There is more life in a shrimp pond than the animals themselves. The pond ecosystem also supports bacteria, protists, viruses, phytoplankton and zooplankton. As well as complex, a healthy pond must be in a stable state of equilibrium; any deviation from ‘normal’ pond conditions can have negative consequences on shrimp health and growth.
The organic matter within the pond drives many of the pond interactions. Intensive, or semi intensive, aquaculture requires a lot of organic input, primarily through the feed. Uneaten feed, feces and dead or dying phytoplankton all contribute to the overall organic loading. The accumulation and degradation of this organic matter will reduce dissolved oxygen (DO) and produce toxic metabolites such as ammonia (NH3), nitrites (NO2-), nitrates (NO3-) and hydrogen sulfide (H2S). In low water exchange systems, these compounds can build up and the resulting deterioration in water quality has negative effects on shrimp health. Furthermore high levels of organic matter acts as a fertilizer and can cause a phytoplankton bloom. Rapid growth of phytoplankton will further deplete oxygen reserves at night through respiration, and add to the organic matter as the cells die and start to decompose.
All these factors contribute to the contamination of water and soil, creating favorable conditions for pathogens to grow and negatively affecting shrimp health. Under these poor conditions, the shrimp will become stressed and immunocompromised, increasing the risk of infection, and subsequent disease outbreaks.
The use of beneficial bacteria, probiotics, is becoming increasingly popular as a useful and sustainable pond management tool. This biotechnology is called ‘bioremediation’. An effective probiotic solution must provide multiple benefits. Specific strains can produce enzymes that reduce organic matter, whilst simultaneously facilitating the release of highly digestible nutrients. Probiotics can also aid the nitrogen cycle. Specific strains will convert toxic ammonia through to nitrate (nitrification). Although nitrates are less toxic to shrimp, its accumulation can cause problems and encourage phytoplankton growth. Therefore, different probiotic strains must be included in probiotic formulations to convert nitrates back to harmless nitrogen gas (denitrification). Furthermore, certain microbial strains are capable of reducing hydrogen sulfide, improving pond water and sediment, whilst reducing pond odor.
At the same time, probiotics must also control pathogens. Probiotic species, specifically lactic acid bacteria (LAB), produce potent antibacterial substances, such as pediocin by Pediococcus, providing direct antagonism to pathogens. Probiotics can also reduce pathogen abundance through competitive exclusion and may possess quorum quenching properties, disrupting bacterial communication and reducing their virulence. Furthermore, when LAB are ingested they are capable of colonizing the intestinal tract where they drive immunity, allowing the host to improve its immune response and fight pathogens using its own immune system.
Together probiotics can be used to complement good management, improving water and soil quality, reducing organic matter, controlling pathogens, improving shrimp health and survival, and ultimately increasing production. Thus, they not only ensure environmental sustainability, but also profitable sustainability.