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Mullet Fooled into Spawning

By Helen Altonn,  Star-Bulletin Writer 

Honolulu Star-Bulletin 

Thurs., Mar. 25, 1971.H-8 


The mother's delivery was overdue and Ziad Shehadeh paced the floor and wrung his hands, just like in the movies. In this case, however, the mother was a mullet. And when a mullet spawns at the 0 c e a n i c Institute at Makapuu, it's an occasion worth celebrating. 


SHEHADEH is director of the Institute's Food from the Sea Division, which is exploring fish farming as a source of protein-rich food for underdeveloped nations. Working day and night the past month, he has mastered techniques of producing mullet under controlled conditions-a scientific first.  His methods have worked so well, there's barely room for another mullet egg at he Institute. The vats and ponds are full of off spring from his experiments. More than a dozen Institute staff members, officials and a Star-Bulletin team crowded into Shehadeh's laboratory--tabbed the "delivery room"-to witness one of the latest spawnings. The scientist had given the mother injections of salmon hormone on the two previous nights. However, he reduced the amount normally used and wasn't sure of the result. 


THE MULLET ballooned in size from gulping water, a natural process of hydration indicating delivery is imminent. But, nothing happened. The suspense was nerve wracking. And the observers began setting up a pool on when the eggs would arrive. In the tank with the mother were two males. They were supposed to swim around her, touching, nudging and even nipping her. This activity stimulates her to drop her eggs; then the male fertilize them.  But Shehadeh was upset "These guys just aren't paying any attention to her at all he said. He put another male into the tank. Still, no action. Shehadeh paced some more. Finally, in a surge of frenzied activity, the mother dropped her eggs-perhaps as many as a million. Shehadeh was overjoyed. 

Among those watching the (blessed) event was Kenneth S Norris, Institute director. he said Shehadeh has earned an international reputation because of his achievements in rearing the mullet. 


ARTIFICIAL spawnings have been successful before, both at the Institute and at Taiwan, he said. Shehadeh participated in the Taiwan work last year.” We knew we could do it, but we were not quite sure why," Norris said. "Now we have iron-clad control. We really do know what's going on and we can predict it."  The Institute now has five different ways to bring the fish to maturity for spawning, including, surgery and hormone injections, he said. 

One of the simplest and most effective methods is to put the fish into sea grass beds-ponds with artificial ocean bottoms.” We can't prove this, but I think fish in captivity are frightened," Norris said. "I think the stress is suppressed in the sea grass bed. The closer we get to nature, the better."  He said the fish mature naturally in the ponds but grow much faster than in nature "because of the super abundance of food.” 


THE NATURAL spawning season is from December to February. But the scientists want to induce the spawn out of season and more than once a year.  One technique is to cut the light in their tanks to simulate days growing shorter in winter, Norris said. "This fools their physiology and forces them to spawn," he explained. A tank system with special lighting has been installed at the Institute, which, Norris said, "lets us move the seasons."  The survival rate for the mullet babies thus far is about 5 per cent. Considering the number of eggs per spawning, Norris said this isn't too bad. "We could plant five ponds with one fish." But he said they hope to do better. "I see no reason why we can't go up to 50 per cent, and we're working on it.” 


He said the significant thing is that they can now raise a brood stock of fish, which allows them to go into, genetic selection. Through this means, they possibly can double or triple the size of the fish, as has been done elsewhere with trout, he noted. 


ONE OF THE problems with fish cultivation is to find foods the captive fish like. Norris said the mullet larvae are being fed plankton, which they suck off the water surface. And they are very fond of oyster larvae, he said.  He said one of the old Hawaiian fishponds on Molokai is being refurbished for feeding experiments with the fish stocks. 


The next step is to design and build a hatchery and to extend the "farming" methods to other fish species, he said.” I think we can raise moi and papio and other fish this way…"We may see a resurgence of fish farming as a result of this, like they had in old Hawaii. But we can develop better stocks. The quality and quantity of the fish can be improved." 


Norris envisions a portable hatchery that can be placed on a ship and sent anywhere it is needed, "Then we could begin to stabilize pond culture wherever it exists into a true food resource instead of a luxury resource," he said.