What is Dropsy?

I am contacted often regarding fish who have dropsy. Now what is dropsy? Dropsy is coelomic distention due to ascites, or the effusion and collection of fluid freely throughout the coelomic cavity (1). Sometimes, you can see protrusion of the scales that causes them to stand erect from the body, causing lepidorthosis or "pine-cone" appearance (1). Now what is a coelom? A coelom is a single body cavity which is found in birds, many species of reptiles, and of course fish. We as humans have body cavities which are divided into a thoracic cavity and abdominal cavity. For the sake of this talk, we will consider the coelom to be similar to the abdominal cavity.

Dropsy is more of a clinical presentation of disease rather than a disease entity (1). There are several differential (differing) diagnoses that lead to a build up of fluid in the coelom or that cause coelomic distention.

Differential diagnoses for coelomic distension (2):

1. Obesity

2. Hepatomegaly (enlarged liver)

3. Normal ovarian or testicular development

4. Genetic predisposition for polycystic kidney disease

5. Neoplasia/cancer - gonadal and hepatic (liver) neoplasia are most common

6. Nutritional deficiencies

7. Infectious: viruses (rhabdoviruses, infectious pancreatic necrosis, carp edema virus, some herpesviruses, etc), bacterial (vibriosis, Aeromonas, Citrobacter, Pseudomonas, Edwardsiella, Flavobacterium, Mycobacterium, etc), Fungi/fungal-like, Parasites (Protozoa, Metazoan, Myxozoa, Apicomplexa), etc.

8. Inflammation: vasculitis, peritonitis, steatitis, etc

9. Idiopathic: congestive heart failure, egg retention, dystocia, chronic liver disease/polycystic liver, chronic kidney disease/polycystic kidney disease

10. Toxin(s)

11. Trauma

12. Life support system/environment/water quality: high pH

As you can see there are a multitude of possible causes for dropsy/coelomic distention. Now considering all these different causes would explain why some fish respond well to one treatment but others don’t. This is where an aquatic veterinarian can help guide therapy. Through their physical exam, water quality testing, and diagnostics they can hopefully determine etiology (underlying cause), diagnosis, and prognosis. Once a diagnosis has been made, they can present the best treatment plan going forward.

Thanks.

- Robert Martinez, DVM, CertAqV

Sources:

1. Densmore, Christine L. “Coelomic Disorders.” Fish Diseases and Medicine, edited by Stephen A. Smith, CRC Press, 2019, pp. 174-182.

2. Hadfield, Catherine A. “Coelomic Distension." Clinical Guide to Fish Medicine, edited by Catherine Hadfield and Leigh Clayton, Wiley-Blackwell, 2021, pp. 334-336.