While each species spawned at different depths, all larvae swam upward into platelet ice, located just below several meters of surface ice, when they hatched, seeking perhaps a safe area to hide from predators, Cziko said.
The average freezing point of the larval fish fluids was about -1.3 degrees Celsius, according to testing with a nanoliter osmometer. Yet the fish hatch into water at almost -2 degrees Celsius. "With all this ice around, there is no way they can prevent freezing," Cheng said. "At -2 degrees Celsius, internal fluids would freeze instantly and the baby fish would die."
"This 0.7 of a degree Celsius is small but very significant," Cziko said. "In adults, we find ice in their bodies but these small crystals don't grow because of antifreeze proteins. Finding that larval fish don't have enough antifreeze really threw off how we understand survival in fish."
While the larvae of one species, the bald notothen, survives using high levels of AFPs like the adults, the researchers were astonished to find that the dragonfish and silverfish hatchlings have too little to allow survival during direct contact with ice. Looking more closely, the researchers discovered that the gills of all three species were undeveloped at hatching, minimizing the risk of ice passing through them to get inside.
The delicately thin skin of the larval fish may offer additional protection, because their skin hasn't yet been exposed to environmental damages, Cheng said. The skin and undeveloped gills, Cziko said, may combine to allow time for antifreeze levels to rise.
The production of AFPs did not show much increase in the
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Contact: Jim Barlow, Life Sciences Editor
jebarlow@uiuc.edu
217-333-5802
University of Illinois at Urbana-Champaign
13-Feb-2006