Texas Cichlids are native to the southern drainages of the Rio Grande River with its type locality being Brownsville, Texas (Nico and Fuller 2005), but Texas Cichlid populations have invaded other parts of Texas as well as Louisiana and Florida, colonizing urban canals and bayous in suburban areas (Lorenz and O’Connell 2011). Due to their aggressive behavior, invasive Texas Cichlids pose a significant threat to native species (Breau and Grant 2002). H. cyanoguttatus acts aggressively toward native largemouth bass (Micropterus salmoides), western mosquitofish (Gambusia affinis), sailfin mollies (Poecilia latipinna), and blue crabs (Callinectes sapidus) (Lorenz and O’Connell 2011). This type of aggression by invasive species can inhibit growth and reproduction as well as shift habitat use of native species (Schrank et al. 2003). For example, aggression of H. cyanoguttatus appears to cause reproductive failure of native sheepshead minnows (Cyprinodon variegatus) in experimental pools by disrupting spawn sites or in some instances consuming sheepshead minnow eggs (Mire, 2001). It appears to compete for breeding sites and resources with native centrarchids, bluegill (Lepomis macrochirus) in Florida and Louisiana (Courtenay et al.1974).
Texas cichlids have established populations in the Greater New Orleans Metropolitan Area in the past twenty to thirty years (Lorenz and O’Connell 2011). In New Orleans, Texas Cichlids compete with the native bluegill, Lepomis macrochirus and red-spotted sunfish, L. miniatus for territory and resources (Lorenz 2008). Competition for food may be irrelevant for both of these species because of their generalist diets (Ross 2001). Texas Cichlids has an omnivorous diet that consists of vegetable matter or detritus, and filamentous algae (Lorenz et al. 2011). Food resources for H. cyanoguttatus and L. macrochirus may not be a limiting factor. Both species are able to alter their diets as certain foods become scarce. It is possible territories may be held for other reasons besides food resources, like cover from predators (Lorenz et al. 2011). Wading bird (Tringa tetanus) and sparrow hawks (Accipiter nisus) feed on native centrarchids, so cover is a valuable resource (Minderman et al 2006). Bluegills are often forced into open water in areas that are heavily populated with Texas Cichlid as an indirect consequence of resource competition (Minderman et al 2006).
Behavioral trials were performed to determine if aggressive interactions occur between invasive Texas Cichlid (H. cyanoguttatus) and native bluegill (Lepomis macrochirus) (Lorenz et al. 2011). Observations demonstrated lateral displays are the most common display for L. macrochirus and lunges are the most common display for H. cyanoguttatus. When defending their territory, prior resident L. macrochirus aggressive behavior escalated to chasing and biting (Lorenz et al. 2011). L. macrochirus were markedly aggressive, averaging 11.625 aggressive actions per 10-minute behavioral trial (Lorenz 2008). In contrast, L. macrochirus were extremely passive as invaders, with 0.525 aggressive actions per trial (Lorenz 2008). This indicates the perceived value of the territory for prior resident L. macrochirus and their willingness to risk injury by engaging in costly behavior (Lorenz et al. 2011). Herichthys cyanoguttatus were equally aggressive as prior residents and as invaders, averaging 4.875 and 6.025 aggressive actions per trial, respectively (Lorenz 2008). Herichthys cyanoguttatus interacted aggressively with native species whether they held territory or not. The interspecies communication only seemed to break down when H. cyanoguttatus occasionally attempt to ‘mouth wrestle’, a common aggressive behavior in cichlids (Draud and Lynch 2002). The native L. macrochirus did not engage in this behavior and turned away from such challenges.
Interestingly however, red spotted sunfish (L. miniatus) chose to bite H. cyanoguttatus that attempted to mouth wrestle (Draud and Lynch 2002). H. cyanoguttatus demonstrates a higher level of aggression when matched with L. miniatus, especially when H. cyanoguttatus is larger in size than L. miniatus (Lorenz 2008). This indicates that H. cyanoguttatus may be able to adjust its level of aggression depending on species and are able to recognize their size advantage (Lorenz 2008). Communication and interactions between species, blue gill (L. macrochirus) and red-spotted sunfish (L. miniatus) are relevant to the success and effects of Texas Cichlids as an invasive fish in southeastern Louisiana.
