Scientist strives to solve fish’s mystery

A research scientist at the Oceanic Institute in Waimanalo has blown away the record for keeping alive captive-bred yellow tang.

But Chad Callan has more work to do before he will be able to get his young fish to mature into the stage of life where they can safely achieve adulthood in captivity.

"This is a work in progress," he said. "We are making some significant headway, but it’s never as fast as you’d like."

During the first three months of this year, Callan and his Hawaii Pacific University team were able to keep one fish alive for 83 days, which beat the old record of about 40 days by Syd Kraul of Hawaii island.

The research progress could result in a boon for the aquarium industry as well as Hawaii’s coastal environment. Because the fish have not been able to be bred successfully in captivity, more than 300,000 of them are collected from Hawaii reefs each year.

With its solid, bright flash of lemon, the yellow tang is one of the 10 most popular saltwater aquarium fishes in the world. It is found in greater abundance in Hawaii’s waters and is the critical fish for the state’s $2 million aquarium industry, making up nearly 80 percent of ornamental fish exports.

Harvesting reef fish remains controversial, however. Litigation seeking more governmental oversight of the aquarium trade is currently being reviewed on appeal by the state’s intermediate court.

The suit was filed in 2012 by the Earthjustice law firm on behalf of four individuals, the Conservation Council for Hawai‘i, the Humane Society of the United States and the Center for Biological Diversity.

Callan, who has been culturing yellow tang since 2001, said he’s "fairly close" to unlocking the puzzle that makes the yellow tang so difficult to breed in captivity.

Last year, Callan realized a breakthrough in breeding techniques that allowed for culturing eggs in significant quantities and rearing the resulting larvae through their critical first few weeks of life, helping to achieve his own lab record of 21 days.

This time, Callan was feeling optimistic about getting some fish through to the critical juvenile stage of life when there were about 150 fish still alive at day 50. But then the school of larvae appeared to become "stuck" in their development, he said, and by day 65 there were only six alive.

"This indicated to us that something was missing in their diet or their environment that was preventing them from pushing past this point," he said.

While the last fish — it was named Lucky — started showing signs of development, with head-shape changing and spines disappearing, it finally succumbed on day 83.

Callan said he may have to find another live prey item to feed the young fish rather than the newly hatched brine shrimp he was using.

His next batch of larvae is already a couple of weeks old.

"We now know that each attempt is going to be at least three to four months long," he said. "I’m confident we will get back to this point again and hopefully push past this stage."