Background. Probiotics are known as immunostimulants as well as growth and survival promoters in fish, but despite the plethora of studies on the effect of probiotics on the fish non-specific immune responses, very few information is available for ornemental fish. Thus, this study was carried out to investigate the effects of short-term dietary administration of Bacillus probiotics (B. subtilis and B. licheniformis) on the immune responses of tinfoil barb, Barbonymus schwanenfeldii (Bleeker, 1854). Materials and methods. Three experimental diets were prepared by supplementing the diets with different concentrations of probiotics including 0 (Control), 1 × 104 (T1) and 1 × 13306 (T2) CFU · g–1 diet. Tinfoil barb weighing 16.20 ± 0.13 g were fed with the different diets for 15 days. At the end of the experiment, blood samples were collected in order to estimate the hematological (total protein, albumin, and globulin) and immune (total antiprotease, plasma peroxidase, and bactericidal activities ) parameters. Results. The plasma total protein, albumin, and globulin of fish were not affected by dietary probiotics. A six-fold increase in the plasma total antiprotease activity of fish fed 1 × 106 CFU · g–1 diet was observed. Moreover, the plasma peroxidase and bactericidal activities of fish significantly increased in T2 treatment compared to control. On the other hand, plasma natural haemolytic complement and lysozyme activities did not significantly vary between diets although the highest level of these parameters was observed in the probiotic treatments. Conclusion. This study showed the ability of dietary probiotics to enhance some innate immune responses of tinfoil barb especially after a 2-week administration of 1 × 106 CFU · g–1 diet (T2). Further study should focus on the effect of this dietary bacterial concentration on the fish response to bacterial and parasitical challenges in order to test its potential protective effect against the common pathogens of tinfoil barb.

Ornamental fish, immunostimulant, innate immunity, Bacillus subtilis, Bacillus licheniformis