Texas Cichlids are resistant to high-energy events. They weathered Hurricanes Katrina and Rita, which struck New Orleans in 2005; such resistance likely stems from their tolerance of wide ranges of temperature, salinity, pH, and pollution (Lorenz and O’Connell 2011). Moreover, after the disturbance wrought by the hurricanes, they were able to colonize more places in New Orleans, thereby increasing their population density in the region and magnifying their ability to compete with native species (Lorenz and O’Connell 2011). Growth of H. cyanoguttatus was not affected by a salinity level (8 psu) typical of the estuarine habitats surrounding the GNOMA, nor by a high salinity level (16 psu) much higher than usually found in this area (Lorenz et al. 2011). Herichthys cyanoguttatus appears to have little difficulty surviving and growing in brackish conditions (Lorenz 2008). Even with a relatively rapid rise in salinity, both salinity treatments resulted in positive growth of H. cyanoguttatus (Lorenz 2008). Temperature could also be a potential factor, especially because the family Cichlidae is a tropical family of fishes that shows more aggression at higher temperatures (Ratnasabapathi et al. 1992)
Texas Cichlids’ success as an invasive species can be attributed to their tolerance to temperature andsalinity changes, and human activity as well as their aggressive interaction with native species like bluegill (Lepomis macrochirus) (Breau and Grant 2002). Their native habitat is the southern drainages of the Rio Grande River but the species has been introduced into multiple other drainages in Texas like the Guadalupe River Basin, the San Antonio area, and the Edwards Plateau region. Outside of Texas, Texas Cichlid (Herichthys cyanoguttatum) populations have only been established in Florida and Louisiana, especially New Orleans (Nico and Fuller 2005). In Florida, their success has been confined to artificial canals (Fuller et al. 1999) Researchers suspect that Texas Cichlids were intentionally introduced into the environment by fish farms or aquariums in Florida (Lorenz and O’Connell 2011).In Florida, it remains abundant at Six-Mile Creek, where the species first were first reported, as well as in other localities in Hillsborough county and Big Pine Key (Shafland 1996). It was also reported in abundance in an abandoned phosphate pit near Mulberry in Polk County, Florida (Courtenay et al. 1974).
The suspected source of Louisiana H. cyanoguttatum population is multiple aquarium releases. In New Orleans, Texas Cichlid (H. cyanoguttatum) species resides in freshwater urban canals and bayous adjacent to the Mississippi River and Lake Pontchartrain (Lorenz and O’Connell 2011). The presence of Texas Cichlids in New Orleans was confirmed in the region since 1996, but evidence suggests that they may have resided there for up to twenty or thirty years (Fuentes and Cashner 2002). The first H. cyanoguttatus known in the New Orleans area was caught in southeastern Lake Pontchartrain on 17 June 1996 (Fuentes and Cashner 2002). From 1996 to 1998, less than 5 Texas Cichlid fish were caught at various sites within GNOMA (Greater New Orleans Metropolitan Area) (O’Connell et al. 2002). Large numbers of H. cyanoguttatus were caught beginning in 30 May 1998 with a fish kill of 23 H. cyanoguttatus and since then reproducing increasing populations were found (O’Connell et al. 2002).
To understand the dynamics of early stages of species invasion, a dispersion model was constructed to examine where H. cyanoguttatus originated and how it was dispersing (O’Connell et al. 2002). The model suggests that Texas Cichlids expanded into the area through estuarine corridors of Lake Pontchartrain (Lorenz and O’Connell 2011), coming from central Jefferson Parish. The model also suggested that the Texas Cichlid could and would invade and expand beyond their artificial, man-made habitats into nearby natural habitats (Lorenz and O’Connell 2011). Texas Cichlids experience no increase or decrease in growth when exposed to salinities between 0 psu (low salinity)-16 psu (high salinity), which is at a lower and higher salinity than H. cyanoguttatus is typically found (Lorenz and O’Connell 2011). For example, in Lake Pontchartrain H. cyanoguttatus was found at 8.0 psu. One important implication is that estuarine habitats may not serve as a barrier to continued H. cyanoguttatus expansion beyond the GNOMA and into valuable nearby fishery habitat.
Population density surveys before and after Hurricane Katrina and Rita showed the Texas Cichlid population increased. Their success after Hurricane Katrina can be attributed to flooding. The levee failures that followed hurricanes in 2005 inundated large portions of the GNOMA with estuarine waters which increased the salinity in the area (Lorenz and O’Connell 2011), and dispersed H. cyanoguttatus population. Despite the fluctuations in water salinity caused by incoming sea water, the Texas cichlids seem to be unaffected. The estuaries and urban canal in the New Orleans area measured salinity of 7.7 to 8.1 psu during 2006, which was not far off from nesting pairs of H. cyanoguttatus observed in Lake Pontchartrain at 8.0 psu salinity (Lorenz and O’Connell 2011). Temperature might limit the spread of cichlid because of the tropical origin of this fish (Courtenay et al.1974). Temperature did not fluctuate much between 2006 and 2007. Therefore temperature was not a deterrent in population growth, because Texas Cichlid population remained similar in New Orleans (Lorenz and O’Connell 2011).
