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For trout, stocking rates of 30 to 50 kg/m 3 are normal at the end of a rearing cycle, while for marine species, such as sea bass and sea bream, the achievable load is lower, between 15 and 20 kg/m 3. The total volume required for a raceway is calculated by dividing the total amount of fish in kg by the desired stocking rate in kg per m 3. [17]
Large aquaculture facilities (i.e. those producing 20,000 pounds (9,100 kg) per year) which discharge wastewater are required to obtain permits pursuant to the Clean Water Act. [167] Facilities that produce at least 100,000 pounds (45,000 kg) of fish, molluscs or crustaceans a year are subject to specific national discharge standards. [168]
A number of countries have created their own national standards and certifying bodies for organic aquaculture. While there is not simply one international organic aquaculture standardization process, one of the largest certification organizations is the Global Trust, [9] which delivers assessments and certifications to match the highest quality organic aquaculture standards.
Urea is the most used fertilizer in the world, due to its high content of nitrogen, low cost and high reactivity towards water. [32] When exposed to ocean waters, urea is metabolized by phytoplankton via urease enzymes to produce ammonia. [33] + +
A maize crop yielding 6–9 tonnes of grain per hectare (2.5 acres) requires 31–50 kilograms (68–110 lb) of phosphate fertilizer to be applied; soybean crops require about half, 20–25 kg per hectare. [21] Yara International is the world's largest producer of nitrogen-based fertilizers. [22]
Typical build ratios are .5 to 1 square foot of grow space for every 1 U.S. gal (3.8 L) of aquaculture water in the system. 1 U.S. gal (3.8 L) of water can support between .5 lb (0.23 kg) and 1 lb (0.45 kg) of fish stock depending on aeration and filtration.
In addition, 1.3 million tons of aquatic plants (seaweed etc.) were captured in wild fisheries and 14.8 million tons were produced by aquaculture. [2] The number of individual fish caught in the wild has been estimated at 0.97-2.7 trillion per year (not counting fish farms or marine invertebrates). [3]
On a dry-dry basis, 2–4 kg of wild-caught fish are needed to produce 1 kg of salmon. [23] The ratio may be reduced if non-fish sources are added. [20] Wild salmon require about 10 kg of forage fish to produce 1 kg of salmon, as part of the normal trophic level energy transfer. The difference between the two numbers is related to farmed salmon ...