Use of Fish Somatic Indices to Assess Pollutant Exposure and Effects: A Case of Two Urban Rivers and a Wastewater Sedimentation Pond in Lake Victoria Basin

Abstract

Aquatic ecosystem health assessment is critical for early detection of disturbances and water habitat degradation. This study assessed the ecological status of two urban rivers as well a wastewater sedimentation pond in Kisumu City, Kenya using physico-chemical water quality parameters and the African catfish, Clarias gariepinus somatic indices. Site association of somatic indices was derived from Principal Component Analysis (PCA) whereas the relationship between water quality parameters was examined by Redundancy Ordination Analysis (RDA). PCA results revealed an increase in Gill Somatic Index (GSI) in the wastewater sedimentation ponds while Fulton’s Condition Factor (CF) increased in the midstream of Auji river and Kisat river mouth. Similarly, RDA showed that dissolved oxygen, temperature, total phosphorus, alkalinity and total nitrogen influenced the condition indices upstream of Kisat river and up-stream and midstream of Auji river. However more impact on somatic indices were recorded in the wastewater sedimentation pond. Although specific pollutants other than the physico-chemical parameters were not identified, application of somatic indices in the African catfish demonstrated that the two rivers as well as the wastewater sedimentation pond were contaminated by pollutants that can compromise the ecological health of the aquatic systems. The results of this study emphasized the negative impacts of anthropogenic activities on the environment.