Probiotics as an alternative to antimicrobials: limitations & advantages
In recent years, disease problems caused by Vibrio spp. and viruses have emerged as major constraints in aquaculture production. The application of antibiotics to culture ponds is not only expensive but also detrimental, i.e. selection of bacteria that are drug-resistant or more virulent, prevalence of drug residues in reared animals ready for consumption.
Probiotics can be a valid alternative to the prophylactic application of chemicals (antibiotics and biocides). Beneficial bacteria, which compete with bacterial pathogens for nutrients and/or inhibit the growth of pathogens, can be applied to the water or to the feed. These probiotic strains are not therapeutic agents but will alter directly or indirectly the composition of the microbial community in the rearing environment and the shrimp intestinal tract. Many bacterial strains are commonly used as probiotics in aquaculture. However, much doubt on the efficacy and safety of probiotics on the market comes from the use of ineffective bacterial species, unrealistic claims, lack of scientific evidence and poor quality control during production of the finished product, or inappropriate delivery methods leading to contamination or reduced performance. The development of suitable probiotics is not a simple task and requires empirical and fundamental research, full-scale trials, as well as the development of appropriate monitoring tools and controlled production!
Following an extensive research programme, the research company of the INVE group (INVE Technologies), developed a mixture of Bacillus strains for use as probiotics in shrimp aquaculture. Spore-forming Bacillus species are generally considered to be environmentally ubiquitous and have been reported in marine sediments. They are therefore naturally ingested by animals such as shrimps that feed in or on the sediment. Bacillus strains were selected for their ability to inhibit pathogenic Vibrio that had been isolated from the haemolymph of shrimp in both Asia and Latin America (Figure 1), grow under conditions prevailing in larval or pond rearing systems and to degrade waste products both under aerobic and anoxic conditions. The best performing strains were then included in bioassays and challenge tests in order to confirm the lack of toxin production and pathogenicity to shrimp and humans.
Figure 1: Selection procedure of Bacillus strains for their ability to inhibit pathogenic Vibrio
The performance of various formulations with the best performing Bacillus strains was repeatedly assessed in several hatchery (Figures 2 and 3) and growout tests (Figure 4) in various Asian and Latin American countries for P. monodon and L. vannamei. These numerous tests carried out under commercial or pre-commercial conditions confirmed that probiotics have the potential to produce results similar to those obtained with antimicrobials and, importantly, in a cost-effective manner (see Figure 4 legend).
Figure 2: In three separate tests run over a period of 1 year, Penaeus monodon nauplii were reared until PL10 and fed a combination of Chaetoceros, Artemia nauplii and Lansy Shrimp (40% live food substitution) INVE larval diet. Various applications of a number of probiotic formulations were studied in 175-L tanks (Â¡Ã3 replicates per treatment) and compared to negative control and prophylactic antibiotic treatments. In these replicated tests, the daily application of SANOLIFE® MIC probiotics at a final concentration of 1-5x104 cfu/ml of tank water gave results similar to those observed with prophylactic application of antibiotics.
Figure 3: In this commercial evaluation in a Brazilian hatchery, the performance of Sanolife MIC was compared to prophylactic antibiotics (in combination with formaldehyde treatment in early PL stages) and negative control (no chemicals added). Each 20MT tank was stocked with 5 million Litopenaeus vannamei N3/.tank. Water disinfection procedure included chlorine addition followed by neutralisation with thiosulphate). Shrimp larvae were fed microalgae, Artemia and larval diets.
Figure 4: A combination of SANOLIFE® PRO-1, PRO-2 and PRO-W was evaluated in India, with 3 ponds per treatment. Higher survival and harvested shrimp biomass were observed from ponds treated with the Sanolife probiotics. Lower FCR was observed in ponds receiving the Sanolife treatments, i.e. 1.52 Â¡Ã€ 0.13 compared to 1.6Â¡Ã€ 0.18 for the negative control ponds. Furthermore, bigger sized shrimp were found only in ponds treated with the probiotics. This led to a more than 10-fold increase in benefits with the Sanolife treatment.
INVE Aquaculture Health has recently released the following 4 probiotic products for shrimp aquaculture (Figure 5):
Following germination in sterile water, the SANOLIFE® MIC is added daily to the larval tanks at a concentration of 0.5ppm (till zoea 2 stage) or 1ppm (from zoea 3 stage till harvest).
SANOLIFE® PRO-1 and PRO-2 (1-5g/Kg feed) are mixed with feed and used each day during all feeding of the first month of culture (PRO-1) and from the second month of rearing till harvest (PRO-2). They Improve health of shrimp, control pathogenic vibrios in the intestinal tract, the faeces and uneaten feed, and degrade waste products in the pond.
SANOLIFE® PRO-W is additionally applied directly to the pond water when high stocking densities prevail. Sanolife® PRO-W inhibits pathogens while beneficial natural flora becomes established and is combined with organic fertilizer during algal bloom development.
Obviously, minimizing the risk of vibriosis demands a multi-disciplinary approach, including good hygiene and sanitation measures to reduce the input of potential pathogens, as well as a suitable farm management.
Figure 5: Range of Sanolife probiotics for shrimp aquaculture
1. O. Decamp and D. J. W. Moriarty
2. INVE Technologies nv, Hoogveld 93, 9200 Dendermonde, Belgium
3. Centre for Marine Studies, The University of Queensland, Queensland 4072, Australia
4. INVE Aquaculture Health, Thailand