Temporal variation in fish community structure in a newly created wetland lake (Lake Agmon) in Israel

Lake Agmon was constructed in summer 1994 in the northern part of the drained Lake Hula swamp, as part of the Hula Reclamation Project. One of the main goals of the project was to attract aquatic and semi- aquatic birds to the area as a basis for planned eco-tourism and one of the main concerns of the project was the potential for increased proliferation of mosquitoes (including vector species of malarial parasites). There was a perceived need, therefore, to establish and maintain a suitable fish community. This present study documents the developments in the fish community in Lake Agmon between May 1995 and December 1996. The lake was initially stocked with two fish species, Tilapia zillii and Gambusia affinis, to control mosquitoes and to provide suitable small- bodied forage species for piscivorous birds. Subsequent stocking also included Oreochromis aureus, and Cyprinus carpio. Additional species were established by immigration from the Jordan River. Relatively large species ( e.g., Clarias gariepinus and C. carpio) flowed into the lake as eggs or juveniles, whereas the smaller species ( e.g., Hemigrammocapoeta nana, Pseudophoxinus kervillei and Aphanius mento) entered the lake as adults. In the first year, eight fish species were found in Lake Agmon: T. zillii, G. affinis, C. gariepinus, C. carpio, Capoeta damascina, P. kervillei, Acanthobrama lissneri and H. nana. Of these, T. zillii, G. affinis and H. nana were dominant, though the relative abundance of H. nana was very low in spring, and increased during summer. In the second year, O. aureus, A. mento and Anguilla anguilla also occurred in the lake. The density of P. kervillei increased, in comparison with the previous year. The relative proportions of juvenile and adult fish also changed in the second year. A high percentage of young T. zillii was found during the first spring, decreasing in the summer and autumn. The proportion of juveniles of both G. affinnis and H. nana was very low during the first year, but increased during the second. These results indicate that the fish community of Lake Agmon had not stabilized by the end of 1996 and that further changes in relative abundances, and species, age and sex compositions should be expected.