Dr. Karthik Ramachandran
Introduction Aquaculture production has grown enormously in recent years worldwide, especially in Asia, due to its high economic value and export. Aquaculture is the fastest growing food production sector in the world also, providing almost half of the global fish/shrimp supply. It is estimated that aquaculture will grow by 40 % to meet global fish and shrimp demands by 2030. Shrimp and fishes are rich in proteins, vitamins, omega 3 fatty acids, selenium and essential minerals and is recommended for the maintenance of strong body and healthy bones. With increasing population and health awareness, the demand for high quality fish and shrimp is increasing.
The pollution caused by the effluent discharged from the shrimp farms is a big matter of concern.It is responsible for the conflicts between aqua-culturists and activistsworldwide. Some cases are reported in Tamil Nadu.
Uneaten feed and fecal material in shrimp pond lead to accumulation of ammonia, nitrite and phosphate. These compounds are potentially toxic to shrimp and it will reduce the shrimp growth or promoting shrimp disease outbreaks and it normally affects the surrounding environment by eutrophication and depletion of natural habitats.
The mechanical and chemical treatment and other processes to remove the excess of ammonium and phosphate from waste water from the culture ponds are also used, but it is very expensive and may also affect the environment. To achieve sustainability, it is necessary to intensify the production by using low cost technologies and treatments like biodegradable bio-filters. Moreover, fish feed contributes to more than one-half of the variable operating cost in the aquaculture sector, thus, knowledge on nutrition and practical feeding of fish are essential to a successful aquaculture.
Studies have shown that some animals being fed diets containing halophytes had impaired growth and decreased food conversion efficiency. However, it has been used in agriculture for soil fertility, vermicomposting, in pharmaceutical as an anticancer, antibiotic, anti-hyperglycemia, anti-diabetes, antihypertension and antihypotension and in cosmetic industries. Therefore, halophytes plants have a potential ingredient and a good source of protein in the fish feed formulation.
Integrated multitrophic aquaculture techniques are good candidates to overcome these above problems. Coculture is a modern term that is used to describe a form of polyculture in which two or more complementary organisms are grown together in the same culture medium (Neoriet al., 2004).
Co-culture with species of the same trophic level is generally not beneficial to the system. However, integrating species of different trophic levels can be greatly beneficial to all facets of the system (Chopin et al., 2001; Hayashiet al., 2008 &2010;). This form of aquaculture has recently been described as Integrated Multi-Trophic Aquaculture System (IMTAs) (Neoriet al., 2000). An example of IMTA is the integration of shrimp culture with the culture of seaweed (referred to as the inorganic extractive) and/or shellfish (referred to as the organic extractive) (Chopin et al., 2001). In such a system, wastes (inorganic ammonia, phosphorous and organic solids) from one organism are used as inputs (fertilizers, food) for another. This results in the optimal use of resources and reduces the risk of eutrophication (Naylor et al.,2000;).
One of the main aims of IMTA is that all cocultured species become harvestable crops with some commercial value (Neoriet al., 2000). IMTA therefore creates balanced systems for environmental sustainability and product diversification (Neoriet al., 2004). Integrated multitrophic aquaculture techniques are good candidates to overcome these sustainability problems (Chopin et al., 2001). This treatment technique was considered to be the most inexpensive and environmentally sounded (Neoriet al., 2004). Regarding the environmental benefits of integrated seaweed and shrimp production, seaweed culture can also benefit by increasing their economic viability. Integrated aquaculture provides nutrient bioremediation, mutual benefits to the co-cultured organisms, economic diversification and increased profitability. Ideally, nutrient process in polyculture system with two or more ecologically compatible species should be balanced, waste from one species are recycled as fertilizer or feed by another without conflicting with each other (Neoriet al., 2000).
In seaweed culture, Kappaphycusalvarezii (Rhodophyta) is one of the main seaweed cultivated in several countries such as Philippines, Indonesia and Tanzania (Hayashi et al., 2010). It is a red algae and commercially known as “Cottonii” in international seaweed market and its main raw material of kappa carrageenan, natural polysaccharide (carbohydrate), which has several uses in industry, a hydrocolloid used as a food additive, acting as a gelling, emulsifying, thickening and stabilizing agent in both pharmaceutical and nutraceutical products and its farming technology based on vegetative propagation, new potential applications are of interest in several branches of the carrageenan industry (Pickering et al., 2007).
Among several applications, one of the most important is in the food industry, where the use of carrageenan in dairy products is still growing because of its reactivity with milk proteins. In processed meats, carrageenan can avoid water loss during cooking and acting as water binding agent and improving the quality (BixlerandPorse, 2011). According to the FAO database (FAO, 2011), the production of Kappaphycusalvarezii in 2009 was 1,755 tons, worth almost US$ 203 million.
Seaweed can absorb significant amounts of waste nutrients, controlling eutrophication, and consequently, improving the health and stability of marine ecosystems (Buschmannet al., 2001; Chopin et al., 2001; Troellet al., 2003; Fei, 2004; Neoriet al., 2004). The physiological mechanisms of seaweed bio filtration have been studied in, filter-feeding bivalve culture systems (Fang et al., 1996), fish cage farms (Troellet al., 1997; Neoriet al., 2004; Hayashi et al., 2008), shrimp culture ponds (Jones et al., 2001; Nelson et al., 2001).
There have been several studies that demonstrated the beneficial effects of culturing shrimps with other aquatic species. Shrimps have been polycultured with other fish such as tilapia, several species of macroalgae and shellfish (Bunting 2006 and Da Silva-Copertinoet al., 2009). The use of these secondary species in shrimp ponds provided benefits such as reducing the amounts of dissolved nutrients, filtering suspended solids, feeding on excess organic matter, improving water quality and enhancing disease resistance against pathogens (MartínezPorchaset al., 2010). The use of polyculture system of aquaculture has been studied in white shrimps together with oysters and clams (MartinezCordova and MartinezPorchas 2006), seaweeds (Lombardi et al 2006) and red tilapia (Yuan et al., 2010).
In all these studies, co-culturing white shrimps with these aquatic species resulted in positive effects on both the primary and secondary species. However, no such studies were done in economically important seaweed. Implementation of this co-culture technology will help in seaweed production by uptaking the nutrients (shrimp wastes) from the culture pond and treat effluent water, also save the surrounding environment from eutrophication and depletion, by the way farmers also will yield and get dual income by implementing this integrated multitrophic technology.
(The author is the Director-Techno Marketing, Vetbiotics Animal Healthcare Pvt Ltd Mumbai. Views expressed are his personal.)