After many years of regular visits to natural habitats of cichlids, which extends to most of my life, I have first-hand experienced the constant deterioration of many of them, with the related loss of biodiversity, both species getting extinct or having their populations significantly reduced. It has been so depressing that at times I have decided never to come back to certain localities I used to frequently visit, to remember them as I once knew them.
While certainly anthropomorphic damage to habitats and species is nothing new, it is clear that it has significantly accelerated in recent decades, which let you thinking about what will be of the habitats and their species in a few decades to come if this trend maintains.
As aquarists, we are most times isolated from this reality, and when it is brought up to us it seems that it is contradicted by the increase in available species that we see offered by commercial sources all around us, and hence it is not until we become more immersed and knowledgeable in fish that we start to realize the bleak situation, either because we cannot find one particular species anymore, or because we have traveled to the natural habitats of our beloved species to better understand them, and we get face-to face-with the devastating situation.
I have a clear memory of the words that the great American ichthyologist Seth Eugene Meek wrote when in 1904 explained the meaning of the name he gave to the Middle American cichlid genus Thorichthys: “These little fish (i.e. Cichlasoma helleri) are exceedingly numerous in small isolated ponds, especially where there is a considerable amount of vegetation. They are attracted by anything which enters the water and will jump out of it in an apparently playful mood. When abundant they are easily caught, for as soon as your finger touches the water, they will come leaping towards you”. The name Thorichthys derives from Greek and means “leaping fish”. Never in my life have I ever seen this sort of behavior, having visited over a hundred places where Thorichthys inhabit and having seen all of the species in the genus multiple times in their natural habitat.
Back in the 1970s and 80s the number of fish that I used to see in many places was significantly larger than it is today, and from Meek’s words, it appears that years back the number was even much larger. I remember for example how a single cast of a net in parts of the Grijalva, Usumacinta, Coatzacoalcos, and other rivers in Mexico would produce dozens of individuals for a fisherman, while nowadays dozens of throws are required to produce one or two specimens. In part, this has happened by the larger availability of cast nets at lower prices, which turn many people into fishermen. Fish populations have hence decreased and the remaining fish have learned to avoid cast nets.
Fishermen have largely abandoned cast nets and now they use spear guns. For biparental cichlids, this is devastating since fishermen mostly capture those specimens that are brighter and remain almost motionless close to them, which are those that are protecting their eggs of fry. The removal of a parent has enormous implications, since many times a single individual won’t be able to bring up a batch of fry, and all the energy that was placed in the breeding effort is lost. The pressure on fish populations is huge since human populations have been growing tremendously and the natural environment is being abused.
Even with the many fry that many cichlids produce (for some species in the thousands) in each breeding effort, of which there can be several each year, in the end, the population remains stable. This means that the pressure by predators on the fry and the population as a whole is huge, and it has to be balanced with the fry.
Any aquarist who can get a fish breeding for the first time may think of all the money that he is potentially going to make by selling the babies to aquarium stores, but she realizes the flaw in this logic when the market is quickly flooded and nobody wants to buy any more fish, or even get them for free.
This situation illustrates a very important property of cichlid (and other fishes) populations, that of resilience. Resilience is the capacity of populations to recover quickly from difficulties. The single capability that has supported many fish populations to our days is that of resilience, and without it, many species would now be extinct. Some species have a bigger resilience than others.
It seems however that their resilience is not enough anymore for many species populations to remain stable. We humans have taken fishes resilience beyond the limits evolution has shaped. Take for example fish populations that are caught to support the economy of the many fishing communities around the world. As human populations have increased, the pressure put on the fish has increased accordingly, taking many species to the edge of extinction. Even a high resilience has not been enough to save many of them.
Resilience is considered medium for a fish (fishbase.org, 2020) when a population can double in 1.4 - 4.4 years (Froese et al., 2017). This may seem high, but some species like Metriaclima zebra in Lake Malawi can double their population in less than 15 months, which is considered high resilience. Most cichlids fall into these two categories.
Causes of loss of diversity
Cichlid populations experience many pressures, the most important being:
Destruction of habitat:
Habitats are being destroyed by humans in many ways; one of the most widespread is the pollution of water bodies.
