ABSTRACT
In this study, in order to use prebiotics as one of the best solutions to maintain the health of farmed aquatic animals and increase their resistance against pathogenic instead of antibiotics, the effects of different levels of isomaltooligosaccharide (ISO) prebiotics on growth performance, biochemical body composition, and mucosal immunity of red tilapia (Oreochromis mossambicus × Oreochromis niloticus) were investigated. For this purpose, 300 pieces of red tilapia were randomly divided into 15 aquariums with capacity of 100 L in 5 treatments with 3 replications. Experimental treatments as described in the control treatment without ISO, first treatment: the diet containing 2.5 g/kg of ISO, second treatment: the diet containing 5 g/kg of ISO, third treatment: the diet containing 10 g/kg of ISO, and fourth treatment: the diet containing 20 g/kg of ISO. Therefore, the fish were fed ad libitum three times per day for 8 weeks. The result showed that the used prebiotic ISO improves growth and nutritional performance, body biochemical composition, and some biochemical parameters of blood serum in red tilapia. In addition, the mucosal immunity indices of fish were improved under the effect of diets containing prebiotic ISO. Among the experimental treatments, the third treatment had the best performance in terms of final weight (13.4±0.31g), food conversion factor (1.02±0.02), percentage of protein content of body (13.49±0.25), blood serum protein (4.66±0.10 gr/dl), globulin (3.23±0.02 g/dl), and mucus immune indices such as mucus protein (20.29±1.05 mg/ml), immunoglobulin (62.0±0.32 mg/ml) 7), and lysozyme activity (9.14±0.24 u/ml). Therefore, it could be concluded that the use of ISO prebiotics at the level of 1% can have beneficial effects on performance of juveniles red tilapia fish.

1. INTRODUCTION
Proper nutrition is considered a key factor in promoting the growth and health of fish. Through appropriate nutrition, not only the physiological needs of fish should be met, but also the conditions for their well-being should be provided (Lee et al., 2015). Over the past decade, antibiotics have commonly been used for managing fish diseases and improving growth and feed conversion ratio (Akrami et al., 2010). However, the widespread distribution and emergence of antibiotic-resistant bacteria have raised concerns about the transfer of these resistant bacteria from aquaculture environments to aquatic ecosystems, potentially harming microbial communities and the immune systems of aquatic organisms (Sapkota et al., 2008). Furthermore, antibiotics can disrupt the growth of beneficial gut bacteria, accumulate in fish bodies, and have adverse effects on fish health (Merrifield and Ringo, 2014).
As a result, the use of antibiotics as growth promoters in aquaculture systems is restricted and prohibited. Therefore, alternative strategies have been considered for nutrition and health management of fish. These strategies include the use of novel dietary supplements such as probiotics, prebiotics, synbiotics, phytochemicals, and other functional feed additives, which contain various compounds aimed at enhancing growth, stimulating immune responses, improving feed efficiency, reducing mortality rates, enhancing digestion, promoting the growth of beneficial gut microbiota, influencing appetite, and increasing nutrient intake (Denev et al., 2009). Additionally, enhancing the mucosal immune system in fish to increase resistance and reduce the risk of diseases through the use of dietary supplements such as immune stimulants, probiotics, prebiotics, and synbiotics has gained considerable attention (Merrifield and Ringo, 2014).
2.MATERIALSAND METHODS
In a study, a total of 300 Red Tilapia fish with an initial average weight of 0.65 ± 1.1 grams were obtained from a commercial Tilapia farm in Yazd province, Iran. The fish were randomly distributed among 15 aquariums, with each aquarium having a water volume of 100 liters (20 fish per aquarium or replication). The study included five treatments with three replications each, consisting of four experimental treatments and one control group. A period of acclimation was conducted for the fish to adapt to the new conditions two weeks prior to the start of the experiment. The experimental treatments were as follows:
1. Control Treatment: Basal diet without isomaltooligosaccharide.
2. Treatment 1: Diet containing 2.5 grams of isomaltooligosaccharide per kilogram of feed.
3. Treatment 2: Diet containing 5 grams of isomaltooligosaccharide per kilogram of feed.
4. Treatment 3: Diet containing 10 grams of isomaltooligosaccharide per kilogram of feed.
5. Treatment 4: Diet containing 20 grams of isomaltooligosaccharide per kilogram of feed.
3. RESULTS
The evaluation of growth and nutritional indices in the treatments containing prebiotics showed improvement compared to the control treatment (p < 0.05). The results of assessing the total protein content of Red Tilapia fish at the end of the experimental period showed a significant increase in the total protein content in the treatments containing prebiotics compared to the control group (p < 0.05). Furthermore, the body fat content in the prebiotic-treated groups significantly decreased compared to the control group (p < 0.05).
The protein, globulin, and albumin levels in the prebiotic-treated groups showed an increase compared to the control group, with the highest significant increase observed in Treatment 3 (1% prebiotic) (p < 0.05). The evaluation of mucosal immune indices of the fish at the end of the experimental period showed a significant increase in the total protein and immunoglobulin levels in the mucous of the prebiotic-treated groups compared to the control group (p < 0.05).
4. DISCUSSION AND CONCLUSION
The results of this experiment demonstrate that the use of different levels of isomaltooligosaccharide prebiotic leads to an improvement in growth and nutritional performance in Red Tilapia fish. Among the treatments, fish fed with 1% or 10 grams of prebiotic per kilogram of feed exhibited the best performance.
In terms of the beneficial effects of the used prebiotic, it can be stated that oligosaccharides, due to their specific structure and the absence of hydrolytic enzymes in fish for breaking down β-type linkages between monosaccharide units, are resistant to digestion and can only be metabolized by certain anaerobic bacteria present in the digestive system (Merrifield and Ringo, 2014). Therefore, the predominant bacteria involved are lactobacilli, bifidobacteria, and many lactic acid bacteria, which can utilize oligosaccharides through fermentation and thereby have beneficial effects on the host. Additionally, due to the reduction in intestinal pH caused by the fermentative conditions and acid production by the beneficial bacterial population, it can inhibit the activity of harmful and pathogenic bacteria in the digestive system. Moreover, it can enhance mineral absorption (Merrifield and Ringo, 2014). In conclusion, based on the obtained results, it can be stated that the use of diets containing isomaltooligosaccharide prebiotic has improved growth, nutrition, carcass composition, blood biochemistry, and mucosal immunity indices in Red Tilapia fish.
ACKNOWLEDGEMENT
The officials of Khorramshahr University of Marine Science and Technology are sincerely thanked and appreciated for their support in conducting this research as part of a Master's thesis.
REFERENCES
Lee, C.S., Lim, C., Gatlin, D.M. and Webster, C.D., 2015. Dietary Nutrients, Additives, and Fish Health. Wiley‐Blackwell.
Akrami, R., Ghelichi, A. and Gharaei, A., 2010. The use of prebiotics in aquaculture. 2010. Journal of Fisheries, 4(1), pp111. (In Persian)
Merrifield, D.L. and Ringo, E., 2014. Aquaculture Nutrition: Gut Health, Probiotics, and Prebiotics. Wiley Blackwell.
Denev, S., Staykov, Y., Moutafchieva, R. and Beev, G., 2009. Microbial ecology of the gastrointestinal tract of fish and the potential application of probiotics and prebiotics in finfish aquaculture. Journal International Aquatic Research, 1(1), pp. 129.