Yellow tangs raised in captivity on Oahu

After a decade of trying, Chad Callan and his team at the Oceanic Institute of Hawaii Pacific University have finally unlocked the mystery of the yellow tang.

The researcher said Tuesday that his latest batch of the popular Hawaiian reef fish has survived the tricky larval stage and has now stabilized into a group of full-fledged juveniles that can safely mature into adulthood.

What that means is the world’s first captive-bred yellow tangs — about 150 of them, from about 72 to 87 days old, the size of a quarter — are now swimming around in a couple of large tanks at the Waimanalo research facility.

“It’s exciting,” Callan said, “a huge success.”

The news could have far-reaching implications for Hawaii’s reefs and the state’s $2 million aquarium industry, which currently sustains itself by harvesting hundreds of thousands of fish from the wild each year.

While the aquarium industry says it conducts harvesting in a sustainable way, conservationists have condemned the practice for supposedly depleting fish populations and threatening the health of reefs.

Last week the state Office of Environmental Quality Control and the state Environmental Council urged state Department of Land and Natural Resources Chairwoman Suzanne Case to issue an emergency moratorium on the collection of reef wildlife for aquarium purposes because of the ongoing coral bleaching problem in Hawaii.

Both Jessica Wooley, OEQC director, and Joseph Shacat, Environmental Council chairman, called for an environmental review of the aquarium industry under the authority of the Hawaii Environmental Policy Act.

The brightly colored yellow tang, part of the surgeonfish family, is one of the most recognized of all Hawaii reef fishes and is one of the the most popular saltwater aquarium fishes in the world, comprising nearly 80 percent of ornamental fish exports from Hawaii.

Callan said his technique, built on top of Oceanic Institute research going back to 1999, could also be used to captive-breed other tropical fish.

But there’s more work to be done before it can become commercially feasible to the point where it will help to meet the demands of a market reaching into the hundreds of thousands of fish per year, he said.

In 2013 Callan realized a breakthrough in breeding techniques that allowed for culturing eggs in significant quantities and rearing the larvae through their critical first few weeks of life. The milestone helped to achieve his own lab record of 21 days.

Then, in the first quarter of 2014, Callan and his team were able to keep 150 yellow tangs alive for 50 days before they appeared to stall in their development.

While they did break the old record in captivity of about 40 days, only six fish were alive by Day 65 — and the last one gave out on Day 83.

Looking back, Callan said few, if any, of the signs of developing juveniles were there, including the transition from clear to yellow and settling to the bottom of the tank. The newly hatched brine shrimp used for food during the transitional stage apparently was not right.

This time, he said, a variety of food items were used in a “shotgun approach,” he said.

And that did the trick. The fish became larger and more developed at a younger age. The team started seeing fish settling on Day 55, and most had turned yellow by Day 65, which matches the timing seen in the wild.

In the ocean, yellow tang larvae remain in the water column clear and colorless — a defense mechanism — before they settle into the reef and turn yellow in a couple of days. As adults the yellow tangs are herbivores that clean the reefs of algae.

“They’re nearly all completely yellow now and look like miniature adults,” he said of the captive bunch.

It took approximately two months for the fish to go from egg to the size of a quarter.

“That’s in line with what we’re seeing in the wild,” he said.

Callan, who said he’s working with enough funding for only one year, said he’s hoping to gain enough funds to underwrite at least three more years of research.

“There’s a lot of work to do,” he said.