Encyclopedia of Environmental Science and Engineering, Volume I and II

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POLLUTION EFFECTS ON FISH

INTRODUCTION

During the past twenty-five years, man has subjected the

earth to an ever increasing variety of chemical substances

never before encountered by living organisms. Many of

these foreign substances, which originated from industrial,

agricultural and municipal sources, are seriously threaten-

ing the natural environmental conditions established over

geologic time by evolutionary processes. Organisms, includ-

ing man, are finding it more and more difficult to escape

the consequences of exposure to these compounds, many of

which are known to interfere with life sustaining biochemi-

cal and reproductive mechanisms. Little is known, however,

concerning the effects the vast majority of these pollutants

will have on plants and animals that inhabit this planet.

The aquatic environment is the ultimate destination of most

of these contaminants as a result of rainfall and runoff from the

lands. The establishment of water quality requirements for the

protection of fish life must, therefore, become an item of first

priority. The task is complicated, however, by the fact that dif-

ferent species of fish as well as different developmental states

of the same or different species exhibit wide variations in their

sensitivity or tolerance to foreign materials. In addition, the

basic biochemical and physiological information needed to

evaluate the harmful effects foreign substances have on organ-

isms is severely lacking for fish and other aquatic organisms.

It is the purpose of this chapter to briefly discuss the

current state of knowledge in regard to the response of fishes

to environmental contaminants. Because of the serious lack

of information in the area of fish toxicology, † it is not pos-

sible, nor is it within the scope of this discussion, to pre sent

even an outline of the toxic effects of the many foreign sub-

stances which fish encounter. Instead, representative com-

pounds have been selected to illustrate the principles that

are believed to play a major role in determining how fish

respond to environmental contaminants. Unfortunately,

these principles are based almost entirely on research per-

formed over the last several decades dealing with the toxi-

cologic responses of mammalian species, including man,

to drugs and foreign compounds. Until equivalent research

is performed on fishes, we will be forced to rely on these

mammalian principles when attempting to evaluate the

effects foreign compounds have on fish species.

MECHANISMS OF TOXICITY

Foreign substances can injure organisms through a vari-

ety of mechanism but these can generally be grouped into

two categories: specific and non-specific injury. Chemicals

that produce non-specific injury usually do so at the site of

exposure, such as skin, respiratory membranes, oral mucosa,

and intestinal mucosa. Frequently, such injury is the result

of the caustic or corrosive nature of the chemical with the

cellular responses being directly related to the concentration

of toxicant within the cell or tissue involved. Agents pro-

ducing this type of injury are commonly referred to as “pri-

mary irritants” because they induce local, minor to severe

inflammatory responses and occasionally extensive necrosis

(death) of cells. Excellent examples of these chemicals are

acids, bases and aldehydes, all of which are strong irritants

to mucous and gill membranes.

Other compounds, unlike the non-specific action of the

primary irritants, can have a high degree of specificity and

act at low dose levels at certain receptor sites to produce

pathological change in specific cells with subsequent altera-

tion of the function of organ systems. The degree of injury is

dependent on the efficiency of the repair mechanisms for the

tissue involved. If a cell is not irreversibly damaged, func-

tional and structural characteristics may return to normal.

Cells that are permanently injured at usually replaced by

fibrous (scar) tissue. Fibrosis can seriously impair the func-

tional capability of the tissue or organ involved.

Examples of substances that exhibit specific toxicologi-

cal actions are those that produce mutations by interfering

with the genetic machinery of germ cells. Mutation of a

dominant gene may express itself immediately and produce

fatal abnormalities (teratogenic effects) or early fetal death.

Other mutations may not express themselves for several gen-

erations and then suddenly appear creating serious abnor-

malities for that individual and its offspring. Chemicals may

be carcinogenic (e.g. diethylnitrosamine and aflatoxin) and

initiate the growth of malignant tumors in fish and mammals

(Stanton, 1965; Ashley et al. , 1964). Many toxicants directly

or indirectly affect reproductive mechanism, gonadal growth

and development, spawning behavior, and fry survival by

specific toxicological actions. This can frequently result in a

depletion or extinction of a susceptible species.

† Toxicology is the scientific discipline that deals with the quantita-

tion of injurious effects on living systems resulting from chemi-

cal and physical agents that bring about alterations in cell or organ

structure and function.

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