"We thought, something is going on during this period, in which the proportional number of larvae dying is greatest," said Dr. Holzman. "Our goal was to pinpoint the mechanism causing them to die. We saw that even under the best controlled conditions, 70% of fish larvae were dying within the two weeks known as the 'critical period,' when the larvae detach from the yolk sac and open their mouths to feed," said Dr. Holzman. "What was going on? We turned to physics as a source of the problem."
Eating soup with a fork
The physical structure of the larvae and their flawed interaction with the physical environment provided the answer Dr. Holzman was looking for. Over the course of two years, he and doctoral student Victor China observed fish larvae at three significant points in their development (at the beginning, middle, and end of that "critical period" eight, 13; and 23 days old). They found that the "stickiness" of the water the viscosity of the surrounding ocean water was hampering the larvae's attempts to feed.
"All that determines the larvae's feeding ability is viscosity not age, not development. Only their interaction with the surrounding water," said Dr. Holzman. "Because the water molecules around you have weak electrical bonds, only a thin layer sticks to your skin a mere millimeter thick. If you're a large organism, you hardly feel it. But if you're a three-millimeter-sized larva, dragging a millimeter of water across your body will prevent you from propelling forward to feed. So really, its all about larval size, and its ability to grow fast and escape the size where it feels the water as viscous fluid."
The researchers found that in less v
|Contact: George Hunka|
American Friends of Tel Aviv University