Closed or re-circulating system

Recirculating systems are usually characterized by minimal connection with the

ambient environment and the original water source. These systems have minimal exchange of water during a production cycle, hence the description as ‘closed systems. Water is added to offset the effects of evaporation or incidental losses or, more frequently, to maintain water quality. Some water is dis-charged and replaced each day in most recirculating tank systems with intensive culture. This arises from aspects of the regular maintenance system, such as removing accumulated solids from filters. Water quality in completely closed tank systems with intensive culture is much more difficult to maintain than in systems in which there is a regular 5% or more replacement per day. Even with some limited water exchange each day, water quality within a recirculating tank system will only be maintained by artificial manipulation. At high stocking densities without recirculation technology, a water exchange in

excess of 100% per hour would be required to maintain water quality during

maximal production. In recirculating tank systems, water quality is maintained by pumping the culture water through specialized filtration and aeration equipment. The cost of construction and production in intensive recirculating tank systems

has limited the commercial development of these systems for grow-out production.

Advantages of closed systems

1. Easily harvesting.

2. High stocking density.

3. Require minimal water

4. Food and drugs can be added efficiently into the system

 

5. Complete control of water condition

Disadvantages of closed systems

1. High capital coast

2. Require very careful management

3. Rapid spread of disease.

Exercise 51. Test yourself by answering these questions and summarize given information.

Unit 9

Text A

Fish farming methods

Read the text and translate. Be ready to discuss.

Fish farms or fish farming is a form of aquaculture. The act of fish farming is about raising fish commercially in tanks or enclosures for human consumption. There are different types of fish farms that utilize different aquiculture methods.

       The first method is the cage system which use cages that are placed in lakes, ponds and oceans that contain the fish. This method is also widely referred to as off-shore cultivation. Fish are kept in the cage like structures and are “artificially fed” and harvested. The fish farming cage method has made numerous technological advances over the years, especially with reducing diseases and environmental concerns. However, the number one concern of the cage method is fish escaping and being loose among the wild fish population.

The second method is irrigation ditch or pond systems for raising fish. This basic requirement for this method is to have a ditch or a pond that holds water. This is a unique system because at a small level, fish are artificially fed and the waste produced from the fish is then used to fertilize farmers’ fields. On a larger scale, mostly in ponds, the pond is self-sustaining as it grows plants and algae for fish food.

The third method of fish farming is called composite fish culture which is a type of fish farming that allows both local fish species and imported fish species to coexist in the same pond. The number of species depends, but it is sometimes upwards of six fish species in a single pond. The fish species are always carefully chosen to ensure that species can coexist and reduce competition for food.

The fourth method of fish farming is called integrated recycling systems which is considered the largest scale method of “pure” fish farming. This approach uses large plastic tanks that are placed inside a greenhouse. There are hydroponic beds that are placed near the plastic tanks. The water in the plastic tanks is circulated to the hydroponic beds, where the fish feed waste goes to provide nutrients to the plant crops that are grown in the hydroponic beds. The majority of types of plants that are grown in the hydroponic beds are herbs such as parsley and basil.

T he last type of fish farming method is called classic fry farming this method is also known as “flow through system”. This is when sport fish species are raised from eggs and are put in streams and released.

Exercise 51. Test yourself by answering these questions and summarize given information.

Text B

 The most common fish spices raised on fish farms.

prominent	[ˈprɒmɪnənt]	известный
invasive	[ɪnˈveɪsɪv]	агрессивный
catadromous fish		катадромная
resilient	[rɪˈzɪlɪənt]	упругий; эластичный
soybean	[ˈsɔɪbiːn]	соя
cod	[kɒd]	треска
channel catfish	[ˈtʃan(ə)l| |ˈkatfɪʃ]	проточный сом
tilapia		тилапия
carp	[kɑːp]	карп
salmon	[ˈsamən]	лосось европейский

Exercise 39. Read and translate the following words and word combinations from English into Russian. S altwater fish, Atlantic salmon, eel farming, recirculating tank, intensive pond facilities, profitable, emerge, carnivorous, catadromous fish,  fish farming industry, tropical fish, predominant, extremely difficult, albacore, tuna, stunted growth, net pens offshore, cereal-based diet, invasive fish species, additional medication.

Read the text and translate. Be ready to discuss.

There are a number of different fish species that are raised on fish farms, the most common fish spices raised are salmon, carp, tilapia, catfish and cod.

Catfish farming

Catfish are easy to farm in warmer climates. Catfish are predominantly farmed in fresh water ponds and fed mostly soybeans, corn and rice. Catfish are often considered one of the more sustainable fish specifies for fish farming purposes. Cultivating catfish first began in the 1900s and became commercialized in the 1950s. Catfish is populous because of its health benefits and market demand. Farm-raised catfish are usually harvested at 18 months of age where as wild catfish usually get much bigger. There are a number of catfish species, but the three most prominent ones are blue catfish, channel catfish, and flathead catfish.

Tilapia farming

Tilapia is the third most popular fish used in fish farming or aquaculture, with the first two being carp and salmon. They have increased in popularity due to their high protein, large size and growth capabilities. Tilapia is a tropical fish that requires warmer water to survive. The ideal water temperature is usually between 28 to 30 degrees C. Tilapia fish are known to reproduce rapidly and this is a challenge for managing tilapia fish species for farming use. If not managed properly, fish will aggressively compete for food which may result in stunted growth. Therefore, males are almost used exclusively. Tilapias are resilient towards fighting off diseases and parasites. Tilapia fish farming originated in Africa and is popular in Honduras, Papua New Guinea, Philippines and Indonesia. Tilapia fish require a cereal-based diet and don’t eat other fish, but they are also considered to be one of the most invasive fish species.

Salmon farming

Salmon is one of the most popular fish species with the most commonly farmed being Atlantic salmon. There are two other varieties of Pacific salmon that are also farmed – Chinook and Coho. Farmed salmon are vaccinated to prevent disease outbreaks and only on rare occasions do they require additional medications. There are often questions about the different colours between wild and farmed salmon – farmed salmon aren’t dyed, their colour comes from their food. Salmon feed is made to conserve wild fish stocks.

Tuna farming

Tuna fish are saltwater fish and are important in the commercial fish farming industry. Japan is the biggest consumer of tuna and has invested a significant amount of research into studying the fish. There are different species of tuna including, bluefin, yellowfin, and albacore. Bluefin tuna populations have dropped significantly in some regions due to over fishing. Farming tuna is complex as the fish are “massive” and are very active - so simulating their natural environment is extremely difficult. Most tuna for human consumption are caught in the wild and raised in a facility to increase weight gain. Tuna are carnivorous and eat other fish. Tuna are typically farmed in net pens offshore and in some cases are farmed in recirculation systems.

Eel farming

Eel fish farming emerged in the early 1950s and it is considered one of the most profitable in terms of export value in the fishing industry. However, the profit value is largely driven by the Asian markets and is culture specific. Eels are a carnivorous and catadromous fish, which means that when they are young they live in fresh water, but as they mature they migrate to the sea for breeding –spending anywhere from 8 to 30 years in freshwater before they migrate. The majority of eel farming takes place in Asia, with China, Japan and Taiwan leading as the biggest producers. Glass eels are preferred over elvers because they are easier to transport and wean onto artificial diets. Eel farming can take on one of two different forms – high intensity recirculating tank (indoors) or intensive pond facilities.