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.
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