of alien fry the same size and age as it's own progeny. Parental pairs readily adopt such fry. Neetroplus goes Herotilapia one better in this regard, however, pairs will actively seek out and kidnap heterospecific fry of the appropriate developmental stage from their biological parents. The selective payoff to both species is doubtless the same. Unlike Herotilapia, Neetroplus does not appear to ripen a second clutch of eggs while tending a brood of fry. Hence a pair is unlikely to respawn unless its brood is lost in toto or becomes independent of its control. The latter point is typically reached c. 12 weeks posthatching. In captivity, it is not unusual for these youngsters to begin emulating their parents ten to twelve weeks later.

From the aquaristic standpoint, Herotilapia and Neetroplus have many points in common. Both are on the small side as Central American cichlids go, rarely exceeding 10.0 cm SL. Both are easily maintained cichlids that will prosper over a wide range of water conditions and on easily supplied diets. Neither could be described as a difficult fish to breed in captivity, while it would require the wisdom of Solomon to determine which of the two makes the more reliable parent. Yet cichlid fanciers regard each very differently. Herotilapia is almost invariably described as the ideal beginner's cichlid, while Neetroplus is regarded as a fish for the experienced breeder of Neotropical cichlids.

History is, to a certain extent, responsible for this dichotomy. Herotilapia has been available through commercial channels longer than Neetroplus. The rainbow cichlid could be found in shops throughout the U.S. and Canada when Neetroplus first made its aquaristic debut in 1974-75. Differences in coloration are also a factor to be considered in this context. There is no question that the brilliant gold, black and iridescent blue coloration of the rainbow cichlid is much more appealing to the average aquarist than the much more subdued gray, beige and black of sexually inactive Neetroplus. Yet an absence of brilliant coloration has not hindered the popularity of such species as Cichlasoma bimaculatum, Mesonauta festivum, or for that matter, Pterophyllum scalare! Finally, it must be admitted that Neetroplus is an aggressive little cichlid, whose peppery disposition is not likely to contrast favorably with the mellower temperament of Herotilapia. Against this must be arrayed the popularity of equally aggressive and much larger fish, such as Aequidens rivulatus and 'Cichlasoma' festae, not to mention that of such diminutive but equally bellicose African species as Neolamprologus brevis and N. meeli.

I suspect that the reason for the "love it or loathe it" attitude surrounding Neetroplus has more to do with its personality as an aquarium resident than with any of these more objectively definable factors. Neetroplus distills into one compact package all the behavioral qualities that characterize Cichlasoma-group cichlids. It is a curious, outgoing, uninhibited little fish with a "take charge" attitude more appropriate to an animal ten times its size. It exaggerates these attributes by living at 78 rpm in a 33-1/3 rpm world. Such behavior is hardly restful for its tank-mates to experience and doesn't seem to do the nerves of any number of aquarists much good either! I also suggest that it is perceived as threatening by many aquarists who feel a need to be in total control of their fish rooms. It is, I suspect, more than a coincidence that most people I have spoken to with negative feelings about this species usually mention at some point in the account of their experiences that, "... the fish simply got out of hand." It wouldn't surprise me at all to discover that most members of the Neetroplus antifan club also have problems getting along with cats!

The Neetroplus fan club, on the other hand, seems made up of aquarists who could, themselves, be described as curious and outgoing, who take their acquaintances, be they people or fish, as they find them and who harbor a real, if sometimes unexpressed, pleasure at seeing the underdog in a contest of strength win the day. Neetroplus may never enjoy the seemingly universal regard among aquarists that Herotilapia and many other cichlids do. Yet, as long as the tropical fish hobby can count a reasonable number of such persons among its ranks, the future of Neetroplus as an aquarium resident is secure.