The other day I did the first few hours of my required 50 hours of undergraduate demonstration. Which involves being present at, and assisting with undergraduate practices. Luckily enough for me it was an old favorite of mine, the good old fish dissection. The aim of the practical was for the undergrads to familiarise themselves with morphometrics, dissection and otolith extraction. The dissection species was the Atlantic mackerel (Scomber scombrus) which were freshly caught. S.scombrus are a commercially important pelagic fish in Europe. The pelagic schooling species can be found on both sides of the North Atlantic ocean. S.scombrus is by far the most common of the 10 species of the family caught in British waters. S.scombus is extremely common in huge shoals migrating towards the coast to feed on small fish and prawns during the summer.
So as the practical got underway, I was wondering around the class occasionally answering questions or just watching the dissections. While one undergrad was asking if they had cut the fish correctly, which they had, we noticed some movement in the fishes muscle. It was a nematode, about 3-4 centimeters long, and then there was another and before you knew it there where worms crawling out of pretty much every fish in the class. Now it’s not surprising to find parasites in freshly caught marine animals, but the size of these worms was new to me. I know I’ve mentioned I’ve worked with nematodes before with Dr. Rae at good old LJMU, but them worms, Phasmarhabditis hermaphrodita were small rarely reaching 1cm. So seeing a 4cm worm coming out of the cavities and muscles of these fish did surprise me, and I know animals can have much larger parasites and worms, but I guess I just got used to seeing smaller worms such as Phas.
I was interested a few weeks ago about parasites that I could encounter when doing fieldwork on Brown trout (Salmo trutta). As I know there is a degree of dissonance between research groups in regard to the effect of salmon farms and sea lice infections, and while I was looking up parasites, I thought I may as well look at nematodes that affect these fish, a few different species came up, Anisakis and Phocanema decipiens seemed to be the most cited, therefore I assume the most common in anadromous and marine fish. So I looked up some facts on these nematodes, both are zoonotic, therefore can be transmitted to humans. However are usually asymptomatic in healthy individuals, although they can cause diarrhea, vomiting and stomach pain. I knew that the giants that came out of the mackerel were probably not Anisakis as the species in this genus usually grow to around 1.5 to 2cm, and our worms were double this. So that narrowed it down, I remembered that P.decipiens grew to that length, so I looked up other large parasites in S.scombrus and all the literature was suggesting that it was indeed P.decipiens. I just thought it was really cool to see these parasites, and eventually so did the undergrads. It was amusing to see a lot of them going from looking horrified at these worms to actually being quite keen on adding to the petri dish that i was collecting a few of the worms in just to show other undergrads and talk about zoonotic infections and parasitology.
I just thought I’d blog about this as it reminded me of the work I did back with Dr. Rae in lab 333 in LJMU. I was just amused as I found myself getting as excited about these fish parasites in the same way he got excited by finding Phas or other slug and snail parasitic nematodes.