Juvenile fish in aquarium with looming shadow of large, menacing fish in polluted river.

Tank Busters: The Hidden Threat of Juvenile Fish Sales in Brazil

Samir D’Costa in Climate & Environment August 2025 • 4 min read.

"Unregulated aquarium trade poses a significant risk to native ecosystems. Learn how small fish today can lead to big problems tomorrow."

The global aquarium hobby, enjoyed by people of all ages, has shown to improve well-being. As aquarium keeping gains popularity, many hobbyists are unaware of the environmental consequences of their actions. The informal sale of non-native, large-bodied aquarium fish, known as "tank busters," is growing in Brazil, creating a significant ecological threat.

A recent study investigated the unregulated trade of these fish on Facebook from May 2012 to September 2016, gathering data on traded species, their origins, sizes, and behaviors. The research also assessed the invasion risk of frequently sold species using the Fish Invasiveness Screening Test (FIST).

The study identified 93 taxa from 35 families, with Cichlidae as the dominant family. Most species originated from South America and were sold at small sizes (under 10 cm). The southeast region of Brazil showed the highest trading activity. The FIST analysis indicated that Arapaima gigas, C. kelberi, and C. temensis pose high invasion risks due to aquarium dumping.

Why Juvenile Fish Sales Are an Environmental Time Bomb

Juvenile fish in aquarium with looming shadow of large, menacing fish in polluted river.

Many aquarium enthusiasts are drawn to the allure of owning exotic fish, often without considering the long-term implications. Juvenile fish of large species are particularly popular due to their manageable size and vibrant colors. However, these small fish quickly outgrow their tanks, leading owners to seek alternatives. One common and detrimental solution is aquarium dumping, the release of unwanted fish into local waterways.

Aquarium dumping introduces non-native species into environments where they don't belong, disrupting the natural balance and threatening native biodiversity. These introduced fish can compete with native species for resources, prey on them, and alter habitats, leading to declines in local populations and even extinctions. The consequences of such actions can be far-reaching and difficult to reverse.

Ecological Disruption: Non-native fish can outcompete native species for food and habitat.
Predation: Introduced predators can decimate local fish and invertebrate populations.
Habitat Alteration: Some species can modify their environment, making it unsuitable for native organisms.
Disease Transmission: Non-native fish can introduce diseases and parasites to which native species have no immunity.

The study emphasizes the need for management strategies to mitigate the risks associated with aquarium dumping. These strategies include trade regulations, monitoring, euthanasia programs, and educational initiatives. By raising awareness and promoting responsible fishkeeping practices, it is possible to reduce the threat posed by the unregulated aquarium trade.

Protecting Brazil's Aquatic Ecosystems: A Call to Action

The findings of this study serve as a critical reminder of the hidden dangers associated with the aquarium trade. By implementing trade regulations, monitoring programs, and educational campaigns, Brazil can protect its aquatic ecosystems from the devastating impacts of invasive species. It is up to hobbyists, retailers, and policymakers to work together to ensure a sustainable future for Brazil's native fish and aquatic environments.

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This article is based on research published under:

DOI-LINK: 10.1590/1982-0224-20170033, Alternate LINK

Title: Small Size Today, Aquarium Dumping Tomorrow: Sales Of Juvenile Non-Native Large Fish As An Important Threat In Brazil

Subject: Aquatic Science

Journal: Neotropical Ichthyology

Publisher: FapUNIFESP (SciELO)

Authors: André L. B. Magalhães, Mário Luis Orsi, Fernando M. Pelicice, Valter M. Azevedo-Santos, Jean R. S. Vitule, Dilermando P. Lima-Junior, Marcelo F. G. Brito

Published: 2017-12-18

Everything You Need To Know

What makes the sale of small aquarium fish a potential ecological problem in Brazil?

The unregulated sale of juvenile, large-bodied aquarium fish, particularly "tank busters" in Brazil, poses a significant ecological threat. These fish, often appealing due to their manageable size and vibrant colors, quickly outgrow home aquariums, leading to aquarium dumping. When introduced into local waterways they disrupt the natural balance and threaten native biodiversity. This is because they may compete with native species for resources, prey on them, alter habitats, and transmit diseases.

Can you explain what 'aquarium dumping' is and why is it harmful to local aquatic ecosystems?

Aquarium dumping refers to the irresponsible release of unwanted aquarium fish into local waterways. This introduces non-native species into environments where they don't belong. For example, releasing Arapaima gigas, C. kelberi, and C. temensis introduces species that can devastate native fish populations. This disrupts ecosystems, potentially leading to declines and extinctions of local species, with far-reaching and often irreversible ecological consequences. Effective management strategies are crucial to curb this harmful practice.

What is the Fish Invasiveness Screening Test (FIST) and how was it used in the study?

The Fish Invasiveness Screening Test (FIST) is used to assess the invasion risk posed by frequently sold aquarium species. It helps identify species that are likely to establish and cause harm in new environments if released. The study used FIST to determine that Arapaima gigas, C. kelberi, and C. temensis, all pose high invasion risks in Brazilian ecosystems. This assessment guides management strategies and trade regulations aimed at mitigating the introduction of potentially harmful species.

What species and areas of Brazil are most affected by the aquarium fish trade, according to the study?

The study identified 93 taxa from 35 families being traded, with Cichlidae being the dominant family. Most of these species originated from South America. The southeast region of Brazil showed the highest trading activity. The prevalence of South American species highlights the risk of disrupting local ecosystems through the introduction of non-native fish, while the concentration of trade in the southeast region indicates a key area for targeted management and regulation efforts.

What measures can be taken to address the environmental threats posed by the unregulated aquarium trade in Brazil?

To mitigate the risks associated with the unregulated aquarium trade, management strategies such as trade regulations, monitoring programs, euthanasia programs, and educational initiatives are crucial. These strategies aim to prevent aquarium dumping and promote responsible fishkeeping practices. Trade regulations can limit the sale of high-risk species, while monitoring programs can track the presence and impact of introduced fish. Educational campaigns are essential for raising awareness among hobbyists and retailers about the environmental consequences of their actions, encouraging responsible practices and informed decision-making.