Cichlids are seasonally monogamous fish and the male and female each contribute to offspring care (Makie 1985). Females are ready to mate by the time they are about 2-3 inches long. Males are ready to mate after they develop a nuchal hump on their forehead. During mating season, the underside of both sexes will turn completely black and three black bars will intensify in color (Berg 2010). Males engage in interspecific fights for access to females while females engage in interspecific fights for access to nesting sites. During field observations where researchers followed the behavior of Texas cichlids, no single individuals were seen maintaining a territory prior to laying eggs (Itzkowitz and Nyby 1982). Thus, territory formation only occurs after pair bonding (Itzkowitz and Nyby 1982). Once a pair has formed, they will look for nesting sites for spawning. There are several major factors that affect the ability for a pair to find and acquire a spawning site. Site availability is often a major limiting factor – rocks that serve as suitable spawning sites are often widely dispersed in the riverbed (Itzkowitz and Nyby 1982). Another factor that contributes to difficulty in acquiring a spawning site: the location of other pairs. Since cichlids are often very aggressive and territorial, an existing territorial pair will sometimes chase out nearby pairs looking for a spawning site (Itzkowitz and Nyby 1982). Once a spawning site has been acquired, the parents will need to prepare their territory for the female’s eggs. Since cichlids participate in substrate brooding, the practice of laying and fertilizing eggs upon a flat surface, within sediment, or inside a crevice, a site within the territory is chosen and nipped clean by the parents. After the substrate has been cleaned, the eggs are deposited by the female and fertilized by the male. The eggs are then fanned and protected for several days. Cichlids fan their eggs to maintain an increased level of oxygenation so that the eggs can respire more easily. In addition to increased oxygen, fanning prevents aquatic debris from landing over the eggs.
Although both sexes fan and take care of the eggs, males tend to spend more time protecting the spawning territory while females more frequently fan and tend to the eggs (Itzkowitz 1984; Itzkowitz 1985). While the female is tending to her eggs, the male continues to protect the territory while also preparing and digging a pit for the offspring to be deposited in once they hatch. Even though males spend more time protecting the territory, they tend to fend away and chase conspecifics less often than females since they tend to rely more on lateral displays (Itzkowitz and Nyby 1982). Since males are usually larger than females, intruders are more likely to flee from a large male’s displays before initiating a fight. Females will sometimes leave their offspring, even when males are not available to watch over the eggs, to quickly chase away intruders before returning. This chasing behavior in female Texas cichlids is unusual compared to other cichlid species (Baylis 1974; Smith-Grayton and Keenleyside 1978).
If the parents successfully protect their eggs, wrigglers will begin to hatch about a week later. The newly hatched young wrigglers, which are surrounded with yolk sacs, are transferred to the predug pits. After about a week, the yolk sacs are absorbed and the young become free-swimming frys. Around this time, the sex difference between male and female parental care tends to dissipate; during the wriggler and fry stages, both parents stay close to their offspring. The frys slowly move around their territory in tightly knit “clouds”. At this point, the free-swimming fry can feed on their own and eat organic matter like baby brine shrimp and other kinds of zooplankton (Barlow 2002). The adults provide their offspring with parental care and defense throughout the entire process (Itzkowitz and Nyby 1982).
There is sexual dimorphism between male and female Texas cichlids. Breeding males are larger and can reach a length of 12 inches; females are usually smaller (Loiselle 1997). Beyond size, males also have a nuchal hump on their forehead, while females usually have a large black spot on their spiny dorsal fin, a characteristic that males lack (Loiselle 1997). Spawning occurs in early spring as the slight increase in water temperatures triggers reproduction. After a couple has formed, both male and female cichlids are known to engage in interspecific competition for nesting sites. Once a couple has successfully obtained a nesting site, usually in warm waters with riffles and mixed substrate, they will spawn at the bottom of a dug out nest in the substrate (Miller, 2005; Robertson and Winemiller 2003). A single spawn can produce several thousands of embryos, though most of them will not survive to adulthood (Loiselle 1997).
Before a couple can spawn, however, they must compete for a nesting site; this competition is often a source of aggression in both male and female cichlids.
The Texas cichlid indeed engages in aggressive behavior, although such fights often follow “rules of engagement”, an escalated series of aggressive moves and displays, likely favored by natural selection, that allows bouts to end before a full fight, thereby reducing the risk of injury to the individuals involved while simultaneously delivering accurate assessments of relative resource holding power (Draud et al. 2003). Such aggressive behavior is used during male-male competition for mates. Females also engage in competitive encounters, though these are against other females for spawning territory. The motivation behind male-male competition differs from female-female competition. When females fight for territory, they are motivated by reproductive condition and a participant’s perceived value of a particular resource. Their fights are mostly determined by Resource Payoff Value (RPV). In contrast, when males fight for reproductive resources, like access to females and their nests, it is thought that these resources basically have the same value to every male – therefore, their fights are mostly determined by differences in Resource Holding Power (RHP).
RHP is the ability for an organism to succeed in a full fight, if one were to take place. In cichlids, RHP is visually assessed by the contestants through comparison of body size; when there is a large difference in size among contestants, escalating aggressive behaviors, like mouth wrestling and tail beating almost never occurred. Instead, fish assumed dominant and subordinate roles – smaller males performed more displays (subordinate behavior) and larger males performed more chases (dominant behavior) (Itzkowitz 1985; Draud et al. 2003). In staged, intrasexual male contests where males were similar in size, however, escalated aggressive behaviors were observed more often, likely because size difference was not as good a predictor of RHP (Draud et al. 2003). The male that wins a fight exhibits better RHP and therefore, successfully obtains mates and/or nesting sites.
