Subedited by Dr Phil Tucak
Keeping fish is growing in popularity within Australia. The ornamental aquarium fish trade in Australia is estimated to be worth $350 million annually. Many of these animals are highly valued by their owners, not only in monetary terms but also for species conservation and as long-term companions. As such, there is a growing demand for veterinary services in this industry.
Kevin, a three-year-old white-spotted pufferfish, presents an interesting case for review. White-spotted pufferfish are found throughout Australia and the Indo-Pacific region. They are frequently kept by hobbyists in Australia and famous for their ability to distend their abdominal pouch with water or air when threatened. A common misconception is that they are poisonous when handled. Tetrodotoxins are only a risk to humans if the fish is ingested.
Kevin lived in a 4000L aquarium system with other sizeable marine fish, most of which came from the Red Sea region. Initially, Kevin’s owner contacted The Fish Vet to investigate a high mortality rate after relocating his fish to a new tank.
An outbreak of Cryptocaryon irritans (white spot disease) was diagnosed through microscopic examination of wet mounts prepared from mucus scrapes and gill biopsies. White spot disease is a common and often challenging ectoparasite encountered in marine systems. Symptoms can include small white patches on the skin, difficulty breathing, rubbing of the body, flashing the abdomen, inappetence, lethargy, hiding and a high mortality rate. Outbreaks are often exacerbated due to poor husbandry such as overcrowding, aggression, poor diet and water quality.
This case was treated successfully with quinine hydrochloride and malachite green baths at 20mls per litre of tank water once daily for four consecutive days a week. Four weeks of treatment were required. Metronidazole 10mg per litre of tank water every other day for a total of three treatments was also used. These medications were selected over more traditional treatments such as copper, as there were also invertebrates in the tank.
During the following six months, there had been no further mortalities. Then, over the course of three days, the owner noted the sudden appearance of large, flat white patches on Kevin’s skin.
Kevin then became inappetent, lethargic and dyspnoeic, he also developed hypo-buoyancy issues, and his coelomic cavity was distended. Hypo-buoyancy or sinking to the floor of the tank is often caused by the accumulation of fluid or tissue within the body.
There was a recent history of pica, with Kevin observed to be chewing on rocks within the tank. Most frequently this is caused in pufferfish due to an inappropriate diet or dental disease. The owner had also not seen Kevin defecating. Unfortunately, Kevin was found dead in the tank the morning of his consultation.
A post-mortem examination was then conducted to further investigate the cause of Kevin’s disease and sudden death. The post-mortem evaluation revealed that Kevin was in good nutritional condition. No external parasites were found. There were numerous well-demarcated areas of pale, discoloured skin dorsally, measuring approximately 10 x 5cm. Samples of the gill tissue were normal on microscopic examination.
The coelomic cavity contained a large amount of free salt water—confirmed using a refractometer, and sand. The liver was grossly normal. The first intestinal loop was perforated with a purulent discharge. Examination of the intestine did not demonstrate any other pathology, except for containing a large amount of sand.
No other foreign material was found within the coelomic cavity that could have caused a perforation. The findings indicate that death most likely occurred due to sand impaction, leading to intestinal rupture, peritonitis and septicaemia.
Pica and sand impaction has been well documented in other unusual pet species such as reptiles, axolotls and tortoises, but I have not been able to find any reports of this condition occurring in fish. Modification to husbandry and diet, along with medical and surgical management, has been shown to resolve this condition in other species.
Extrapolating from knowledge in other species, treatment options to consider could include: the administration of liquid paraffin, magnesium sulfate baths and correcting dietary deficiencies—such as vitamin, mineral or chitin. Providing materials such as clams to aid the grinding down of teeth would also be potentially beneficial, and lastly, surgical repair may also be possible.
Dr Karlee Hirakis
Dr Karlee Hirakis is a member of The Fish Vet’s team, located in Sydney and offers mobile veterinary services for aquatic patients.
Since graduating from the University of Sydney in 2013, she has worked in rural mixed and small animal practices on the central coast of NSW and in Sydney.
Dr Hirakis has kept numerous different types of fish throughout her life and enjoys the challenges that come with practising veterinary medicine in a unique environment.
At home, she is kept busy looking after her two Doberman dogs, a cat and seven fish tanks.
Dr Hirakis is a certified aquatic veterinarian through the World Aquatic Veterinary Medical Association. This program includes over 150 hours of theory and practical work in aquatic animal medicine.