Abstract
Tilapia lake virus (TiLV) causes an emerging viral disease associated with high mortality and economic damage in tilapia farming around the world. The use of probiotics in aquaculture has been suggested as an alternative to antibiotics and drugs to reduce the negative impact of bacterial and viral infections. In this study, we investigate the effect of probiotic Bacillus spp. supplementation on mortality, viral load, and expression of immune-related genes in red hybrid tilapia (Oreochromis spp.) upon TiLV infection. Fish were divided into three groups, and fed with: control diet, 0.5% probiotics-supplemented diet, and 1% probiotics-supplemented diet. After 21 days of experimental feeding, the three groups were infected with TiLV and monitored for mortality and growth performances, while organs were sampled at different time points to measure viral load and the transcription modulation of immune response markers. No significant difference was found among the groups in terms of weight gain (WG), average daily gain (ADG), feed efficiency (FE), or feed conversion ratio (FCR). A lower cumulative mortality was retrieved from fish fed 0.5% and 1% probiotics (25% and 24%, respectively), compared to the control group (32%). Moreover, fish fed with 1% probiotic diet had a significantly lower viral load, than those fed with 0.5% probiotic and control diet at 5, 6, 9, and 12 days post infection-challenge (dpc). The expression patterns of immune-related genes, including il-8 (also known as CXCL8), ifn-γ, irf-3, mx, rsad-2 (also known as VIPERIN) showed significant upregulation upon probiotic treatment during the peak of TiLV pathogenesis (between 9 and 12 dpc) and during most of the study period in fish fed with 1% probiotics-supplemented diet. Taken together, these findings indicate that dietary supplementation using Bacillus spp. probiotics may have beneficial effects to strengthen tilapia immunity and resistance against TiLV infections. Therefore, probiotic treatments may be preventively administered to reduce losses caused by this emerging viral infection in tilapia aquaculture.
Highlights
Tilapia are the most economically important farmed fish species produced in aquaculture systems worldwide [1]
All probiotics and control diets fed red tilapia that cohabitate with IP-injected fish showed similar clinical signs of tilapia lake virus (TiLV) infection, starting at 7 dpc
To further investigate the beneficial effects of Bacillus spp. as probiotics dietary supplementation against TiLV infections in tilapia, we examined the transcription of a selection of pro-inflammatory cytokines and markers of the antiviral response in internal organs sampled at time points after TiLV
Summary
Tilapia are the most economically important farmed fish species produced in aquaculture systems worldwide [1]. In 2018, global tilapia production was estimated at 6.8 million tonnes, accounting for an economic value of USD 11 billion [2]. Tilapia can adapt and tolerates variable farming conditions, recent outbreaks of emerging bacterial and viral diseases pose severe threats to the global tilapia aquaculture production [3]. The outbreak of a new viral disease, caused by tilapia lake virus (TiLV), has drawn attention due to the rapidity of it spreading between farms and countries [4,5]. The virus was classified as a new species, Tilapia tilapinevirus, under the genus Tilapinevirus, but in the family Amnoonviridae [8]. All stages of tilapia farming including fry, juveniles, adults, and broodstocks are susceptible to TiLV infection, with a wide range of morbidity and mortality ranging from 5 to
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
