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Prolonged low-salt immersion effectively controls Flavobacterium columnare infection in Murray cod Maccullochella
Zhenguo Zhang1, Shuang Hao, Xiaohui Bai
1College of Fisheries, Tianjin Agricultural University, Tianjin 300384, PR China.
Abstract:
A disease outbreak occurred in Murray cod Maccullochella peelii peelii in a recirculating aquaculture farm in Tianjin city, China, in 2019. Strain MRX-2019 was isolated and considered to be the etiological pathogen; it was identified as Flavobacterium columnare based on a 16S rDNA gene sequence analysis and physiological and biochemical tests. The effect of salinity on the growth of MRX-2019 was investigated in vitro. Salinity >4‰ (i.e. 6‰) inhibited MRX-2019 growth, whereas 8 and 10‰ salinity killed it. The effect of 4‰ salinity on F. columnare was not significant (p > 0.05). When MRX-2019-infected Murray cod were treated with 4, 6, or 8‰ salinity, the mortality rate was reduced by 8.9, 67.76, or 75.56%, respectively, compared with that of the control. However, the mortality rate increased by 7.77% at 10‰ salinity. In this study, we found that maintaining the fish in freshwater with 6-8‰ salinity effectively reduced the mortality of these fish when infected with F. columnare. The findings provide an environmentally friendly control strategy for columnaris disease in Murray cod.
Insights
Columnaris disease in Murray cod can be managed using salinity. Maintaining fish in freshwater with 6-8‰ salinity significantly reduced mortality caused by Flavobacterium columnare.
Area of Science:
- Aquatic animal health
- Fish pathology
- Microbiology
Background:
- A disease outbreak caused by Flavobacterium columnare (MRX-2019) affected Murray cod (Maccullochella peelii peelii) in a Chinese aquaculture facility.
- Flavobacterium columnare is a significant pathogen impacting freshwater fish species.
Purpose of the Study:
- To investigate the efficacy of salinity as an environmentally friendly treatment for columnaris disease in Murray cod.
- To determine the optimal salinity range for inhibiting Flavobacterium columnare growth and reducing fish mortality.
Main Methods:
- Isolation and identification of the etiological agent, Flavobacterium columnare (MRX-2019), using 16S rDNA gene sequencing and biochemical tests.
- In vitro assessment of salinity's effect on MRX-2019 growth.
- In vivo trials exposing infected Murray cod to varying salinity levels (4‰, 6‰, 8‰, 10‰) to evaluate mortality rates.
Main Results:
- Salinity above 4‰ inhibited MRX-2019 growth, with 8‰ and 10‰ proving lethal to the bacteria in vitro.
- Treatment with 6‰ and 8‰ salinity significantly reduced mortality in infected Murray cod by 67.76% and 75.56%, respectively.
- Salinity of 4‰ showed no significant effect on mortality, while 10‰ increased mortality.
Conclusions:
- Maintaining Murray cod in freshwater with 6-8‰ salinity is an effective strategy to control columnaris disease.
- Salinity manipulation offers a practical and eco-friendly approach to managing Flavobacterium columnare infections in aquaculture.
