There are 100 million tons of fish eaten world-wide each year, providing two and a half billion people with at least 20 percent of their animal protein intake (Mietzner, 2010). The contribution of fish to diet is even more substantial in developing countries, especially small island states and in coastal regions, where it frequently makes up over 50% of people's animal protein. However overfishing of the oceans has rendered certain wild populations of fish and marine organisms dangerously scarce, collapsing a large percent of commercial fisheries. The practice of cultivating aquatic animals and plants in managed aquatic environments is one solution that will be able to satisfy demand of this crucial staple. The Food and Agriculture Organization (FAO) predicts that by 2020 there will need to be an additional 37 million tons of farmed fish per year to maintain levels of seafood consumption (Packard, 2009).
Currently, hundreds of species of finfish, crustaceans, mollusks, and plants are raised in aquaculture. Most are finfish species, and many of these are grown as food fishes. The most common fresh-water aquaculture species are carp, tilapia, catfish, and trout. When choosing which species to cultivate in new areas it is important to consider growth rate, position in the food chain, climate and environmental adaptations, disease resistance, breeding characteristics, compatibility with other fish species in cultivation, and conversion efficiency (the ratio of feed required to pounds of meat harvested) (FAO, 1997).
Over 70 percent of freshwater comes from low-income, food-deficient countries. These nations in Asia, Africa, and Central and South America export at least a small percent of their aquaculture products to Europe and the United States. Benefits of aquaculture include reclaiming saline soils, increasing the supply of highly valued species, improving the reliability of fish supplies in the marketplace, offsetting losses in capture fisheries or in native fish populations, controlling parasites like mosquito and snail larvae that cause diseases such as dengue fever and malaria, and earning foreign exchange (UN/FAO, 1998).
Some of the costs of aquaculture include the fish meal and fish oil required to feed the farmed fish. Currently about a third of wild-caught fish are converted into fish meal. Salmon, one of the most popular farmed fish, requires nearly three pounds of feed fish for every pound of commercial salmon produced (SeaWeb, 2010). However, recent advancements have been allowing for a reduction in this feed-conversion ratio.
Integrated Multi-Trophic Aquaculture
Integrated Multi-Trophic Aquaculture (IMTA) is a specialized type of aquaculture which integrates different aqua-cultural methods into a single system and uses the waste byproducts from one process as input for another process. The two main processes which compose IMTA are:
- Fed Aquaculture
Fed Agriculture involves the breeding of species like shrimp and finfish. Requires supplemental feeding and can often result in eutrophication in the system.
- Extractive Aquaculture
As the name suggests, Extractive Aquaculture involves the extraction of plankton and nutrients from the surrounding environment and is used to produce bivalve mollusks and algae. This process can have a positive effect on eutrophic waters.
Eutrophication is a phenomenon that occurs when a water body is ‘over-fertilized.’ Thus resulting in large population growth of phytoplankton. The negative impacts of eutrophication are :
- Unnatural populations of phytoplankton
- Toxic plankton species in the body of water
- Decrease in certain species of algae
- Increased turbidity of the water
- Decrease in dissolved oxygen, resulting in hypoxia and possibly anoxia
- Reduction in harvestable fish
The purpose of IMTA is to address these issues. Fed Aquaculture, when practiced independently, often leads to eutrophication of the water body. Integrated Multi-Trophic Aquaculture, however, uses both the above methods in tandem so as to prevent eutrophication and form a sustainable environment (Rawson et. al., 2002).
The first process forms the main commercial component of IMTA while the second serves as a technique to prevent a negative impact on the ecosystem while still maintaining commercial viability. Studies have shown that although IMTA might decrease yield in the early stages of aquaculture, the healthy environment results in an overall increased yield over time. This is largely due to the fact that over-fertilization of lakes is prevented and the phytoplankton populations in the water body are restricted. This in turn helps form a sustainable environment for the species being raised in fed aquaculture.
The benefits of using both these techniques together are:
- Effective utilization of food supplies
- Improved water quality
- Reduced costs of production
- Increased productivity and yield in the long run
- Product Diversification
- Risk Reduction (due to natural control of eutrophication)
- Better Management Practices
Hypothetically, in a fish/bivalve/seaweed farm, at least 60% of the nutrient input should reach commercial products. This is three times more than in modern net-pen farms. The expected yield of a 1 hectare system were 35 tonnes of seabream, 100 tonnes of bivalves and 125 tonnes of seaweed (Chopin et all 2004, Krom MD and Neori A. 1989, Shpigel et all 1993, Krom et all 1985).
That being said, the purpose of using IMTA is often not to boost yield by a large amount but instead to form a sustainable production system which will not decrease in yield over the course of time.
Based on our classification system, Solution 2 will work in places with:
- Rural Coastal Areas
- Climate: A - Tropical, C- Temperate
- Land Grade: Grade 3 (Coastal Areas / Open Water Areas)
- Water Availability: NA
- Technology Access: High-Med (T1,T2,T3)
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