UNR researcher aids Mekong giant catfish restoration

This largest fish was one of 1,500 mostly juvenile fish raised at the Freshwater Aquaculture Research and Development Center and released into a fish sanctuary in the Tonle Sap Lake to restore populations of the Mekong’s endangered largest freshwater fishes. (Photo: UNR)

University of Nevada, Reno

Sunday, March 13, 2022

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Working to save some of the world’s most critically endangered fish, an international team of scientists and fisheries professionals released a large assemblage of iconic fish species into Southeast Asia’s great lake, Tonle Sap Lake.
“This is the first step in an effort to restore populations of the Mekong’s largest freshwater fishes," Zeb Hogan, a fish biologist at the University of Nevada, Reno who works cooperatively with the U.S. Agency for International Development to lead the Wonders of the Mekong project. "Fish reserves have been shown to be an effective tool at protecting aquatic biodiversity and boosting fish biomass. It’s one action, of many that are needed, to bring these species back from the brink of extinction.
"We've had a great few days here out on the Tonle Sap Lake with a very successful fish release and research project."
Among the fish species released March 5-6 are the critically endangered Mekong giant catfish, which is the current world-record holder for the world’s largest freshwater fish at 646 pounds; the endangered striped river catfish, once a staple food in the region, whose population has dramatically declined; and the critically endangered giant barb, the world’s largest carp species and Cambodia’s national fish.
"It's a great project, releasing the world's biggest fish into one of the largest networks of freshwater fish sanctuaries," said Hogan, a research professor in the university's Department of Biology. "We transport the fish by car from the Freshwater Aquaculture Research and Development Center in Bati Village where the fish were raised. The reserve is in the middle of a giant lake so the last stage is by boat. There are many different sizes of the three species, ranging from about 10 inches to a 5-foot long Mekong giant catfish."
As many as 1,500 individual fish were released into the government-operated fish reserve, former fishing lot No. 4 in the Tonle Sap Lake, a short drive and boat ride from the city of Siem Reap and the famous ancient temples of Angkor Wat. The fish are mostly juveniles that have been reared by the Cambodian Fisheries Administration in partnership with the USAID supported Wonders of the Mekong cooperative project. By tagging the fish prior to their release, researchers will have a unique opportunity to study the animals’ survival, growth and movement.
“The purpose of this event is to reintroduce captive-reared endangered fishes to the wild and track their fate," said Ngor Peng Bun, fish ecologist and Dean of Faculty of Fisheries Science at the Royal University of Agriculture. "We need to better understand the effectiveness of fish reserves as a refuge for threatened fish; this release today will inform future conservation practices, and help us understand whether such methods are effective in supporting the restoration of these species’ wild populations.”
The Tonle Sap, Southeast Asia’s largest lake and home to over 300 species of fish, is a hotspot for freshwater biodiversity and a UNESCO Biosphere Reserve. Historically, it has served as a crucial nursery ground for endangered giant fish and for many other migratory fish populations in the Mekong River basin. In recent years, these fish have come under increasing threat from dam building upstream, overfishing and drought.
To combat these threats to fish populations, a series of government-run fish sanctuaries and community conservation areas have been established in the Tonle Sap Lake, forming one of the largest networks of aquatic conservation zones in the world.
“The Cambodian government has taken action to establish fish sanctuaries, protect core areas of the Tonle Sap Biosphere Reserve and formalize community fisheries and associated reserves - these characteristics make Cambodia an ideal place for endangered fish restoration work," said H.E. Poum Sotha, director general of the Cambodian Fisheries Administration. "Today is part of a multi-year effort to test the efficacy of using the Tonle Sap’s world’s large network fish reserves for reintroduction of captive-reared endangered fishes into the wild. The ultimate goal is to protect fish until they grow large enough to reproduce, in order to support fisheries and biodiversity.”
The release of endangered species into the Tonle Sap Lake is expected to be the first of many to come, and researchers are optimistic that a sustained commitment to protecting some of the world’s most endangered freshwater giants will bear fruit.
“Assuming the supplementation program is continued in subsequent years, and that favorable habitat and harvest conditions exist to support the full life cycle of these fishes in the wild, this research is part of longer term goals of increased population sizes, natural reproduction and self-sustaining populations of these rare and remarkable animals,” Hogan said, adding that other actions, such as the protection of migration corridors like the Tonle Sap River and spawning grounds in the upper Cambodian Mekong, are also needed.
Sudeep Chandra, Hogan's research partner, co-principal investigator in the Wonders of the Mekong project and the director of UNR's Global Water Center, said "the efforts undertaken by Wonders of the Mekong, our in-country partners and the local community are a needed step in understanding the importance of fish sanctuaries for sustaining endangered migratory fishes of the Lower Mekong. Ultimately, cooperation and proactive management is needed to sustain the fishery of Southeast Asia’s Great Lake, the Tonle Sap."
This project is a partnership between the Cambodian Fisheries Administration, Siem Reap Fisheries Administration Cantonment, and USAID Wonders of the Mekong, with additional contributions from recreational anglers through a unique collaboration with Gilham’s Fishing Resort in Thailand.
• For information on the efficacy of fish reserves: “A network of grassroots reserves protects tropical river fish diversity” by Aaron Koning: https://www.nature.com/articles/s41586-020-2944-y
• Information on the Wonders of the Mekong project: https://www.usaid.gov/cambodia/fact-sheets/wonders-mekong
• Information about Zeb Hogan: https://www.nationalgeographic.org/find-explorers/zeb-s-hogan

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