Fish Biological Control of The Israeli National Water Carrier And Dual-Purpose Reservoirs (Fish Culture/Crop Irrigation): The Israeli Concept

The location of Israel in a semi-arid part of the globe and the seasonal rainfalls that are limited to short periods in wintertime (about 50 days of rain with ~650 mm average precipitation in the north of the country), are the main causes of chronic water shortage and frequent droughts. The Israeli Water Authority planned and constructed the National Water Carrier (NWC) to convey water from the sole Israeli source of fresh water, Lake Kinneret in the north, through the country to the Negev Desert (10 mm average precipitation) in the south. The water is transferred through a system that combines pipes (108 inch diameter), canals, tunnels, and reservoirs. Because the water is intended for human consumption, the reservoirs were stocked with a complex of fish for biological control. To support agricultural irrigation, regional local authorities and private fish farms have also constructed dual-purpose reservoirs in various parts of the country. These reservoirs store water for crop irrigation and also serve for fish culture. Some of them are used solely for irrigation, but in some reservoirs, fish are reared as a by-product. About 250 dual-purpose reservoirs of various capacity and surface areas (10-40 ha) have been constructed in Israel in the last two decades. The first fish species, tilapia, Oreochromis aureus (Steindachner), was stocked in reservoirs in the early 1960s, and common carp, Cyprinus carpio L., was stocked in reservoirs in the end of 1960s in an attempt to control phyto- and zooplankton. Although the results were positive, it soon became obvious that these species were prolific and had multiplied extensively, which resulted in overcrowded populations of stunted fishes and caused management difficulties. Consequently, a group of Chinese carp was introduced, namely: the phytoplanktophagic silver carp, Hypophthalmichthys molitrix (Val.), the macrophytophagic grass carp, Ctenopharyngodon idella (Val.), the zooplanktophagic bighead carp, Aristichthys nobilis (Richardson), and the malacophagic black carp, Mylopharyngodon piceus (Richardson). In addition to these four species, predatory (or "police") fish have been integrated into the fish complex; these include the marine European seabass, Dicentrarchus labrax (L.), or the hybrid striped bass, Morone saxatilis (Walbaum) and white bass, M. chrysops (Rafinesque), or red drum, Sciaenops ocellatus (L.). Red drum is also considered to be a high quality consumer fish. These fish are capable of controlling efficiently the unwanted spawning of carp and tilapia. With these combinations of fishes, various species play specific roles by utilizing specialized feeding niches without competing with other species. Due to the variety of conditions in the reservoirs, the composition of fish species is modified according to individual characteristics of each reservoir (soil, area, depth, source of water, role of the fish, etc.). Adequate stocking of species into reservoirs may positively affect synergism amo