Sodium and Hypertension in Marine Fish
By Lew Wirelewski
Sodium has been identified as an important component in vascular hypertension and is the main contributing factor in hypernatremia. Levels above 180 mEq/L1 in blood serum are often attributable to high mortality rates in humans. The USEPA has set a secondary maximum contaminant level of 250 mg/L2 for drinking water.
Hello everyone, Iím Lew and I suppose you were expecting an article on marine Polar Bears. Unfortunately when we had an Amber alert called on my missing little sister the police came to the house and saw my bear tank. They called in animal control because there was some sort of ordinance against keeping Polar Bears in my town. They forced me to get rid of it. Youíd think the police would be more interested in finding my missing sister, it has been over a year now, than bothering defenseless bears. Anyway I checked and saltwater fish are allowed around here so I started a FO (fish only) tank. I had lots of spare equipment from the bear tank so it didnít cost very much.
While reading through Reefkeeping Magazine, I found an article by Randy Holmes-Farley3 where he said that saltwater contained 10,800 mg/L of sodium. Wow, I read that sodium for humans should be less than 2.300mg/L per day4 and my fish are a lot smaller than even I am. That left me thinking and I saw there were only limited options. I could get some really big fish like a Giant Tuna but they are not all that colorful. I could find something to replace the sodium in the saltwater. This I tried but it really didnít work out all that well. I figured that salt substitute might work but I was watching a PBS show5 and they were using potassium, the same stuff in salt substitute, as part of the drugs used in lethal injections for the condemned. That didnít sound too promising. A RO/DI would remove it but then why mix in salt mix in the first place? I placed some hamster watering bottles in the tank with fresh water but they fish didnít seem to drink it nor did they wash their food with it before they ate it. I swiped some cesium from the high school chemistry lab but I had no idea that it would wreck the basement when I mixed it with water. Boy was my mom mad and I would have been grounded if I wasnít in intensive care for three weeks after that experiment. Clearly there must be a better way, so I thought about the problems that it causes and that is high blood pressure. Maybe I could just treat the fish to control it?
To test this out I set up two 20-gallon (74.7L) fish tanks and filled each with artificial seawater mix (Instant Ocean, Aquarium Systems Inc., Mentor, OH); mixed to specific gravity 1.026 using RO/DI water (Culligan, Rosemont. IL). I used Visatherm heaters and Seaclone skimmers, which surprisingly were unbroken from being used in the bear tank, in each aquarium. Into each tank I added ten 4-striped Damselfish Dascyllus melanurus, (K-Mart, Pet Section). I selected damsels as this species is hardy and cost less that $5 at any K-Mart. The fish were fed freshly chopped frozen cod mixed with some spinach (Kroger, Cincinnati, OH). The fish were kept for two months to check out for signs of disease. The one group was given Monopril (My step dadís nightstand) and the other control group Tic-Tacs (Ferrero USA, New York, NY) as a placebo. The Tic-Tacs were selected as they look like Monopril tablets and my step dad wouldnít notice the switch when he took his daily dose. He did remark they had improved the taste of his blood pressure medicine to my Mom.
I first tried to use both the Monopril and Tic-Tacs whole but the Damsels couldnít swallow them. I also figured two tablets daily might be too much for a small fish. I therefore chopped up the tablets and mixed them into the food. This worked well but it made it difficult to tell the dose each fish received. Being Damsels they fight a lot and not all would get the same amount of food. I wanted to take the blood pressure on both the treated fish and the control but they donít have blood pressure cuffs that small. My friend, Waterkeeper, once mentioned they had small ones they used on him when they were testing his E.D. (no explanation necessary) but they donít seem to carry them at Walgreenís. I therefore carefully watched each group of fish for signs of a heart attack such as pains radiating out to their left pectoral fins or shortness of breath. During the trial neither group seemed to show any symptoms. The experiment lasted for about 15 weeks but I was forced to abandon it at that point as I could not get anymore Monopril. My step dad had a coronary and passed away about two months into the experiment and I therefore had no way to obtain more pills. My mom will be going to the doctor soon and maybe they will find out she has high blood pressure and I can resume my research.
Do to the short length of this experiment it was impossible to tell if medicine for high blood pressure is a proper treatment regime for fish. It does appear to be beneficial for humans as my step dad illustrates. At the moment I cannot recommend its routine use on fish. I notice that one Visatherm heater does have a crack in it so I may get a grounding probe. That way I can replace that heater and only turn the broken one on if I see a fish having a heart attack.
I wish to thank Waterkeeper for helping me with this article as it is part of my science project for 7th grade. He wrote the opening paragraph so youíll need to ask him what hypernatremia means. Also, to my classmate Mary Ellen Easydate who allows me to play doctor with her after school.
1 New England Journal of Medicine, Vol XI, Oct. 1991
2USEPA, Secondary Drink Water Standards, U.S. Government Printing Office
3What is Seawater, Randy Holmes-Farley, Reefkeeping, Nov. 2005
4Readerís Digest, Laughter, the Best Medicine, Mar, 2008
5Frontline, Executionerís song