Fish, chitin, and chitosan production 295Data in Table 6.5 were obtained by using a feeding rate of 20% body
weight/day. In studies in which excellent FCRs of 2.5 or less were reported, a
feeding rate of less than 10% body weight/day was used (Edwards et al. 1987).
6.7 Public health aspects and public acceptance
Since organic wastes such as sludge and animal manure can contain a large
number of pathogens, fish rearing in a waste-fed pond obviously have a risk of
becoming contaminated by these pathogens. In this regard, fish are considered
to be indicators of the sanitary condition of the fish pond water, in which the
microbial flora present in the fish body directly reflects the microbiological
condition of the water from which they are taken.
According to Feachem et al. (1983), three distinct health problems associated
with fish culture in ponds enriched with human and/or animal wastes are:
- The passive transference of pathogens by fish, which become
contaminated in polluted water. - The transmission of certain helminths whose life cycles include fish
as an intermediate host, and - The transmission of other helminths with a life cycle involving other
pond fauna such as snail hosts of schistosomes.
The first problem is a cause of concern worldwide, whereas the second and
third apply only in areas where the helminths concerned are endemic.
The passive transference of pathogens occurs because fish can carry these
pathogens, especially bacteria and viruses on their body surfaces or in their
intestines, which can later contaminate people who handle or eat these fish raw
or partially cooked. Pilot-scale experiments on waste-fed ponds were conducted
at the AIT using septage, composted nightsoil and biogas slurry as organic
wastes feeding into Tilapia ponds (Polprasert et al. 1982 and Edwards et al.
1984). Within the organic loadings upto 150 kg COD/(ha-day), the total
coliform and fecal coliform bacteria and the E.coli bacteriophages (a viral
indicator) were found to be absent in the various fish organ samples such as
blood, bile and meat. These microorganisms were found at high densities in the
fish intestines (up to 10^9 /mL), as normally expected. The levels of total
coliforms and fecal coliforms in the fish pond water were 10^3 -10^4 no./100 mL,
comparable to those in the control ponds without septage feeding.
Fish have been shown not to be susceptible to the same enteric bacterial
diseases of humans and animals (Allen and Hepher 1976; and Jansen 1970).
Therefore, several human bacterial pathogens, which have been shown to be