Abstract

The National Aquarium in Baltimore obtained four John Dorys, (Zeus faber) from Sea Life Centre, Weymouth, Dorset, England in early September 1989. These fish arrived with a heavy infestation of free living and anchored copepods. They had multiple epidermal ulcers from the parasites and transport trauma. During the days following arrival the fish were treated with 0.01% formaldehyde dips to remove the external parasites. Approximate 98% of the parasites were removed with the first dip. The remaining copepods dropped off with a second dip.

Because these fish had darkened skin, ulcers and hemorrhagic fins they were placed on antibiotics. During the following 2 weeks, 3 of the fish died. Gross postmortem examinations revealed numerous motile protozoan parasites in the liver, intestinal tract and kidney.

Metronidazole therapy was initiated in the remaining John Dory after the protozoans were discovered in the autopsy specimens. Three days following treatment skin color improved and ulcers began to heal. The fish's appetite improved rapidly and the animal has remained healthy for two month.

Histopathology of tissues collected from the dead fish that showed numerous protozoan parasites in the liver, intestines, swim bladder, spleen, kidney and gills. These parasites resembled Uronema spp. in the tissue sections. Some of these parasites were intravascular, indicating possible hematogenous spread.

This case report demonstrates the importance of a complete gross postmortem examination for diagnosis and subsequent therapy. Histopathology in such cases not only confirms the gross findings, but also characterizes the full extent of the disease process and the host response.

History

The National Aquarium in Baltimore obtained four John Dorys, (Zeus faber) from Sea Life Centre, Weymouth, Dorset, England in early September 1989. These fish arrived with a heavy infestation of free living and anchored copepods. They had multiple epidermal ulcers from the parasites and transport trauma. Their skin appeared dark, which can be a sign of stress in these animals.

On the day following their arrival one fish (#l) became moribund and was given 10 mg Chloramphenicol IP. Later that day it was euthanized and necropsied. The remaining animals were given 0.01% formaldehyde dips to remove the external parasites. Approximate 98% of the parasites were removed with the first dip. The remaining copepods dropped off with a second dip. Because the fish had large ulcers, tetracycline was administered in food fish (10mg/food fish). This form of treatment was chosen to decrease the amount of handling stress, unfortunately feeding was sporadic at best.

Four days after arrival, onefish (#2) developed hemorrhagic fins. Its color was still dark and it was not eating. Multiple ulcers were present over the body. No parasites were seen on a gill biopsy and skin scraping. Chloramphenicol (10 mg IP) was administered but the fish died later that day.

Two weeks after arrival the third fish (#3) died. That fish and the remaining living fish had been receiving tetracycline medicated food fish but had eaten infrequently.

Based on the postmortem findings in the first three fish, the last John Dory was treated with Metronidazole (250 mg/gal). This dose was diluted by 10% water changes over the next several days. Within 3 days the skin lost its dark coloration and the fish started eating well 7 days following treatment. This fish remains healthy and is on display at the National Aquarium in Baltimore.

Gross Pathology

 Fish 1 Ciliates noted in gills and intestines.

 Fish 2 No ciliates noted, metazoans noted in intestines.

 Fish 3 C Ciliates noted in liver, stomach and intestines.

Histopathology

Fish 1 Protozoans were noted in gills, swim bladder and liver. Some of these parasites were located within blood vessels. Multiple cestodes were found in the intestines. Iron pigment was demonstrated within the apex of the intestinal epithelia] cells.

Fish 2 A cestode was encysted in the peritoneal cavity. Iron pigment was also present in the intestinal mucosa. Renal tubules contained large hyline droplets.

Fish 3 Protozoans were observed in parenchyma and blood vessels of liver, stomach, intestine, swim bladder and spleen. Iron pigment was also present in the intestinal mucosa. Renal tubules contained large hyline droplets.

Figure 1. Multiple parasites located in hepatic veins. (H&E X400)

Discussion

This case report demonstrates the importance of gross postmortem and histopathologic findings when diagnosing fish diseases. The fourth John Dory was treated with metronidazole because two of the fish had definite protozoan infections. The protozoans in fish 1 and 3 were frequently located in parenchyma and blood vessels of the intestinal tract. Iron in the intestinal epithelium may have been resorbed following hemorrhage and hemolysis induced by the parasites. All the fish had iron pigment in the intestinal epithelium. Although no protozoans were noted in fish 2, the disease process appears to have been similar in this fish.

Metronidazole is a synthetic antibacterial and antiprotozoal agent. The parent compound and metabolites posses in vitro bactericidal activity against many anaerobic bacteria (PDR 1989). It is also an effective treatment for several types of protozoan infection in humans and animals (Gilman 1980, Kirk 1983).

The response in this fish to the treatment was dramatic. It is uncertain, however, if the improvement was due to the antimicrobial, antiprotozoal or a combined effect. Some microbial infections are associated with protozoan infections (Jacobson, 1983). It is possible that the such an association was present in this case.

References

1.  Gilman, A.G., Goodman, L.S., Gilman, A., The Pharmacological Basis of Therapeutics. MacMillan Publishing Co., Inc., New York. 1980.

2.  Jacobson, E.R., Parasitic diseases of reptile. In: Current Veterinary Therapy VIII. Kirk, R.W. (ed). Philadelphia, W.B. Saunders Co., pp. 599-606,1983.

3.  Kirk, R.W., Current Veterinary Therapy VIII. Philadelphia, W.B. Saunders Co. 1983. Physicians' Desk Reference, 44ed, Barnhart, E.R., Medical Economics Company, Inc. Oradell, N.J. 1990.