While relative size accurately predicts outcome, duration, and frequency of aggressive behavior in males, it does not for females (Draud et al. 2003). Instead, female contest structure and outcome were determined by Resource Payoff Value (RPV).
Resource Payoff Value (RPV) is used to determine outcomes of contests when physical size differences do not matter. RPV predicts that the individual who values a resource more is expected to expend more energy and/or take bigger risks in a contest and therefore win, all else equal (Draud et al. 2003). Since females do not rely as heavily on RPH (Draud et al. 2003), physical size differences are not important in female intrasexual contests. RPV asymmetries cannot be as readily assessed by the contestants as RPH asymmetries, since RPV is not dictated by obvious physical differences. If females cannot readily assess how highly their opponent values a resource, then females may set their defensive strategies based only on their own RPV. This means that female contests are not marked by increasingly risky aggression, but are settled with consistent, uniform aggressiveness. The winner of these intersexual female contests is expected to be the contestant that is more persistent and better endowed. Along with RPV, the current reproductive condition of the contestants may affect the outcome of a fight in female cichlids. Resources that females use for the production of eggs (nest sites and foraging material) are thought to be valued differently by different females depending on their current reproductive condition. Consistent with this, aggressiveness in females is highly variable over time and tends to be highest late in the ovarian cycle, when they are about to spawn (Holder et al. 1991).
By understanding the differences (or lack thereof) between male and female contests, more insight can be provided into the many mechanisms of selection and competition and how they are related to the overall ecology of cichlids (or any taxa of interest).
The Texas Cichlid (Herichthys cyanoguttatus) is native to the Rio Grande valley in southern Texas, but has spread into northern Mexico, Louisiana, and Florida, as well as a few Caribbean islands. These cichlids are popularly kept as pets, so some invasive populations are likely the result of releases by careless aquarium keepers, as well as escapes from flooded fish farms (Rio Grande Cichlid, BTNEP). However, the species seems to be quite capable of spreading on its own as well. This may be because the species can quickly adapt to varying levels of salinity and thereby uses brackish waterways to move from one watershed to the next.
Acclimation to Salinity
In its native habitat, the cichlid inhabits freshwater lakes and rivers, living in riffles as fry and deeper water as adults. However, they have also been observed living in waters up to 5,000 parts per million salinity in the wild and up to 16,000ppm salinity in captivity (Oldfield). For comparison, the average salinity of ocean water is about 35,000ppm and the salinity of brackish water can vary from 5,000ppm to 35,000ppm (less saline after heavy rains or floods). Lab experiments have shown that this species can acclimate to water as saline as 35,000ppm in as little as a week, with about 50% of individuals surviving when suddenly (without acclimation)exposed to 16,000ppm salt water (Lorenz 2008). Such adaptive abilities are in-line with the capabilities of the family Cichlidae, and make spread and colonization easy – especially after heavy rains when brackish water is less saline; the time it takes for salinity to increase back to a region’s normal levels provides acclimation time to any cichlids that spread while water levels were high.
The effect of invasive Texas cichlids on native fish has not yet been demonstrated, but it may pose a number of threats to native species. Populations of Texas cichlids can become quite dense relative to competing species (i.e., other cichlids, sunfish). As Texas cichlids are strong competitors (due to their ability to acclimate to saline water, their aggressive behavior, and their prolific foraging behavior) (Lorenz 2008), it is likely to compete with native species for food, like small invertebrates and aquatic plants, thereby driving down native population sizes.
Aggressive Behavior
In concert with their strong competitive abilities, Texas cichlids are also highly aggressive. The Texas Cichlid shows aggression at every life stage, not just as breeding adults (unlike other fishes). Females are just as aggressive as males, with some exceptions (Nico). This behavior can cause injury to other species of fish, but can also drive them away from resource-rich habitats and into more open waters where they are more likely to be predated upon (Nico). Increasing population sizes will bring it into agonistic encounters with native species increasingly often; indeed, the cichlid has been documented showing aggression to other fish in invaded habitats (Lorenz 2011). The combination of aggression and other competitive advantages makes the Texas cichlid a ready invader and Texas cichlids seem to outcompete similar native fish, paving the way for additional invasive species to colonize.
The male Texas cichlid is, like most male cichlids, especially territorial, though only after securing a mate (Lorenz 2011). When ready to breed, males develop a fatty mass above their eyes called a nuchal hump. Though its exact function remained a mystery until the past decade, it is now hypothesized to be used for sparring with males (intrasexual selection) or for attracting mates (intersexual selection) though. Evidence has debunked both ideas (in reference to cichlids, at least). There is no measurable advantage in a fight for a male with a larger hump, and competing evolutionary stresses make intersexual selectionunlikely (Barlow 1997). Males with smaller humps, for example, may produce fewer male hormones (nuchal hump development is associated with male genitalia and hormones) while males with larger humps would be less recognizable to females as a member of the female’s species. The likely purpose of the hump is species recognition (Barlow 1997).
