Researchers Helps Fight Cod Parasite

Cod aquaculture may be a budding business in Atlantic Canada, but for all its promise it is also literally plagued with a huge problem – an affliction that a University of New Brunswick biology student is studying in order to help find a solution.

NB Business Journal reports that many of these fish, which are stocked at high densities in aquaculture sites across the Maritimes, are infected with a parasite called Loma morhua that reduces their growth rates erodes their immune systems, and can even leave them literally belly up in the water.

The parasite forms white cysts half a millimetre wide in tissues that have high blood flow such as the spleen, heart and gills. It is at the gills that the parasites are passed on – bursting like a tiny boil, oozing out contagious microscopic spores into the surrounding water, in turn infecting neighbouring fish.

"We've developed a test that determines whether or not a cod is infected with this parasite," said Aaron Frenette, a biology graduate student who has focused much of his studies on honing that test. "What we want to do is modify the test so we can not only know whether there is presence/absence of Loma infection, but also determine infection intensity in fish via a quantitative method."

The diagnostic test employs the polymerase chain reaction (PCR). The key instrument to implement it is called a thermal cycler, which looks like a generic desktop printer without a tray to feed paper inside.

Instead, it has a tiny heating block under a lid on its upper left hand corner.

The PCR technique allows for what Mr Frenette calls "amplification of DNA", causing the tiniest sample to bloom into millions of copies. He uses the thermal cycler to repeatedly heat and cool the DNA sample in order to achieve near-natural melting and enzymatic replication – in essence, Mr Frenette and his research team use this technology to copy DNA into quantities big enough to examine easily, and have developed a parasite-specific test to go along with it in order to better diagnose the fish pathogen.

He said: "Think of it as a book with hundreds of specific pages that you want to photocopy.

"You do that by earmarking those pages, so that you have copies of the right pages to be distributed and read. It's a matter of copying the DNA of interest so that you have a high enough amount to observe properly."

Mr Frenette can then separate that copied DNA on a gel matrix to verify whether or not it is plagued by the parasites, reports NB Business Journal.

"The trouble with these parasites is not only are adult cod susceptible, but juveniles are as well," he said. "Those who survive infection have reduced growth rates, and this chronic disease can also cause mortalities within fish populations. And since this is far from the only pathogen out there that they can catch, it has become a huge problem.

"Cod aquaculture is a fairly new endeavour, and these diseases pose an imminent threat to it reaching its potential. It's simply crucial to better understand and diagnose these diseases, so we can better combat them."