A project undertaken at the Department of Life & Environmental Sciences, Deakin University and supervised by Paul Jones
Murray cod is an icon Australian freshwater fish, with a well established cultural and historical significance. It is a top order predator and is Australia’s largest freshwater fish, with specimens reaching 114kg. The recent closure of the last wild Murray cod fishery and its national listing in 2003 under the Environment Protection and Biodiversity Conservation Act, as a ‘vulnerable’ species highlights the necessity for understanding the biology and ecology of this enigmatic fish.
Figure 1. CED affected Murray cod showing focal erosion of the skin overlying sensory canals of the head and flanks (lateral line), and severe erosion of the fins.
Figure 2. Histological section of the anterior mid-section of the lateral line pore canal of a healthy (top) and CED affected (bottom) Murray cod
Murray cod presently form the focus of a developing freshwater aquaculture industry in Australia and is presently cultured in systems where groundwater is the primary water resource. Drought has exacerbated the use of groundwater in various agriculture areas and presently comprises in excess of 18% water use in Australia. Murray cod, together with other fish species, are known to suffer from various diseases when they are grown in water that doesn’t suit their physiology or is of poor quality in general. One such condition, known as chronic erosive dermatopathy (CED), has been linked to growing fish in groundwaters of various ionic compositions. This syndrome results in degeneration, necrosis and sloughing of skin tissue in the region of the lateral line and sensory canal system and in severe cases results in the loss of one or both eyes and most of the fins, consequently affecting health and overall survival. From the few studies conducted, CED is thought to be caused by incorrect water chemistry and to be non-organismal in origin although the causitative agent/s is/are yet to be identified. CED is also thought to be the result of a negative interaction between unsuitable water chemistry and an inadequate diet. Presently, we are investigating various groundwater types and treatment methods to determine their impact on the incidence and severity of CED from histological, haematological and physiological perspectives. In addition, we are also investigating a possible dietary link by growing fish on fortified diets and chemically examining tissues (muscle, skin, liver) from fish afflicted with the syndrome.
Overall, we hope to be able to identify the cause/s of the syndrome and provide a more detailed understanding of its/their impacts on the physiology, chemistry and ultimately health of the fish, and to develop practical cost-effective ways to prevent its occurrence.