Impacts of parasite infection on columnaris disease of tilapia

Authors: Xu, Dehai; Shoemaker, Craig; Lafrentz, Benjamin; Zhang, Dunhua

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/21/2016
Publication Date: 2/20/2017
Citation: Xu, D., Shoemaker, C.A., Lafrentz, B.R., Zhang, D. 2017. Impacts of parasite infection on columnaris disease of tilapia. In: Aquaculture America 2017 Conference, San Antonio, Texas, February 19-22, 2017. p. 513.

Interpretive Summary:

Technical Abstract: There is no information available on whether parasite infection will increase the susceptibility of tilapia to Flavobacterium columnare and whether parasite treatment could improve fish survival after F. columnare exposure. Two trials were conducted to evaluate 1) the susceptibility of hybrid tilapia (Oreochromis niloticus × O. aureus) to F. columnare after parasitism by Ichthyophthirius multifiliis (Ich) and 2) formalin treatment of hybrid tilapia parasitized by Trichodina sp. to improve fish survival after F. columnare exposure. In trial I, hybrid tilapia were divided into 18 tanks with 20 fish per tank that received the following treatments: 1) non-infected control; 2) infected with 30,000 Ich theronts fish-1 alone; 3) infected by F. columnare ALM-05-53 at 4.59×107 CFU L-1; 4) infected by 30,000 Ich theronts fish-1 and exposed to F. columnare ALM-05-53; 5) infected by F. columnare TN-3-2012 at 4.27×107 CFU L-1; 6) infected by 30,000 Ich theronts fish-1 and exposed to F. columnare TN-3-2012. For challenge, fish were immersed in water in buckets with F. columnare for 15 min. Fish not exposed to the bacterium were held in water with Shieh broth for 15 min. After challenge, the fish and challenge water were poured into the appropriate tanks and water flows were adjusted to 0.4 – 0.5 L min-1. Fish mortality was recorded and dead fish were examined for Ich and F. columnare infection twice daily for 17 d. At 3 and 6 days post F. columnare challenge, two fish were randomly sampled from each tank to check for Ich infection and then gill and kidney were collected to quantify F. columnare in tissues by real-time polymerase chain reaction. The fish showed 2.1% mortality when infected by Ich alone and 29.1% mortality when challenged with F. columnare ALM-05-53 alone. Mortalities significantly increased in co-infected fish (60.4%; Ich and F. columnare ALM-05-53). The bacterial load in gill of parasitized fish was 5702.5 genome equivalents per mg of gill tissue (GEs mg-1), 14 fold higher than non-parasitized fish (415.4 GEs mg-1) 3 days post exposure to F. columnare ALM-05-53. In trial II, hybrid tilapia parasitized by Trichodina sp. were divided into 3 treatment groups. The first group of fish received no parasite treatment. The second group of fish were bath treated once with 150 mg L-1 formalin for 1 h. The third group of fish bath treated two consecutive days with 150 mg L-1 formalin for 1 h. All fish were then immersion challenged with F. columnare (ALM-05-53). The tilapia not treated with formalin showed significantly higher mortality (37.5%) than those treated with formalin (= 16.7%) after exposure to F. columnare. Fish treated twice showed lower mortality (6.37%) than those treated only once (16.7%). The non-treated fish showed significantly higher load of F. columnare in gill, kidney and liver compared to those treated with formalin following exposure to F. columnare. The bacterial load of non-treated fish was 27075 GEs mg-1, 12 fold higher than those treated once with formalin (2250 GEs mg-1) or 39 fold higher than those treated twice with formalin (699 GEs mg-1) after exposure to F. columnare. Results of studies suggest that prevention of parasite infection in fish will not only reduce the direct damage caused by the parasite but will also reduce mortality due to F. columnare co-infection. Formalin treatment for Trichodina sp. parasitism reduced bacterial infection as suggested by reduced loads of bacteria in fish tissues and subsequently decreased fish mortality.