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 ponds release their effluents containing

elevated levels of nutrients as a result of fertilizers and feeds used during pond

management activities to the same streams. This study was done at a fish farm located

along Sasala Stream within Lake Victoria North catchment. The objective was to assess

the effect of discharge from earthen fishponds on the water quality of the stream using

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 Stream is located in the outskirts of Kakamega town and

supports a number of fishponds. Six sampling sites (marked 1 to 6) were established

along the stream: one upstream; two were in ponds, each stocked with Nile Tilapia

(Oreochromis niloticus and Catfish (Clarias gariepinus) respectively. Three sites were

situated downstream after the ponds. Water and macroinvertebrates samples were

collected in triplicate at intervals of fourteen days in the months of March to August.

The samples were examined both in the field and the laboratory to determine the

physicochemical state of Sasala Stream. Temperature, pH, Electrical conductivity, Total

dissolved solids, Turbidity, Dissolved Oxygen were measured in situ with a Portable

multi-parameter meter; Biological Oxygen Demand, Ammonia and Phosphate

phosphorus were determined in the laboratory based on standard methods developed by

The American Public Health Association,1998. Macroinvertebrates Species composition

and diversity were determined using Shannon-Weiner and Simpson diversity Indices.

The relationship between selected physicochemical parameters and between

physicochemical parameters and macroinvertebrates was carried out using One Way

Analysis of variance (ANOVA). In cases where ANOVA showed significant

differences, Tukey test was used to separate the differences. Spearman rank order

correlation was applied to determine the relationships between physicochemical

parameters; and between physicochemical parameters and macroinvertebrates. All

statistical analyses were done using Sigmaplot 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. Ammonia values were 113.14μgl-1in the upstream site and

431.57 μgl-1 in the catfish site. Phosphate-P values ranged between 1727μgl-1 in site 2

and 3 and 1692μgl-1 in site 6. From the observations earthen fish ponds discharge

affected 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. Most of the macroinvertebrates families showed significant positive

correlations with pH, TDS, Turbidity, Biological Oxygen Demand, ammonia and

phosphorus. Sustainable fish farming will involve production systems that focus on the

relationships between the culture techniques and the environment. Hence, regular

monitoring of fish farms, good farm management and suitable planning of fish farms.