As some of you may have heard (because I mention it constantly), I'm doing a thesis project on Discus! Specifically, as an Honors student at my university I'm required to complete some kind of thesis project related to my major in conjunction with a faculty advisor. My major is marine science/aquaculture, and one of my good friends at the university (a professor who teaches Biology of Fishes and Biology of Sharks among other classes) happens to be an avid freshwater aquarist like me, so I approached him about doing a project on discus. We chose discus because they are quite poorly studied due to their expense and relative difficulty of care, yet they are an important and growing part of tropical aquarium aquaculture. With both of our backgrounds in freshwater fishkeeping, we felt it was a challenge we could take on in order to break some interesting new ground with these fish.
The broad focus of the project is examining immunological aspects of discus mucus. There are quite a few reasons for doing this. Fish mucus in general is an important aspect of fish's immune health- the mucus itself is a barrier to pathogens, and also contains various innate and adaptive immune factors that are secreted into it by the fish. We are still discovering all kinds of new ways that fish mucus stops pathogens. In discus, the mucus is also used as a food for fry, which makes them a particularly interesting object of study, since very few other fish do this. Also, discus are both expensive and awesome, so studying their mucus (as opposed to studying, say, their blood or tissues) allows us to get samples without killing the fish. This means we can get a lot of data from a small number of fish.
There's some broad questions this research is going to be looking for answers to, or at least clues to answers. The very first of these is, how does protein expression in discus mucus vary with different physiological factors? We'll be looking at a couple of different circumstances- juvenile, adult, stressed (controlled and limited stress under safe lab conditions), and spawning (throughout the spawning process). We'll be using gel electrophoresis to sort the proteins by molecular weight and look for patterns of expression- basically, looking for proteins that might be showing up in multiple circumstances, vs ones that are only showing up under one condition. After we look at patterns of expression we can start narrowing our research based on what we find with that.
Two major hypotheses, the dumb one (mine) and the smart one (my advisor's): The first is that there will be a significant overlap in expression between stress response and spawning responses. This is because fry do not yet have fully functional immune responses- particularly an adaptive immune response- and so the mucus must be as free from pathogens as possible to protect the fry. It's also a stress on the parents as they are bitten constantly by the fry. The 2nd hypothesis is that we expect to see IgT- a form of antibody unique to fish- being passed from the adults to the fry through the mucus. This is because in other fish, it has been found that the eggs receive deposits of other antibodies as sources of nitrogen and an initial boost to adaptive immunity. We suspect that discus may do the same but through their mucus, and IgT is specifically a mucosal antibody. It might help explain why the survival rate for non-parentally reared discus is so abysmally low.
Over this summer, while I'm playing around with parasite-infected lobsters, I'll also be working on this. I've got a 125 gallon growout tank, several 55 gallon tanks set aside for spawning pairs, and access to a stupid amount of RO
water. The research will likely be going on for the next year and a half, finishing right around the beginning of my final semester at university. This summer we'll at least get some results on juvenile discus, and as the discus mature and hopefully I can get them to spawn, we'll collect that data and use it to figure out where to go next. Ultimately we'd like to get this research published in a scientific journal.
I imagine that many of you might be interested in this, since many of you keep discus, and because aquarists tend to be big fans of science. I'm going to be doing this kinda like a build thread, keeping you updated as I go and showing off any cool results I get. If any of you have questions, I'd love to answer them! If you have suggestions, criticisms, whatever, I'd love to hear it! I want anyone who is interested to feel involved with what I'm doing.
Geez, that was a gigantic wall of text. Anybody still with me? I hope that you guys are interested and that you'll stick around as this project progresses! Thanks for reading and being interested!