Pesticide Residues in Fish - Pesticides: Evaluation of Environmental Pollution - page 381

Victoria, Uganda, in Africa (Kasozi et al. 2005). Also, the levels were quite high when com-
pared with the allowable Federal Environmental Protection Agency (FEPA) (now Federal
Ministry of Environment) limit and can be harmful if the trend is not checked. The study
also showed that the concentrations of OCPs were higher in adult than in juvenile fish in
most cases, and there was no correlation observed between the fat content and the total
concentration of OCPs (Adeyemi et al. 2008).
13.5 Effects of Pesticide Residues on Fish Population
Fish species are sensitive to enzymic and hormone disruptors. Chronic exposure to low
levels of pesticides may have a more significant effect on fish populations than acute
poisoning. Doses of pesticides that are not high enough to kill fish are associated with
subtle changes in behavior and physiology that impair both survival and reproduction
(Kegley et al. 1999). Biochemical changes induced by pesticidal stress lead to metabolic
disturbances, inhibition of important enzymes, retardation of growth, and reduction in
the fecundity and longevity of the organism (Murty 1986). Liver, kidney, brain, and gills
are the most vulnerable organs of a fish exposed to the medium containing any type of
toxicant (Jana and Bandyopadhyaya 1987). The fish show restlessness, rapid body move-
ment, convulsions, difficulty in respiration, excess mucus secretion, change in color, and
loss of balance when exposed to pesticides. Similar changes in behavior are also observed
in several fish exposed to different pesticides (Haider and Inbaraj 1986).
Singh and Singh (2008) reported that the ovary is an important organ for the bioaccu-
mulation of OCPs. Their study indicated that during the reproductive phase, OCPs are
transferred to the ovary from the liver, which may cause reproductive disorders. They
observed a decrease in gonadosomatic index (GSI) and plasma levels of testosterone and
17β-estradiol in female fish captured from polluted rivers (Ganga and Gomti River) com-
pared to the same species from unpolluted ponds. The ratio of pesticide levels in fish and
water equaled 100:1.
The Great Lakes fish are contaminated with chlorinated pesticides such as DDT, DDE,
mirex, and dieldrin as well as trace amounts of metals such as lead and mercury (Susan
et al. 2001). Lake trout, which became extinct in the Great Lakes in the 1950s, has been
shown to be very sensitive to dioxins and polychlorinated biphenyls (PCBs) when exposed
as embryos. Several species of salmon introduced into the Great Lakes have severely
enlarged thyroid glands, which is a strong evidence of hormone disruption. Salmon in the
Lake Erie shows a variety of reproductive and developmental problems, for example, early
sexual development and a loss of the typical male secondary sexual characteristics, such
as heavy protruding jaws and red coloration on the flanks.
Some pesticides can indirectly affect fish by interfering with their food supply or
altering the aquatic habitat, even when the concentrations are too low to affect the fish
directly. Other agricultural chemicals are capable of killing salmon and other aquatic
animals directly and within a short period of time. For example, in 1996, the herbicide
acrolein was responsible for the death of approximately 92,000 steel-head, 114 juvenile
Coho salmon, 19 resident rainbow trout, and thousands of nongame fish in the Bear
Creek, a tributary of the Rogue River. Several laboratory experiments show that sublethal
concentrations of agrochemicals can affect many aspects of salmon biology, including a
number of behavioral effects.