Mixotrophic Method of Aquaculture
By Dr. Farshad Shishehchian, Blue Aqua International
Up until the 1970s, aquaculture was not a significant contributor to the global market for seafood. However, in the last 40 years’ global aquaculture has expanded from an estimated 3.5 million tonnes in 1970 to about 73.8 million tonnes in 2014. Furthermore, government restrictions to preserve populations of certain native species have increased the demand for seafood produced in controlled artificial environments such as in aquaculture ponds. The production of catfish in catfish farms is one example of the growing, large-scale aquaculture industry. Other species produced by the aquaculture industry include crayfish, oysters, shrimp, Tilapia and Striped Bass.
According to the Food and Agriculture Organization of the United Nations (FAO) Fisheries and Aquaculture Department, the contribution of world aquaculture to global fish production reached 46.0 percent in 2018, up from 25.7 percent in 2000, and 29.7 percent in the rest of the world, excluding China, compared with 12.7 percent in 2000.
With aquaculture now making up a significant portion of total seafood supply, the increased production from aquaculture has also led to significant environmental impact and competition for diminishing natural resources from other sectors such as agriculture. In particular, pond production continues to dominate aquaculture production and is especially vulnerable to water scarcity. Aquaculturists have thus been under pressure to intensify production and grow more seafood with less water and land.
As aquaculture production intensified over time, providing enough oxygen in the pond environment also became a major challenge. If not enough oxygen is supplied, anaerobic conditions may appear and toxic gas production (hydrogen sulfide, ammonia) increased, affecting shrimp health and, thus, leading to disease outbreak. In the early days pond production was limited to the biomass that could be sustained with only natural weather driven re-aeration. Over the years, first emergency aeration, then routine nightly aeration and finally 24 hour aeration was added, which is now standard practice in the industry. However, 24hour aeration is expensive especially in areas with limited access to electricity and/or fuel. As a general comparison, in important shrimp farming countries such as Indonesia, India, and even Ecuador, existing aquaculture methods achieve a stocking density of 200, 100 and 30 post-larvae per square meter, respectively.
Even if oxygen needs are met, concentrations of nitrogenous compounds from waste decomposition often reach limiting or toxic levels. The aquatic environment may also comprise other organisms apart from the farmed organisms, such as plankton, algae and bacteria. Pathogenic or undesirable organisms may affect the growth, health and quality of the farmed species. Problems such as algal “blooms and crashes” may also be experienced at high production rates, discouraging high stocking densities. For example, a rapid growth or accumulation in the populations of unwanted algal species in the aquaculture pond, in particular blue green algae, can result in an undesirable “off flavour”, causing the flesh of the fish to have an unacceptable taste and odour.
According to the FAO, China, Thailand, Viet Nam, Indonesia and India dominate the global production of shrimp and prawns.
Open and closed systems
Open system shrimp farms are generally open to the environment, such as open-air ponds constructed near oceans to contain and grow shrimp. These open shrimp farms suffer from vagaries of predators, the weather, diseases and environmental pollution. Saltwater from the ocean must be continually circulated through the ponds and back to the ocean to maintain adequate water chemistry for the shrimp to grow. The shrimp farmers must supply daily additions of dry food pellets to the shrimp as they grow.
Closed shrimp farms are generally self-contained aquaculture systems. While closed shrimp farms have greater control over the artificial environment contained therein, they have not been entirely satisfactory because of the limited production rates, water filtration, treatment problems, and manufactured feed. Although some of these shortcomings can be overcome by increased capital expenditures, such as for water treatment facilities, the increased capital, labour and energy costs may be prohibitive.
All in all, there still is a need in this technical field for improved aquaculture methods, in particular methods that increase the production intensity by providing increased oxygen levels and reduced levels of nitrogenous compounds in the pond environment.
State of the Art Technology
As global aquaculture is developing towards intensification, farmers are expected to cope with challenging situations such as disease outbreaks, water quality deterioration, and higher operations costs. Intensification regimes have also led to the use of legal and illegal drugs and antibiotics aimed at improving both survival rate and health status. As a result of their continual use over the years, antibiotic-resistance can be induced from the antibiotic-resistant bacteria strains to the non-resistant ones.
New practices and technologies are arising to render the sector more sustainable and consumer friendly over the time. Particularly, those news alternatives are: probiotics and minerals. Farm management is a holistic practice that stabilizes the pond preventing from disease, independently its origin.
The key success of farm preparation is to overcome traditional methods for farming.
Problems can be caused by the following factors:
The negative impacts of farm practices may show up after several crops. Liming, for example, has been traditionally applied to increase water pH, disinfect and create the conditions for phytoplankton growth; however, without considering soil pH and its lime requirements, or lime solubility itself. It has been proven that not dissolved lime accumulated at the pond bottom, induces gill clogging in the shrimp, impairing its respiration, besides inducing another impacts unknown nowadays.
