Dr. Garth Fletcher (L) and biochemistry student Heather Young at his lab in the Ocean Sciences Centre.

By Deborah Inkpen
Dr. Garth Fletcher, professor emeritus at the Ocean Sciences Centre, has been working with his colleague, Dr. Peter Davies, Queen’s University, for over 30 years on antifreeze proteins in fish.

A number of marine fish produce antifreeze proteins to protect themselves from freezing in a sub-zero, ice-laden marine environment.

“The research we are carrying out focuses on these antifreeze proteins, their physiological regulation, mechanisms of action, diversity, evolution and potential economic value in the field of biotechnology,” said Dr. Fletcher.

Drs. Fletcher and Davies’ collaboration with graduate student Christopher Marshall, Queen’s University on the winter flounder was recently published in Nature magazine.

“The winter flounder can survive in polar oceans at temperatures as low as minus 1.9 degrees Celsius, the freezing point of seawater,” said Dr. Fletcher.

How the flounder does this is a mystery.

“The fish only seemed to have enough ‘antifreeze’ protection to cater for temperatures down to minus 1.5 degrees Celsius.”

The solution to the mystery is a newly identified antifreeze protein present in the fish's blood that has a remarkable protective capacity.

“It was there all along, but we missed it and it took 30 years to find it.”

Fish that live in polar oceans survive at low temperatures by virtue of antifreeze plasma proteins (AFPs) that bind to ice crystals and prevent them from inflicting cellular damage. The winter flounder (Pleuronectes americanus) has a much-studied AFP known as type I, but it is this new protein that enables the fish to withstand freezing sea water. This additional AFP is hyperactive, offering a level of protection equivalent to that of an insect AFP.

“The new protein may be the product of a flounder gene of previously unknown function, called 5a,” said Dr. Fletcher. “It irreversibly loses all activity at room temperature and at low pH – conditions formerly used in purifying antifreeze proteins – which may explain why it remained undetected for 30 years.”