The study investigated effect of dietary supplementation with malic acid, Bacillus subtilis and a mixture of the two (3 × 2 factorial trial) on Nile tilapia (Oreochromis niloticus) health. Treatment groups (T1-T6) were fed diets containing three levels of malic acid bacterial count in the gut and faeces was detected in fish from group T6. The values of haematocrit, haemoglobin, red blood cells, white blood cells, total protein, albumin and globulin were significantly higher (p < .05) in fish from groups T4 and T6 (diets supplemented with malic acid and B. subtilis). As compared to the control fed fish, te mixture of these substances are promising as immune enhancher in aquacultured fish.
K E Y W O R D SBacillus subtilis, blood parameters, growth, gut microbiota, Nile tilapia, organic acid
| INTRODUCTIONMicrobial balance and proper pH in the digestive tract eliminate pathogenic microorganisms. This is necessary to maintain fish health in a satisfactory state and to achieve expected production levels.Over the last decade, research has focused on the application of probiotics and prebiotics to replace antibiotic growth promoters in the fish farming industry (Irianto & Austin, 2002;Yanbo & Zirong, 2006) and to enhance the growth and health of the host (Gatesoupe, 1999;Kesarcodi-Watson, Kaspar, Lategan, & Gibson, 2008).Most commercial probiotics currently being tested in aquaculture are lactic acid bacteria (e.g., Lactobacillus), the genus Bacillus, photosynthetic bacteria (e.g., Rhodobacter sphaeroides) and the yeasts foods as a flavour enhancer and for pH (1% malic acid solution is about 2.3) and microbial control, because it inhibits the growth of pathogenic bacteria and pathogenic fungi (Ricke, 2003). An exceptionally valuable nutritional property of this acid is that after oral administration, it stimulates the secretion of gastric juices and increases peristalsis. Small doses of malic acid have prebiotic properties, stimulating the development of non-pathogenic, acidophilic and saprophytic bacteria whereas at higher doses it can exhibit bacteriostatic and bactericidal properties (Salou, Leroy, Goma, & Pareilleux, 1991).An extensive review of the literature on this topic revealed that there are no reports on the in vivo kinetics of probiotic bacterial growth in the presence of organic acids. In in vitro studies, Lactobacillus plantarum exhibited better growth in the presence of malic acid as compared to the control group (Passos, Fleming, Hassan, & McFeeters, 2003).Therefore, in the authors' opinion, the current study is innovative and facilitates a better understanding of the interactions occurring among probiotics and malic acid in the gastrointestinal tract of fish. In summation, the aim of the current investigation was to assess the dietary inclusion of malic acid, Bacillus subtilis or a mix of the two on the growth performance, feed utilization, gut microbiota and haematological and biochemical blood parameters of Nile tilapia (Oreochromis niloticus;Linnaeus, 1758). After carp, the tilapia species c...
