The microbiological and sensory quality of septage-raised Nile tilapia ( Oreochromis niloticus)

Abstract

Septage is widely used in aquaculture, especially in developing countries where artificial fertilisers and feeds are expensive. Previous studies in this field have concentrated on the microbiological quality of the fish at harvest, and the physiological effects on the fish. No work to date has investigated the implications of septage-use on the sensory and microbiological quality of fish during post-harvest storage. Tilapia ( Oreochromis niloticus) were cultured in three levels of septage (0, 150 and 300 kg COD/ha/day); fish in the 0 kg COD/ha/day pond were fed with commercial pellets. The quality of the water was monitored during the growth of the fish. At harvest, fish were assessed for microbiological quality, growth characteristics, proximate composition, and sensory quality. Fish were then stored on ice and their microbiological and sensory quality monitored at 3-day intervals until rejected by the taste panel. Data indicated that the use of septage influenced the quality of the water, with more faecal organisms isolated from septage-fed ponds. More faecal organisms were also isolated from fish from these ponds. Growth and proximate analysis data indicated that the septage-fed fish were smaller, and contained less fat, than pellet-fed (control) fish. These data also indicated that tilapia will survive and grow where septage is the only added source of nutrient. Fish quality data indicated that there was a preference for the flavour of the septage-fed fish at harvest, but that this difference did not persist. There were no consistent significant differences between sensory scores for control and septage-fed samples during the storage period. There was no evidence that the use of septage had influenced either the microbiological or the sensory quality of the fish samples during iced storage.