In this article I write about the different foods cichlids eat, and give examples of the particular evolution of their feeding apparatus that allows them to efficiently capture and process those foods. Practically anything edible is consumed by cichlids in one way or another.
Probably the most generally available food for cichlids to eat is detritus, and many species rely on it for survival. Detritus in this context is organic matter produced by the decomposition of organisms, being plants or animals. Detritus is accompanied by bacteria, which decompose it. Cichlids eat the detritus, and in at least in some cichlid species, these bacteria form part of the nutriment obtained from it. Although low in nutritious value, there is often an abundance of detritus to feed upon. Cichlids that do, often have very long intestines enabling them to capture its low nutritious value. Long snouts are often part of the morphological adaptation in several detritivores, which allows them to introduce its snout into soft areas of the sediment and get mouthfuls of bottom detritus.
Some examples of cichlids that feed on detritus are Herichtyhys bartoni, Chuco intermedium, and Mayaheros urophthalmus from North America; Oreochromis niloticus, Cyathopharynx furcifer and Orthochromis kasuluensis from Africa; Iranocichla hormuzensis from the middle-east. In South American the earth-eaters of the genus Satanoperca are specially adapted to collect and eat detritus. These are just a few examples, and I believe that when more studies are carried out a larger number of cichlids will be found that are at least partly detritivorous.
Carnivorous cichlid species are normally large fishes with equally large mouths, large teeth and short intestines. Carnivores can either ambush or chase their prey, and are normally non-discriminating about their selection, which can be invertebrates, insects, amphibian, crustacean, or fish, among others. The Guapotes of the genus Parachromis from North America are perfect examples. The Oscar, Astronotus ocellatus, is an example of a carnivore from South America. In Africa, species in the genus Hemichromis are.
Some carnivorous cichlids have specifically evolved to eat other fishes; this specialization is often accompanied by a streamlined morphology that allows for fast swimming and large mouths to produce strong vacuum forces to suck in fish, often with large teeth to hold their preys. The more specialized, the more these traits have been developed.
In North America, the perfect example of a piscivore is given in Petenia splendida: stream-lined, light, with a huge, highly-protrusible mouth and an inconspicuous coloration.
Among the carnivores are those that specialize in eating crustaceans or insect larvae, capturing them in the soft substrate where they hide; these are the substrate pickers and substrate sifters. Substrate pickers detect prey under the surface and go directly to it. In Lake Malawi, species in the genus Aulonocara represent this type. They have enlarged pores in the head that, when kept close to the substrate, help them detect the tiniest vibration in the sand. A similar technique is used by Thorichthys species in North America (think of the fire-mouth cichlid, T. meeki) although the way they detect prey has not been studied to my knowledge. Other parasite pickers, such as Rheoheros lentiginosus in North America, push over pebbles on the bottom of a fast-flowing stream, areas with abundant invertebrate life, thus uncovering their prey, which they then quickly devour.
Substrate sifters rely on dirt processing rather than locating individual prey. They spend their days plunging their usually long snouts into the substrate and then processing the material obtained, filtering out the creatures hiding in it. Of this type there are numerous examples, some of which are: in North America species of the genus Crybroheros, in Lake Tanganyika species in the genus Xenotilapia, in Lake Malawi species in the genus Taeniolethrinops, and more.
Some species capture snails and have strong muscles and specialized mollariform teeth on their pharyngeal jaws to help them crush them, like Herichthys labridens in North America.
Although more commonly known in coral reef fish, the feeding of parasites off the skin of other fishes is also present in cichlids. In freshwater, feeding of parasites, so-called cleaning, have been studied in the orange chromide, Pseudetroplus maculatus from Asia, which cleans its much larger cousin Etroplus suratensis from parasites. The client presents its flank and darkens its skin, presumably for an easier detection of parasites. In Lake Malawi, cleaning behavior has been observed in several species, including Caprichromis liemi, juvenile Docimodus evelynae, Melanochromis loriae, Metriaclima lanisticola, juvenile Mylochromis melanonotus, and Pseudotropheus crabro.