Eating Habits
The eating habits of the Texas cichlid are similar to those of other cichlids: they sift sand through their mouths to filter out crustaceans, insects, and worms (supplemented with algae and plant matter) (Brough). Pharyngeal teeth help cichlids with this behavior.Pharyngeal teeth are bony protrusions in the throat (under muscular control) that help to grind prey once it has been swallowed whole. Numerous fishes have pharyngeal jaws that they use in diverse ways (including, in some cases, vocalizations). Cichlids have evolved a series of pharyngeal jaw modifications. The lower pharyngeal jaws are immovable in cichlids, while, unlike most fish, the top ones are jointed and supported by additional muscle growth not seen in other families (Liem). As such, cichlids have the unique ability to actively masticate with these teeth in addition to the grinding and trapping functions shared by other species. The ability to “chew” food in this way freed cichlids’ mandibular teeth to specialize and diversify, performing new functions, such as extending, sucking, or filtering sediment. As such, cichlids rely on such diverse food sources as plants, fish, sponges, snails, and fish scales; when hunting other fish, extendable jaws make ambush-hunting more effective. In the case of the Texas cichlid, the front jaws have specialized to filter sand and trap invertebrates.
Movement
As aggressive as they are, Texas cichlids tend not to hide, relying instead on hardened fin spines for protection in open (though usually shallow) waters. The spines are used exclusively for defense against predators, unlike some fish which use them for other things like locking themselves into a burrow or envenomating prey. Cichlids’ spines and fins inhibit speedy swimming, so the fish have evolved instead to be agile (Brough). Agility is useful given their desire to protect their nests and their lack of predatory behavior; quick turns can allow for an efficient escape or accessing unprotected parts of a threatening fish to attack.
Chemoreception and Mechanoreception
Cichlids sense their environment through two main mechanisms. The first is a developed sense of chemoreception (Caprona). Unlike most fishes which have two sets of nostrils, cichlids only have one nostril opening on each side of their face. Chemoreception occurs predominantly by swallowing and immediately regurgitating water, “tasting” it in the process (Caprona). This method of chemoreception is only found in cichlids and closely-related damselfish.
Mechanoreception is accomplished by the lateral line system common to all fish. Only two genera of cichlids (Teleogramma and Gobiocichla) have an uninterrupted lateral line; the rest, including the Texas cichlid, have a lateral line that is separated vertically into two parts. The presence of multiple or split lateral lines can increase the sensitivity of the system (Bleckmann). Vibrations in the water that are farther away, weaker, or partially masked by “background noise” can be more effectively detected by a split lateral line. In the same way that a lateral line on each side of a fish can give the fish a sort of depth perception (analogous to how binocular vision allows the brain to build three-dimensional images), separating the lines once more in an additional special dimension increases their sensitivity and functionality.
Location: Texas Cichlids are native to the Rio Grande and Pecos river drainages (Brown 1953), as well to northeastern Mexico (Page and Burr 2011). They were introduced northwards to Central Texas in the Edwards Plateau region (Birkhead 1980). Established populations exist as far north in Texas as the San Gabriel River in the Brazos River system (Hubbs et al. 1991).Outside of Texas, there are established, non-native populations in Florida and Louisiana (Fuller et al. 1999).
Texas Cichlids occur in freshwater riffles or other areas with some degree of water flow over mixed substrate types (rocks, sand, mud, clay) in ponds, lagoons, creeks, rivers, and springs. They prefer vegetation of green algae, water lilies, and water hyacinth (Miller et al. 2005). The species thrives in slight to strong currents, and clear to murky or turbid water (Robertson and Winemiller 2003; Miller et al. 2005). They prefer warm water (minimum temperature tolerance between 14 degrees Celsius and 19 degrees Celsius (Page and Burr 2011; Hubbs 1951). They are found at depths up to 2.75 m, but usually 1.5 m or less (Miller et al. 2005). Breeding pairs prefer shallow water - breeding was observed in water less than 30 cm (Itzkowitz and Nyby 1982). As substrate breeders, rocks serve as spawning sites (TSU).
Although Texas Cichlids are freshwater fish, the species has a high salinity tolerance. They have been observed in salinities of at least five parts per thousand (ppt), and experimentally up to 16ppt (EIS; Lorenz and O’Connell 2008). Fresh water is less than 1ppt and ocean water is about 35ppt (W2U). This adaptation allows the species to spread and colonize easily, using brackish estuarine waterways to disperse (O’Connell 2002; Lorenz and O’Connell 2011). In addition to tolerating a wide range of acceptable water habitat, the invasive ability of the Texas Cichlid is increased by its generalist omnivorous diet, which makes establishing populations in non-native habitats feasible (Buchanan 1971). Introductions into Florida and Louisiana are likely from fish farm or aquarium releases. In Florida, the invasive population is limited to man-made habitats such as canals (Fuller et al. 1999). A population in the New Orleans area has been studied (Lorenz 2008) for invasive impacts. Populations in Louisiana also occur in freshwater canals and bayous, and the study aimed to determine if Texas Cichlids are capable of expanding beyond the artificial habitats. An important implication is that estuarine habitats may not serve as a barrier to continued expansion, and populations occur adjacent to the Mississippi River, Lake Pontchartrain, and natural swamps and marshes in Bayou Sauvage National Wildlife Refuge and La Branche Wetlands. A population was found in Lake Pontchartrain in oligohaline conditions (5 to 12ppt), supporting the results of a dispersal model (O’Connell et al. 2002) that proposed that Texas Cichlids are capable of expanding via estuarine passageways.
