United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S1-85/012 Sept. 1985
Project Summary
Bacteria of Public Health
Significance Associated with
Fish Reared in Treated
Wastewater
Ronald P. Phelps
The suitability of tertiary wastewater
ponds for aquaculture was evaluated in
terms of fish productions obtained and
the significance of bacteria in the
wastewater and from fish. Silver carp
Hypophthalmichthyes molitrix were
stocked into tertiary wastewater ponds
at 10,000 fish per hectare (ha) and
cultured for five months. Fish growth
was determined monthly. Bacterial
evaluations of water and fish were made
monthly. Pour plates of the appropriate
media were made to determine total
plate count, fecal coliforms, and fecal
streptococci. Enrichment procedures
were used to isolate Salmonella. The
relative abundance of selected bacterial
colony types was found over the course
of the experiment. Selected isolates
were identified.
Net production of fish was 1,309.2
kg/ha with the average weight of fish
produced being 204.6 grams. Fecal
coliforms and fecal streptococci were
commonly found from both the water
and fish. Salmonella was rare in the
wastewater ponds and very rare from
the fish. Changes over time in fecal
coliform or fecal streptococci from
water generally were not represented
by a corresponding response for that
bacterial count from fish. Correspond-
ing trends were more evident in total
counts from water and fish. Certain
colony types were much more common
in water than fish, while others were
more common from fish. Klebsiella
pneumonias was the most common
fecal coliform from the water while
Aeromonas hydrophila was the most
common from fish. Streptococcus
faecalis was the most common fecal
streptococcus from both water and fish.
This Project Summary was developed
by EPA's Health Effects Research Lab-
oratory, Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Aquaculture is an effective way to
provide quality protein. It is taking on a
more important role in the world food
supply as the traditional capture fisheries
are reaching their production limits, while
the human population continues to grow.
In the United States, aquaculture is a
rapidly growing industry meeting the
American consumers' demand for more
lean, nutritious meats.
The basic objectives of aquaculture are
to provide a suitable environment for
growing the organism and producing an
acceptable product. To meet these objec-
tives requires an adequate availability of
land, water, and nutrients, and culture
systems that will produce an acceptable
product. The competition in the United
States for land, water, and nutrients has
resulted in culture systems with high
input costs aimed at producing luxury
products. Where input costs can be
lowered, other aquaculture systems can
be developed to produce products for
other markets.
A rich source of water and nutrients
that is going underutilized in the United
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States is domestic wastewater. The use
of this water would allow the development
of aquaculture systems that otherwise
would not be practical. An appropriate
use of wastewater is the culture of filter
feeding fishes in tertiary wastewater
lagoons. Tertiary wastewater lagoons are
rich environments for aquaculture with
an abundance of natural food organisms
as a result of the natural food chain based
on photosynthesis. The wastewater held
in ponds is further purified through
biological action while at the same time
stimulating the production of algae and
other food organisms. Planktonic algae
are the primary producers in a wastewater
pond. Other organisms feed on this
production and pass this energy on
through the food chain. Each time that
energy is passed through the food chain
there is a significant loss in efficiency.
Ideally in aquaculture a desirable orga-
nism can be produced that takes direct
advantage of the primary production
without having to pass energy several
steps, thus increasing the efficiency of
the system by reducing the steps in the
food chain.
There are several species of fish which
can directly utilize the primary production
of planktonic algae in wastewater ponds.
A species showing a great deal of promise
is the silver carp Hypophthalmichthyes
molitrix. It is a filter feeding fish with very
closely set gill rakers that form a matrix
capable of removing 8/urn algae and other
suspended matter from the water column.
It has the potential for rapid growth and
is able to convert a less usable biomass,
i.e., algae into a more usable one, i.e.,
fish.
The culture of silver carp or other fishes
in wastewater could become widespread
if the product were considered acceptable.
A major factor in determining whether
such a product is acceptable and to what
use it could be put, is what public health
dangers might exist. These dangers could
include the presence of significant
amounts of pathogenic viruses, bacteria,
parasites, or toxic chemicals. Secondarily
treated domestic wastewater will contain
low levels of human pathogens and toxic
elements. But the presence of these
agents in the water supply or the pond
environment does not necessarily imply
that aquaculture organisms produced in
that environment would contain these
agents in hazardous levels or be of
unacceptable quality.
One of the indices of the quality of a
product is the type and abundance of
bacteria associated with the product. The
bacterial flora of fish is often thought to
be a reflection of that of the environment.
In a domestic wastewater pond, that
environment would include human fecal
bacteria. The degree in which silver carp
reared in wastewater are a reflection of
the bacteria in the water column will
strongly influence how the fish produced
from such an environment can be used.
This study focused on the culture of
silver carp, their bacterial flora, and how
it reflects the bacterial flora of the envi-
ronment. Several issues were addressed:
the suitability of ponds receiving second-
arily treated wastewater for the culture of
silver carp; the nature of the bacterial
flora of the water and fish and their
interactions; antibody production by silver
carp; the effect of exposing silver carp to
water containing Salmonella; and a com-
parison of bacterial flora before and after
processing from wastewater and non-
wastewater cultured fish.
Tertiary wastewater lagoons are good
environments for the culture of silver
carp. The fish grew well and were able to
tolerate the environmental stresses en-
countered. No disease outbreaks among
the fish occurred although such fish
pathogens asAeromonas were present.
Fecal conforms, fecal streptococci, and
Salmonella were present from fish cul-
tured in the wastewater environment.
The levels of bacteria were similar to
those reported from domestic livestock
with the exception of fecal coliforms
which were higher. Aeromonas, a sapro-
phytic water bacteria, was a common
component of the fecal coliform counts
from fish. Thus the fecal coliform counts
were distorted from the more classically
considered components. Bacterial counts
from both wastewater and non-waste-
water cultured fish were similar after the
fish had been processed. The levels foum
were similar to those reported for othe
forms of processed meats.
Silver carp are capable of being carrier:
of Salmonella when experimentally ex
posed to high concentrations in the wate
column. The fish can retain Salmonella ir
the intestine for 15 days after the fish an
transferred to freshwater. Salmonellt
was rare from the fish cultured in th<
wastewater and was confined to th<
intestine.
In general, the levels of bacteria en
countered in this study were within th<
range of levels encountered from com
mercially sold fish. The absence of Sal
monella from the mucous or flesh, aftei
processing of fish which carried Salmo
nella in the intestine, suggests that sucf
fish could be successfully processed foi
consumption.
The relationships of total plate count
fecal coliform, and fecal streptococci frorr
the wastewater and the fish are noi
simple. Bacterial counts from influent
waters had little relationship to those
from fish. Total plate counts of mid and
effluent waters had some relationship tc
mucous and intestine counts of fish. This
was not apparent for the fecal coliform or
fecal streptococci. Various genera ol
bacteria would be present at more than
one site, but its relative abundance would
be different. Data obtained in this study
would suggest that the bacterial flora of
fish is not a good reflection of its aquatic
environment.
The full report was submitted in fulfill-
ment of CR-810418 by Auburn University
under the sponsorship of the U.S. Envi-
ronmental Protection Agency. This report
covers a period from November 1982 to
December 1984, and work was completed
as of December 1984.
Ronald P. Phelps is with Department of Fisheries and Allied Aquaculture, A uburn
University, Auburn, AL 36849.
Norman E. Kowal is the EPA Project Officer (see below).
The complete report, entitled "Bacteria of Public Health Significance Associated
with Fish Reared in Treated Wastewater." (Order No. PB 85-217 677/AS; Cost:
$11.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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