Interesting Science

What's 34 centimeters (13.39 inches) long, likes the cold and has an interorbital pit with two openings? The answer is Cryothenia amphitreta, a newly discovered Antarctic fish discovered by a member of a research team from the University of Illinois at Urbana-Champaign. (A pen-and-ink drawing of the fish can be seen here)

"The fish was placed into the genus Cryothenia because of its overall similarity to the notothenioid Cryothenia peninsulae that has only been found near the Antarctica Peninsula. The species name was chosen to help researchers easily distinguish the two species in the genus Cryothenia, which translates from Greek as 'from the cold,' while amphitreta literally means 'an orifice with two openings.'" (U. of I.)

The new species of nototheniid fish, Cryothenia amphitreta, is detailed in the December issue of the quarterly journal Copeia [1] (published by The American Society of Ichthyologists and Herpetologists). Paul A. Cziko, a research specialist who had graduated with bachelor's degrees in animal biology and biochemistry from Illinois six months earlier, and research diver Kevin Hoefling, discovered it in McMurdo Sound [3] in the Ross Sea region of Antarctica in November 2004.

They were diving in the area in search of eggs laid by naked dragonfish (Gymnodraco acuticeps) for a study, published earlier this year [2], about levels of antifreeze proteins in newly hatched notothenioids in the salty icy waters where the temperature is rarely above the freezing point of seawater.

"We just came across this fish," Cziko recalled. "It was just sitting on the bottom, like most other fish in the area. There are only about a dozen species that swim in the area, with four to five easily distinguishable species. This one jumped out at us. First of all it was pretty big, and it looked quite different than the others."

Cziko and Hoefling guided the egg-laden fish into a mesh bag and surfaced.

"It was about twice as big as what you normally see swimming around," said Arthur L. DeVries, a professor of animal biology who many years earlier had discovered antifreeze proteins in notothenioids. "Its profile was much different than other common local notothenioids. Its center part is much higher. Most of the other species in the area have big heads and have bodies that taper back narrowly."

Cziko and co-author Chi-Hing (Christina) Cheng, professor of animal biology, studied the purple-gold-colored fish, comparing its measurements and perch-like appearance with all known species of fish that inhabit the icy waters of Antarctica. X-ray radiographs of bone structures were taken at the U. of I. College of Veterinary Medicine.

The new fish, which DeVries theorizes may have been looking for a place to lay its eggs in a flat, clear area near an intake pipe that feeds water into the McMurdo Station, was placed into the genus Cryothenia because of its overall similarity to the notothenioid Cryothenia peninsulae that has only been found near the Antarctica Peninsula.

Although bigger in pelvic-fin length and body size, as well as having more vertebrae, what sets C amphitreta apart from C. peninsulae is head morphology, specifically in the area between the eyes.

The new fish has a "wide, well-defined, two-holed interorbital pit divided by a raised medial ridge, scales anterior to this depression in the interorbital region, and a dark pigmentation of the mouth, gill and body cavity linings," Cziko and Cheng wrote.

The species name was chosen to help researchers easily distinguish the two species in the genus Cryothenia, which translates from Greek as "from the cold," while amphitreta literally means "an orifice with two openings."

"Even though we know a lot about Antarctica," Cziko said, "we still don't know everything about the ecosystems and the animals in them. There's probably a lot more to be learned about how these fish evolved and survived."

The area where C. amphitreta was found is the most-frequented location in McMurdo Sound explored by divers and fished with hand lines. DeVries has been going to the site for more than 40 years.

The new fish was located on a large flat rock in water that was minus 1.91 degrees Celsius and 20 meters deep.

"Art has been swimming there for more than 40 years," Cziko said. "You'd think he would have caught everything." DeVries does have an Antarctic fish named after him: Paraliparis devriesii.

National Science Foundation grants to Cheng and DeVries funded the research.

