Pathophysiology of experimental Aeromonas hydrophila infection in goldfish, Carassius auratus (L.) (original) (raw)

1986, Journal of Fish Diseases

Fish farming for sport or food has grown rapidly in the past 25 years. The incidence of disease outbreaks among pond-cultured fish has also increased (McDaniel 1975). Most baeteriaassociated fish deaths occur in late winter and spring in hatchery and wild fish populations. Decreased immunological resistance offish in these seasons is attributed to reduced winter feeding and subsequent low antibody levels (De Figueiredo & Plumb 1977). One of the common fish bacterial disease syndromes, motile Aeromonas septicaemia (MAS) is caused by Aeromonas hydrophila. An outbreak of MAS among wild or pond-raised fish is difficult to control despite corrective action by fish biologists. It appears that once the infection is established, rapid growth of the bacterium and elaboration of its toxic products may cause irreparable systemie damage which leads to death. The present study describes the pathophysiological ehanges associated with MAS infection of goldfish during the first 36 h following infection. Strain AM3 was obtained from D. H. Lewis, College Station, Texas, USA. This isolate (LD,o 5x10^ cfu) produeed 72% mortality in goldfish within 48 h (92% within 72 h) after intramuscular inoculation of 1-5x10^ efu. Comet goldfish, Carassius auratus (L.), 7-9 cm length, were obtained from commercial suppliers and were treated prophylaetically with Maracyn-Two and Marieide (Mardel Laboratories Inc., Villa Park, Illinois, USA) for 3 days. For experimental studies, strain AM3 was grown 18 h at 20°C in brain-heart infusion broth (Difco, Detroit, Michigan, USA); the cells were pelleted, washed once in saline and resuspended to 40% transmittance at 435 nm (3x 10^ cfu/ml; Spectronic20 spectrophotometer, Bausch and Lomb). Goldfish were injected intramuscularly (im) with 50 jul of the bacterial suspension (1-5x10^ efu) into the left caudal peduncle using a Hamilton syringe. Control goldfish received an inoculation of PBS. Histological, bioehemical and haematological studies were made with groups of 130, 60 and 50 infeeted goldfish, respectively. The details of each experiment are described. For evaluation of histologieal ehanges, 130 goldfish were injected at time zero with 50 //I oiihcA. hydrophila suspension and 60 goldfish were injected with 50 //I PBS. Three infected fish were killed by severing the dorsal aorta each hour for the first II h. Six infeeted and control fish were killed at 12, 24 and 36 h. Animals surviving beyond 36 h were killed at 72 h. Samples of the spleen, liver, heart, mid-kidney, duodenum and musele from the injection site were then removed and fixed in 10% neutral buffered formalin, embedded in paraffin wax.