Influence of fish pond fertilization mode on microbiota at sagana fish farm, Kirinyaga district
Njeru, Jamlick Mutegi
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In order to stimulate growth of phytoplankton to serve as fish food, fish farming in Sagana is integrated with livestock and poultry keeping. Ponds are fertilized by use of fresh cattle manure, chicken manure or inorganic fertilizers. A cattle zero grazing unit has been constructed adjacent to the ponds while a chicken house has been put up above the ponds for direct discharge of fresh wastes into the ponds. The aim of this study was to investigate influence of different modes of fertilization on fish ponds. During the study presence of human disease causing bacteria were investigated. The physico-chemical properties of the different ponds were also investigated. Mean aerobic mesophilic colony counts (AMCC) in tilapia reared in the a chicken waste fertilized pond (Pond A2) and a cattle waste fertilized pond (Pond P2) were 8.2 x 107 CFU g-1 and 7.8 X,10 7 CFU 9-1 respectively. Catfish from ponds A2 and P2 had mean AMCC of 7.8 x 107 and 6.1 x107 CFU g-1 in the same order. The two mode of fish pond fertilization produced fish with AMCC above accepted level set by the International Commission on Microbiological Specification for Food (ICMSF) of 106 CFU g-1. Mean coliform bacteria count in tilapia fish reared in pond A2 was 6.45 X 102 while in the catfish reared in pond P2 was 5.3 x 102 MPN g-1. These counts are above the accepted limit of 4 x 102 MPN g1 by ICMSF. Aerobic plate count (APC) of the water samples from the ponds at 22°C and 37°C ranged from 1.4 x 103 to 1.8 x 105 CFU ml- 1. The APC were above accepted levels of 10 and 100 CFU ml" according to Word Health Organization (WHO) and the European Union (EU) standards for drinking water respectively. Coliform and feacal coliforms counts range of 7.1 x 101 to 4.13 x 103 MPN/100 ml in the fish ponds water samples, were above 0 - 25/100 ml accepted for untreated water for drinking by American Public Health Association (APHA). Escherichia coli were detected in fish and pond water. Temperature and DO stratification was noted in the study ponds at around midday while isothermal and uniform levels of DO were recorded in ponds during the late night and early morning. Among the phytoplankton divisions, Chlorophyta and Cyanobacteria had the highest number of species in the three study ponds. A distinct temporal variation in biomass of the main phytoplankton divisions as well as the biomass of dominant species was noted in the study ponds. Tilapia from pond fertilized with inorganic fertilizers (131) had a poor health status (Kn = 0.78). Although none of the investigated pathogenic bacteria (Salmonella, Shigella and Vibro cholerae) was detected in fish and pond water, this study recommends that fish from Sagana Integrated Fish Farm should be thoroughly cleaned with potable water to reduce high bacterial loads before human consumption. The study further recommends that pond fertilization with agricultural wastes should be controlled to avoid fish pond environmental changes that may be harmful to the survival of reared fish. Finally, test on other known waterborne animal feacal pathogens should be done in order to declare quality of fish from Sagana Fish Farm satisfactory.