Microbial quality of tilapia reared in fecal-contaminated ponds

The microbial quality of tilapia reared in four fecal-contaminated fishponds was investigated. One of the fishponds (TDP) received treated sewage with an average fecal coliform count of 4×103 cfu/100 mL, and feed of fresh duckweed grown on treated sewage was used. The number of fecal coliform bacteria attached to duckweed biomass ranged between 4.1×102 and 1.6×104 cfu/g fresh weight. The second fishpond (TWP) received treated sewage, and the feed used was wheat bran. The third fishpond (FDP) received freshwater, and the feed used was the same duckweed. Pond 4 (SSP) received only settled sewage with an average fecal coliform count of 2.1×108/100 mL. The average counts in the fishponds were 2.2×103, 1.7×103, 1.7×102, and 9.4×103 cfu/100 mL in TDP, TWP, FDP, and SSP, respectively. FDP had a significantly (P<0.05) lower fecal coliform count than the treated sewage-fed ponds and SSP. The microbial quality of the tilapia indicated that all tissue samples except muscle tissues were contaminated with fecal coliform. Ranking of the fecal coliform contamination levels showed a decrease in the order intestine>gills>skin>liver. Poor water quality (ammonia and nitrite) in SSP resulted in statistically higher fecal coliform numbers in fish organs of about 1 log10 than in treatments with good water quality. Pretreatment of sewage is therefore recommended.