Histological and computed tomographic evaluation of a parasitic conjoined twin in hybrid catfish (Ictalurus punctatus [Rafinesque] X Ictalurus furcatus [Lesueur]).

There is growing use of hybrid catfish (Ictalurus punctatus ♀ X Ictalurus furcatus ♂) in commercial aquaculture to utilize hybrid vigour to improve production A conjoined twin specimen found during the course of production studies by the United States Department of Agriculture Catfish Genetic Research Unit (USDA-CGRU) was submitted to the Aquatic Research and Diagnostic Laboratory (ARDL). After preliminary inspection, it was transported to Mississippi State University, College of Veterinary Medicine for further evaluation. The specimen was examined using both computed radiography and computed tomography antemortem. Following humane euthanasia, the specimen was examined both grossly and histologically. Tissues from both fish were also submitted for genetic analysis to determine whether twins were derived from the same egg. This report records the presentation and examination of a pair of conjoined hybrid catfish (I. punctatus X Ictalurus furcatus).

Physiological and biochemical effects of acute exposure of fish to hydrogen sulfide.

1. Exposure of channel catfish to 0.5 mg/l H2S at 20 degrees C resulted in hyperpnea, followed by apnea, and finally respiratory arrest. 2. Catfish brain cytochrome oxidase activity was inhibited in vitro 18% by 10(-7) M H2S, 64% by 10(-6) M H2S, and 100% by 10(-4) M H2S. 3. When channel catfish were exposed to 0.1 mg/l H2S at 20 degrees C for 30 min, the cytochrome oxidase activity of the brain was inhibited 40% and that of the gill was inhibited 74%, while blood lactate rose from 11.6 to 38.1 mg/100 ml. 4. Catfish with nitrite-induced methemoglobinemia showed less inhibition of brain and gill cytochrome oxidase when exposed to hydrogen sulfide than did control fish. 5. Sulfide-inhibited brain cytochrome oxidase recovered from a 50% inhibition to control levels in channel catfish after 6 hr in freshwater at 10 degrees C. 6. Management practices are recommended which may help the commercial fish farmer alleviate the problem of the toxicity of sulfide to fish during harvest operations.