Tilapia is a species widely used in aquaculture, given its ability to adapt and reproduce in a great variety of environments. In Galapagos, it is a highly invasive species that has wrought havoc on the ecosystems of "El Junco" Lagoon.

"El Junco" Lagoon is home to one of the smallest endemic animals of the Galapagos. It is a Calanoid copepod, a tiny crustacean that plays an indispensable role in all life that depends on the lagoon.

Copepods serve as filters in the lagoon, preventing algae from reproducing excessively.

	Tilapia could have caused great harm to the "El Junco" Lagoon on San Cristóbal Island and with it the most important indicator of the climate and the El Niño - Southern Oscillation Syndrome worldwide.

Without this copepod, the algal bloom would have increased the turbidity that, in turn, would have prevented light from penetrating to the bottom of the ecosystem. Consequently photosynthesis, which produces free oxygen, would have been impossible on the bottom of the lagoon. The radical alteration of the environment posed by these changes, would have made the existence of most of the species that previously formed the ecosystem unviable.

Tilapia Oreochromis niloticus was detected in the "El Junco" Lagoon on San Cristóbal Island in 2006. Because of its rapid reproduction it was consuming all of the food in the lake, namely copepods. When eradication operations began, the situation was so critical that larger tilapia were eating smaller ones, due to lack of food.

The "El Junco" Lagoon would disappear and with it, the most important indicator of the climate and the El Niño - Southern Oscillation Syndrome worldwide.

Eradication of tilapia

The Directorate of the Galapagos National Park staff, with the collaboration of scientists from the United States Government (Technicians from the Department of the Interior, DOI), implemented a Plan of Action for the eradication of tilapia from "El Junco" Lagoon that consisted of:

	ERADICATION OF TILAPIA » Process of eradication of tilapia

• Record the physical and chemical characteristics of the lagoon and determine the size and population structure of tilapia.
  
• Perform water quality monitoring in the "El Junco" Lagoon and in the gorges before and during application of rotenone.
  
• Perform toxicity tests.
  
• Apply rotenone to the "El Junco" Lagoon.

About rotenone

Rotenone is extracted from tropical leguminous plants such as common mullein, which is toxic to cold-blooded animals but harmless to warm-blooded animals, including humans.

The effect of rotenone has been known for at least two thousand years, when it was already being used as a fishing technique in the rivers and lakes of Asia, Africa, and South America. Early hunters could not have known that the rotenone from plants is easily absorbed by the gills of fish, they knew only that if they threw certain branches and leaves into the water, the fish surfaced and died.

Today, it is commercially presented as a crystallized, white, odorless powder, insoluble in water. It is easily degraded by light and heat, therefore it is not persistent and decomposes quickly.

Results

• Monitoring and physical data collection was performed to detect chemicals in the "El Junco" Lagoon and the surrounding gorges in the following areas: "El Chino" (two gorges), "Cerro Gato" (three gorges), and "Los Arroyos" (two gorges). Data such as conductivity, temperature, salinity, pH, and geographical position were recorded. This data was also collected daily in the Lagoon and recorded in a database for later analysis.

	» Tilapia in the Galapagos

• With the application of rotenone the collection of 39,958 tilapias was recorded. Also, 30% of the total were measured, weighed, and recorded in a database.
  
• At each sampling point within the lagoon, the following data was collected: dissolved oxygen, hydrogen potential, total dissolved solids, salinity, conductivity, water temperature, turbidity, and ambient temperature.
  
• Endemic and native invertebrates were collected from the "El Junco" Lagoon (quirodominos, copepods, and decapods), and stored in 500-liter containers of water prior to their reintroduction, which was carried out normally.

For the future

Thanks to the control and eradication efforts, catastrophic damage to the "El Junco" Lagoon, and to all the species of plants and animals whose relationships to each other and with the Lagoon comprise the ecosystem has been prevented.

Today, the Lagoon is monitored monthly to detect any possible resurgence or reintroduction, thereby ensuring its natural integrity.