Microscopic view of Amazon fish in river with bacteria.

Amazon Fish Under the Microscope: What Bacteria Lurks Beneath?

Rhea Morgan in Science & Nature September 2025 • 3 min read.

"Unveiling the Microbiota of Butterfly Peacock Bass and Piramutaba for Safer Consumption"

The Amazon River teems with life, holding immense potential for fishing industries. Among the diverse species, the butterfly peacock bass (Cichla ocellaris) and piramutaba (Brachyplatystoma vailantii) stand out as commercially important fish. They are prized for their economic value and nutritional benefits.

Like all fish, these Amazonian species are highly perishable. While enzymatic and chemical reactions initiate spoilage, microbial activity ultimately dictates their shelf life. Understanding the specific bacteria present is crucial for ensuring freshness and safety.

A recent study investigated the microbiota of butterfly peacock bass and piramutaba in the Belém-Pará region of Brazil. The goal was to identify the types of bacteria present and how they might impact spoilage, paving the way for better preservation techniques.

Decoding the Bacterial Landscape of Amazon Fish

Microscopic view of Amazon fish in river with bacteria.

Researchers collected samples of butterfly peacock bass and piramutaba from the Ver-o-Peso Market in Belém, Brazil. They then conducted a thorough microbiological analysis, including:

By identifying and understanding these microorganisms, scientists and food industry professionals can develop targeted strategies to minimize spoilage and ensure the safety of these valuable food resources.

Counts of total mesophilic aerobic bacteria, which thrive in moderate temperatures.
Counts of psychrotrophic bacteria, which flourish in colder environments.
Detection of coliforms at 35°C and 45°C to assess hygiene levels.
Isolation of bacteria using specific agar surfaces, including Violet Red Bile Glucose (VRBG) for Enterobacteria and Baird-Parker Agar for Staphylococcus species.
Identification of isolated bacteria using API 20E kits for Enterobacteria and API Staph for Staphylococci.
Testing the temperature limits for bacterial growth to inform refrigeration practices.

Sixteen different strains of bacteria were isolated. Predominant species included Staphylococcus hominis, Staphylococcus aureus, Stenotrophomonas maltophilia, and Enterobacter intermedius. When exposed to temperatures of 10°C and 15°C, these strains did not achieve significant growth within six hours.

Protecting Quality: The Way Forward

The study reveals that Amazonian fish marketed in Belém have high counts of mesophilic and psychrotrophic bacteria. While some isolated mesophilic microorganisms didn't grow under refrigeration for more than six hours, the high concentrations of psychrotrophic bacteria necessitate additional preservation methods beyond refrigeration alone. By understanding the specific microbial landscape, we can develop targeted strategies to ensure the safety and quality of these valuable food resources.

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Everything You Need To Know

What types of fish were studied, and why are they important?

The study focused on the butterfly peacock bass (*Cichla ocellaris*) and the piramutaba (*Brachyplatystoma vailantii*). Both are commercially important fish species in the Amazon region, valued for their economic contribution and nutritional benefits. Their significance lies in their role within the fishing industry and their potential as a food source.

What methods were used to analyze the bacteria found in the fish samples?

The analysis involved multiple microbiological techniques. Researchers collected samples of butterfly peacock bass and piramutaba and performed several tests: counting total mesophilic aerobic bacteria and psychrotrophic bacteria, detecting coliforms at 35°C and 45°C, isolating bacteria using specific agar surfaces (like Violet Red Bile Glucose for Enterobacteria and Baird-Parker Agar for Staphylococcus species), identifying bacteria using API 20E kits for Enterobacteria and API Staph for Staphylococci, and testing the temperature limits for bacterial growth.

What were the main bacterial species identified in the butterfly peacock bass and piramutaba?

The study identified sixteen different strains of bacteria. The predominant species found included *Staphylococcus hominis*, *Staphylococcus aureus*, *Stenotrophomonas maltophilia*, and *Enterobacter intermedius*. These bacteria are key players in the spoilage process of the fish, therefore, understanding their presence helps in the development of preservation techniques.

How does bacterial growth impact the shelf life of the butterfly peacock bass and piramutaba?

Microbial activity, not just enzymatic and chemical reactions, ultimately dictates the shelf life of the butterfly peacock bass and piramutaba. High counts of mesophilic and psychrotrophic bacteria in the fish, as revealed by the study, directly influence spoilage. The presence of these bacteria indicates a need for effective preservation techniques beyond simple refrigeration. The study found that certain isolated strains did not grow significantly in refrigerated conditions within a short period; however, high levels of psychrotrophic bacteria call for additional methods to extend shelf life.

What are the implications of this study for the food industry and the consumer?

The study provides critical insights for the food industry and consumers by highlighting the bacterial landscape present in the butterfly peacock bass and piramutaba. This knowledge enables the development of targeted preservation strategies, such as improved handling and storage methods, to minimize spoilage and ensure the safety of the fish. For consumers, this translates to access to safer, higher-quality products. Understanding the specific bacteria (*Staphylococcus hominis*, *Staphylococcus aureus*, *Stenotrophomonas maltophilia*, and *Enterobacter intermedius*) present helps in formulating better preservation techniques for these valuable food resources, therefore improving food safety.