Friday, June 24, 2016

A farmer’s perspective on probiotics in shrimp culture

The application and dosage of probiotics should be culture specific with more clarity and understanding provided to the farmers.

For many years, the major focus of the shrimp industry in India was on the farming of the black tiger shrimp, Penaeus monodon. The economic benefits led to high stocking densities and use of spurious post larvae which in turn led to constant threat of diseases. Shrimp farmers began to use of antibiotics and water sanitizers routinely. This indiscriminate use of antibiotics brought negative impact on the environment and food safety as well as introduced a trade barrier for our final products in international markets.

The government reacted with strict food safety protocols in all the shrimp farming areas to disallow the use of banned chemicals. Culture techniques following Good Management Practices (GMP), Best Management Practices (BMP), organic farming, and zero water exchange systems were examined. However, probiotic claim to have a major role towards a more sustainable industry. In India, there are more than 100 companies producing probiotics targeted for the aquaculture industry. However, farmers usually do not have sufficient knowledge on microbiology and they are unsure on the benefits of probiotics.

The science behind probiotics in shrimp culture
The historic definition for probiotic as per Fuller (1989) is ‘a live microbial feed supplement which beneficially affects the host animal by improving its intestinal balance’. However, in aquaculture recently, the scientific definition of probiotic was given by Merrifield et al. (2010). According to this group, probiotics are defined as ‘microbial cells that are administrated via the diet or rearing water, with the aim of improving health and disease resistance, growth performance and feed utilization, stress response, general vigour, carcass and flesh quality and reduced malformations.

They classified probiotics into three groups: gut probiotics, water probiotics (as in bioremediation) and soil probiotics (as in detritus management system). Probiotic inoculates are either in the form of spores or as resting bodies of one or more species in a medium design to prevent germination or to retard growth. All these available probiotics are either in liquid or granular form coated with bacterial propagules.

Mode of action
Probiotics containing multiple strains of bacteria spores or resting bodies produce extracellular enzymes to degrade large molecules into smaller particles that can be absorbed for further degradation by enzyme-catalyzed reactions within their cells. It should be obvious that enzyme additions cannot speed up degradation of organic matter or toxic substances unless bacteria are present. Probiotics within shrimp or in their environment adhere to host surfaces and have the ability to colonize and to prevent the establishment of potentially pathogenic bacteria.

A farmer’s view:
The farmer’s understanding and definition for probiotics is simply; ‘single or multi-brand microbial products when used singly or mixed should benefit shrimp and culture ponds’. In their view, the probiotics are only of two types; feed and pond probiotics. The possible benefits of probiotics are;
  • Improve health when probiotics competitively exclude the pathogenic bacteria or produce substances that inhibit the growth of the pathogenic bacteria
  • Provide essential nutrients to enhance the nutrition of the cultured shrimp
  • Improve growth and feed conversion when probiotics provide digestive enzymes to enhance the digestion of the shrimp.
  • Lower environmental impact when probiotics directly uptake or decompose the organic matters or toxic materials (metabolites such as NH3, NO2, H2S, PO4, CH4, etc.) in the water, thus improving the quality of the culture water.
In addition, under investigation are other claims such as improvement of the immune response of the shrimp against pathogenic microorganisms by activating both cellular and humoral defenses (non-specific immune system) and having anti-viral effects.

However, farmers consider probiotics as miracle products, giving them quick and positive results after application. Probiotics become a curative tool rather than prophylactic. On the other hand too, farmers are often discouraged by the increased cost of operations. Probiotics are still accepted or adopted in the primary culture protocols.

This can be divided into the following phases
  • Phase 1: Pre-culture application
  • Phase 2: In-culture application
  • Phase 3: Post-culture application
Phase 1: Pre-culture application
Pre-culture application probiotic has to be catalyzed by proper BMP protocols. This mainly involves the proper design and construction of all the culture ponds followed by proper pond preparation. The main catalytic steps to improve the probiotic effects after pre-culture application include proper drying and ploughing before starting the crop, followed by compact and levelling after ploughing. Incoming water should be well filtered and pond preparation follows the steps shown in Chart 1.

