United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
/1
Research and Development
EPA-600/S3-81-048 Sept. 1981
Project Summary
Influence of Diet and
Starvation on Toxicity of
Endrin to Fathead Minnows
(Pimephales pro me las)
Goran Dave
Endrin toxicity to fathead minnows,
Pimephales promotes, was deter-
mined in flow-through toxicity tests at
25°C for periods of up to 30 days.
Three months prior to endrin expo-
sure six groups of fish were fed artifi-
cial diets containing an increasing
percentage of fat, and two groups
were fed either a high or low ration of
frozen brine shrimp. Fish fed frozen
brine shrimp showed better growth,
survival and fewer deformities
(hemorrhagic kidney lesions and
iordosis) than fish fed artificial diets.
Based on 96-hr LCso values, fish fed
diets low in dietary fat were 2.4 times
more susceptible to endrin than fish
fed frozen brine shrimp. On the same
basis (96-hr LCeo) fish fed a low ration
level of brine shrimp were 2.0 times
more susceptible to endrin than fish
fed an unrestricted ration level of brine
shrimp.
In another series of experiments,
adult fathead minnows starved for 80
days were 2.0 times more susceptible
to endrin than recently fed fish. Fat-
head minnows captured in a small
pond on April 30 were also about 2.0
times more susceptible than recently
fed fish. There was no detectible rela-
tionship between body weight and
susceptibility of fathead minnows to
acute endrin toxicity.
The reduced tolerances to endrin
caused by a low percentage of dietary
fat, reduced ration level and starvation
were correlated to an increased total
body water content. The underlying
reason is assumed to be a concomi-
tantly decreased total body lipid
content.
This Project Summary was develop-
ed by EPA's Environmental Research
Laboratory. Duluth, MN, 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).
Introduction
The purpose of this study was to
examine the influence of dietary compo-
sition and ration level (including starva-
tion) on the toxicity of a fat soluble
chemical, endrin, to the fathead
minnow (Pimephales promelas).
Special emphasis was focused on lipid
metabolism by depleting depots in the
minnows prior to testing the endrin
toxicity by subjecting the fathead
minnows to starvation for up to three
months.
For the diet influence study, one
group of minnows was fed a commer-
cially available reference research diet,
five groups were fed this same diet
compounded with varying amounts of
lipids (corn oil, salmon oil, or a mixture
of the two oils), and two groups were fed
frozen brine shrimp, one of these at
restricted ration. The dietary pretreat-
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ment continued for 78 to 100 days prior
to toxicity testing. In order to insure that
previous history was eliminated as a
variable, three sources of fathead min-
nows were used in making up the
groups — laboratory, stock, wild
minnows which were kept in the labora-
tory for several months and fed labora-
tory diet, and wild minnows which were
captured in the spring and used immedi-
ately.
Eight other groups of fathead min-
nows were established, from the same
three sources, and were starved up to
95 days in order to deplete lipid depots
before exposing them to endrin.
All 16 groups of minnows were
exposed to endrin under controlled
conditions, at 5 different concentrations
for up to 29 days. Mortality rate, growth
rate, rate of development of deformities
(nemorrhagic kidney lesions and/or
lordosis) and total body moisture con-
tent (an inverse relationship between
body water content and lipid content
has been established for fish) were
monitored.
The effect of the percentage of dietary
fat, reduced ration level and starvation
on tolerance of endrin was determined,
and the reduced tolerances to endrin
were correlated to increased body water
content (decreased total body lipid con-
tent).
Conclusions
1. Fathead minnows (Pimephales
promelas) fed frozen brine shrimp
showed better growth and surviv-
al, and fewer deformities (hemor-
rhagic kidney lesions and lordosis)
than those fed recommended
reference research diets. In those
fish fed only the reference
research' diet supplemented with
either 10% corn oil, 10% salmon
oil, or a mixture of the two oils, no
improvements were observed in
survival, growth or the number of
deformities.
2. Acute toxicity to endrin was in-
creased 2.4 times by lowered
percentage of dietary fat (the ref-
erence research diet alone), 2.0
times by a restricted ration (brine
shrimp), and approximately 2
times by starvation for 80 days
prior to exposure to endrin. There
appeared to be no significant dif-
ference between the diets supple-
mented with corn oil or salmon oil.
Fathead minnows trapped in a
pond in the spring were approxi-
mately two times more suscep-
tible to endrin than the laboratory
stock fed brine shrimp. The higher
susceptibility in wild minnows
reflected their poor nutritional
status in the spring.
3. Starved minnows had greatly
increased total body moisture
contents over minnows receiving
a diet of brine shrimp. Compared
to minnows fed brine shrimp,
which had body water contents of
about 68%, starved minnows
approached 85% (post-mortem
determinations of total body water
content reached nearly 87%).
Minnows fed the reference re-
search diet alone had total body
water contents of about 79%,
whereas those receiving lipid sup-
plements ranged from 70% to
74%. An increased susceptibility
to endrin was positively correlated
with increased total body water
content, which is assumed to
reflect a lowered total body fat
content. Relocalization of endrin
in non-target tissues such as
adipose tissue seems to be an
important mechanism for resis-
tance to the toxic effects of endrin.
4. A dose-related reduction in total
body water content of fathead
minnows exposed to endrin was
also observed.
5. There was no detectable relation-
ship between body weight and
susceptibility of fathead minnows
to acute endrin toxicity.
Recommendations
1. Reference research diets should
not be used for the culture of fat-
head minnows (Pimephales
promelas) since they result in an
increased mortality, a greater
incidence of deformities (hemor-
rhagic kidney lesions and lordosis)
and decreased growth compared
to fish fed frozen brine shrimp
(Anemia salina).
2. A lowered level of dietary fat, a
lowered ration level and long-term
starvation prior to toxicity tests
with a lipophilic chemical such as
endrin can produce significantly
lower LCso values. This should be
considered in standardized toxic-
ity tests with this type of chemical.
3. No influence of acclimation to test
temperature from 2 to 23 days
was evident on the acute toxicity
of endrin in wild fathead min-
nows. On the other hand, feeding
for one week prior to exposure
made the wild minnows more
resistant to endrin. Therefore, a
more detailed study of the differ-
ences in susceptibility to lipophilic
chemicals between laboratory fish
and field-collected fish on a sea-
sonal basis should be made. Such
a study should be preferably
complemented by measurements
of condition factor, water content
and lipid content for different
groups of fish, in order to achieve a
better understanding of the varia-
tions in susceptibility of different
lots of fish.
4. Considering the findings in the
present study, acclimation to test
conditions for one week without
feeding, with both laboratory stock
and wild fish, seems to be a sound
basis for the comparison of 96-hr
LCso values.
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Goran Dave is with the Department of Zoophysiology, University of Goteborg,
Pack, 400 33 Goteborg, Sweden.
James M. McKim is the EPA Project Officer (see below).
The complete report, entitled "Influence of Diet and Starvation on Toxicity of
Endrin to Fathead Minnows fPimephales promelas/" (Order No. PB
81-244 436; Cost: $9.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
6201 Congdon Blvd.
Duluth, MN 55804
U.S GOVERNMENT PRINTING OFFICE; 1981—559-017/7365
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