Effects of Adding Brevibacillus laterosporu FAS05 to Feed on the Growth, Disease Resistance, and Immunity of Litopenaeus vannamei

Abstract

Litopenaeus vannamei is one of the important crustaceans in aquaculture in China. In recent years, the shrimp culture industry has gradually developed into an intensive and high-density model, which can lead to environmental deterioration and large-scale outbreak of diseases. The widespread use of antibiotics has led to the increase of pathogen drug resistance, environmental pollution, and ecological imbalance, resulting in secondary pollution in the water. Probiotics are live microbial additives that promote good health and are environmentally sustainable and safe for use. They are often used as important substitutes for antibiotics. Brevibacillus laterosporu, as a biocontrol probiotic, is commonly used for disease control of crops, animals, and poultry, but its use is rarely reported in aquaculture. A 28-day breeding experiment was carried out with L. vannamei weighing (1.00±0.08) g, to study the effects of adding B. laterosporu FAS05 in the feed on the growth, disease resistance, and immunity of L. vannamei. The experiment was divided into four groups with three replicates in each group, and 50 shrimps in each replicate were fed with the experimental feed supplemented with 0 CFU/g (group C, as the control group), 105 CFU/g (group BL1), 107 CFU/g (group BL2), and 109 CFU/g (group BL3) of B. laterosporu FAS05. B. laterosporu FAS05 was isolated from the aquaculture pond with a low number of Vibrio in summer. The bacterium was added into the basic feed with fish meal, soybean meal, and corn meal as the main protein source, fish oil and phospholipid oil were added as the fat source, wheat flour as the main sugar source, and inorganic salts and vitamins as supplements. L. vannamei was purchased from a prawn farm in Weihai City, Shandong Province. The temperature was 25–28 ℃ and the salinity was 27–30. During the breeding experiment, eight shrimps were randomly selected in each tank every two weeks and their body length, weight, and plumpness were measured. The phagocytic activity assay was modified on the basis of the method reported by Delaporte et al (2003). Fl-1 channel flow cytometry was used to detect and analyze the offset of respiratory burst peak. The blood lymphocytes, serum, and hepatopancreas of shrimp were collected 24 hours after the experiment. The activities of immune related enzymes in hepatopancreas, such as superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), and alkaline phosphatase (ALP) levels, and the activities of immune related enzymes in serum, phenol oxidase (PO), and lysozyme (LZM), were determined by kits. The phagocytic activity was measured, and the assay was modified on the basis of Delaporte et al (2003). Fl-1 channel flow cytometry was used to detect and analyze the offset of respiratory burst peak. After the feeding test, a one-week infection test of Vibrio parahaemolyticus was carried out to determine disease resistance. The experimental results were expressed as Mean±SD. One-way ANOVA analysis was conducted for all data using statistical software SPSS 16.0, and significance level was defined as P 0.05), and the body length, body weight, and specific growth rate of shrimps in the BL1 and BL2 groups were significantly higher than those in group C (P 0.05). Compared to that of group C, the phagocytizing rate of shrimp blood cells in the BL1 to BL3 groups increased significantly (P 0.05). The PO of shrimps in the BL2 group was significantly higher than those in other groups (P < 0.05). The ALP and SOD in the BL1 and BL2 groups were significantly higher than those in group C and BL3 (P < 0.05). The above results showed that B. laterosporu FAS05 as a feed additive could promote the growth of shrimp, activate the immune system, improve disease resistance, and inhibit the growth of Vibrio in the surrounding environment. The reference dosage was 105 CFU/g. When the infection is serious, the dosage can be increased to 107 CFU/g to further improve the non-specific immunity of shrimp. The results of this study can provide basic data for the application of B. laterosporu FAS05 in shrimp culture and production.

Keywords

• litopenaeus vannamei
• brevibacillus laterosporu fas05
• growth
• immunity
• disease resistance