Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 1/16/2015
Publication Date: 2/20/2015
Citation: Xu, D., Shoemaker, C.A., Lafrentz, B.R. 2015. Parasitism by Ich enhanced susceptibility of tilapia to Flavobacterium columnare [abstract]. Aquaculture America 2015. p. 506.
Technical Abstract: In aquaculture systems, fish are commonly infected by two or more pathogens. Bacterium Flavobacterium columnare and parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish and result in heavy economic losses for aquaculture. There is no published information available on whether parasite infection will increase the susceptibility of tilapia to F. columnare. The objective of this study was to evaluate the susceptibility of hybrid tilapia to F. columnare after parasitism by I. multifiliis. Hybrid tilapia (Oreochromis niloticus × O. aureus) with an average length of 9.1 ± 1.1 cm (mean ± SD) and weight of 12.4 ± 4.6 g were used in this trial. Fish were divided into 18 tanks (triplicate tanks/treatment)with 20 fish per tank that received the following treatments: 1) non-infected control; 2) infected by I. multifiliis at 30,000 theronts/fish alone; 3) infected by F. columnare ALM-05-53 at 4.59×107 CFU/mL; 4) infected by I. multifiliis at 30,000 theronts/fish and exposed to F. columnare ALM-05-53 at 4.59×107 CFU/mL; 5) infected by F. columnare TN-3-2012 at 4.27×107 CFU/mL; 6) infected by I. multifiliis at 30,000 theronts/fish and exposed to F. columnare TN-3-2012 at 4.27×107 CFU/mL. To challenge with F. columnare, fish were immersed in water in buckets with ALM-05-53 or TN-3-2012 for 15 min. Fish not exposed to the bacterium were kept in water with Shieh broth for the same duration. 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. Fish mortality was recorded and dead fish were examined for I. multifiliis 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 I. multifiliis infection and then gill and kidney were collected to quantify F. columnare in tissues by real-time polymerase chain reaction (qPCR). The fish showed 2.1% mortality when infected by I. multifiliis alone at 30,000 theronts per fish. The fish yielded 0% mortality when challenged with F. columnare TN-3-2012 alone and 29.1% mortality when challenged with F. columnare ALM-05-53 alone. Mortalities were significantly increased in I. multifiliis parasitized fish than non-parasitized fish after exposure to F. columnare. The parasitized fish showed a 25.0% and 60.4% mortality after exposure to F. columnare TN-3-2012 and ALM-05-53, respectively. Flavobacterium columnare in fish tissues was quantified by qPCR and reported as genome equivalents per mg of tissue (GEs/mg). No F. columnare was detected in tissues of parasitized or non-parasitized fish prior to exposure to F. columnare. The bacterial load in gill of parasitized fish (5702.5 GEs/mg) was 14 fold higher than non-parasitized fish (415.4 GEs/mg) 3 days post exposure to F. columnare ALM-05-53. Similarly, the bacterial loads in the kidneys of parasitized fish were significantly higher than non-parasitized fish after exposure to F. columnare. This study suggests that prevention of parasite infection in fish will not only reduce the direct damage caused by the parasite but will also reduce fish mortality due to F. columnare co-infection.