7794

• UCREFRP Catalog Number: 7794
• Author: Williams, J. E., et al.
• Title: American Fisheries Society Guidelines for Introduction of Threatened and Endangered Fishes
• USFW Year: 1988
• USFW - Doc Type: Fisheries
• Copyright Material: YES

Unwanted parasites and diseases frequently have been
introduced through fish transfers (Hoffman and Schubert
1984). Samples of the introduction stock should be examined
by a qualified fish pathologist prior to shipment. ldeally,
the sample should be quarantined for at least two weeks
so that parasites may complete their life cycle or become
numerous enough to detect (Hoffman and Schubert 1984).
Stock held in culture facilities often are subjected to crowded
conditions that may produce higher parasite loads. Culture
stocks should be regularly inspected for undesirable para-
sites and diseases. If sufficient introduction stock is available,
Ossiander and Wedemeyer (1973) recommended a sample
of at least 60 fish to determine the presence or absence of
a pathogen in the population.

The authors recognize that conditions may not allow for
the necessary quarantine and inspection of the introduction
stock. In a crisis situation where the last population of a
species is imminently threatened, for example, no time may
be available for a quarantine. Also, the transfer of wild stock
within a drainage presents a lower risk of introducing a new
parasite or disease. In such cases, a quarantine may not be
required.

D. Obtain introduction stock of sufficient number and
character.
An introduced population should be founded with enough
individuals to adequately reflect the genetic composition
present in the source population. Estimating the precise
number of individuals necessary to accurately reflect the
source population may be enigmatic. In general, a popu-
lation of fish from a homogeneous habitat (such as a small
stenothermal spring) may possess a narrower range of
genetic variability than a population from a heterogeneous
habitat (such as a eurythermal stream) (Vrijenhoek et a1.
1985). Therefore, a smaller number of individuals may be
required to encompass the available genetic variability from
a constant environment habitat compared to a variable
environment. If the source population is not threatened by
imminent loss, no more than 10% of the available stock
should be utilized annually for introductions.

Other important considerations include sex ratio and age
structure of the introduction stock. A sex ratio near 1: 1 and
a range of age classes should increase the chance of a
successful translocation. No ideal number exists, although
researchers have suggested that 25 males and 25 females
of the proper age and condition is an absolute minimum
to establish salmonid populations in highly controlled hatch"
ery settings (Allendorf and Ryman 1987; Ryman and Stahl
1980). Less controlled environments, where each individual
does not contribute equally in reproduction, require a greater
number of fish.

Collection techniques should disrupt natural habitats as
little as possible. Spring systems often are particularly
sensitive to small amounts of human disturbance.

E. Carefully and quickly transport stock.

A stress response usually results when fish experience
fright, discomfort, or pain (Schreck 1981). Transported stock
are most commonly stressed by physical handling and by
confinement of large numbers of individuals in small con-

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tainers. Loss of mucus or scales, disturbance to integument,
or damage to internal organs can lead to shock, increased
susceptibility to infection, immune system suppression and/
or delayed mortality (Mazeaud et al. 1977; Schreck 1981).
The detrimental effects of repetitive stress are cumulative
(Schreck 1982). Therefore, an adequate recovery period
should be provided between each stressful event. Stress
also can impair a fish's ability to learn for up to several
weeks (C.B. Schreck, personal communication). This could
block imprinting processes needed for adult homing or
migration. Stress can be reduced by darkness or the use of
anesthetics (Schreck 1981).
A general discussion of handling live fish is presented by
Stickney (1983). In addition, Johnson (1979) presented data
on numbers and weights of fish that can safely be transported
in plastic bags containing water saturated with oxygen.
E Introduce stock under most favorable conditions.
Stock should be introduced during favorable weather and
hydrologic conditions. Thermal stock should be avoided by
equalizing the transport water temperature to that of the
habitat. Further, introducing stock at the proper time of
day can reduce initial predation losses. For example, because
sight-feeding predators would be less active at night, in-
troductions into waters containing such predators should
occur during dark conditions.
G. Document the translocation.
It is vital that the procedures and location of introductions
be made available in the scientific literature. Simply filing
the appropriate data in a handy institutional cabinet is
insufficient to allow necessary accessibility. Introduction
data should be made available through regularly distributed
scientific literature, or through administrative reports of the
lead agency. At a minimum, the following should be
reported: identity of those conducting the introduction,
taxon involved, source of the introduction sample, numbers
of introduced individuals and their sex, age and/or size
distribution, date of introduction, and precise location of
the receiving habitat.

3. Post-Introduction Activities

A. Conduct systematic monitoring of introduced popula-
tions.
Regular surveys should be conducted to determine initial
survival, recruitment of young, and persistence through
environmental stochasticity (such as floods, drought, or
fire). During the first year, quarterly monitoring may be
warranted. If the population becomes established, annual
monitoring should be continued for many years to deter-
mine long-term survivorship. Life history studies of intro-
duced populations are advisable. Rapid evolution of life
history strategies has been documented in introduced pop-
ulations of guppies, Poecilia reticulata, as a result of new
predators and/or novel habitats (Reznick and Bryga 1987).
B. Restock if wananted.
In some cases, it may be advisable to supplement the initial
stocking of the endangered or threatened fish in order to
facilitate establishment or increase gene flow. Subsequent
electrophoretic analysis of the introduced population would
reveal loss of genetic variation by founder effect, genetic

Fisheries, Vol. 13, No.5