The Texas Cichlid, also known as the Rio Grande Cichlid, is the only cichlid native to the United States. The species is native to thelower Rio Grande drainage in southTexas. These freshwater fish can grow up to 30 cm, and are distinguished by the cream to blue speckles covering their bodies. Cichlids engage in aggressive, intraspecific competition for resources like mating sites and foraging material. In addition, cichlids are monogamous fish that have biparental offspring care. The Texas Cichlid has evolved a number of functional adaptations that enable it to survive in its native habitat as well as thrive as invasive species. These adaptations are closely tied to their evolutionary history and predisposition toward rapid development of variation within populations. Although native to the Rio Grande, Texas Cichlid populations have been reported in New Orleans,Louisiana and Florida. Due to their aggressive behavior, they outcompete other native species like bluegill, large mouth bass, western mosquitofish, sailfin mollies, and blue crabs for resources and mating grounds.
Body shape and size: Oval, almost square, up to 30 cm (12 in) total length (TSU; Page and Burr 2011).
Body color: The Texas Cichlid belongs to the genus Herichthys, whose members “[share] a color pattern of short vertical bars or black spots posteriorly from the middle of the side” (Kullander 1998; Lorenz 2008). Background color varies from light cream or dusky gray to dark olive. After pair formation, breeding individuals (both the male and female) that are ready to spawn change coloration to have a half-and-half pattern: a white head and front half of body, black rear half of body (Page and Burr 2011, Kullander 1998). Very appropriately, the specific epithet, cyanoguttatus, is Greek for “blue-spotted” (Tomelleri and Eberle 1990). The head, body, and fins are speckled with white to turquoise spots. Adults can also have iridescent blue-green vertical wavy lines along the body. Four to six dark blotches are present along the center of the body, starting behind the pectoral fin and extending posteriorly, with the most distinct blotch at the base of the caudal fin (Page and Burr 2011).
Other characteristics: Outside of body coloration, fin characteristics are helpful for distinguishing Texas Cichlids from similar species. They have 15 to 17 dorsal spines and ten to 12 dorsal rays, 5-7 anal spines and 9-10 anal rays (Page and Burr 2011; Hubbs, Edwards, Garrett 2008). Both the dorsal and anal fins are long and tapered, extending posteriorly behind the caudal peduncle (TPWD). Breeding males develop a nuchal hump (a distinct mass of fatty tissue above their eyes) as they age, which is used for species and sex recognition, and attracting potential mates (Page and Burr 2011; Barlow and Siri 1997). Like all cichlids, Texas Cichlids have only one nostril opening (rather than two, which is standard in fish) on each side of the head. Also common to the family, they have a discontinuous (2-part) lateral line, with the front portion higher on the body than the rear portion (Page and Burr 2011). In the Texas Cichlid, the lateral line is doubled for a short part of the caudal peduncle (Tomerelli and Eberle 1990). Cichlids have pharyngeal jaws: a second set of jaws within the throat where the primary processing of prey occurs (Hulsey 2006).
Sex discrimination: If a nuchal hump is not present, sex can be determined by the shape of the female ovipositor (an external organ used for laying eggs), which is broad and blunt and can be differentiated from the male intromittent organ, which is slender and sharply pointed (Draud et al. 2004). Male dorsal and anal fins have pointed extensions (SF). Females may also be less colorful than males(Stevenson 1976).
Juvenile: As a juvenile, the Texas Cichlid has a pearly gray background color, with white dots on the body and fins. Two dark blotches are present along the side of the body, one in the center and one at the base of the caudal fin (TFHM). The body is more oblong and slender than adult shape.
The family Cichlidae is one of the largest fish families and a model for studies of adaptive radiation and diversification of life on Earth (Lundberg). There is contention, however, about when exactly these fishes evolved and how they came to inhabit the areas they do today. Continued efforts to construct a Cichlidae phylogenetic tree in addition to studies of distribution and fossils are making the place of cichlids in the tree of life clearer every day.
There are nine subfamilies of cichlid (Nelson 2004). The Texas cichlid (Herichthys cyanoguttatus) is in the subfamily Cichlasomatinae. Before molecular phylogenetics, the two most important features used to distinguish major cichlid lineages were the pharyngeal jaws and the otoliths (Barlow 2000). The jaws vary among cichlid subfamilies and were used in conjunction with otoliths to build the cichlid phylogenetic tree. Fish otoliths differ dramatically from other vertebrates, primarily because fish gravity and acceleration differently when moving through water (as opposed to moving through air). Genetic studies resolved many uncertain branches in the cichlid phylogeny, helping to establish the tree accepted today (Sültmann).