2. Chlorination and other disinfectant application
In the case of other chemicals such as trichlorfon, molluscicides, insecticides or disinfectants, accumulation occurs in the trophic chain or pond bottom, causing toxicity or impairing immunity response in fish and shrimp against environmental stressors such as low oxygen or toxic gases. Other compounds such as chlorine, widely used in the industry as disinfectants, hamper phytoplankton growth by killing the ‘seed’.
At this point, the use of antibiotics inducing bacterial resistance and other banned chemicals needs no further discussion.
Feeding is the main source of nutrients and energy to the shrimp and pond environment, that’s why water and soil quality are directly dependent on feeding management.
Sulphur, silicon, phosphorus and nitrogen biochemical cycles in the pond, are strongly unbalanced when aquaculture farms operate, i.e. inputs of feeding, shrimp metabolism, etc. The nitrogen cycle is considered a very important cycle in the pond because many organisms and biochemical compounds are involved in it.
Pond preparation before shrimp stocking
4. Pond Aging Syndrome
If farmers effectively manage and balance nitrogen cycle in the pond, pond productivity improvement will be expected, while ineffective feeding leads to an unbalanced system of low overall productivity.
Organic matter accumulation throughout successive crops causes several changes in the soil and water quality, defined as Pond Aging Syndrome.
- The breaking down of the organic matter by decomposers induces a drop in pH that gradually leads to soil acidification.
- There is an increase in the oxygen demand required to break down excess organic matter and sustain the biomass in the pond.
- In this condition, dissolved oxygen concentrations drop under optimal levels, especially at early morning time.
- Accumulation of nutrients, organic matter and sludge leads to anaerobic conditions or sudden phytoplankton blooms.
- In the worst case, under anaerobic and acidic conditions heavy metals precipitate.
- Continuous use of natural ponds induces low mineral availability and pH fluctuations.
Water quality instability:
An environment of increasingly deteriorating conditions becomes harsh for shrimp and also for phytoplankton and benthic organisms that contribute as natural food and can cause these effects:
5. pH fluctuation
An excessive accumulation of nutrients induces sudden phytoplankton blooms that lead to wide daily pH and DO fluctuations.
6. ORP fluctuation with impact on nitrification
Continuous use of the pond gradually decreases dissolved oxygen in the water. Under these conditions, anaerobic areas where ORP values are negative arise and hamper nitrification process. For an efficient conversion of ammonia into nitrites and further into nitrates, not only dissolved oxygen is necessary for bacteria.
7. Toxic gas accumulation C: N compounds and H2
Alkalinity and ORP values out of the optimal range for nitrification cause ammonia and nitrite build up with deleterious effects on fish and shrimp health.
Other toxic gases such as hydrogen sulfide accumulate in the anaerobic areas in the interface between water column and soil bottom.
Effluent with high organic or chemical load induces eutrophication and threatens aquatic diversity in the surroundings and it is a sign of nutrient accumulation in the pond.
8. Bacterial colonization
High organic loads favour bacterial growth, increasing the probabilities of disease,
9. Blue Green Algae (BGA)
Growing and the bloom of deleterious phytoplankton species such as BGA or dinoflagellates that produce toxins and outcompete beneficial species such as diatoms and green algae.
MixotrophicTM System: Moving towards a natural system
The Mixotrophic system is a patented culture system specially developed by Blue Aqua International to manage super intensive and intensive aquaculture systems.
The main concept describes how to manage and improve water and soil quality by managing and balancing phytoplankton and bacterial communities throughout stages of production cycle. These microorganisms, bacteria and phytoplankton, influence nutrient cycles in the water and soil interphase, and indirectly, water quality parameters and its stability which are critical factors affecting animal health, growth and production. Proper and efficient management of water quality would help to reduce stress and disease outbreaks and thus increase in productivity in intensive culture.
MixotrophicTM System accomplishes its benefits by:
- Using a combination of species of microorganisms for bioremediation.
- Achieve ‘Zero Water Exchange’ by integrating special probiotics, nutrients, and scientific management know-how.
- Stabilize the food chain in the pond, allowing higher biomass in the system.
The system takes into account the balances and ionic proportions of major ion concentrations in the pond that are also crucial for animal growth and for the maintenance of stable water environment.
This technology balances the pond ecosystem by stimulating natural food productivity, thus enhancing the availability of natural food organisms, and balancing important ion concentrations and bioavailable minerals in the pond water and soil.
The system is secured by advantageous bacterial activities that degrade organic matters, reduce effects of toxic gases, and discourage the proliferation of pathogenic bacteria in the pond.
The MixotrophicTM System has a proven track of results even for high intensification and comes with a step-by-step protocol to help farmers achieve good performance at ease. The balance and environmentally friendly system works in synergy with biosecurity to prevent diseases for highly profitable and successful production, in the move towards the future of aquaculture.