Fish, chitin, and chitosan production 297viruses have a low infective dose, their presence in the fish pond water or
wastewater to be fed to the fish pond should be of a major concern.
The second public health problem is related to the helminths requiring fish as
intermediate hosts. The major and common types of these helminths associated
with waste-fed fish ponds include Clonorchis and Opisthorchis (Feachem et al.
1983). The excreted eggs of these helminths, once discharged into a pond, will
release miracidium (a larvae), which after ingested by specific species of
freshwater snails will develop and multiply into free-swimming cercarial larvae.
Within 1-2 days these cercaria have to find a fish as second intermediate host, in
which they penetrate under the fish scales and forming cysts in the connective
tissues. When the fish are eaten raw or partially cooked, the cysts enter the
human body and developing into worms in the digestive tract. Female worms
will lay eggs, which will come out with the feces. If this feces is discharged into
a pond, this transmission cycle of the helminths could start again.
The third public health problem concerns with schistosomiasis in which
specific species of freshwater snails serve as intermediate hosts for certain
Schistosome helminths. The schistosome eggs that are discharged into a pond
will release miracidium. After ingested by the snails, these miracidium will
develop and multiply into infective cercarial larvae that can penetrate directly
into human skin. Once entered human body, these cercaria will develop into
mature worms and the female worms will lay eggs that will come out with the
feces again, and the transmission cycle is repeated.
Table 6.6 Threshold concentrations of microorganisms inoculated to fish (adapted from
Buraset al. 1985)
Threshold concentration, no/fish
Micro organisms Tilapia aurea Cyprinus carpio
Bacteria
E. coli 2.5x10^6 1.5x10^6
Clostridium freundii 9.3x10^3 -
Streptococcus faecalis 1.9x10^4 4.0x10^4
Streptococcus Montevideo 1.8x10^4 3.7x10^4
Bacteriophages
T2 Virus 4.0x10^3 4.6x10^3
T4 Virus 2.0x10^4 -It appears that the cooking and eating habits of the people will have great
impact upon the people who handle and eat the waste-grown fish. Fish that are
well cooked will have all the pathogens that are on or in the fish body killed.
However, disease transmission during fish harvesting, cleansing, and
preparation prior to cooking can occur, depending upon the types of the diseases
present. In areas where there are endemics or outbreaks of diseases related to