Introduction: In recent decades, the fish farming industry has grown significantly in many countries to provide part of their animal protein, so that the production of aquatic species has expanded significantly and is expected to grow in line with the increasing population and human need for protein sources (Abdel‐Latif et al., 2020). The quality of the diet received is very important in the growth process of fish, so with careful study, this process can be improved by achieving optimal food combinations and their appropriate amounts in a balanced diet (Glencross et al., 2020). Nile tilapia, Oreochromis niloticus, has the highest global consumption and distribution, and is currently being concentrated in some parts of the world. Given the nutritional value of seaweeds as feed additives or food supplements, their availability and low cost have led to their use in aquaculture. The purpose of the present study was to replace the red algae in the diet with enzymes and its impact on the tissue of the Nile tilapia gastrointestinal tract. Khuzestan province has suitable climatic conditions for tilapia farming, which has high economic value in terms of providing food protein, export, employment, and foreign exchange. Therefore, given the reasonable price and ease of access to this type of algae, a recent study was conducted to investigate the possibility of replacing red seaweed with fish meal in the diet and its effect on the bacterial microflora of the Nile tilapia intestine. The bacterial flora of the digestive tract includes a collection of bacteria that live in the digestive tract of fish, and the intestine is the main place for these microorganisms to settle in the fish (Mahmoud et al., 2020).
Material and Methods: For this purpose, 120 tilapia providing preparations and adaptation with an average weight of 30 ± 1 g were fed for 8 weeks in 100-liter aquariums with a Biomar diet containing 0, 3%, 6%, and 9% of the food weight with red algae in three replicates and based on the research of other researchers in each treatment. After the end of the breeding period, the fish were anesthetized with cloves and after opening the abdominal cavity, 1gr of midgut samples from different groups were homogenized with 99ml of normal saline serum and mixed (Moradkhani et al., 2020). The homogenized mixture obtained was combined with 9ml of physiological serum, and serial dilutions up to 8-10 were prepared. Gram staining was used to isolate and purify bacterial strains from nutrient agar medium and to identify morphology. Also, Simon citrate, MR-VP, SIM medium, and oxidase tests were used for biochemical studies. To count bacteria, after dilution, samples from the experimental and treatment groups were transferred to Petri dishes containing transfer medium and spread (Wardani et al., 2020).
Result and Discusion: In this study, in order to investigate the effect of oral administration of red algae on the intestinal bacterial microflora in Nile tilapia, four experimental diets were administered, including a control treatment without algae that received only the basal diet, and three diets containing red algae at a ratio of 3% of the food weight, treatment two containing red algae at a ratio of 6% of the food weight, and treatment three containing red algae at a ratio of 9% of the food weight, for 8 weeks. Based on the results of the present study, it was determined that the more the percentage of algae added to the diet, the greater the amount of gastrointestinal microflora in the species in question, based on the total bacterial count graph shown in Figure 3. Researchers have also stated that algae are rich in antioxidants and protect fish intestinal cells from oxidative stress and help maintain the health of the intestinal microbiota (Strassert et al., 2021). As observed in a recent study and in comparison with similar studies and in line with the present study (Kord et al., 2024), which stated that the use of red algae in the diet of Nile tilapia at the aforementioned level had no side effects and its use in this fish improved the parameters and tissue structure in the intestine and digestive enzymes. Using seaweed in the form of extract or feed as an additive to the basal diet in food has many benefits due to the presence of micronutrients, including health and palatability, increasing food quality, increasing growth and safety in aquatic animals, and improving the natural flora of the stomach and intestines.The results of the present study showed that in the control group, the colonies belonged only to Bacillus, and in the treatment group, the colonies belonged to Bacillus and Coccus. The results of total intestinal bacterial count showed a significant difference between the different treatments (p<0.05). The highest number of intestinal bacteria in the fish was in the 9% treatment and the lowest was in the control group. Some algae have been reported to be able to bind to heavy metals and other toxins and reduce their harmful effects, providing a safer environment for beneficial bacteria to grow (Pan et al., 2022). Seaweeds also contain compounds that help fish cope with environmental stressors such as temperature changes, high salinity, and poor water quality. Reducing stress levels can lead to a more stable and healthy gut microbiota. In general, adding algae to fish diets can lead to significant improvements in the growth and activity of beneficial gut bacteria, suppressing harmful bacteria, and promoting overall gut health (Radhakrishnan et al., 2015).
Conclution: According to the results of the present study, it can be stated that the possibility of using red algae in the Nile tilapia diet at the mentioned level will improve the intestinal bacterial microflora. According to the studies of other researchers and the results of the present study, considering the positive effect of this type of algae on the intestinal microbiota in terms of not causing losses or diseases and appropriate growth and weight compared to the control group, it can be a suitable alternative to fish meal in the Nile tilapia diet, along with possible alternatives to other animal and vegetable proteins for feeding this fish, which will ultimately reduce costs and reduce dependence on fish meal to provide the protein needed by Nile tilapia. Also, considerations related to the amino acid profile and digestibility of the algae under study can be searched and expressed in other similar studies. |
