Malachite Green - Lingering Poison in BC’s Native Salmon

In 1992, malachite green was banned from use in aquaculture in Canada by Health Canada, yet traces were detected in Canadian and imported farmed salmon and trout in 2005.

by Delores Broten 

This is a fishy story. Its central character is avolunteer who, in that obsessive way some humans develop, is passionate about fish. He volunteers at a coastal fish hatchery where various kinds of native salmon are reared, and traded quite widely around the coast. A fish hatchery strips the eggs from salmon returning to spawn, fertilises them, and rears the smolts until they can be released back to the stream and then the ocean. 

There are many issues surrounding fish hatcheries – do they interfere with the natural genetics of each race of salmon? Does the output of the hatcheries lead to a deceptive overfi shing of the wild stock? Are they helping or hindering truly wild fish? The Department of Fisheries and Oceans has sometimes attempted to limit the impact of hatcheries but when salmon returns plummet, citizens rise up and start enhancement of the runs with hatchery fi sh. The people of the West Coast understand the ecological terror of empty creeks. 

There’s no doubt the hatchery is an artificial environment, and one of the big problems all fi sh raised in captivity experience is disease. In this case, specifi cally, fungi growing on the eggs. 

It was while our fi shy volunteer was working with the fish eggs in the summer of 2001 that he noticed his hands had turned green. Green from the compound used to control fungus growth on the eggs. Green from malachite green. The volunteer told the Watershed Sentinel that his hands continued to turn green when he worked with the eggs for the next 3 years. They should not have. 

Malachite green is recognised among all fi sh enthusiasts as one of only three effective treatments for fungi growing on cultured fi sh eggs, the other two being high-salt water and formalin, itself a toxic, but not persistent in fi sh fl esh. 

Unfortunately for fi sh farmers and hatchery managers, malachite green (C23-H25-N2.Cl, also called benzaldehyde green or aniline green) was banned from use in aquaculture in Canada in 1992. Health Canada set zero tolerance for its residues in food.

 It is internationally recognised as a carcinogen, causing liver tumours in rats. Its breakdown product, leucomalachite, is extremely persistent in fi sh fl esh. In 2005, traces of malachite green or its metabolite, leucomalchite green, were detected in farmed salmon and trout in Canada and in imported farmed fi sh, leading the Canadian Food Inspection Agency to a program of testing samples from all imported fi sh products from Asia. 

So what was malachite green doing on west coast fi sh hatchery eggs in 2002? The answer lies with Canada’s haphazard and lax toxics regulation. Usually when a compound is banned, the ban does not take effect immediately, or distributors are allowed to sell all of their current product, and, subsequently, users to use it. This was probably the case with the hatchery in question. Further, malachite green is still perfectly legal for other uses, such as dying paper and fabric, as well as for some laboratory testing. It is also freely available from US aquaculture supply stores for about $55 US for a one lb. bottle. 

In 2005, malachite green was found in Canadian farmed salmon from two farms, one specializing in organic Chinook, near Tofi no on BC’s west coast. Neither farm could understand the presence of the contaminant in its product. With great puzzlement, the fi sh were immediately pulled from the market among assurances that levels were way below the European Union standard of 2 parts per billion. 

But are they always? Our fishy volunteer got suspicious and sent some samples of fi sh which had returned to his hatchery off to the lab in Vancouver. The fi sh were taken from among those distributed to the public for smoking or eating after the eggs were harvested from the returning salmon. Two of the three samples came back clean, but the last one was an eye-opener. Far from a minimal amount of malachite green, this prime salmon intended for public consumption registered 13.2 parts per billion of a banned “zero tolerance” substance. Not mysterious. Defi nitely, dangerously, fishy.

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[From WS March/April 2006]

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