Pollution has many effects and habitats don't need to be so polluted that they can no longer support any major life to cause negative effects on fish populations. In Lake Victoria, increased eutrophication due to pollution has increased turbidity, constraining color vision and interfering with mate choice, since many Haplochromines rely on male color to select the right mate; this has led to increased hybridization between species. In this way, human activities are destroying both the mechanism of diversification and that which maintains diversity (Seehausen et al., 1997).
Although thankfully it has not been so far a great problem to cichlids, overexploitation of water resources has been a great problem for fish species native to arid lands. Take for example the several species of pupfish from North America that have gone extinct because the springs or creeks where they inhabited have been exploited to a point where they have dried out. In the valley of Sandia in the Mexican state of Nuevo León, four different species got extinct because of this. Of those four, just two: Cyprinodon veronicae and C. longidorsalis remain in captive populations. The same end was experienced by two other species in the Potosí pluvial lake also in Nuevo León: Cyprinodon alvarezi and Megupsilum aporus. Of these, just C. alvarezi remains in captive populations while M. aporus has been lost, a tragic event since it was a unique species, a carnivorous which prevented hybridization by having one less chromosome than the sympatric C. alvarezi — from which likely evolved. What we could have learned about evolution from these species is lost.
Some cichlids species face vulnerability in regards to overexploitation of aquarium resources, such as the species of Danakilia from Ethiopia. Danakilia franchettii endemic to Lake Afrera (Lake Giulietti) faces the exploitation of salt from the lake, which requires canalization and drops in the water level of this already very fragile habitat. This species is currently classified as endangered by the International Union for the Conservation of Nature (IUCN) (Getahun, 2018).
In Lake Kinneret in Israel, two species of cichlids: Tristramella sacra and T. simonis have gotten extinct, it is not known exactly why, but it is believed that the destruction of marshes, which were the breeding area of the species, could be the reason (Goren, 2014).
It is sometimes hard to understand how dams affect fish populations since their construction produces a larger body of water. Doesn’t fish live in the water? The reality is that dams change the environment completely, destroying fragile riverine habitats and producing the extinction of fish that cannot adjust to lacustrine life. Additionally, dams produce lower water levels in rivers below, affecting the ecosystem. Dams also cut the migration routes of many fish, affecting their survival.
Construction of dams along river courses is another way to destroy habitats, unfortunately, harder to stop since the benefits of dams for the human economy (at least in the short run) politically outweigh ecological considerations. Such has been the case with the construction huge Belo-Monte hydroelectric dam in Brazil, in full operation since last year as the fourth largest in the world by installed capacity, which diverts the course of the Rio Xingu, part of the Amazon forest and one of the richer in biodiversity in the word. The construction of the dam devastated an extensive area of the Brazilian Amazon rainforest, displacing a large amount of Brazilian indigenous people. The Xingu river has an estimated 600 fish species, many endemic, some of the most emblematic species with most of their range now flooded or desiccated are the cichlid Teleocichla centisquama and the zebra pleco, Hypancistrus zebra. It is estimated that the dam will cause the extinction of many endemic species of animals and plants.
Destruction of forests is another form of habitat destruction, since, without the absorbing capability of a forest, runoffs carry silt and clay into the riverbeds, clouding the water, covering the bottom, and hence changing the habitat. Deforestation also produces increases in water temperature and reduces the amount of rain, leading to a lower level. All these effects affect biodiversity. In Madagascar, Ptychochromis onilahy is extinct due at least in part to deforestation which leads to loss of habitat through increased sedimentation (Sparks, 2016).
Introduction of exotic species
The most impacting case of a mass extinction caused by the introduction of exotic species is doubtlessly the Lake Victoria introduction of the Nile Perch, which directly decimated many endemic species. Particularly sad is the fact that most Lake Victoria cichlids are undescribed and poorly known, and it is estimated that many had already gone extinct.
The introduction of exotics species can have many effects. In 2012 (Lehtonen et al., 2012) the effect of the introduction of the predatory Eleotrid Gobiomorus dormitory in Lake Apoyo, Nicaragua, natively present in other crater lakes like Xiloa but absent in Apoyo, was reported. The researchers noted that breeding pairs of the native and critically endangered cichlid Amphilophus zaliosus, when protecting their fry, would allow the exotic to approach at an unusual distance. This gave the big-mouth sleeper goby an advantageous position to prey on their fry, something they would not allow with other native predators. In fact, in the ecologically similar Lake Xiloa, the similar cichlid species A. sagittae, which has co-evolved with the predator, would not allow them that close to their fry.
