Wildlife scientists have been scrambling for months to determine why puffer fish are dying around the Hawaiian Islands, and still do not know whether they will identify the killer.

Thierry Work, a wildlife disease specialist with the U.S. Geological Survey, said Wednesday that scientists had conducted 72 necropsies on diseased puffer fish that have been found on all the islands except Kauai.

Finding the cause is critical because it could affect the ecosystem or human health, said Work, who is with the USGS’s National Wildlife Health Center.

"It’s part of understanding the health of the marine ecosystem," Work said. "There’s something awry in the marine environment."

Scientists learned about the deaths in June but realized the fish have been dying in large numbers since March. Work suspects fish collected so far are just a small number of those that have died.

According to longtime ocean users who have reported seeing dead puffer fish, the die-off surpasses any recent mass death of puffer fish, he said.

The killer is striking mostly stripped puffers, leaving them floating upside down on the surface or washed up on shore with enlarged livers. Some of the fish have gills that shed cells, leaving only the cartilage.

Most dead puffers have been female, until Work did a necropsy Tuesday on five male fish from Molokai.

Why those fish were all males and other questions remain unanswered because not much is known about puffer fish.

They are considered hardy, surviving longer than other fish in aquariums and live among coral reefs, feeding on crustaceans. Puffer fish inflate when frightened and have poisonous meat.

Die-offs of fish have occurred in the past — most recently of triggerfish on Niihau, but scientists could not determine the cause because of a lack of samples, Work said.

He hopes to change that outcome for the puffer fish.

Lab tests have come up negative for bacteria, fungal diseases and parasites, and scientists suspect the cause to be a virus or a toxin.

Marine experts are covering new ground searching for the natural poison or virus. They are using molecular testing to find a virus that is causing the deaths out of the millions of possible viruses. At the same time, they are growing fish cells to test the effect of viruses in the fish in labs on the mainland and in Hawaii.

Meanwhile, Work is asking the public to look out for sick, dying or dead puffers.

Sick or dying fish should be placed in a bag on ice (do not freeze) or in a bucket of sea water in the shade. Call an expert (see accompanying box) who will pick up the fish if it is alive or sick. Dead fish are usually too decomposed to be of much help.