Introduction
Due to the limited biological capacity of resources and natural resources in aquaculture ecosystems, many issues related to environmental stressors have emerged. Typically, diseases can be contracted due to immunosuppression caused by increased stocking density, poor water quality, and abnormal weather conditions. Most antibiotics are used to treat infectious diseases, but frequent chemical use causes many problems related to human and systemic health. Therefore, many countries have banned the use of antibiotics in livestock, poultry, and aquaculture sectors. Consequently, the demand for natural alternatives that can help reduce antibiotic use without adverse effects on aquatic animals has increased. Alternatives can be effectively used by incorporating them into the diet throughout the culture period. Many types have been successfully used, including probiotics and botanicals.
The diversity, absorption capacity, and digestibility of probiotics lead to improved gut immunity. Bacillus bacteria are among the most important probiotic species because their spores are easily supplemented in aquatic environments, with a relatively long survival capacity in feed. In Nile tilapia (Oreochromis niloticus), the benefits of Bacillus spp. are associated with enhanced digestibility, gut immunity, and humoral immune responses, as well as increased resistance against outbreaks and environmental pollutants. Another type of feed additive is extracts used to improve the growth and health status of aquatic animals. Spirulina platensis is one of the most important species used in the preparation of medicines for humans and animals. Because it contains many active compounds, including phenols, amino acids, vitamins, and minerals, which can enhance immunity and antioxidant capacity. Results from numerous studies conducted on tilapia supplemented with spirulina show significant improvements in growth rate, immunity, and disease resistance.
Nile tilapia holds an important position among aquatic animals due to high demand, rapid growth, and reasonable prices. Typically, only one type of feed additive is used during feeding, but a mixture of several types appears to be more effective. Therefore, the main objective of this study was to ascertain the efficacy of using Bacillus and spirulina as feed additives in tilapia diets.
Research Methods
EXPERIMENTAL DESIGN
Nile tilapia were collected from a local farm and transported to the Department of Fish and Fisheries Sciences, Kafrelsheikh University, Egypt. Fish were kept in glass tanks (60 L) and fed a control diet for 2 weeks for laboratory acclimatization. Fish with an initial body weight of 24.95 ± 1.12g were evenly distributed into 12 glass tanks (10 individuals per tank).
An extruded pellet diet (30% crude protein) was considered the basal diet (Table 1). One control diet and three experimental diets were supplemented with SP (S. platensis) at 1g/kg, BA (Bacillus amyloliquefaciens) at 100 mg/kg, and SP/BA at 1 g/kg + 100 mg/kg. SP and BA were mixed with a vegetable oil source. A grinder was used to produce the pellets (2 mm). The pellets were dried and sealed in vacuum-packed bags and stored in a refrigerator (4°C). New experimental diets were prepared every 2 weeks to ensure the actual probiotic count. Fish were fed their respective diets twice daily (08:00, 16:00) for 60 days. Fish were fed to apparent satiation, and feed consumption in each aquarium was recorded. Light-dark cycle (12h:12h). Water temperature was 26.1 ± 1.2 °C, pH 7.7 ± 0.43, TAN 0.05 ± 0.01 mg, DO < 5 mg/L.
Table 1. Dietary formulation analysis
