Thursday, August 19, 2010

Veterinary fact of the day: fish medicine

Today we had a lecture on fish medicine. The veterinarian who gave the lecture told us that she went to vet school so that she could work with fish. It must have been frustrating to her to have only two hours total devoted to her species of choice. And here I get frustrated when I have to learn about pigs.

What should I share with you about fish? Turns out that if you want to draw blood from a fish, you are in trouble; phlebotomy is “not routine” in fish. You can do it with bigger fish (“bigger than a salmon,” she says, assuming we all know exactly how big that is) by drawing from the caudal vein (back near the tail). In smaller fish you have to draw from the heart, which is terminal. So if you have small but valuable fish, you keep an extra to sacrifice (a sentinel animal), for use in diagnosing problems that affect all or most of your animals.

Valuable fish? Sure, koi can get very valuable. Of course, fish farmers consider their stock to be valuable overall, even if individual animals are not. And laboratory research is done on fish, so you have herd health issues there, too.

Speaking of research on fish, the lecturer mentioned in passing that you can measure stress in fish by measuring the cortisol in the water. Then she left before I could ask for more information. Here is what went through my head: Cortisol in the water! They must pee it out. Wait, they don’t pee, I bet it comes out of their gills. I bet it is not cortisol, I bet it is cortisol metabolites. Amazing that they use cortisol just like us, not even a cousin like corticosterone. Why do people measure it, I wonder? Some sort of diagnostic reason — to tell if the fish is sick, maybe? Or is it used as part of stress research studies? How similar is the fish HPA to the mammalian HPA? Ah, if only I had time to wander Google Scholar, reading random papers, as I did a week ago.

What I did today
Up extra early. Gym! (It seems to prevent the stress headaches, which I imagine will go away when I readapt to the pace of vet school after a year away from it.) Suture practicing with classmates. Two hours of small animal medicine lecture (the last of the cardio unit). Lunch! (Tried to catch up on science blogs reading.) Two hours of anesthesia lecture. Two hours of zoo medicine lecture (fish medicine). Suture practicing with an ex-classmate who already knows it all. Home!


  1. I am not sure if it's urine, or if the stuff just leaks out through gills (adults) and skin (larvae).

    A friend of mine, many years ago, designed an automated system in which Zebrafish larvae were kept in a 96-well plate, one animal per well, each in some water. A pump would take a little bit of water every couple of hours (and replace the equal volume with fresh water) and store the aliquots for the melatonin assays later on. That way one could monitor (by measuring melatonin cycles) circadian rhythms in zebrafish larvae over several days and see what happens to the rhythm when something is done to the animals - a shift in light cycle, etc.

    One also needs to take the blood directly from the heart in snakes - but in them it is not terminal, just cannot be done too often. Search my blog for "copperheads" for an anecdote about an experiment we tried to do...

  2. Yes, I realized after I posted this that I really have no clue about where urea goes post-kidney in the fish. They do have kidneys, but do they have urinary bladders and ureters and the like? Lecture was uninformative.

    Circadian rhythms in zebrafish larvae: very cool! I need to post what I learned last year about circadian rhythms of cortisol in dogs at some point. (In my Copious Free Time.)