Cichlids are incredibly numerous in Africa and South America, but also extend into Mexico, the Caribbean, the Middle East, and India. Invasive populations have been established in eastern Asia and Australia (Stiassny). This distribution suggests a Gondwanan origin: cichlids may have evolved on the continent of Gondwana during the Triassic period (Stiassny). Gondwana then fragmented into South America, Africa, and the Indian subcontinent, creating the disjunct distribution observed today. Contrasting dispersal hypotheses for the present day geographic distribution would depend on migration through saltwater oceans without colonizing any waters between their starting point and their end point (for example, they are native to Africa and South America, but no waters in-between). , which seems less likely (Stiassny).
The diversity of cichlids arose rapidly, and they are a textbook example of adaptive radiation after colonization of a new environment (Brawand). Cichlid populations harbor a great deal of genetic and morphological variation for selection to act on once populations invade a new range (Brawand). An example of a trait with such potential for variation is the unique pharyngeal jaws. With pharyngeal teeth that could chew, mandibular teeth needed only to perform the function of catching food (Liem). Thus, cichlid species diversified their mandibles to specialize on many diverse prey types.
Cichlids first appear in the fossil record during the Eocene era (34-56 mya) in Tanzania (Murray). Assuming a Gondwanan distribution, these fossils are at least 100 million years younger than the first cichlids. The temporal origin of cichlids is disputed, however. Different molecular clocks place the origin of cichlids as early as 200mya or as recent as 60mya in the Paleocene era (Friedman, Genner). These estimates straddle the fragmentation of Gondwana 180mya. These disputes highlight the debate between modern distributions being the result of continental drift versus being the result of migration over time.
The Texas cichlid (Herichthys cyanoguttatus), also known as the Rio Grande cichlid, is a freshwater fish of the cichlid family, and the only cichlid species that is native to the United States. It is found in the lower Rio Grande drainage in Texas near Brownsville and northeastern Mexico.
Herichthys cyanoguttatus can grow to be over 13 in (33 cm) and are differentiated by their distinctive characteristics and specific habitat needs. This cichlid is recognized by its cream and turquoise spots.[2] Adult males also develop a nuchal hump on their head.[2] This cichlid also prefers the water temperature to be between 68 and 82 °F (20–28 °C) and are negatively affected by rapid changes in temperature.[3][4]
The Texas cichlid was originally part of the genus Cichlasoma until that group was restricted to South American cichlids.[5] The species has been transferred to the genus Herichthys, which is described as cichlids that
The cichlid is known for its complex reproductive behavior with a long parental care period. The mating habits of the cichlid are tied to the monogamous nature of the fish. The competitive pairs always consist of a larger male and a smaller female.[6] These pairs travel long distances between the months of March and August to mate and aggressively defend their mating sites against other pairs of cichlids.[5][7]
Prior to spawning, a site, generally consisting of rocks in water less than 30 cm deep, is chosen by both parents and cleaned by nipping the surface. No individual cichlid appears to maintain territory prior to mating. After a territory is selected and cleaned, the eggs are deposited.[6]
Females release between 1-5 eggs at a time.[8] Males then go to the eggs and excrete a seminal fluid onto the egg. This process is repeated until around 2,000 eggs have been distributed.[8] During the egg stage, both parents alternate in the parental tasks, though males spend more time patrolling territory and females spend more time actively attending to the offspring by fanning the eggs. At certain intervals, the female cichlid stops fanning the eggs and begins nipping at them. The eggs then hatch into wrigglers with yolk sacks which are absorbed after one week and the wrigglers become free-swimming fry.[6]
The fry form a small group that slowly moves around the territory with the parents stationed in the middle. Both parents defend this small territory against intruders. At all stages, the female violently chases the intruders more often and faster than the male parent. It is very rare that both cichlid parents either leave or remain with their young. Typically, the roles are exchanged, but this exchange becomes less frequent during the fry stage as both parents tend to stay with the young.[6]
The cichlid has an omnivorous diet that consists of vegetable matter or detritus, often feasting on plants, insects, and smaller fish as well as fish eggs.[5][7][9] The cichlid, in certain situations, can also be described as an "opportunistic carnivore", feeding on small vertebrates and invertebrates, including small frogs and water snakes. The cichlid is a "deliberate hunter" and it depends on the camouflage of its skin in order to sneak up on its prey.[10]
The Texas cichlid has several qualities that contribute to its success as an invasive species. The cichlid is not greatly affected by high-energy wave events, nor pollution from outfall canals. These cichlids also have very high tolerance for salt water and high salinities that would normally act as barriers to the entrance of invasive fish.[9]
The cichlid can disrupt the food web with their flexible diet, which can shift depending on what fish are around it. They are aggressive whether they are holding territory or not. This aggression can inhibit growth and reproduction of native species and the effects can be far-reaching. The cichlid also drives other fish into open areas, which lowers the population count of the other species through incidental predation. The cichlid is a pioneer species that paves the way for other fish to invade, which has occurred in Six Mile Creek, Florida, and in the upper San Antonio River, Texas.[5] The actual effects of the cichlid on the environment are, at this point, unknown.[11]
In Florida, the success of the fish has been limited to artificial canals.[5] It is unknown how the fish first got into Florida, but it is believed that the fish was introduced in Florida from Texas stocks in 1941 by a private individual. Other theories are that fish farms were flooded and the result was that this fish escaped.[11]
In Louisiana, the fish has slowly taken over the waters of New Orleans. The fish has a high salinity tolerance (up to 8 ppt), but it is likely that this is caused by the interbreeding of this fish and the related lowland cichlid (Herichthys carpintis), which makes it an ideal invader for the brackish conditions of southern Louisiana.[5] It is believed that this fish has entered into the New Orleans area through multiple aquarium releases in central Jefferson Parish in 1989. Since the fish has a short mating cycle, it did not take long for the fish to make its way through the canal system and into Lake Pontchartrain.[12] Pump stations and Lake Pontchartrain aided to the spreading of the fish into other canals.
