FunNature & AnimalThe black bass, an invader of our rivers

The black bass, an invader of our rivers

Currently, biological invasions represent the main factor in the loss of biodiversity on the planet. The most sensitive ecosystems are island and freshwater environments. Each basin acts, in terms of ecosystem, as an island with respect to neighboring basins, and that makes them vulnerable areas.

Very rich and biodiverse ecosystems develop in rivers, lakes, lagoons and other forms of continental wetlands. Unfortunately, in Spain, these ecosystems are seriously affected by a multitude of invasive species that have established themselves in these wetlands or on their banks. And among them, the American perch or ‘black bass’ ( Micropterus salmoides ) stands out.

An invader introduced for pleasure

The largemouth bass, native to the Mississippi River basin, has been introduced to rivers on every inhabited continent. He arrived in Spain in 1955 with a single purpose: sport fishing . Since then, there has been a translocation of specimens between basins.

An adult specimen of largemouth bass can exceed 40 centimeters in length. It behaves like a very voracious predator ; It feeds on aquatic invertebrates, fish, amphibians and can even attack small mammals and reptiles.

In fact, the largemouth bass has a high trophic plasticity, that is, a great ability to acclimatize to different forms of food, depending on the ecosystem in which it settles. They are more flexible the younger they are, and in the regions where they invade they have shown to be more generalist than in their native distribution area, that is, they accept more different sources of food.

Regarding environmental conditions, the presence of largemouth bass is directly related to temperature; It has a preference for warm waters, and with abundant vegetation, it does not invade very cold waters. It also prefers calm waters , expanding through lower and middle sections, reservoirs, lakes and lagoons. In fact, these environments promote the success of your invasion.

This species is regulated by the Spanish Catalog of Invasive Alien Species since its implementation in 2013 and, according to the Global Invasive Species Database (GISD), is on the list of the 100 most harmful invasive species of the world .

Largemouth Bass Impacts

Once introduced, the largemouth bass increases predation, altering, through a cascade effect, the natural cycles of the ecosystems in which it settles. Based on the basic functioning of ecosystems, it is expected that greater predation on primary consumers will generate an alteration in the very structure of the ecosystem ; although, there are still no studies to confirm these predictions.

Apart from its effects on the structure and functioning of ecosystems, largemouth bass generates direct impacts on biodiversity . On the one hand, the damage caused by predation, which affects populations of insects, fish, amphibians, reptiles and small mammals. On the other hand, it transmits diseases that can affect other animals; among them, parasites such as cestodes, trematodes or nematodes.

And even more, it monopolizes resources , competing with other predators, both fish and waterfowl, which are displaced from the environment. In fact, invasion by black bass is considered to be the main cause of the extinction of the Atitlan grebe ( Podilymbus gigas ), a bird endemic to Guatemala, where the largemouth bass is also invasive.

Sport fishing as a possible management tool

Since the legislation on invasive species came into force in 2013, and as stated in its article 7, actions or behaviors aimed at promoting this species must be avoided , and any specimen extracted from nature, whatever the procedure, cannot be returned to the natural environment. This contrasts with certain activities that are proposed from the sport fishing sector, which promote and publicize calls for fishing without killing this animal and other invasive fish species.

It is not ruled out, however, that sport fishermen could play an active role in the control , management and, if possible, eradication of black bass from invaded places. The Catalog of Invasive Alien Species itself suggests, as a control measure, the establishment of awareness and sensitization campaigns for this group and their involvement in monitoring, surveillance and elimination of specimens. In this way, if every time a fisherman catches one of these animals , he extracts it from the ecosystem instead of releasing it again, the collective would become part of the solution, thereby really promoting the conservation of river ecosystems.


Almeida, D. et al. 2012. Trophic plasticity of invasive juvenile largemouth bass Micropterus salmoides in Iberian streams. Fisheries Research, 113(1), 153-158. DOI: 10.1016/j.fishres.2011.11.002

Bae, M.-J. et al. 2018. Temperature and hydrologic alteration predict the spread of invasive Largemouth Bass (Micropterus salmoides). Science of The TotalEnvironment, 639, 58-66. DOI: 10.1016/j.scitotenv.2018.05.001

BOE. 2013. Royal Decree 630/2013, of August 2, which regulates the Spanish Catalog of invasive alien species. BOE , 185 (Sec. I.), 56764-56786.

CABI Invasive Species Compendium. 2019. micropterus salmoides (largemouthbass) (N.o 74846).

Pereira, F. W. et al. 2019. The largemouth bass Micropterus salmoides (Lacepède, 1802): impacts of a powerful freshwater fish predator outside of its native range. Reviews in Fish Biology and Fisheries, 29(3), 639-652. DOI: 10.1007/s11160-019-09570-2

Simberloff, D. et al. (Eds.). 2019. 100 of the World’s Worst Invasive Alien Species: A Selection From The Global Invasive Species Database. En Encyclopedia ofBiological Invasions (pp. 715-716). University of California Press. DOI: 10.1525/9780520948433-159

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