Probiotics In Fish And Shrimp Feed

Currently, there is growing interest in the use of beneficial bacteria, probiotics, as an alternative strategy to antimicrobial compounds. These naturally occurring live microorganisms can improve growth and survival of fish and shrimp.

A diverse range of beneficial bacteria is used as probiotics in aquaculture. Their selection and ability to thrive in the gut play a key role on the success of its application. The mode of action of probiotics include competitive exclusion of pathogenic microorganisms based on mechanisms like production of bactericidal substances, competition with pathogenic bacteria for nutrients and intestinal adhesion sites and modulation of the immune system. Ultimately, probiotics should contribute to efficient production in a sustainable way, promoting healthy and robust animals (Brittain et al., 2002).

Disease prevention and control in aquaculture are now priority research topics. This article reports on in vivo trials using beneficial strains as a probiotic feed additive in cultured aquatic species.

Probiotic inclusion in fish feed

Increased stocking densities in intensive fish production systems lead to more challenging production conditions. This brings the need for solutions focusing on improving fish performance and survival in a sustainable way. Several studies have demonstrated the efficacy and certain mechanisms of action of probiotics included in fish feed.

Adhesion and colonisation of the mucosal surfaces are possible protective mechanisms against pathogens through competition for binding sites and nutrients (Westerdahl et al., 1991). In a trial conducted by Kidchakan (2006) of the Prince of Songkla University, colonisation of the intestine was investigated with a commercial probiotic product containing Enterococcus faecium (AquaStar®, BIOMIN GmbH, Austria) in Nile Tilapia.

In this study it was shown that the probiotic E. faecium colonised the gut and it was even detected in the gut and faeces after 10 days of the product administration (Table 1). Different lactobacilli have reduced the adhesion of A. salmonicida, C. piscicola and Yersinia ruckeri to intestinal mucus of rainbow trout (Balcazar et al., 2006).

Chang and Liu (2002) showed that survival rates of European eels fed with Enterococcus faecium were significantly higher than in the control groups after being challenged with Edwardsiella tarda.

More possible benefits for fish linked to the administration of probiotics have been suggested: B. subtilis and B. licheniformis fed fish displayed a significant improvement of feed conversion ratio (FCR), specific growth rate (SGR) and protein efficiency ratio (Merrifield et al., 2009). Other protective mechanisms of probiotics against pathogens are production of inhibitory compounds with antibacterial activities and effects on the immune responses, such as modulation of the white blood cell counts.

In a recent study conducted by BIOMIN (2010) the effects of dietary application of probiotics on health and growth performance of Tra catfish were investigated.

Two different multi-species probiotic products, AquaStar® Growout (Bacillus sp., Enterococcus sp., Lactobacillus sp., Pediococcus sp., colongy forming units (CFU) one multiplied by 109/g) and AquaStar® Shield (Bacillus sp., CFU one multiplied by 109/g + cell wall fragments) were tested.

Groups of 40 fish (66.3 ± 0.3 g) were stocked into 300 L tanks and fed to satiation three times daily during an eight week period.

The experiment was set up using five treatments and five replicates per treatment with both probiotics tested at two inclusion levels (AquaStar® Growout one g/kg and three g/kg, AquaStar® Shield one g/kg and two g/kg feed).

At the end of the trial blood samples from three fish per tank were taken for determination of haematological parameters (trombocytes, lymphocytes, monocytes and polymorphonuclear leucocytes). Dietary application of probiotics had a positive effect on several fish performance parameters. These effects were dose dependent and varied between the two probiotics.

Feed application of AquaStar® Growout at three g/kg and AquaStar® Shield at one g/kg resulted in increased (P < 0.05) weight gains of 12 per cent and 11 per cent, respectively (Figure 1).

At those inclusion levels, these probiotics were also effective in improving FCR by 10 per cent and nine per cent, respectively, when compared to the control. Application of AquaStar® Growout at one g/kg and AquaStar® Shield at two g/kg improved fish performance but was not significant (P > 0.05) when compared to control.

The haematological parameters shown in Table 2 indicate that AquaStar® Growout (one g/kg) induced a significant reduction (20 per cent) in trombocytes and an increase (30 per cent) in lymphocytes when compared to the other treatments. Levels of monocytes and polymorphonuclear leucocytes were not affected by the treatments.

Results showed that probiotic application in fish feed can be an effective solution to improve growth performance and health status. Moreover, dosage application should be adapted to the composition of bacterial strains used.

Probiotic inclusion in shrimp feed

In the economically important panaeid shrimp, Vibrio species have become a major constraint on production and trade during the past two decades. They are responsible for several diseases and mortalities of up to 100 per cent, causing global losses of around US$ three billion.

There is already experimental evidence that the prophylactic use of probiotics to control pathogens by competitive exclusion can improve health and performance of cultured shrimp. The positive impact of added probiotics on bacterial ecology in shrimp gut was shown in a trial conducted with white shrimp (Litopenaeus vannamei).

A multi-strain probiotic mixture containing E. faecium (AquaStar®, BIOMIN GmbH, Austria) fed to shrimp 5 times daily during a six week period at an inclusion rate of five g/kg feed has reduced the total number of Vibrio spp. found in the hepatopancreas and intestine of shrimp. This evidence showed that probiotic Enterococcus can colonize the shrimp gut and reduce the number of pathogens through competitive exclusion (Supamattaya et al., 2005).

Furthermore, the non-specific immune system can be stimulated by probiotics. Rengpipat et al. (2000) indicated that the use of Bacillus sp. in tiger shrimp provided disease protection by activating both cellular and humoral immune defenses.

In a recent study, Jintasataporn et al. (2010) investigated the effect of AquaStar® Growout (BIOMIN GmbH, Austria) in white shrimp (Litopenaeus vannamei) production performance parameters. Groups of juvenile white shrimp (0.86 ± 0.31 g) were stocked into 240 L glass aquaria, at a density of about 100 shrimp/m², and fed four times daily for eight weeks.

A commercial type diet was used as a control. AquaStar® Growout was supplemented to the feed at an inclusion rate of three g/kg.

Considering the shrimp production per square meter, the results in Table 3 and Figure 2 show that shrimp production was improved by 9.40 per cent in the group applied with AquaStar® Growout compared to the control. The analysis regarding the CFU of LAB showed significantly (P < 0.05) higher levels in the probiotic group. Lactic acid can enhance growth performance due to optimum acidic conditions in the digestive system which promote nutrient digestion and absorption.

Conclusion

Maintaining the balance of critical parameters is a fundamental requirement for successful aquaculture. In order to withstand the high stocking densities in shrimp and fish production probiotics are a promising feed additive to stimulate animal growth and secure a low disease response. The data of these studies suggest that the use of AquaStar® improved survival, growth rates and the general health status of fish and shrimp while also reducing pathogenic Vibrio spp.

More research effort is needed to secure even better results in the future. Probiotics have to be extensively investigated in terms of new bacteria strains, their mechanisms of action, efficacious level of administration alone or in combination with other natural products with ascertained health promoting activities (Ringo and Olsen, 2008).

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