Collecting tropical fish for the aquarium market is depleting wild populations and harming coral reefs. Conservationists are developing techniques to breed highly sought fish in captivity to spare their wild cousins.

A fishing industry based on capturing fish alive, often with the help of cyanide poison, has become highly controversial because of its purported impacts on coral reef ecosystems. Now, conscientious tropical fish collectors and scientists hope to alleviate the consequences of the marine aquarium trade by farming the most valuable ornamental fish.

Divers capture about 30 million ornamental fish annually, with about 16 million entering the United States, according to a report from the U.S. National Marine Fisheries Service. Virtually all these fish are wild-caught and most come from the Philippines and Indonesia, where many collectors, using snorkeling gear, squirt cyanide into coral cracks and crevices to stun their colorful quarry.

Cyanide, however, also kills coral and numerous other invertebrates, fish and microscopic animals. Mortality estimates vary, but it is likely that millions of creatures die at the hands of collectors and importers for each wild-caught fish placed in a retail outlet tank. A 2016 report from the environmental groups Center for Biological Diversity and For the Fishes found that 6 million of the ornamental fish imported into the United States each year have been exposed to cyanide, and that the poison killed another 14 million in the wild or during transit and handling. Even in the absence of cyanide use, the collection trade has depleted reef fish populations. The Banggai cardinalfish, for example, has been depleted by collectors in its native waters of Indonesia and was recently listed by the U.S. government as threatened and there is a debate over how significantly the collection industry of Hawaii has impacted nearshore fish populations.

The world’s coral reefs are gravely impacted by changing ocean chemistry due to climate change – especially rising temperatures and acidification. Cyanide fishing may kill coral directly, while overfishing can do so indirectly. Since many wild-caught fish – both those targeted for food markets and for the aquarium trade – eat algal vegetation, they play the key biological role of keeping the coral structure clean. When these species are depleted, coral may become overwhelmed by algae, which may impact coral polyps’ ability to reproduce.

“You can wind up with these algafied coral reefs that can’t recover,” said John Gorman, the head curator at the Maui Ocean Center, an aquarium in Wailuku that is promoting captive breeding of aquarium species and by 2020 hopes to have 20 percent of its display fish acquired from aquaculture facilities. In 2014, Rene Umberger, a Hawaii-based activist and director of For the Fishes, introduced a smartphone app called Tank Watch that lists the 50-plus reef fish species that are widely available through captive breeding programs. The idea is to help hobbyist fish collectors determine whether ornamental fish in retail stores have been caught in the wild or bred in captivity.

“We’re trying to get hobbyists to only buy fish that are captive-bred,” Umberger said.

The Tank Watch “good” list includes various blennies, dottybacks, gobies, certain cardinalfishes and numerous species and breeds of clownfish. Much of the fish farming takes place at Oceans, Reefs & Aquariums, in Ft. Pierce, Florida; Sustainable Aquatics in Jefferson City, Tennessee; and Sea & Reef Aquaculture in Franklin, Maine.

However, about 2,000 other species, including the coveted yellow tang, royal blue tang and peppermint angelfish, are not farmed commercially and remain the targets of collectors who have depleted populations and damaged reefs around the world.

Experts disagree on how collectors, as opposed to fishers in other industries, are impacting target species in Hawaii. Cyanide is rarely, if ever, used in Hawaii, for instance. Still, data shows that some species have declined significantly in abundance. Hawaii’s Department of Land and Natural Resources states on its website that the state’s “existing aquarium fishing practices are sustainable and environmentally sound.” Data collected by the department shows significant declines in several valuable aquarium species, including the Achilles tang, ornate wrasse and fourspot butterflyfish. Other species, including the yellow tang, have become more numerous, according to the department.

Umberger, who disagrees with claims that Hawaii’s collection fishery is managed sustainably, said she has personally watched high-value target species decline on Hawaii’s reefs since she began diving here in the early 1980s.

“The difference between then and now is huge – it’s like, ‘Where have the fish gone?’” said Umberger, who believes they have largely gone to fish tanks.

