Tropheus moorii

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Tropheus moorii
Tropheus.jpg
Tropheus moorii
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Cichlidae
Subfamily: Pseudocrenilabrinae
Tribe: Tropheini
Genus: Tropheus
Species: T. moorii
Binomial name
Tropheus moorii
Boulenger, 1898
Synonyms
  • Tropheus moorii moorii Boulenger, 1898

The blunthead cichlid, Tropheus moorii, is a species of cichlid endemic to Lake Tanganyika in Africa. There are over 40 different color morphs of this species dispersed throughout the lake ranging from dark green to flame red and yellow. They mostly feed on filamentous algae on the rocky shallows that they inhabit.[2] T. moorii are maternal mouthbrooders so eggs are fertilized and carried in the mouth of the female while they hatch and develop.[3]

Territorialism[edit]

Both male and female adults occupy individual feeding territories.[4] T. moorii inhabiting territories at greater depth tend to have smaller adult body sizes and larger territories.[5] Males have larger territories than females. A female will leave her territory to pair up with a male and usually visits several territories multiple times before choosing a male. After the male and female form a pair bond the female will forage in his territory for up to three weeks under his protection before spawning. A female's ovaries do not fully mature until she pairs up with a male and feeds from his territory. After spawning, the female will leave the male's territory to occupy a small unclaimed area for the mouthbrooding period. In contrast to the frequent movement of females, a male usually remains in his territory for months even if he is never visited by females.[4]

Inter-species interactions[edit]

Often T. moorii feeding territories will be adjacent to territories of conspecific and heterospecific neighbors. A male T. moorii will usually court a female conspecific who visits his feeding territory.[5]

In Lake Tanganyika, T. moorii coexist with other herbivorous cichlids P. trewavasae, P. orthognathus, P. polyodon, and T. temporalis.[5][2] T. moorii, P. polyodon, and T. temporalis individuals are not aggressive towards one another but are aggressive towards individuals of other species and con-specifics. Although their territories often overlap, individuals of the three species do not usually interact due the dietary differences that exist. For example, P. polyodon and P. trewavasae mostly feed on unicellular algae rather than filamentous algae.[2]

Having overlapping territories with P. polyodon may benefit T. moorii individuals since P. polyodon removes silt from the rock surface as they feed. This allows T. moorii to easily scrape filamentous algae from the rocks.[2] Having overlapping territories with P. trewavasae may benefit T. moorii individuals because both will defend their territory from much larger P. orthognathus individuals. They will also be able to drive them away, whereas an individual T. moorii may not be able to defend territory successfully. This is an example of commensalism rather than mutualism because individuals would defend their territory regardless.[5]

Size-dependent dominance hierarchies[edit]

T. moorii participates in size-dependent dominance hierarchies when defending territory from intruders. If an individual intrudes on a T. moorii territory, the interaction may be a one-sided (territory owner towards the intruder) attack, one-sided display (spread and quiver fins/tail to intimidate), mutual attack, or mutual displays. These usually occur at or near the borders of the territories. In a one-sided attack, the territory owner will chase the intruder until it leaves the territory.

Interactions will vary depending on the relative size of the territory owner and intruder. Individuals tend to perform one-sided attacks on neighbors smaller than them and perform one-sided displays towards those larger than them. Attacks may occur inside or outside the feeding territory of the territory owner, while displays usually take place within the territory. Displays are very rare when there is a large difference in body size (more than 2.5 cm) and more common when the difference is smaller (less than 2 cm). Mutual attacks are very likely to occur when the individuals are similar sizes. Neighbors (having an adjacent territory) are more likely to respond to an attack with a display compared to a non-neighbor. In observed interactions between specifically P. orthognathus and T. moorii individuals with adjacent territories, the larger fish attacked the smaller one regardless of species, and no displays occurred.[5]

Mating and reproduction[edit]

The mating system of T. moorii is serial monogamy. A male and female will establish a temporary monogamous pair bond and spawn. The female will mouthbrood the eggs and young with no direct assistance from the male, so after spawning the male is free to pair bond with other females.[3] T. moorii broods show genetic monogamy, with all eggs having been fertilized by a single male.[6] Other cichlid species that exhibit similar social monogamy in mating, such as V. moorii, do not always show genetic monogamy due to parasitic spawning (males fertilizing eggs of a female paired to another male).[7] Spawning occurs on a rock surface, with the female laying up to 20 eggs which are bright orange in color. Eggs are incubated for 30 to 35 days, and when the young emerge from their mother's mouth they are advanced enough in their physical development to live like adult T. moorii.[8]

Buccal feeding[edit]

