Bras d’Or cod are ‘wormy’

Skyler Jeddore caught this mighty Bras d’Or cod in August, 2019.

I have been told that Bras d’Or cod (Mi’kmaq: peju) are “wormy.” The Mi’kmaw term for worm is “weti” but there isn’t a term that is specific for the cod parasitic worm.

I know exactly what a wormy cod looks like because some of my childhood was spent in a large wooden rowboat on Bedford Basin jigging cod with my father. Why have Bras d’Or cod gained this wormy reputation and what do we know about this unappealing little parasite? There is a bit of mystery associated with the cod worm in the Bras d’Or estuary which inspired a young William Black to research and publish a PhD thesis at McGill University in 1956. He followed on the heels of Dr. D. Scott who started a Bras d’Or study in 1949 to investigate the mystery of the very wormy cod in much of the Bras d’Or estuary which contrasted with the wormless cod situation in Whycocomagh Bay.

It takes a mystery like that to fuel scientific curiosity resulting in a PhD thesis or two. As is the case with many aquatic parasites, there are several hosts in this worm’s life cycle and the absence of any of the other hosts can break the cycle and contribute to a much more appealing cod dinner. So, the young Mr. Black began by looking at the other animals that lived with the wormy cod in Baddeck Bay and Kempt Head and the wormless cod in Whycocomagh Bay. He found that small shrimp-like creatures called mysids were common in the two wormy sites and less abundant in the site with wormless cod. To add fuel to that fire, he found many more mysids in the guts of the wormy cod. So, Mr. Black’s research path seemed to be clear.

According to Robin Stuart, who has a lifetime of experience in the Bras d’Or estuary, “way back when cod were plentiful the nearshore waters sometimes came alive churning with cod that were after the plentiful shallow water shrimp.” Those energetic cod were getting more than the shrimp (mysids). They were closing the lifecycle of the cod worm in the process.

Pictured is seal worm in a herring.

Now, there is another player in this lifecycle drama. It is well known that cod frequenting waters with seals have an abundance of the parasite. In fact, it is often called the seal worm. Seals are common in the Bras d’Or estuary making it easy for the little nematode (roundworm) to secure a safe place to lay its eggs.

Let’s look at the life cycle of the worm starting in the gut of the seal. The worm that we are looking at is a close relative of the worm that you avoid by not eating raw pork (Ascarid). The adult seal worm lodges itself in the stomach of marine mammals such as seals. Eggs produced by adult females are passed in the seal droppings. The eggs hatch in the water and larvae emerge. Mysids and other small creatures eat the worm larvae which then grow inside their bodies. The larval worms migrate from the fish’s intestine to its muscles. Local fishers have told me that the worms can also appear in herring and haddock. These species probably fit into food webs similar to the one of the Bras d’Or cod. If the fish is then eaten by a mammal, the worm can often complete its life cycle within its warm body and grow into an adult. We know what happens if that final host is a marine mammal such as a seal. The cycle continues on as I have described.

What if that mammal is a human, excited to feast on his/her ‘catch of the day’? Many fishers look at the worms as extra protein which is the case if the fish is properly cooked (fillet temperature of 63o C or higher) or solidly frozen. If the fish isn’t cooked well or frozen solid, the live worm larvae can penetrate the intestinal mucous membranes of the unsuspecting connoisseur, causing various unpleasant symptoms such as nausea and abdominal pain.

Joe GooGoo, who has fished Bras d’Or cod all of his life, feels that the cod in Whycocomagh Bay remain worm-free because of the lower salinity. Perhaps that is why the worm life cycle is broken in that bay. The mysids that cod crave do not like the fresher water. Robin Stuart has sent along a bit of advice. He says that Bras d’Or trout may be a better choice for fish eaters who are not too fond of seal worms. The trout are not part of that life cycle.

Dr. Annamarie Hatcher is a consulting ecologist and a board member of the Bras d’Or Lake Biosphere Reserve Association (BLBRA). For more information about the Bras d’Or Lake Biosphere Reserve Association, please visit: http://blbra.ca/or our Facebook page: (https://www.facebook.com/blbra/).