Paedophages and ovophages
One common feeding specialization is eating fry of other species. Although many cichlid species would eat fry from other fish, some species have developed morphological and behavioral adaptations that allow them to obtain maximum efficiency and feed almost exclusively of larvae and eggs out of the mouths of mouthbrooding cichlids.
Almost all endemic cichlids of Lake Victoria are mouth-brooders and various species have found a way to extract eggs, larvae and fry out of the mouth of mouth-brooding females. Examples are the species Haplochromis previously known in the genus Lipochromis. In Lake Malawi cichlids members of the genus Hemitaeniochromis are paedophagous.
As for the ovophages, some species in Lake Malawi, like those in the genus Caprichromis even ram the obviously mouth-brooding females from below in the throat to force the release of the eggs and fry, which then they quickly ingest. Melanochromis crabro feeds seasonally on the eggs of the large catfish Bagrus meridionalis, the Kampango, with which it has a symbiotic cleaner-fish relationship, picking the fish-louses from the catfish’s skin.
Many cichlid species have evolved to feed from algae, often with great specialization. Algae are eaten in different ways:
Algae combers use their many teeth to rake the loose material (diatoms and loose algal strands) from the periphytum (a.k.a. aufwuchs) growing on rocks without cutting or tearing the algal matrix. In this group we have species in the genus Metriaclima in Lake Malawi or Petrochromis in Lake Tanganyika.
Algae cutters normally have sharp-edged teeth that allow them to cut strands of the algal matrix in the periphytum. Species in this group include the Lake Tanganyika Tropheus species.
Algae pickers often defend a feeding territory in which they allow the growth of a dense algal matrix. They bite in the dense layer and ingest anything they can remove. Examples in this group include the overly aggressive Chindongo mbuna species of Lake Malawi.
Algae pullers use the small and densely-set teeth to grab the algal matrix and forcefully tear off strands, usually by swinging their bodies. Species in this group include Herichthys tamasopoensis in North America and the Tropheops species in Lake Malawi.
Algae scrapers use their chisel-shaped teeth to grab the full algal matrix on the surface of the rocks. The Eretmodus species from Lake Tanganyika are examples of this feeding technique, but also the North American Paraneetroplus species, as well as Neetroplus nematopus.
Some herbivorous species of cichlids eat fruits that fall from trees into the water. The fig eater Tomocichla tuba from Nicaragua and Costa Rica is in example. The North American species in the genera Cincelichthys and Vieja often use this behavior to add to their menu. For these species, larger water plants are also regularly a food source.
Many species of cichlids feed on tiny floating organisms, referred to as plankton; either phyto-plankton or zoo-plankton; unlike detritus, plankton is nutritious, but requires time to get in sufficient amounts. Some plankton eaters, like Cyprichromis species in Lake Tanganyika, have small but protrusible mouths and elongated snouts that allow them to easily suck in individual planktonic organisms. These small cichlid species congregate in big numbers in the water column, obtaining protection in numbers. The related species of the genus Paracyprichromis have bigger eyes that allow them to feed in low light during particularly rich plankton hours of dawn or dusk, and the species in the genus Benthochromis do the same, but at great depths under constant low-light conditions. All these species specialize in zoo-plankton.
In Lake Malawi two groups of rock-dwelling species are specialized in plankton feeding: Cynotilapia and Copadichromis.
One amazing feeding adaptation in cichlids is that of eating scales and fins. To this end the attacker often disguises itself as a harmless creature, mimicking some peaceful species of the local community. In Lake Malawi, Genyochromis mento grabs scales and/or fins of displaying, fighting, or otherwise distracted fish, sometimes much bigger than itself. The variability of this species mimicking a local, peaceful herbivore is amazing.
