From Biblical time the people prayed for rain that was in shortage. But praying is not enough; even if God blessed the land with rain, the hilly and mountainous land cannot keep the water. To deal with these impediments, different solutions and methods to maximise water use have been developed. These solutions include:
1) Reservoirs to store rainwater during the wet season. Israeli agriculture is now largely intensive and depends on irrigation from these reservoirs during the dry summer. Recently, it has become common to use irrigation reservoirs for fish culture in integrated farming systems. These integrated agriculture-aquaculture systems use the water twice: within an aquaculture production system, and subsequently to supply irrigated agriculture systems. This system, now a few decades old, was a significant step in the intensification of inland fish culture in Israel.
2) Large-scale recirculating systems, in which water from outdoor fish ponds, raceways and tanks, is passed into sedimentation ponds to remove the solids. The water is then passed to an adjacent water reservoir, and good quality water is returned from the reservoir to the fish rearing systems.
3) Highly-intensive recirculating systems (RAS) that incorporate water filtration systems, such as drum filters, biological filters, protein skimmers and oxygen injection systems. Culture is intensive, as the stock is entirely dependent on a comprehensive artificial diet and there is acute management of water parameters. These systems are usually compact, take up a relatively small area and are extremely efficient with water usage.
Fish farming in Israel started in the 1930s, when the common carp (Cyprinus carpio) was imported from (former) Yugoslavia, and production practices common in Central European countries were implemented. In addition to the common carp, freshwater fish farms grow also tilapia species, flathead mullet (Mugil cephalus), rainbow trout and rock bass (hybrid striped bass). Marine culture focuses on production of gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax). Coldwater and tropical ornamental fish are also bred in Israel. The most important species are the cold-water koi carp and goldfish, and the tropical cichlids (mainly angelfish), and livebearers such as guppy, platy, swordfish and molly.
Tilapias are currently the leading species in Israeli fresh-and brackish-water aquaculture. Tilapias are tropical fish of the Cichlidae family and are native to Africa and Israel. Israel is on the northern border of the natural distribution of this family. Tilapias are omnivores, with preference for plant materials (live and dead algae). As members of the Cichlidae family, tilapias are characterized with well-developed and specialized parental care systems. Tilapias produced in Israel are maternal mouth-brooders (females incubate the fertilized eggs in their mouth until after hatching). These include hybrids between the local blue (or Jordan, as it is called in Hebrew) tilapia (Oreochromis aureus) and the introduced Nile tilapia (Oreochromis niloticus), as well as a number of red tilapia strains.
A relatively low number of eggs are spawned per female – from a few hundreds to 2,000, depending on the female's weight. The spawning season starts in the spring and continues throughout the summer. The optimum temperature for reproduction and development is between 25 and 28°C. Because of their tropical origin, tilapias are sensitive to low temperatures. At temperatures of 18°C they stop eating and growing, and they cannot survive in temperatures below 10-12°C. To overcome this limitation, Israeli scientists and fish farmers developed various strategies for over-wintering the young tilapia produced during the hot season for grow-out in the following season.
Traditionally, fish are raised in ponds, and less frequently in floating cages in the sea or lake. There is a wide range of pond types, which differ in structure, type of bottom and depth:
1. A typical fish pond (earthen pond) is dug in the ground and has a soil bottom. The sizes of ponds in Israel are usually between 100 m2 and 10 hectares. Small ponds are used for reproduction, nursery and holding for overwintering and the larger ones are used for fattening to market size. The average depth of an earthen pond is 1-2 meters. When used for fish production, these ponds may yield 0.7-0.8 kg of fish/m2 of water.
2. Reservoir: Reservoirs where dug to preserve the precious water during the wet season. Israeli agriculture depends, to a large extent, on irrigation of crops during the dry summer. Nowadays, one of the common usages of irrigation reservoirs is for fish culture. Depth of reservoirs range from 6 to 12 meters and surface area from 5 to over 10 ha. A dual-purpose reservoir for irrigation and fish culture fills up during autumn with spring water and early winter rains. The fish grows in late spring or early summer, water are pumped for crop irrigation and the water level in the reservoir drops gradually, while fish are being grown. By September/October, only 1-2 meters of water is left and the fish farmers start to thin out the fish population and prepare for final draining of the reservoir and harvesting the fish. Fish production in reservoirs reach up to 1.5 kg of fish/m3 of water. Thus the smallest aquaculture reservoir, which holds 500000 m3 of water, yields around 750 metric tons.
The fish farmers developed various technologies for efficient harvesting of fish from the reservoirs. These include a) built-in concrete pits at the end of the reservoir's outlet pipe, that enable convenient harvesting of fish from the reservoir, and handling after they are removed via the pipe. The pits have filters for separating the fish from the water as well as revival equipment to ensure the welfare of the fish; b) vacuum pumps or conveyer-belt lifts to bring fish concentrated by nets up to the pond bank; and c) lift-nets that enable thinning-out fish from the reservoirs during the culture season without draining the water.
3. Concrete tanks: A third type of pond has walls and usually also a solid bottom. These ponds are used for intensive fish production, where a much higher density of fish is produced than in earthen ponds and reservoirs. This requires water circulation in the pond to collect the feces and unconsumed feed and remove them from the pond, as well as from the ponds to a reservoir from which high-quality water is fed back to the intensive ponds. Fish yield in this system may reach up to 15 kg of fish/m3 of water. Highly-intensive recirculating systems (RAS) may support up to 50 kg of fish/m3 of water.
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