Tilapia zillii (Gervais, 1848), commonly known as St. Peter Fish, (TZ) is a very common cichlid in Lake Kinneret . The fish is also common in the Jordan River System and throughout the Israeli Coastal Plain rivers. The fish originates from African lakes and rivers [1] - [3] . The salinity tolerance of this fish is very high, and a specimen of it was documented in the Mediterranean [4] . TZ belongs to the Family Cichlidae, of which more than 100 genera with more than 1,300 species are known. The native zoogeographical range of distribution cuts across the tropical and subtropical Africa, the Near East, West and East Africa, as well as Israel and Jordan Valley . The body of TZ is yellowish in color with vertical black stripes. The stripe colors of black and silver pattern are frequently changed, with respect to the spawning season when the lips turn white. It was suggested that the Kinneret population of TZ should include more than one species or sub-species due to a high variation in body color. Most common total length of adult varies between 12.0 - 22.0 cm ( Plate 1 ) [2] . There is a big black spot on the dorsal fin which disappears in big size individuals, and sometimes, the whole body color turns black. The total number of soft rays and spines in the dorsal fin of TZ is 27 or more. In the first gill arch, there are about 8 - 9 gill rakers, unlike other Tilapias, Sarotherodon galilaeus, Oreochromis aureus, Tristramella simonis simonis, and Astatotilapia flaviijosephi. TZ is not a mouth breeder; rather, it is a guarding nest spawner. The nest and brood care by TZ are dependent on the nature of the substrate and on the exposure of the nesting location to wave action [5] . Ben-Tuvia [2] documented the spawning season of TZ starting from the month of April to the end of August, with several reproduction cycles in a year. The nests containing the eggs are guarded by both the male and female TZ. The TZ lays and fertilizes a higher number of eggs in comparison with the mouthbreeder Tilapias. The parental nest guarding is more intensive in exposed substrate, or between aquatic plants, where simple nests are constructed on a sandy-clay bottom and abbreviated on excavated deep (20 - 80 cm ) brood chambers. The reason for choosing TZ as a typical presenter of the Kinneret Ichthiofauna is due to the existence of its dense population and the wide range of tolerance to environmental conditions. The fish is very common throughout the entire lake in all seasons and known as a nest constructor in the shallows.

TZ is a significant obligatory territorial fish breeder. Like other tilapias which originates from Tropical-Ethiopia, its breeding season is in summer. Territorial site selection is initiated by the male, and the female joins later. The bi-parental coupling behavior continue during most part of the year. The nest construction is carried out bi-par- entally. Breeding efficiency differs among nest builder fishes under various environmental conditions. These types of environmental alterations frequently occur in shallow lakes, and also, in deep lakes, like in lake Kinneret ( 44 m and 26 m maximum and mean depths, respectively). High amplitude and frequencies of inundation by the Water Level Fluctuations (WLF) in Lake Kinneret, generate environmental changes in the shallows and in the vegetation beach belt. Consequently, fishes are confined to suboptimal habitats. The bi-parental guarder monogamous TZ covers a wide range of nesting behavior in different exposed of plant, or covered substrates in Lake Kinneret [5] . The common seasonal fluctuations in WL (Water Level) are obviously elevated during winter (January-May), and it declines from mid-May to November, and very minor increase is experienced in December. Nevertheless, due to the national constraint in water pumping from Kinneret, aimed at domestic supply, which generates long term changes and differ in volume with precipitation: decline through sequential droughts and exceptional increase during heavy rainy winter. A decline in WL exposes the beach belt, which is immediately covered by vegetation, mostly Phragmites australis australis, and an abrupt increase in WL the subsequent year, create extremities of habitat changes for spawning fishes. The different nesting strategies and structural adaptations of TZ [5] enable it to exploit the Kinneret ecosystem. Two major nest types were found: Shallow “plate saucer” shape, where many guarded eggs are laid and fingerlings are also protected on a sandy-muddy substrate, densely covered by submerged and emerged plants. The female and male TZ guard the eggs together during the incubation period and remove the unfertilized eggs. After incubation, they protect the larvae and young fingerlings. This type of nest is differs from the “shallow saucer” nests of SG by several parameters: SG preferred exposed substrate plants are absent, and the number of eggs laid is much lower and they

Plate 1. Adult Tilapia zillii (TL 20 cm) [2] .