Herichthys cyanoguttatus has been present in natural and degraded habitats of the Greater New Orleans Metropolitan Area for at least 20 years. The first time it was ever recorded that the cichlid had been caught in New Orleans was on 17 June 1996. In May 1998, 23 fish were caught in a Jefferson Parish canal. Between 2006 and 2007, the number of cichlids increased significantly in sites such as Pontchartrain Lagoon, Bayou Metairie, and Marconi Lagoon. The effect of the invasive fish in the area is as of now, uncertain, but many studies have been done to figure out what exactly is going on.[5]
Some of these studies have shown that this cichlid has spread into Bayou St. John and City Park. The cichlid acts aggressively toward native Largemouth bass, Western mosquitofish, sailfin mollies, and blue crabs. This aggressiveness can occur in the form of tail beating and mouth wrestling.[13] The fish also appears to cause reproductive failure of sheepshead minnows.
The Texas cichlid was largely unaffected by abiotic events like Hurricanes Katrina and Rita because of its high tolerance for salt-water intake.[5] In fact, these hurricanes actually helped the fish to take over the bayous of New Orleans. When the park flooded during Katrina, it helped the cichlid to spread.[14]
In Bayou St. John, the cichlid threatens to overwhelm native species and ruin the efforts of the Louisiana Department of Wildlife and Fisheries to restore the historical fishery of Bayou St. John. Because the fish competes with native fish for shallow mating sites, it reduces the chances of the diverse fishery ever being fully recovered.[15]
The fish has already eliminated several smaller fish in this bayou, including killifish and sheepshead minnows. In fact, if the Louisiana Department of Wildlife and Fisheries did not routinely re-stock several midsized species, it is likely that the cichlid would have eliminated these fish too.[7] Because of this, there is even a competition at the "City Park Big Bass Fishing Rodeo & Fishtival". to catch the most cichlids. According to a fisherman Joe Adams, who participates in the competition,
Despite these efforts, there is practically no chance of eradicating this fish from New Orleans' waters, mainly because of its quick mating cycle.[7]
Texas cichlids have been deliberately and accidentally introduced into the wild throughout the subtropical southern United States from Texas to Florida (where water temperatures rarely dip below 48 °F (9 °C), where they have flourished, and are often caught incidentally when fishing for sunfish and other panfish.
Most anglers outside South and Central Texas do not recognize the fish and they are released, however these fish are considered invasives and should be destroyed if caught outside their natural range. They are regularly targeted in both South Texas, where they are known as "Rio Grande cichlid" and Northern Mexico, where they are known as "Mojarra de Norte". Lake Guerrero, Tamaulipas, is recognized for its excellent largemouth bass fishing (another often-invasive species); there, the locals consider the Texas cichlid to be the best eating fish in the lake.
Texas cichlids taste is similar to commercially raised tilapia, an African cichlid species to which they are distantly related.
The fish is caught on light tackle with small hooks (#4 to #8) like that used for other panfish, with live crickets making excellent bait, however they will strike a wide variety of baits. They fight similarly to bluegill sunfish, making tight circles and then darting off in a broadsided run. Average size of adult fish in the wild is 5–6 inches, and 1 pounds, with 2 pounds not being uncommon.[16]
The Texas cichlid is commonly found in the aquarium trade and became relatively popular in the 1980s with cichlid enthusiasts because of its iridescent blue and green markings.[7]
The "green Texas cichlid" commonly seen in pet stores is another species, Herichthys carpintis, whose range does not actually extend as far as Texas. The "red Texas cichlid" is not a genuine Texas cichlid but rather a common cross-genus hybrid of Herichthys and Amphilophus parents. The common names come from the physical similarity to Herichthys cyanoguttatus.[17]
{{cite web}}: CS1 maint: url-status (link) {{cite web}}: CS1 maint: url-status (link) {{cite news}}: CS1 maint: url-status (link) Wikimedia Commons has media related to Herichthys cyanoguttatus. The Texas cichlid (Herichthys cyanoguttatus), also known as the Rio Grande cichlid, is a freshwater fish of the cichlid family, and the only cichlid species that is native to the United States. It is found in the lower Rio Grande drainage in Texas near Brownsville and northeastern Mexico.
