The green terror (Aequidens rivulatus) is a colorful freshwater fish in the cichlid family. The fish originates from the Pacific side of South America in the coastal waters from the Tumbes River in Peru to the Esmeraldas River in Ecuador. Males and females may reach lengths of 30 centimetres (12 in). Females are sexually mature at around 12 centimetres (4.7 in).
As the name implies, late-juvenile-phase and adult-phase specimens can be very aggressive. This is not guaranteed, however, and peaceful individuals can be observed. Juvenile green terrors are often sold in pet and aquarium stores for the aquarium hobby. This species is not to be confused with the blue acara cichlid, Andinoacara pulcher), which is similar in appearance; the Blue Acara is not as aggressive and does not grow as large as the Green Terror.
The fish is somewhat deep-bodied, possessing a prominent forehead. Adult males develop a pronounced forehead hump, composed of fatty tissue. Juveniles are tan colored with silver-blue flecks and lack the bright iridescent blue, green, and orange coloration and long, flowing fins of adult specimens.
In the aquarium hobby
The Green Terror is a popular fish in the aquarium trade and is noted for its hardiness as well as its aesthetic appeal. These characteristics make it ideal for beginning aquarists or for enthusiasts who prefer to avoid managing the strict water parameters required for other fish species. They are ambitious eaters, and do well on a variety of foods including cichlid pellets, flakes, bloodworms, and shrimp. Some owners report that a varied diet improves the coloration of the fish. There are also reports of fish with mild temperament getting along well with other cichlid species. Others find the fish to fully live up to its name, “terror”. Generally, aggressiveness increases with size/maturity. Aggressive, territorial behavior increases markedly during breeding time, especially during brooding. If the aggressiveness of the breeding pair threatens tankmates, aquarists usually move them to a separate "breeding tank" during the spawning and brooding phases.
Size potential and factors influencing growth in aquarium environment
The Green Terror may grow up to 30 centimeters (12 inches) in length; however, 6–8 inches is more typical. Factors influencing maximum size attainment can be size of the aqaurium relative to population density or the size of the tank relative to the maximum size potential of the fish, water condition and availability of food.
Generally, if kept alone or with few other fish, a 75- to 90-gallon aquarium is adequate to realize the full size potential of most cichlids with an upper size limit of 10–12 inches. Despite the ethic relating "inches of fish" to "gallons of water," many cichlid keepers subscribe to a more cichlid-specific ethic in which the maximum size potential of a fish is considered relative to the aquarium dimensions. Cichlid enthusiasts have long realized that a 15-gallon aquarium is not adequate for a 15-inch fish, as the base dimensions of a typical 15-gallon aquarium are usually around 12 inches by 18 inches. This would render a 15 inch fish practically immobile, preventing the fish from being able circulate water over its gills.
The "inches to gallons" ethic may still be applicable for, say, ten 1-inch fishes in a ten-gallon aquarium, as their total biomass would occupy very little of the available square inches of space.
Similarly, if the number of fish an aquarium impedes free movement, or if territorial disputes frequently occur, growth will retard in response to the restrictive environment. In addition, increased susceptibility to disease or a disease-like state will be conferred upon cohabitants. In overpopulated tanks, it becomes difficult to maintain healthful water parameters; metabolic waste (excrement) accumulates rapidly, even when a highly efficient filter is employed. Frequent gravel vacuuming is required to keep nitrate and nitrite levels within acceptable parameters. Although bona fide infectious diseases such as Ichthyophthirius multifiliis (Ick) do not spontaneously appear due to overcrowding itself, a disease-state results from elevated nitrates. Fish will gasp at the surface in a futile attempt to absorb oxygen because the elevated nitrates block the metabolism of oxygen from the water i.e., the fish begin to suffocate. Also, in crowded aquariums, there is often an increased incidence of fin-nipping, which can lead to infection, decreased fitness, elevated stress and death.
Feeding is the most obvious factor contributing to growth. Two approaches are commonly applied to assess adequate food intake. First, some aquarists like to let the fish eat all they want for several minutes. When active feeding abates, any excess food is removed from the tank to prevent clouding. Second, the specimen's bellies can be evaluated for "roundness." This is a prime opportunity to assess the health of the fish. Those who do not eat will have a characteristically concave-looking belly. Such a fish may be sick or unfit for cohabitation due to incompatible temperament. Feeding should follow a somewhat-regular daily pattern. Some feed once a day, others feed smaller portions 2–3 times per day. Some aquarists have found that multiple feedings coupled with lower-limit temperatures decreases aggression.
Breeding and assimilation of offspring
Green Terror Cichlids can be successfully bred around 8 centimetres (3.1 in). Reproduction can be incited by isolating a breeding pair (each from distinct lineage), raising the water temperature to around 80 degrees F, and providing a flat, textured surface (such as a flat rock or pottery fragment) for the hen to deposit her eggs on. Upon reaching 3–4 inches in length, Green Terrors may be integrated into aquariums with larger cichlids. It should be noted that a significant size disparity between newly added fish and existing fish can retard optimum growth rates of the still-maturing fish. Larger fish, particularly A. Ocellatus (oscar cichlid), may feed so aggressively that smaller fish may be unable to ingest adequate quantities of food-staples.
Compatibility with other cichlid species
The inherent aggressiveness of Green Terror cichlids make them ideal for aquarists who wish to add variety to their cichlid aquarium. With the exception of fully mature P. Dovii (wolf cichlid) and P. Managuense (jaguar cichlid), who rarely cohabit peacefully, Green Terrors are cunning enough to survive—and even thrive—with larger cichlids. However, as a rule, a predating cichlid is capable of consuming any animal whose dimensions are inferior to that of the predating cichlid's fully expanded jaw. Green terrors of appropriate size can often be assimilated with A. ocellatus (oscar cichlid), R. octofasciata (Jack Dempsey cichlid), A. citrinellus (midas cichlid), T. meeki (firemouth cichlid), flowerhorns (no scientific designation), smaller P. managuense (jaquar cichlid) and P. dovii (wolf cichlid) and other similarly aggressive cichlids.
Role in Hormone Research
Connections to McDaniel
The green terror will also soon become the new mascot for McDaniel College in Westminster, Maryland. This change will be implemented next year[when?], after all sport seasons have closed. This change is coming because of the controversy surrounding the current mascot and because the green terror can be implemented as the new mascot without a change to the team's name.
- "Aequidens rivulatus". Integrated Taxonomic Information System. Retrieved June 22, 2005.
- Green terror on FishBase
- Schaafsma, Sara M.; Ton G. G. Groothuis (January 2011). "Sex-specific effects of postnatal testosterone on lateralization in cichlid fish". Animal Behaviour 81 (1): 283–288. doi:10.1016/j.anbehav.2010.10.019. Retrieved 23 February 2013.
- Schaafsma, Sara M.; Ton G. G. Groothuis (February 2012). "Sex-specific effects of maternal testosterone on lateralization in a cichlid fish". Animal Behaviour 83 (2): 437–443. doi:10.1016/j.anbehav.2011.11.015. Retrieved 23 February 2013.