In Lake Tanganyika, cichlids in the genus Perissodus have adapted to rip off scales from the flanks of other cichlids, developing specialized teeth to this end. P. straeleni is known to use four different techniques for attacking its prey: pursuing, waiting, mingling, and aiming. This species resembles Cyphotilapia frontosa so closely that even at close quarters they are difficult to tell apart from its model. They apparently mimic this species to deceive other cichlids to which C. frontosa is not a threat. One amazing adaptation is that of Perissodus microlepis, which possesses an asymmetric mouth that opens wider either on the left- or on the right-hand side, a perfect adaptation to steal scales from, respectively, the right or left flank of its victim.
One of the less desirable foods has to be sponges, filled with razor-sharp spicules, low nutritious value. Although sponges are not abundant in freshwater, many lakes are known to host them, but they are not always a source of food. In Lake Barombi-Mbo in West Cameroon one cichlid species, Pungu maclareni, is specialized in eating them, having evolved thick lips, strong mouth musculature, and large teeth to perform the chore. Other species known to feed on sponges include Coptodon spongotroktis from Lake Benin, also in Cameroon, and Julidochromis marlieri in Lake Tanganyika.
Omnivorous cichlids would eat any source of food that is available to them. Omnivorous may have a preference, but would eagerly eat anything else that is available to them. Let’s take as an example Rocio octofasciata, the Jack Dempsey from North America. Stomach examinations show that Rocio octofasciata feeds primarily on aquatic invertebrates and filamentous algae, both quite different items. It may be that the Jack Dempsey captures invertebrates among the algae, and consumes the algae as well.
It is also the case that during the development of a fish it may evolve from one source of food to another. This occurs when the morphology of a young fish is not suitable for the food it will eventually specialize on as an adult. Think of a piscivore, which may not be able to capture any fish as a baby.
Most cichlids, regardless of their feeding specialization, are to varying degrees opportunists. There are, however, some species that are so specialized that may not fit this label, but most species would take advantage of an easily available source of food, which may be temporal. This is quite understandable since when a cichlid estimates that it can get a nutritious food at a low cost, it will take it.
One example to illustrate what is it being opportunistic is the Cuatro Ciénegas cichlid of Mexico, Herichthys minckleyi. This species is polymorphic, with an ancestral detritivorous form that radiated into three distinct forms; each one specialized in capturing and processing a different source of food; the ancestral detritivore, a specialized piscivore and a mollusk eater. This radiation allows the number of individuals of this species to be larger than if all specimens would just feed on a single food source. When a source of food is easily available however, let’s say a nutritious insect that fell into the water, the three forms would forget their specialization and go get it! That is quite understandable since the energy expended to capture it is less than that necessary to get their regular food, and the item may even be more nutritious.
The lessons that we can draw from feeding specializations for aquarium keeping are several. First, the opportunistic cichlids are the easiest to feed since most of them take any food being offered; however, extreme specializations may be counterproductive, since offering a highly nutritious food to a species which has evolved to process low nutritious food may cause serious harm. Let’s think of the well-known case of bloat, where for example Tropheus or Petrochromis species from Lake Tanganyika, which have evolved the long intestines necessary to process the low nutritious periphyton that grows on rocks. When these fishes are fed with an easy to process, highly nutritious aquarium food, the result may be the collapse of their digestive system, bloating them to death.
Even if no harm is done we may still affect their normal behavior, like for example by keeping the molluscivorous Herichthys labridens in the aquarium under a regime of flake food. We may make them stop their normal feeding behavior of looking for snails on the substrate, including the coloration patterns changes they utilize in their hunt. Also, by lacking some necessary nutrients in the food we offer them, we may prevent them to develop the beautiful bright yellow breeding coloration that attracts most people to this species.
A little research is always important to obtain the best enjoyment and learning of captive fish.
© Copyright 2020 Juan Miguel Artigas Azas, all rights reserved
Artigas Azas, Juan Miguel. (listopada 21, 2020). "Feeding in cichlids – Food selection". Cichlid Room Companion. Źródło: na stycznia 16, 2021, od: https://cichlidae.com/section.php?id=311&lang=pl.