Buccal feeding refers to the feeding a mouthbrooding mother does to feed her young located in her buccal cavity. T. moorii females have unusually high parental investment in their offspring since they produce large eggs and buccally feed their young. Among cichlids, T. moorii has a very high egg to adult body size ratio.[9] In the early stages of mouthbrooding, a female will rarely feed, but after the eggs hatch she will begin feeding to nourish them. The mother effectively starves herself during the mouthbrooding period since all nourishment she takes in goes to feed the young.[10] The yolk sacs of the eggs are depleted around the 25th day of mouthbrooding but the offspring are not released for several more days, so in that time period all of their nourishment must come from buccal feeding.[8] Buccal feeding is costly in terms of energy for the female since it requires more swimming. It has been shown experimentally that buccal feeding does not shorten the mouthbrooding period; instead, young who are fed buccally are larger, heavier, and faster than unfed young. These benefits are very advantageous to the young since it lowers their predation risk and size is usually the determining factor in conflicts over resources.[9]

Sexual selection and color morphs[edit]

Since male T. moorii provide no brood care or other parental investment after spawning, the operational sex ratio in a population is strongly biased towards males. A male's reproductive success will therefore vary based on how many times he can mate during his life. Females, by discriminating between males to decide a mate, strongly influence male reproductive success. Experimentally females have been shown to share preferences for the same males when given two to choose from, meaning some males get to reproduce more often than others.[3]

T. moorii shows very great diversity in color morphs, and color morph is a typical target for mate-choice sexual selection.[3] A female T. moorii is more likely to choose a mate that has the same morph she does and this is probably what drove the proliferation and maintenance of T. moorii's many color morphs.[11] T. moorii individuals of a particular color morph are usually found in the same geographic area, so color morphs are also maintained by the relative isolation of T. moorii populations.[8]

Aquaculture[edit]

T. moorii comes in a dazzling array of colors and color patterns. There are well over 40 different geographical variants of T. moorii, each with its own distinctive morphology. They are found in all parts of Lake Tanganyika where rocks are found, and because they are one of the easier fishes to catch, they are also well represented in the hobby.[citation needed]

As a sexually monomorphic species, T. moorii can be quite challenging to sex. Aside from venting, however, there are a few tips that might clue you in as to their gender. The upper lip of males is more prominent (i.e., larger) than that of females. Males' lips on average tend to be more off-white as well, due to their constant lip-locking aggression. Furthermore, males tend to have a turned-up nose while females tend to have a greater slope and rounded nose, making the shape of their head ellipsoid. Males will generally grow at a faster rate and display their adult colors sooner. Males' coloration is also often more bold than females' because they like to show it off when courting females. Adult males will also tend to have a deeper body, whereas females appear more slim and streamlined. While these characteristics may help an experienced hobbyist, venting is the only sure way to determine gender with Tropheus.[citation needed]

T. moorii is strictly herbivorous like all Tropheus species. They spend the majority of their time scraping algae from the rocks in both the aquarium as well as in the wild. In fact, they are even more effective than plecos at cleaning algae off of glass and rocks. In the wild, T. moorii are found in shallow bays and in the upper reaches of the lake over rocky reefs where the water is quite illuminated. This is because this is where the algae and other vegetable matter grow most thickly. Consequently, they are adapted to bright light.[citation needed]

Using extra lighting to encourage algal growth is encouraged. T. moorii love to graze on it; and you'll probably find they can eat it faster than it will grow. Supplementing their diet with lettuce (e.g., romaine & spinach) is highly recommended. Try feeding a leaf of lettuce each morning before feeding them flakes. Use only green flakes. These have a high concentration of Spirulina and less of wheat and fish meal. The European Shrimp Mix is a great food you can make yourself and is used by most serious Tropheus breeders and hobbyists. The only live or frozen foods that could be used to supplement their diet are Cyclops and Mysis. Avoid any soft or slimy foods, such as brine shrimp, red or white mosquito larvae, and beef heart. These foods are too easily digestible and irritate their bowels, stressing them and consequently making them more susceptible to bloat. Foods should be rough to the touch, high in protein, and low in fat. Pellets should be soaked in tank water for several minutes before feeding.[citation needed]

T. moorii is a very hierarchical species and should only be kept in colony proportions. They do best in groups of 12 or more. It's recommended to have only two males and a dozen or so females. It is very important when setting up a colony of T. moorii to introduce them to the tank all at once. If you add fish later, it will force shifts in their social structure and could throw a well established colony into chaos. This often results in unexpected deaths, either directly or from stress-induced illness.[citation needed]

Males are very territorial. Females, on the other hand, are not territorial unless no male is present, in which case the dominant female will assume the role of the absent male. Each male will occupy a small area in the tank. A cave or a heap of rocks is adequate, but the males will each require something with which to mark their territory.[citation needed]

Males are persistent and aggressive when they want to spawn. In an established, mature colony with at least a dozen females, spawning will be observed about every three days. A male will court a female by diving in front of her, cutting her off, shaking and shimmying until she agrees to spawn. He will lead her to his area where they will assume the classic "T-position." They take turns circling and nudging the other's vent until the female drops the eggs.[citation needed]

