Thin skin, slow-growing gills protect larval stage of Antarctic fish http://www.news.uiuc.edu/news/06/0213coldfish.html

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Latest news RESEARCH NEWS INDEX Archives 2006 February Science Scholar to lecture on General Thin skin, slow-growing gills protect larval African-American Business children's literature Archives stage of Antarctic fish (2/14/06) Slavery, science, theater NEWS INDEX Jim Barlow, Life Sciences Editor among topics in lecture This Year 217-333-5802; [email protected] series at Illinois (2/14/06) 2005 Six Urbana faculty Archives 2/13/06 members named University Scholars PUBLICATIONS CHAMPAIGN, Ill. — Very thin (2/13/06) Inside Illinois but hardy, unblemished skin Four chosen to receive II Archives and slow developing gills II Advertising honorary degrees at U. of About II appear to be keys to survival I. May commencement for newly hatched Antarctic (2/13/06) Postmarks notothenioids, a group of fish Funding of public schools whose adults thrive in icy to be topic of U. of I. QUICK SEARCH waters because of antifreeze symposium in Chicago proteins (AFPs) in their blood. Click photo to enlarge (2/13/06) Go Photo by Bryan Palmintier Early childhood education the subject at U. of I. Such adaptations are Paul A. Cziko, left) and important, researchers at the public forum (2/13/06) MORE Kevin Hoefling, a University of Illinois at Illinois in the News scientific research Contemporary East Asian Urbana-Champaign say, diver, art curators to meet, discuss their discipline Campus Calendar because the larval fish of at prepare to place an least two of oceanic current meter (2/13/06) Other News notothenioids that inhabit the (yellow ball) and its Two elected to Sources at McMurdo Sound home-made stand into membership in National and Terra Nova Bay the water. The Academy of Engineering 250-pound equipment (2/10/06) surprisingly lack sufficient is dropped antifreeze to protect them off the edge of the ice Carr Authors Series to through their first three floe to rest on the sea feature honored writers months of life. floor. A current across genres (2/8/06) meter allows scientists Scholars to meet at Illinois The unexpected discovery, to obtain information to discuss criminal reported online by the Journal on the velocity of trafficking and slavery of Experimental Biology seawater at a single (2/6/06) location. ahead of regular publication, Mantids – the good, the counters the assumption that bad and the just plain these vital proteins must be present from the time of wrong – on view at film hatching – a view held by scientists since fish AFPs were fest (2/2/06) found in the 1960s.

Internal fluids such as blood in many notothenioids are about half as salty as seawater. While seawater reaches its freezing point at –1.91 degrees Celsius, fish fluids will freeze at about –1 degree Celsius. The water where these On the Job: Thomas Korder species dwell rarely rises above the freezing point and is regularly filled with ice crystals.

"The way that we’ve understood how adult polar

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fishes survive has been based on their use of these antifreeze proteins to lower the freezing point of their internal fluids," said lead author Paul A. Cziko, a research specialist in the department of biology. "We finally got a chance to look at the larval fish, and it seems that they don’t always have to have antifreeze proteins to survive." Click photo to enlarge Cziko, who earned bachelor’s Photo by Chrissie Callison degrees in honors biology and biochemistry in 2004 from Paul A. Cziko carries Illinois, studied in his compressed air as an undergraduate with tanks after a dive near animal biology professors McMurdo Chi-Hing (Christina) Cheng station (barely visible and Arthur L. DeVries, who in the background) in discovered AFPs in Antarctica. notothenioids.

The research team, which also included Clive W. Evans of the University of Auckland in New Zealand, studied three notothenioid species: Gymnodraco acuticeps (naked dragonfish); borchgrevinki (bald notothen); and Pleuragramma antarcticum (Antarctic silverfish). All species develop as eggs for between five and 10 months before hatching in icy waters in the Austral spring. Five years of data, collected from 2000 to 2004, were analyzed.

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

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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 larval fish until 84 days after hatching, the researchers found. Adult values weren’t reached for 147 days.

"Amazingly," DeVries said, "for about three months the larval fish must rely only on their skin and gills to prevent ice from entering, and to keep them from freezing solid."

The National Science Foundation supported the research through grants to Cheng and DeVries. Cziko was supported by a grant (Special Undergraduate Research on the Environment) from the U. of I. Environmental Council.

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