Use of broad-spectrum antimicrobials in the eradication of unknown aquatic pathogens in a zebrafish larval rearing system
Russo, R.; Dillehay, D.
Contemporary Topics in Laboratory Animal Science 44(2): 49-51
2005
ISSN/ISBN: 1060-0558 PMID: 15773777 Document Number: 590635
A zebrafish larval rearing system experienced a surge in mortality rates soon after the introduction of new stocks. A comprehensive water analysis of pH, nitrites, nitrates, ammonia, chlorine, carbonate hardness, general hardness, and conductivity identified no anomalies. Observations via light microscopy of affected fry revealed consistent signs of impaired mobility, blood clotting, and eventual heart haemorrhage resulting to the death of 90 to 100% of the fry by the age of 2 weeks. Collection of sufficient tissue samples for a histological investigation proved problematic due to the fry's diminutive size. Because a causal agent could not be isolated satisfactorily, the use of a broad-spectrum antibiotic was deemed necessary. After considering many broad-spectrum antibiotics for treatment, we implemented a two-tiered approach for the treatment. The rearing system was treated with a nitrofurazone derivative, whereas the adult populations were treated using multi-antibiotic food pellets. The rearing system was treated for 3 weeks, and the adult population was treated for 2 weeks. After the completion of the antibiotic treatments, the biological filters of all of the medicated systems were seeded with nitrifying bacterial cultures. Upon the maturation of the rearing systems' biological filters, mortality rates returned to pre-outbreak levels. There have been no re-occurrences of the fish mortality since the completion of treatment. This epidemic provided some valuable lessons, lessons that if followed, will ensure faster response to unknown pathogens in the future.