To reduce the impacts of collecting on wild reef systems throughout the world’s tropical oceans, scientists are studying how to breed high-value species in tanks. The Hawai‘i Pacific University’s Oceanic Institute, in Honolulu, is attempting to breed yellow tangs.

The University of Hawai‘i’s Pacific Aquaculture and Coastal Resources Center, in Hilo, has been focusing on the flame wrasse and the Potter’s angelfish, each a species endemic to the Hawaiian Islands. Richard Masse, who codirects the program with colleague Sydney Gamiao, said breeding the fish successfully and with consistency is the challenge.

“We need to be able to do it not just once, but again and again so that we can eventually go to a commercial producer and say, ‘This is how you do it,’” he said.

Masse said prompting the fish to lay and fertilize their eggs requires providing them with the optimal water temperature, pH, salinity and light level, as well as pairing the right males with the right females – all conditions that vary from one species to another.

Most of Masse and Gamiao’s work has so far focused on the flame wrasse.

“We’re getting very consistent egg production,” he said.

But producing larval fish is just half the battle for aquaculturists.

“You can hatch the fish, but if they don’t have food, they’ll be dead in several days,” said Gorman.

The fish, he said, must be fed natural nutrition through their larval development, a complex task that means essentially building and maintaining a fish tank-scale marine food web. This task is especially difficult for pelagic, or broadcast, spawners – that is, species that release their eggs and sperm into open water, where the larvae develop into small fish while drifting on open ocean currents.

“You need different species of algae and phytoplankton,” Gorman noted.

As the larval fish grow bigger, their dietary needs change, scaling up toward bigger microorganisms, such as copepods and other zooplankton.

Most of the highly valued species in the trade are pelagic spawners, including tangs, angelfish and wrasses. Demersal spawners – such as the famed clownfish – lay eggs on rock or coral surfaces and are relatively easy to breed.

“With the demersal spawners, there is some level of parental care in the fish, which makes it easier for [human] breeders,” said Soren Hansen, owner of Sea & Reef Aquaculture. Hansen founded his company in 2003 and today mostly sells clownfish. The operation is now growing quickly, and Hansen said he hopes in 2018 to focus his research on breeding high-value pelagic spawners.

“That’s the holy grail of aquarium aquaculture right now,” he said. “There are more than 2,000 species that are collected from coral reefs, and they could all potentially be bred in captivity if we could crack the code on breeding pelagic spawners.”

The consequences of such an achievement could go beyond “just selling fish to fish stores,” he said.

“We could help save certain species from extinction, or help repopulate depleted reefs,” Hansen said.

Should the industry standardize the breeding of pelagic spawners, the challenge will remain of lowering costs to compete with wild-caught fish. Yellow tangs are widely available for between $40 and $60 each. Flame wrasse can be purchased in the $100 range.

“If you can’t compete with those prices, you won’t make it,” Hansen said. “In my experience, people aren’t willing to pay more for captive-bred fish.”

Masse said clownfish, dottybacks and other easily farmed species are now cost-competitive with wild fish.

Even so, some hobbyists may not even want them.

“You could call them purists – a very small group of hobbyists who want the wild-caught phenotypes and who aren’t interested in the captive-bred designer breeds,” said Jordan Noe, sales director at Oceans, Reefs & Aquariums, one of the world’s largest suppliers of captive-bred reef fish. Noe is referring mainly to clownfish, which breeders have greatly diversified through selective breeding. He said widespread clownfish breeding “has relieved an immense amount of fishing pressure on wild populations.”

Umberger noted that successfully scaling up breeding programs for reef fish is just one challenge in overhauling the aquarium trade. The other, she said, is educating the public and generating demand for farmed species.

“But most hobbyists don’t know these are wild fish,” Umberger said. “They still aren’t aware this is even a problem.”

While the science of breeding most coral reef species “is still in its infancy,” said Gorman, he believes captive breeding will eventually become the industry standard.

“This is the future.”