Post 2: Bacterial Fin Rot in Aquaculturally Reared Queensland Grouper and Issues Surrounding the Frequent use of Antibiotics

The Queensland Grouper (Epinephelus lanceolatus) is the largest bony fish to reside around coral reefs in the world (Jennings & Lock, 1996). Aqua cultural facilities and aquariums that work in the breeding and rearing of Queensland Grouper for research and/or other purposes sometimes lose fish due to pathogens and parasites. One such pathogen is a disease called Fin Rot, which gets its name from the way it slowly destroys mainly the tail fin (caudal fin) of Grouper and many other fish species and can be caused by either a fungal infection or by a bacterium (Nagasawa & Cruz-Lacierda 2004). In this post, I will be discussing the bacterial fin rot disease which results from a Pseudomonas Fluorescens infection.

Bacterial fin rot affecting the Caudal, Elongated Dorsal and Anal fin

This disease is often associated with poor water quality and dense populations. Poor water quality can increase the stress in cultured grouper which in turn lowers their immune system which makes them more vulnerable to pseodomonas fluorescens (Nagasawa & Cruz-Lacierda, 2004). Queensland Grouper are also cannibalistic and so in dense populations, the larger fish attack the smaller fish and the injuries incurred allow for opportunistic fin rot infections.
Treatment for bacterial fin rot is the simple use of antibiotics, the most commonly used is Oxy-Tetra Cycline (OTC) over a 10 day treatment period (Austin & Austin, 2007). Issues surrounding the frequent use of this however include the bacterium developing an immunity to this. Bacterial resistance for antibiotics has been observed since the 1950's and the two theories surrounding Fin Rot is whether it is the result of bacteria evolving in response to the use of OTC or whether the bacterium already possesses genes which give it immunity (Groisman & Ochman, 1996).
Hopefully with more research, more effective treatments can be found.

References:

Austin, B. Austin, D. 2007, 'Bacterial Fish Pathogens: Disease of Farmed and Wild Fish', 'Springer Science'

Groisman, E. Ochman, H. 1996, 'Pathogenicity Island: Bacterial Evolution in Quantum Leaps', 'Cell', vol. 87, pp. 791-794

Jennings, S. Lock, J. 1996, 'Population and Ecosystem Effects of Reef Fishing', 'Reef Fisheries', vol. 20, pp. 193-218

Nagasawa, K. Cruz-Lacierda, E. 2004, 'Diseases of Cultured Groupers', 'South-East Asian Fisheries Development Centre'

Somga. J, Somga, S. 2002, 'Impacts of Disease on Small-Scale Grouper Culture in the Philippines', 'Primary Aquatic Animal Healthcare', vol. 14, pp. 248-261