Effects of dietary supplementation of Pseudomonas aeruginosa FARP72 on the immunomodulation and resistance to Edwardsiella tarda in Pangasius pangasius.

Edwardsiella tarda is one of the serious bacterial pathogens infecting both cultured and wild catfish urging an immediate need for effective protection strategies. This study assessed the effects of dietary supplementation of Pseudomonas aeruginosa FARP72 at 108 cells/g feed (PA diet) for 30 days on the innate immunity parameters, viz., respiratory oxidative burst (ROB) activity, lysozyme, ceruloplasmin, myeloperoxidase, in-vitro nitric oxide (NO) production in addition to the expression of immune genes encoding interleukin-1ß, C3 and transferrin in yellowtail catfish Pangasius pangasius and their resistance to Edwardsiella tarda challenge at a sub-lethal dose of 1.50 × 107 cells/fish. A significant increase in the innate immunity parameters was noted in PA diet-fed catfish on 30 dpf compared to the control. Post E. tarda challenge, the levels of immune parameters increased significantly and peaked at 5 dpi irrespective of feeding to confer protection against E. tarda. Their levels, however, decreased on and from 10 dpi. The results on the expression of immune genes encoding interleukin-1ß, C3 and transferrin in the kidney and liver tissue samples of PA diet-fed P. pangasius upon challenge with E. tarda further confirmed the ability of P. aeruginosa to stimulate primary immune organs at the gene level. The effects of feeding P. aeruginosa FARP72 on the immune functions of catfish as examined by the functional immune assays, thus, demonstrating the innate immune responses of catfish that are differentially stimulated by the PA diet. The findings of our study would help evolve management strategies to confer protection against E. tarda infection in commercial catfish aquaculture.

Influence of Fluctuating Water Temperature and Dietary Oxytetracycline on the Safety of Monosex Nile Tilapia Oreochromis niloticus Fries.

The influence of fluctuating water temperature and dietary oxytetracycline (OTC) at 0 (0X), 80 (1X), 240 (3X), 400 (5X) and 800 mg (10X)/kg biomass/day for 30 consecutive days on the safety of monosex (all male) Nile tilapia Oreochromis niloticus fries in terms of feeding, growth, survival and histopathology of vital organs were assessed. A dose-dependent decline in feed intake and biomass was recorded. The OTC-dosed groups recorded higher mortalities than the control. The therapeutic OTC-dosing (1X) in conjunction with low temperature caused 75.56 ± 8.01% mortality and 25.75% reduced feed intake in 30 days. The mortalities increased with increasing OTC-doses from 85.19 ± 3.39% (1X) to 95.56 ± 2.22% (10X) and fluctuating temperature (12.00-21.50°C) even after the withdrawal of OTC. Relatively mild to moderate histopathological lesions were observed in the kidney, liver and intestine of OTC-dosed fries. These results suggested that dietary OTC and low water temperature may cause adverse effects on monosex O. niloticus fries.

Adhesion and colonization of potential probiont Pseudomonas aeruginosa FARP72 in the intestine of yellowtail catfish, Pangasius pangasius.

Adhesion is recognized as the first important step of a probiont for intestinal colonization. This study assessed the ability of an antagonistic Pseudomonas aeruginosa FARP72 to adhere and colonize the intestine of yellowtail catfish, Pangasius pangasius both in vitro and in vivo. For the in vitro assay, the whole intestines of each of two starved P. pangasius were introduced separately into tubes containing bluish-green pigment-producing P. aeruginosa FARP72 at 8.00 log10 CFU/mL and physiological saline (0.85% sodium chloride) and incubated for 1 h at 30 ± 1 °C. The homogenate mucus solutions from the intestine samples were serially diluted and plated onto Pseudomonas isolation agar to determine the counts of bluish-green pigment-producing P. aeruginosa (BPPAC). The difference between the numbers of BPPAC and presumptive Pseudomonas counts (PPC) in the treated and control intestines was attributed to the adherence of P. aeruginosa FARP72. The levels of BPPAC and PPC in the treated intestines were 6.09 ± 0.59 log10 CFU/g. Similarly, following 30 days of feeding P. pangasius with P. aeruginosa FARP72 supplemented diet, the intestine of catfish recorded the BPPAC of 5.83 ± 0.64 log CFU/g. In control samples, the BPPACs were recorded as < 3.00 log10 CFU/g. The scanning electron micrograph of the intestines of P. pangasius following the in vitro and in vivo adhesion assays confirmed the ability of this bacterium to strongly adhere to the intestine, thus making it most suitable candidate probiont for use in freshwater catfish aquaculture.