For some ornamental species like Aulonocara baenschi in Lake Malawi, it is the ornamental fish trade that has put it on the edge of extinction. Being so small for fishermen in Lake Malawi to consider it as a regular catch, this species, which is only known from Nkhomo Reef in Malawi, has been almost extirpated by over-collecting. The species is classified as critically endangered by the IUCN (Konings, 2018). This seems amazing if we consider that the species is widely bred in aquariums, but human greed has no limit or concern for life.
Aulonocara baenschi resilience is considered medium for a fish (fishbase.org, 2020), which means a population can double in 1.4 - 4.4 years (Froese et al., 2017). This may seem high, but other Lake Malawi species like Metriaclima zebra can double their population in less than 15 months, which is considered high resilience.
The beautiful population of Tropheus duboisi at Maswa is another case where overexploitation of the aquarium hobby has led it to extinction.
In a recent paper (McMahan et al., 2020) the researchers evaluated the effects of climate change on the population of the highly restricted rheophilic cichlid Chortiheros wesseli, which is restricted to only a few river drainages in the Caribbean slope of Honduras: Rio Jutiapa, Rio Bellaire, and the Rio Hauron, all three within the Rio Papaloteca basin. The research was based on field data and species distribution modeling. Since the habitat where this species can thrive is limited to the area where these species inhabit, composed of areas with riffles, large rocks, and boulders that serve as shelter, the results predict that an increase in temperature will reduce rains and diminish the available habitat, putting it in risk. This is the first study related to climate change that I am aware targets cichlids.
In this article, I have given an overview of the pressures that human activity effect on cichlids' habitats around the world. In the next article of this series, I will focus on the efforts being made to mitigate them.
- Getahun, A. 2018. "Danakilia franchettii". The IUCN Red List of Threatened Species. 2018, e.T181792A7735343. DOI: 10.2305/IUCN.UK.2010-3.RLTS.T181792A7735343.en (crc09835)
- Goren, M. 2014. "Tristramella sacra". The IUCN Red List of Threatened Species. e.T61372A19010617. DOI: 10.2305/IUCN.UK.2014-1.RLTS.T61372A19010617.en (crc12067) (abstract)
- Konings, Ad. 2018. "Aulonocara baenschi". The IUCN Red List of Threatened Species. 2018, e.T61057A148658365. DOI: 10.2305/IUCN.UK.2018-2.RLTS.T61057A148658365.en (crc09834)
- Lehtonen, Topi K & J.K. McCrary, A. Meyer. 2012. "Introduced Predator Elicits Deficient Brood Defence Behaviour in a Crater Lake Fish". Plos One. 7(1):e30064. DOI: 10.1371/journal.pone.0030064 (crc04136) (abstract)
- McMahan, Caleb D & César E. Fuentes, Montejo, Luke Ginger, Juan Carlos Carrasco, Prosanta Chakrabarty, Wilfredo A. Matamoros. 2020. "Climate change models predict decreases in the range of a microendemic freshwater fish in Honduras". Nature Scientific Reports. 10(12693). DOI: 10.1038/s41598-020-69579-7 (crc09825) (abstract)
- Meek, Seth Eugene. 1904. "The fresh-water fishes of Mexico north of the isthmus of Tehuantepec". Field Columbian Museum Publication. 1-252 (crc00159)
- Seehausen, Ole & J.J. M. van Alphen, F. Witte. 1997. "Cichlid Fish Diversity Threatened by Eutrophication That Curbs Sexual Selection". Science. 277(5333):1808-1811. DOI: 10.1126/science.277.5333.1808 (crc05105) (abstract)
- Sparks, John S.. 2016. "Ptychochromis onilahy". The IUCN Red List of Threatened Species. e.T44504A58308545. DOI: 10.2305/IUCN.UK.2016-3.RLTS.T44504A58308545.en (crc12068) (abstract)
© Copyright 2022 Juan Miguel Artigas Azas, all rights reserved
Artigas Azas, Juan Miguel. (Sep 21, 2022). "Cichlid conservation – Loss of diversity". Cichlid Room Companion. Retrieved on Dec 10, 2023, from: https://cichlidae.com/section.php?id=333.