Introduction
Tall oil fatty acids with 9% natural coniferous resin acids (TOFA) is a novel feed ingredient which improves the production performance and intestinal microbiota of farm animals (e.g. Vienola et al., 2018, Uddin et al., 2021). Resin acids are anti-inflammatory and antibacterial secondary metabolites of coniferous trees (San Feliciano et al., 1993). The present study investigated the effects of dietary TOFA on the performance, immunological status and load of the pathogenic bacterium Aeromonas spp. in the intestinal tract and liver of juvenile Asian seabass (Lates calcarifer) in Thailand.
Materials and methods
Juvenile Asian sea bass were allocated into 20 freshwater cages of 2 m3, 15 fish/cage, at a site with a known background challenge of Aeromonas histolytica. The water was aerated to maintain DO >5 mg/l. Feed was of commercial-type, with main ingredients of fishmeal, poultry meal, soybean meal and tapioca, and it was amended with 0 (Control), 0.35, 0.7, or 1.0 kg/ton of TOFA (Progres®, AB Vista, UK) for treatments T1-T4, respectively. The fish were fed 3 times/day at 3-5% of body weight for 16 weeks. Fish weight, weight gain, feed intake and feed conversion ratio (FCR) were determined every 2 wk, and the survival rate every 4 wk. Two fish/replicate were sampled for blood at 8- and 16-wk time points for determining the red blood cell (RBC) count, white blood cell (WBC) count, hemoglobin and haematocrit, and the concentrations of total serum protein and immunoglobulin M (IgM). The same fish were sampled for liver and intestinal contents for determining the number of Aeromonas spp. by plate culturing, using Aeromonas-selective media. The study design was completely randomized. Data was analysed with one-way ANOVA, followed by Duncan’s Multiple Range Test, using P<0.05 as a limit for statistical significance.
Results
Mean weight of the fish was 54.6 g, 111.8 g, and 170.0 g for wks 0, 2, and 4, respectively, without a significant difference between treatments. Dietary TOFA supplementation dose-dependently improved fish weight and weight gain from the 6-wk time point onwards (p<0.05). Table 1 presents fish weight on wks 8 and 16, and FCR for wks 0-8 and 0-16. Feed intake and fish survival rate was not affected by the treatments. At the end of the study, the survival rate was 89.3%, 92.0%, 93.3% and 96.0% for T1-T4, respectively. The treatments significantly affected FCR for the following time periods: wks 0-6, 0-8, 0-10, and 0-12 (p <0.001), with the best performance in T4.
Parameters analysed from blood and tissue samples are reported in Table 1. The TOFA supplementation significantly increased haematocrit (wk 8) and IgM (wks 8 and 16), and decreased Aeromonas spp. density in the liver and intestinal tract (wk 16).
Discussion and conclusions
In the present study, supplementing the diet of juvenile Asian seabass with TOFA promoted the growth performance, feed conversion and immunity of the fish, and at the same time improved their ability to control the growth of Aeromonas spp. in the liver and intestinal tract. Increased haematocrit and the trend towards higher serum protein levels in TOFA-supplemented groups may indicate positive effects on the physiological status of the fish. The effects were dose-dependent, and the treatment with TOFA at 1.0 kg/ton gave the highest responses. The results were in line with previous observations from studies with poultry and swine, in which dietary TOFA had positive effects on performance, gastrointestinal microbiota and disease resistance of animals (Vienola et al., 2018; Uddin et al., 2021). In conclusion, TOFA may function as a dietary strategy to improve the production performance and disease resistance of Asian seabass.
References
San Feliciano A., Gordaliza M., Salinero M.A., Del Corral J.M., 1993. Abietane acids; sources, biological activities, and therapeutic uses. Planta Medica, 59: 485–490.
Uddin, M.K., Hasan, S., Mahmud, M.R., Peltoniemi, O., Oliviero, C., 2021. In-feed supplementation of resin acid-enriched composition modulates gut microbiota, improves growth performance, and reduces post-weaning diarrhea and gut inflammation in piglets. Animals 11: 2511.
Vienola, K., Jurgens, G., Vuorenmaa, J., Apajalahti, J., 2018. Tall oil fatty acid inclusion in the diet improves performance and increases ileal density of lactobacilli in broiler chickens. British Poultry Science. 59: 349–355.