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Fish Parasites

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Monday, December 4, 2017

Summary: Matt Woodstock discusses how parasites can affect deep-sea fish, even in environments which are hostile toward them.

My name is Matt Woodstock and I study parasites in fish.

What is a parasite? A parasite is an organism that lives on or inside another animal (called a host) and derives nutrients at its expense, often resulting in death. An example of a land parasite is a tick that might live on your dog or cat. Some parasites steal nutrients from the tissue or blood. Others sit inside the intestine and eat the food the animal is digesting. Where a parasite lives, what it eats and how it gets into the host depends on the kind of parasite.

The food web is a complex network of organisms that interact within an ecosystem. Parasites are important members of any ecosystem because they steal food from the host, complicating the flow of carbon from one trophic level to the next. Parasites traverse through the food web by making the host they infect more susceptible towards predation. Fishes that have parasites often have slower growth rates, reduced reproductive output, and may behave erratically. Deep-pelagic fishes (deeper than 200 m (656 feet) and off the continental shelf are rarely studied for parasites and little is known about which parasites exist in this realm. Furthermore, we do not know very much about the effect these parasites have on host fishes. Knowing which parasites infect certain hosts and how intensely fishes are parasitized is critical in our understanding of the deep-pelagic food web and the flow of carbon from one trophic level to another.

There are not as many parasites in the deep-sea fish as there are in fish near shore or the ocean floor. This might be because the fish we’re catching do not live as long. Deep-sea fish also do not come across food as often as fish that live in other parts of the ocean. Therefore, the odds of contracting a parasite could be lower.

So far, I have found a bunch of weird looking parasites of different sizes and shapes. They appear to have a huge effect on the fishes they infect, too. Some of the parasites I’ve found live in a fish’s stomach and can grow as large as the stomach itself. If the parasite takes up the entire stomach, the fish will die from the lack of nutrients. No matter how much it eats, it won’t be enough.

Another thing I have found is that larger kinds of fish have more parasites than smaller ones. We don’t know exactly why this happens. It might mean that parasites stay in the host for a long time. Or fish that eat larger prey pick up more parasites. Or it could mean both. That’s the fun part of being a scientist. It is sort of like being a detective. We keep gathering clues until we solve the mystery. Often, discovering the answer to one question leads to another question. Knowing about the parasites that infect fishes is critical to our understanding of deep.

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