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Wow! Look how much I miss when I take my kids out for dinner

Posted By: Dr. Momfish <alexp@idirect.com>
Date: Saturday, 27 March 1999, at 12:14 p.m.

In Response To: Re: Hmmmm... (Alistair)

I was going to write this in my own words, but I'll copy the relevent passages from "An Introduction to the Biology of Marine Life" by James L. Sumich. pp13-14

"The salt concentration of a salmon's body fluids, like those of most other bony fish, is intermediate between fesh water and seawater. As such, the body fluids are hypertonic to fresh water and hypotonic to seawater. Thus these fish never achieve an osmotic balance with their external environment. Instead, they must constantly expend energy to maintain a stable internal osmotic condition quite different from either river or ocean water. In seawater, salmon lose body water by osmosis and are constantly plagued by problems of dehydration, even though surrounded by an ocean of water. To counter this, salmon drink large amounts of seawater, which are absorbed by the digestive tract. The water is retained in the body tissues, and excess salts are actively excreted by special chloride cells located in the gills. Since the kidneys of salmon are unable to produce urine with a salt concentration higher than that of its body fluids, they are of no use in getting rid of excess salts.

When in freshwater rivers and lakes, the osmotic problems of salmon are completely reversed. Here the problem is largely one of osmotic water gain across the gill and digestive membranes, and a steady loss of salts to the surrounding water. Salmon drink very little fresh water, although some is inadvertently swallowed with food. To balance the inflow of water, the kidneys produce copious amounts of dilute urine after effectively recovering most of the salts from that urine. Needed salts are obtained from food and also are actively absorbed from the surrounding water through specialized cells in the the gills. Thus, at considerable expense of energy, salmon maintain a homeostatic internal fluid environment in either river or ocean water."

All freshwater fish must expend energy to maintain homeostatic equilibrium within their bodies.

Most books written for the hobbyist don't go into a lot of detail when it comes to fish physiology and biochemistry. Most hobbyists are not going to wade through all kinds of seemingly irrelevent material. If you are looking for books that address all kinds of these subjects you will have to go to a university bookstore - a university where zoology is studied. Unfortunately textbooks are prohibitively expensive and contain an overwhelming amount of information. So, sites like LOL are a great way to find answers to questions and problems. I've noticed that there are all kinds of people participating in discussions. They have knowledge and experience in subjects that are either directly related to the keeping of loaches and other fish, or subjects that can be applied to the hobby in its entirety.

Bravo for LOL!!!
 

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