North Carolina Veterinary Diagnostic Laboratory--Real World Example

Here is a good example of the work at the North Carolina Veterinary Diagnostic Laboratory (NCVDL). This article was taken from The NCVDL Report Volume 5 Issue 1 and written by Dr. Richard Oliver, Director of the Arden Laboratory in Fletcher.

Western North Carolina was subjected to abnormally low temperatures from late December 2009 through January 2010. Over a two week period that coincided with the onset of sub-freezing air temperatures, an owner reported losing around 30 common carp. The fish were swimming at the pond's surface while lying on their sides. The fish were able to swim away when approached. The pond had a very high stocking density with about 50,000 pounds of fish in approximately 3-acres. It had an iced over surface covered with snow during most, if not all, of this episode.

One 26-lb female carp was submitted for laboratory evaluation. She had a good amount of flesh with respect to skeletal muscle mass yet there was virtually no visceral fat present. The gastrointestinal tract was devoid of content and the majority of the body cavity was dominated by an expanded air bladder along with a vast amount of ovarian tissue which showed some indication of deterioration. Mucus scrapes and gill preps indicated low parasite numbers. Histopathology confirmed widespread, chronic ovarian degeneration. The diagnosis was Dystocia.

In spawning, fish dystocia is the lack of spawn coupled with the non-resorption of eggs in the body cavity. Ovarian swelling induces impingement on the pneumocystic duct and the fish's ability to pnuemoregulate is impaired. (The air bladder swells and can not be properly deflated--you try diving with a life preserver)! Increased pressure in the body cavity also leads to a decrease in feed consumption and ultimately, liver and kidney malfunction. The condition is greatly exacerbated by extreme cold with water temperatures below 37 ^oF being the critical point.

Special thanks to Jeffrey Hinshaw, Ph.D. Associate Professor and Extension Specialist at the Mountain Horticulture Crops Research Station for his assistance on this case. Thanks also to Dr. Richard Oliver for allowing me to post his article to my blog.

Salt as a Treatment for Fish

Salt is a common and relatively inexpensive treatment for fish. The use of non-iodized table salt or rock salt (suitable for consumption by humans or livestock) is acceptable for treatment. For ease of application, many pond owners use 50 lb salt brine blocks. "Brine" blocks are salt blocks. Granular salt can also be purchased in bags or bulk.

Seawater contains 3% (30,000 ppm) salt concentration. Two hundred ppm (200 ppm) to 500 ppm can be used as an indefinite treatment in ponds to relieve stress. Ten thousand ppm (10,000 ppm) to 30,000 ppm can be used as a prolonged treatment in tanks for 30 minutes or until fish show signs of stress. Thirty thousand ppm (30,000 ppm) can also be used as a quick dip (60 seconds) in treatment tanks. To achieve 30,000 ppm in a tank, you add 2 1/2 lbs of salt for every 10 gallons of water. For ponds, 1 ppm is equal to 2.7 lbs/acre-ft of water. You need to know how many acre-feet of water you have in your pond (surface acres x average depth) to determine the treatment rate.