PHYSICOCHEMICAL WATER QUALITY AND MACROINVERTEBRATE OCCURRENCE IN SASALA STREAM RECEIVING WASTEWATER DISCHARGE FROM EARTHEN FISHPOND FARMIN KAKAMEGA COUNTY,KENYA

Abstract

Fish farming is now a major source of global and local fish requirements of food, raw materials, income and ecological considerations supplementing the dwindling output from the wild waters. Several systems are now in place including use of earthen, concrete, liner ponds and race ways.Earthen ponds are of major concern as they mainly depend on natural stream water sources. The pondsrelease their effluents containing elevated levels of nutrients as a result of fertilizers and feedsused during pondmanagement activitiesto the same streams.Thisstudy wasdone ata fish farm located alongSasala Streamwithin Lake Victoria North catchment. The objective was to assess the effect of discharge from earthen fishpondson the water quality of the streamusing macroinvertebrates and the physicochemical state as indicators.The study intended to generate data and information that would be used by stakeholders, scholars, policy makers and natural resource managers to come up with strategies for sustainable aquaculture ventures. Sasala Streamislocatedinthe outskirts of Kakamega town andsupports a number of fishponds.Six sampling sites(marked 1 to 6)wereestablished along the stream: one upstream;two were in ponds, eachstocked with Nile Tilapia (OreochromisniloticusandCatfish (Clarias gariepinus) respectively.Three sites were situated downstream after the ponds. Water andmacroinvertebrates samples were collected in triplicate at intervals of fourteen days in the months of March to August. The samples wereexamined both in the field and the laboratory to determine the physicochemical stateof Sasala Stream.Temperature, pH, Electrical conductivity, Total dissolved solids, Turbidity, Dissolved Oxygen were measured in situwitha Portablemulti-parameter meter;Biological Oxygen Demand, Ammonia and Phosphate phosphorus were determinedin the laboratory based on standard methods developed by The American Public Health Association,1998.Macroinvertebrates Species compositionand diversitywere determinedusing Shannon-Weiner and Simpson diversity Indices.The relationship between selected physicochemical parametersandbetween physicochemical parameters and macroinvertebrates was carried out using One Way Analysis of variance (ANOVA). Incases where ANOVA showed significant differences, Tukey test was used to separate the differences. Spearman rank order correlation wasapplied to determine the relationships between physicochemical parameters; and between physicochemical parameters and macroinvertebrates.All statistical analyses were done usingSigmaplot version 11.The means for the following physicochemical parameters were significantly different within the sampling sites. (p=˂0.05): Dissolved Oxygen, Turbidity, Conductivity, Biological Oxygen Demand and Total Dissolved Solids.Ammoniavalues were 113.14μgl-1in the upstream site and 431.57μgl-1in the catfish site.Phosphate-P values ranged between 1727μgl-1in site 2 and 3 and 1692μgl-1in site 6. From the observations earthen fishponds dischargeaffected the water quality of the stream.Six Orders of macroinvertebrates comprising of 10 families were identified.Insects (83%), Non-insects (17%). Baetis sp.and Velia sp.dominated across the sampling sites while Notonecta sp.and Chironomus sp.were less dominant. Mostof the macroinvertebrates families showed significant positive correlations with pH, TDS, Turbidity, Biological Oxygen Demand, ammonia and phosphorus.Sustainablefish farming will involveproduction systems thatfocus on the relationshipsbetween the culture techniques and the environment.Hence,regular monitoring of fish farms, good farm management andsuitableplanning of fishfarms.