Location: Warmwater Aquaculture Research UnitTitle: When more is actually less-the tale of chronic ammonia toxicity
|KHOO, LESTER - Mississippi State University|
|STEADMAN, JAMES - Mississippi State University|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/18/2015
Publication Date: 3/1/2015
Citation: Khoo, L., Brown, T.W., Steadman, J. 2015. When more is actually less-the tale of chronic ammonia toxicity. Meeting Abstract. P. 8.
Technical Abstract: A commercial catfish producer submitted 7 food-sized fish from a pond that was experiencing mortalities on Jan 24, 2014. The ~ 2.64 acre pond was stocked with hybrid catfish. No gross external lesions were evident except for linear erosions (scratches) on the skin that were thought iatrogenic in origin. Internally, 5 out 7 fish had intestinal intussusceptions and mildly congested spleens. Bacterial cultures of the brain and posterior kidney were performed and these were negative. Although Visceral Toxicosis of Catfish(VTC) was unlikely, bioassays were conducted because of the internal lesions and these were negative. Water quality analysis indicated an elevated Total Ammonia Nitrogen (TAN) - 5.0ppm. This pond was enrolled in production study in March of 2013 had been stocked at approximately twice the industry average with 12,915fish/acre with stockers weighing 98lb/1000fish. Water quality analysis conducted once every two weeks showed TAN levels above 10ppm starting Nov 6, 2013 to Jan 14, 2014 with a high of 11.1 ppm on Dec 3, 2013. Representative samples of brain, gill, spleen, GI tract, liver, eye, muscle and skin as well as the anterior and posterior kidney of 4 of the 7 fish were fixed in 10% neutral buffered formalin. Significant microscopic lesions were limited to liver and posterior kidney. Most of the pancreatic acinar cells were degranulated and there was severe to marked multifocal mononuclear pancreatitis. There was also mild to severe macro and microvesicular hepatocellular vacuolation. Renal tubular cells were vacuolated with rare accumulation of eosinophilic hyaline material in some of these tubules. Unfortunately, the losses occurred close to the time of harvest(survival 61.7%)adversely affecting the feed conversion ratio (3.62; above industry average) although the net production was still relatively good 13,233 lb/acre (twice industry average).