are immediately collected by the males and female, rarely “waiting” to be photographed by divers. TZ spawners also maintain courtship and lay eggs on top of uncovered stones/boulders with no indication of nest structure. Wave action disturbance occurs quite often. The granulometric composition of the nest substrate and the space between, was analyzed (for methods see Bruton and Gophen, 1992). The second type of courtship and nest structure is densely distributed, in fully and partly sheltered open lagoons with clay-mud and claying substrate. The nests are found in very shallow and partly sheltered waters and consist of 1 - 3 brood chambers which are 5 cm - 85 cm deep. In fully sheltered lagoons, 1 - 12 brood chambers are located in the middle compound (15 cm - 45 cm in diameter and 2 cm - 25 cm deep), eggs are laid into the chambers and the larvae in there swim outside from time to time. Parental guarding is maintained close to the chambers, accompanied by fins waving for water (and oxygen) exchange. In one site, 957 nests were counted along the 180 m stripe, and along the 85 cm width of a clayed substrate lagoon bank. Shefler [6] carried out fish (commercial size and fingerlings) distribution survey in the Kinneret shallows (0.3 - 1.0 m depth) during the months of May-August. Commercial fish size (net mesh size > 72 cm ) of Tilapias (>250 g/ind) included only 5% TZ. TZ is a non-commercial fish in Lake Kinneret due to the small size of its adults (11 - 23 cm TL) and unwanted flavor trait. As part of the British Mandate Authority on Palestine (1918-1948) the administrative responsibility included the formulation of fishery regulation in Lake Kinneret (Lake Tiberias, Sea of Galilee). Dr. C. K. Ricardo Bertram, [7] from the Department of Agriculture and Fisheries, Fisheries Office in Haifa, thoroughly investigated the conditions of fisheries in the lake and submitted a report: Abridged Report on the Fish and Fishery of Lake Tiberias No. 9, 1944. In this report, there are various fishing gears techniques with respect to several fish species, including TZ. On one of the Amendments which is part of Rule 6, it is indicated that the minimum size which may be landed or marketed of TZ (Musht Addadi in the report) is 18 cm TL. Consequently, it can be indicated that TZ was commercially utilized in previous decade. Nevertheless, landings of TZ were completely absent from Lake Kinneret’s fishery reports from early 1950’s and onwards. Loiselle [8] studied the colonial breeding and territorial behavior of TZ spawning. In his [8] study on site selection, he documented remarkable observations in nest constructing and the share of activity between male and female. The topics discussed are the suitability of nest building site which only referred to the substrate trait and interference by intruders, but parameters like exposure to wave action and sheltered vegetation were not discussed.

The particle size composition of the nest material and the space between nests in the compound was measured in three Kinneret zones: Inlet zone of the Zaki and Masudiya rivers in the nature Reservation area of Beteicha in the East Northern part of the lake; In the Tsalmon inlet zone, on the western middle part of the lake. In this region, a very dense distribution (800 along 1.5 Km ) of nests of TZ were documented. The results of granulometric analysis are shown in Figure 1. The average of the three locations is shown in Table 1.

The results in the Table 1, Table 2 and in Figure 1 clearly indicates that TZ fishes selected a larger particle size substrate for nest construction within the sheltered region. Cummings [9] indicated that no nests in the open shore sites were free of merged vegetation (reeds). Low densities of vegetation covered zones were preferred by

Tilapias as their breeding substrate [9] . Nevertheless, in several beach segments throughout the entire lake, the shoreline nests of TZ were absent. It is in partial contradiction with [5] , which reported about the TZ breeding activity in those beach segments. Bruton and Gophen [5] concluded that 4 critical substrate parameters control the suitability of TZ breeding: exposure to wave action, granulometric composition, water depth and macrophyte density. Each one of those factors, and any combination of all, might be the limiting factor. A prominent photo pre- sentation of TZ nest with eggs ([5] ; Figure 2, Figure 3) is shown in [9] . Cummings [9] indicated maximal breed- ing activities of S. galilaeus and O. aureus from mid-April to mid-June and that of TZ, later, ((June-September). Moreover, presented photos [9] confirm bottom habitat selection of un-covered sites by submerged vegetation.

The omnivorous trait of the adult food composition which include planktonic and benthic components, together

with high plants debris was documented in [2] . Spataru [20] reported that the ability of TZ to collect zooplankton organisms is low. Zooplankters presented in the gut of adults were probably collected from zooplankton swarms or at high densities in the shallows. Spataru [20] also reported some benthic organisms like Nematods, Ostracods, spicula of Porifera, and even preyed small fingerlings. It was noted that TZ is known as an agressive animal which intensively attack other TZ individuals. In recent studies, the food composition of young TZ was analyzed. The gut content of adult TZ (TL > 10 cm, W = 120 g) in December 2014, was dominated by small foraminifers and sand grains, indicating materials collected from the bottom. The gut content of fingerlings of TZ (TL = 3 - 4 cm ) in July 2015, was dominated by fragments and entire conch of Melanoides sp. The source of bottom burrowing substances is indicated. El-Bolock and Koura [14] suggested that there is plenty of plankton suitable food for S. galilaeus and T. nilotica. Data given here indicates TZ preferential feeding of benthic organisms. It is assumed that the difference in feeding habits and food composition is partially responsible for the low rate of growth of TZ, in comparison with S. galilaeus and T. nilotica.

The biology of Tilapia zillii in Lake Kinneret was evaluated. The food resources for adults and young fingerlings are located at the bottom of the shallow waters. The nest construction is carried out by the male and female, and coarse grain matters in habitats shallower than 2 m , are preferably selected. Nests are constructed in sheltered and in exposed substrate to wave action. Massive fish kill, mostly Tilapia zillii, was the result of extreme temperature decline. Record of water level, epilimnetic temperature and Jordan discharges indicated the impact of heat input in winter through the Jordan discharge. Two independent methods of temperature monitoring in terrestrial habitats accompanied by the winter temperature of the Kinneret Epilimnion partly confirmed the influence of ENSO cases on the epilimnetic heat decline accompanied by increase in fish availability to disease and parasite infection.

MosheGophen, (2016) On The Biology of Tilapia zillii (Gervais1848) in Lake Kinneret (Israel). Open Journal of Ecology,06,167-175. doi: 10.4236/oje.2016.64017