Source: University of Illinois at Urbana-Champaign PR December 19 2006

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[1] Based on the paper:

A New Species of Nototheniid (Perciformes: Notothenioidei) Fish from Mcmurdo Sound, Antarctica

Paul A. Cziko, C.-H. Christina Cheng

Copeia Volume 2006, Issue 4 (December 2006)
DOI: 10.1643/0045-8511(2006)6[752:ANSONP]2.0.CO;2

Abstract

A new species of nototheniid fish, Cryothenia amphitreta, is described from a single gravid female collected in mid-November 2004 by divers in McMurdo Sound in the Ross Sea region of Antarctica. The new species closely resembles the only known congener, C. peninsulae, collected off the west coast of the Antarctic Peninsula, but differs substantially in pelvic-fin length (13.4 vs. 19.3-24.4% SL), total vertebrae (57 vs. 50-53), body size at maturity (261 vs. 100-144 mm), and interorbital-pit morphology. The neutrally-buoyant C. amphitreta is characterized by a wide, well-defined interorbital pit divided by a raised medial ridge, scales anterior to this depression in the interorbital region, and a dark pigmentation of the mouth, gill, and body cavity linings. This species is protected against freezing by high levels of antifreeze proteins in its body fluids. Phylogenetic reconstruction using the mitochondrial NADH dehydrogenase subunit 2 (mtND2) suggests that C. amphitreta falls within the current designation of the nototheniid subfamily Trematominae.

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[2] A paper published by Proceedings of the National Academy of Sciences (PNAS):

Nonhepatic origin of notothenioid antifreeze reveals pancreatic synthesis as common mechanism in polar fish freezing avoidance

Chi-Hing C. Cheng, Paul A. Cziko, and Clive W. Evans

Published online before print June 23, 2006, 10.1073/pnas.0603796103
PNAS | July 5, 2006 | vol. 103 | no. 27 | 10491-10496

Abstract

Phylogenetically diverse polar and subpolar marine teleost fishes have evolved antifreeze proteins (AFPs) or antifreeze glycoproteins (AFGPs) to avoid inoculative freezing by internalized ice. For over three decades since the first fish antifreeze (AF) protein was discovered, many studies of teleost freezing avoidance showed hepatic AF synthesis and distribution within the circulation as pivotal in preventing the blood, and therefore the fish, from freezing. We have uncovered an important twist to this long-held paradigm: the complete absence of liver synthesis of AFGPs in any life stage of the Antarctic notothenioids, indicating that the liver plays no role in the freezing avoidance in these fishes. Instead, we found the exocrine pancreas to be the major site of AFGP synthesis and secretion in all life stages, and that pancreatic AFGPs enter the intestinal lumen via the pancreatic duct to prevent ingested ice from nucleating the hyposmotic intestinal fluids. AFGPs appear to remain undegraded in the intestinal milieu, and the composition and relative abundance of intestinal AFGP isoforms are nearly identical to serum AFGPs. Thus, the reabsorption of intact pancreas-derived intestinal AFGPs, and not the liver, is the likely source of circulatory AFGPs in notothenioid fishes. We examined diverse northern fish taxa and Antarctic eelpouts with hepatic synthesis of bloodborne AF and found that they also express secreted pancreatic AF of their respective types. The evolutionary convergence of this functional physiology underscores the hitherto largely unrecognized importance of intestinal freezing prevention in polar teleost freezing avoidance, especially in the chronically icy Antarctic waters.

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[3] Info on McMurdo Sound:

...Captain James Clark Ross (pictured) discovered the sound in February 1841 and named it after Lt. Archibald McMurdo of HMS Terror. The sound today serves as a re-supply route for cargo vessels and for aircraft that land upon floating ice airstrips near McMurdo Station. However McMurdo Station's continuous occupation by scientists and support staff since 1957-58 has turned Winter's Quarter's Bay into a markedly polluted harbor.

The pack ice that girdles the shoreline at Winter Quarters Bay and elsewhere in the sound presents a formidable obstacle to surface ships. Vessels require ice-strengthened hulls and often have to rely upon icebreaker escorts. Such extreme sea conditions have limited access by tourists, who otherwise are appearing in increasing numbers in the open waters of the Antarctica Peninsula. The few tourists who reach the McMurdo Sound find a spectacular scenery with wildlife viewing ranging from killer whales, seals, to adelie and emperor penquins...

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