Use of histopathology for disease surveillance in juvenile barramundi Lates calcarifer (Bloch, 1790)

Author: Hong Lan Pham

Pham, Hong Lan, 2022 Use of histopathology for disease surveillance in juvenile barramundi Lates calcarifer (Bloch, 1790), Flinders University, College of Science and Engineering

Terms of Use: This electronic version is (or will be) made publicly available by Flinders University in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. You may use this material for uses permitted under the Copyright Act 1968. If you are the owner of any included third party copyright material and/or you believe that any material has been made available without permission of the copyright owner please contact with the details.


Asian sea bass (Lates calcarifer (Bloch, 1790)), also known as barramundi, is an important aquaculture species worldwide, especially in Asia. Barramundi are susceptible to bacterial, parasitic and viral infections. Disease surveillance plays a critical part in early diagnosis of fish disease and abnormalities thus reducing economic losses in aquaculture. Numerous diagnostic methods are used for early diagnosis including histopathology and molecular techniques. Histopathology is broadly used as a primary and efficient method for detection of fish pathology at first. Ideally, histology combined with other methods such as traditional bacteriology, virology, biochemical tests will provide more accurate results. The aim of this study was to conduct disease surveillance in juvenile barramundi at a local South Australia hatchery. Thirty juvenile barramundi were collected every month for regular examination for nine months. Fish were then analyzed by routine histology (H&E staining) for abnormalities. Histologically, there were 18 fish from 270 examined fish, which demonstrated pathological features of Betanodavirus infection but these all showed negative results when examined using the IHC technique. Epitheliocystis was evident in the gills with a high prevalence (118/270) while monogenean Diplectanidae sp. appeared at lower prevalence (36/270). Other abnormal structures found in various organs of sampled fish remain unknown and further research is required to identify these.

This thesis had several original findings:

Clinical symptoms such as skin darkening, lethargy, swimming in a swirling pattern and the appearance of vacuolation in the brain and central nervous system tissues were observed in barramundi fingerlings at a South Australian hatchery. These symptoms normally indicate viral nervous necrosis (VNN) disease however, no positive IHC confirmation of Betanodavirus was observed.

Epitheliocystis and parasitic infections with high prevalence were periodically recorded (every 2 months) without telangiectasis and vice versa.

Unknown pathological agents were observed in fish hatchlings during this study but these were unable to be identified as it was beyond the scope of this project. Nonetheless, this finding may open a new era for further barramundi disease surveillance research.

In conclusion, early diagnosis during regular disease surveillance in aquaculture is very useful. It reduces economic losses through stopping diseases from spreading, thus preventing potential outbreaks. Also, it helps to monitor for other abnormalities that could happen such that quick responses can be enacted. For instance, pathogens detected in this study appeared periodically and were highly associated with each other. This information was quickly reported to the local hatchery and was helpful for their disease management.

Keywords: Barramundi diseases, betanodavirus, histopathology, IHC, fish disease surveillance

Subject: Aquaculture thesis

Thesis type: Masters
Completed: 2022
School: College of Science and Engineering
Supervisor: James Harris