Relative abundance of mosquitoes and snails associated with water hyacinth and hippo grass in the Nyanza gulf of Lake Victoria A. V. O. Ofulla, 1 * D. Karanja, 2 R. Omondi, 3 T. Okurut, 4 A. Matano, 4 T. Jembe, 3 R. Abila, 3 P. Boera 3 and J. Gichuki 3 1 Maseno University, Maseno, 2 Kenya Medical Research Institute, 3 Kenya Marine and Fisheries Research Institute, and 4 Lake Victoria Basin Commission, Kisumu, Kenya Abstract This study was conducted from September to December 2008 to investigate the relative abundance of malaria vectors and schistosomiasis host snails associated with aquatic weeds in Nyanza Gulf (Lake Victoria). Larval and adult’s stages of mosquitoes, lakeflies and snails were collected and identified with standard entomological and malacological tech- niques. The relative species composition and abundance of fish associated with macrophytes were also determined. Physico- chemical parameters were determined with standard analytical methods. Community-based surveys were also conducted, using standard questionnaires, focused group discussions and direct observations. The results of this study indicated that the abundance of malaria-causing mosquitoes was low, accounting for only 0.4% of the total number of mosquitoes and lake flies collected from the gulf. Lake flies (Chaoborus and Chironomus spp.) were the most abundant flying insects asso- ciated with aquatic macrophytes (84.2%), followed by Culicines Culex spp. (12.2%) and Aedes spp. mosquitoes (3.2%). Biomphalaria sudanica and Bulinus africanus, the two most common hosts for schistosomiasis in the gulf, were detected in both types of macrophytes, but were most significantly attached to water hyacinth (P < 0.0001) and hippo grass (P = 0.0003). There were significantly fewer snails attached to the hippo grass, compared with those unattached in the open water (P < 0.05, GENMOD). Different habitats exhibited low Secchi disc transparency values, but elevated total phosphorous (TP), total nitrogen (TN), chlorophyll-a concentrations, as well as algal cell counts. Furthermore, Oreochr- omis niloticus and Haplochromine fishes were more abundant in water hyacinth mats compared with hippo grass mats and open-water habitats. The low mosquito abundance indicated that the sampled habitats were unsuitable for mosquito breeding, likely attributable to water turbulence and ⁄ or predation by larvivorous fish. The strong association between B. sudanica and B. africanus and aquatic macrophytes, and the observation that local communities perform many lake- shore-related activities that bring them into contact with water, can potentially lead to a higher prevalence of schistosomi- asis in the Nyanza Gulf region. Key words aquatic macrophytes, lake flies, Lake Victoria, malaria mosquitoes, Nyanza gulf, schistosomiasis snails. INTRODUCTION Water hyacinth Eichhornia crassipes (Mart.) Solms – Lau- bach, of South American origin, gained attention in the past as an ornamental plant because of its attractive pur- ple flowers. It was first distributed by gardeners and hor- ticulturists more than a century ago. Because of its extremely fast growth rate, however, it soon became the major floating waterweed of tropical and subtropical regions worldwide, dispersing easily, displacing indige- nous floras, increasing waterborne diseases, and creating problems in reservoirs, fisheries, irrigation schemes and transportation routes (Timmer & Weldon 1967; Mitchell & Thomas 1972; Gopal 1987; Epstein 1998; Levy 2004; Ogwang & Molo 2004). Communities living around Lake Victoria have a high dependency on the lake, with many of their daily activities closely linked to it. Questions regarding relationships between human health and water *Corresponding author. Email: ofullavo@yahoo.com Accepted for publication 25 May 2010. Ó 2010 The Authors Doi: 10.1111/j.1440-1770.2010.00434.x Journal compilation Ó 2010 Blackwell Publishing Asia Pty Ltd Lakes & Reservoirs: Research and Management 2010 15: 255–271