Chart 1. Steps in pond water preparation

Day 1 :  Fill water to 1.2 m (average depth) 
Leave for 2 days to settle 
Day 4 :  Chlorination 10pp, bleaching powder 
Dechlorination for 5 days 
Day 9 :  Application of prebiotic media after fermentation 
(jaggery + rice bran + yeast) – Dose 1 
Leave for 1 day 
Day 10:   Application of probiotics for water – Dose 1 
Leave for 5 days 
Day 15 :  Application of prebiotics media after fermentation
probiotics for water (jaggery + rice bran + yeast) – Dose 2 
Leave for 1 day 
Day 16 : Application of probiotics for water – Dose 2 
Leave for 2 days, check water parameters 
Day 19 : Stocking of good quality tested PL 15 

The probiotic works effectively when we apply a good prebiotic carbohydrate source. The water color after application of the prebiotic and probiotic after pond preparation before stocking of post larvae is given in Figure 1. This color shows the efficacy of probiotics with good pond preparation.

Phase 2: In-culture application
As per the guidelines from most probiotic companies, the recommended concentration of probiotics during in-culture application is given below.

Table 1. In culture application of probiotics

Water probiotics 
  • Initial start-up dose followed by weekly doses up to end of the culture recommended by company to company basis and also as per the product specification.
  • Dose 0.5 – 1.0 kg/ha/week (powder), 5 – 10 liters/ha/week (powder) 
Feed probiotics
  • Administrated through feed on a daily basis from day 1 of culture till harvest. Mostly once a day (peak meal)
  • Dose 5 – 10 g/kg feed with a suitable binder. 
The in-culture application of probiotic is mostly catalyzed by proper water quality management, optimum aeration facility, good quality and correct feeding schedule, proper check tray management and strong biosecurity. The main catalytic steps to improve the probiotic effects after in-culture application include optimum water quality parameters for better probiotic efficiency (Table 2); effective aeration for optimum in-culture probiotic effects; competent feeding program and check tray management for optimum in-culture probiotic effects.

Table 2. Optimum water quality parameters.

Dissolved oxygen : > 5 ppm (morning) 
pH : 7.8 to 8.5 
Transparency : 35 – 45 cm 
Alkalinity : > 100 ppm bicarbonate 
Salinity : 12 – 25 ppt 
Temperature : 28 – 32 oC 
Water depth : Average 1.8 m 
Ca : Mg ratio : 1:3 especially for Litopenaeus vannamei 

The impact of in-culture probiotic to maintain the healthy water color is shown in Figure 2.

Figure 2. Impact of probiotic application in shrimp culture pond.

Phase 3: Post-culture application
Post culture application of probiotics in shrimp pond is one of the most important management practices, which is usually overlooked by the farmers. This practice should be done to remove excess amounts of organic load during post culture pond preparation. The post culture application of probiotics followed in our farm (MAPL) is given in Chart 2.

A healthy bottom condition is a result of the application of post culture probiotics. The stocking of good quality shrimp will also help to sustain a good pond bottom condition.

Chart 2. The post culture application of probiotics at MAPL
  • Flushing of pond bottom
  • Application of lime 
  • Filling of water (20 – 30 cm) 
  • Application of probiotics 
Some observations and findings
The following observations and findings have been recorded during several years of culture while applying probiotics (Table 3)

Table 3. Some observations and findings with probiotic applications.

In addition, the best water probiotic effects and performance was observed in salinity close to 20 ppt. Gut probiotic efficacy was the best at the above salinity range. The result of probiotics is purely pond specific and varies from season to season. The age of pond is also a determining factor. The cyclic nature/cropping pattern of shrimp farming also effects the permanent establishment of microbial communities. In spite of various claims, it is very difficult to eliminate blue green algae in shrimp culture ponds through water probiotics. Compared to P. monodon culture, it is easy to control water color in L. vannamei culture pond which could be due to its feeding behavior.

Main constraints of nitrifiers in ponds
Nitrifiers are fragile microorganisms, which are sensitive to acids despite the fact that they produce acid during oxidation of NH3 and NO2. Therefore, if large amounts of nitrogen are available in the water, these organisms can potentially kill themselves by metabolizing nitrogen to nitric acid unless pH is buffered. Nitrifiers are autotrophs and they need oxygen during the degradation of NH3.

The reactions of Nitrobacter spp. are inhibited by small quantities of ammonia gas, which can lead to toxic buildup of NO2, since Nitrosomonas spp. is not inhibited from NH3 to NO2 in the presence of ammonia gas. Both Nitrobacter spp. and Nitrosomonas spp. work in culture pond within pH ranges of 6.8 – 8.5 with the optimum at pH 8.2 to 8.3.

By Manoj M. Sharma
Source: AQUA Culture ASIA PACIFIC Jan. – Feb. 2013

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