After dropping the eggs, she will quickly flip around and scoop them up into her mouth. She then nudges the male's vent, at which time he fertilizes the eggs. Mouthbrooding females should be moved to another tank after 10–14 days because the male will still harass them to the point that it could over stress them. Never keep more than one mouthbrooding female in a nursery tank because they will conflict. Continue to feed the females. They eat even though they are carrying a brood in their mouth. Fry are of considerable size when released. They can be fed crushed flakes, and after 3 months or so, they begin to show interest in lettuce.[citation needed]

References[edit]

  1. ^ Bigirimana, C. 2006. Tropheus moorii. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 11 June 2013.
  2. ^ a b c d Takamura, Kenzi. "Interspecific Relationships of Aufwuchs-eating Fishes in Lake Tanganyika." Environmental Biology of Fishes 10.4 (1984): 225-41. Web. 22 Oct. 2013. <http://link.springer.com/article/10.1007/BF00001476>.
  3. ^ a b c d Steinwender, Bernd, Stephan Koblmüller, and Kristina M. Sefc. "Concordant Female Mate Preferences in the Cichlid Fish Tropheus Moorii." Hydrobiologia 682.1 (2011): n. pag. 31 May 2011. Web. 22 Oct. 2013. <http://link.springer.com/article/10.1007/s10750-011-0766-5>.
  4. ^ a b Yanagisawa, Yasunobu, and Mutsumi Nishida. "The Social and Mating System of the Maternal Mouthbrooder Tropheus Moorii (Cichlidae) in Lake Tanganyika." Japanese Journal of Ichthyology 38.3 (1991): n. pag. 28 June 2010. Web. 22 Oct. 2013. <http://link.springer.com/article/10.1007%2FBF02905572>.
  5. ^ a b c d e Kohda, Masanori. "Intra- and Interspecific Social Organization among Three Herbivorous Cichlid Fishes in Lake Tanganyika." Japanese Journal of Ichthyology 38.2 (1991): n. pag. 28 June 2010. Web. 22 Oct. 2013. <http://link.springer.com/article/10.1007%2FBF02905540>.
  6. ^ Hirschenhauser, K., M. Taborsky, T. Oliveira, A.V. M. Canàrio, and R.F. Oliveira. "A Test of the ‘challenge Hypothesis’ in Cichlid Fish: Simulated Partner and Territory Intruder Experiments." Animal Behaviour 68.4 (2004): 741-50. 25 Aug. 2004. Web. 22 Oct. 2013. <http://www.sciencedirect.com/science/article/pii/S0003347204002349#>.
  7. ^ Sefc, Kristina M.; Karin Mattersdorfer; Christian Sturmbauer; Stephan Koblmüller (2008). "High Frequency of Multiple Paternity in Broods of a Socially Monogamous Cichlid Fish with Biparental Nest Defence". Molecular Ecology 17 (10): 2531–2543. doi:10.1111/j.1365-294x.2008.03763.x. Retrieved 30 September 2013. 
  8. ^ a b c Prusińska, Maja, Andrzej Mamcarz, and Krzysztof Kupren. "Early Ontogeny of Tropheus Moorii Boulenger 1898 (Pisces, Cichlidae, Lake Tanganyika) in Laboratory Conditions." Polish Journal of Natural Science 23.4 (2008): 888-903. Web. 22 Oct. 2013. <http://www.researchgate.net/publication/236334402_Early_ontogeny_of_Tropheus_moorii_Boulenger_1898_(Pisces_Cichlidae_Lake_Tanganyika)_in_laboratory_conditions>.
  9. ^ a b Schürch, Roger, and Barbara Taborsky. "The Functional Significance of Buccal Feeding in the Mouthbrooding Cichlid Tropheus Moorii." Behaviour 142.3 (2005): 265-81. Web. 22 Oct. 2013. <http://www.jstor.org/stable/4536244>.
  10. ^ Yanagisawa, Yasunobu, and Tetsu Sato. "Active Browsing by Mouthbrooding Females of Tropheus Duboisi and Tropheus Moorii (Cichlidae) to Feed the Young And/or Themselves." Environmental Biology of Fishes 27.1 (1990): 43-50. Web. 22 Oct. 2013. <http://link.springer.com/article/10.1007/BF00004903>.
  11. ^ Salzburger, Walter, Harald Niederstätter, Anita Brandstätter, Burkhard Berger, Walther Parson, Jos Snoeks, and Christian Sturmbauer. "Colour-assortative Mating among Populations of Tropheus Moorii, a Cichlid Fish from Lake Tanganyika, East Africa." Proceedings of the Royal Society B: Biological Sciences 273.1584 (2006): 257-66. 2006. Web. 23 Oct. 2013. <http://rspb.royalsocietypublishing.org/content/273/1584/257.short>.