7118 ‎(2)‎

• UCREFRP Catalog Number: 7118
• Author: Gatz, J. A., J. M. Loar and G. F. Cada
• Title: Effects of repeated electroshocking on instantaneous growth of trout
• USFW Year: 1986
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

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bait for fishermen, for insect control, for weed control, for pets, for aquaculture, and
by accident. Most of the deliberate introductions into California were meant to
improve fishing. One of the most successful introductions of this type was carp, now
considered to be a major pest. The introduced catfishes, basses, and sunfishes,
however, form the backbone of California's warmwater fisheries. This is not surprising
considering that the only widely accepted warmwater gamefish native to California is
the Sacramento perch. Forage fishes for the gamefishes were introduced as reservoirs
became one of the main aquatic habitats. These fishes have generally been small
zooplankton feeders such as threadfin shad, Delta smelt (Japanese subspecies), and
Mississippi silversides, although native fishes like tut chubs, hitch, and threespine
stickleback have been tried. Golden shiner, red shiner, and fathead minnow have also
been introduced as forage fish on occasion, but their spread has been mainly the result
of releases from bait buckets or baitfish rearing ponds.
Mosquitofish and, more recently, Mississippi silversides were introduced to help
control mosquitoes and gnats by feeding on the larvae. Mosquito control is likewise
one reason given for introducing the Mozambique mouthbrooder, although it has also
been justified as a sportfish, weed~ontrol agent, aquarium fish, and aquaculture
species. The weakest of these reasons is probably weed control and, as a result, other
fishes (mainly other Tilapia species and grass carp, t:Yenopharyngodon idella) are
constantly being proposed as agents to check aquatic weeds in ponds and canals.
Ti~pla zillii was recently introduced for weed control into the Imperial Valley.
The introduction of these same specs is sometimes argued by their proponents
because they are potentially useful for aquaculture, converting vegetable matter into
useful protein. It is unfortunate, however, That the appeal of these exotics has resulted
in the native fish fauna being ignored as subjects for aquaculture, when some species,
such as Sacramento blackfish, are eminently suited for it. The main fishes raised for
food in artificial systems in California today are various catfishes and trouts.
The pet trade is another source of introductions. Fish dealers have released tropical
fish into desert springs to have a ready ~urce of supply, to the detriment of the
pupfishes and their relatives. In the canals of the Imperial Valley, sailfin mollies,
Trinidad rivulus, and other fishes have become established after escaping from ponds
in tropical-fish farms. Pet-fish owners who have tired of their charges and released
them in the nearest lake or stream are probably responsible for most wild goldfish
populations and for the guppies that frequent sewage treatment plants.
A final source of exotic fishes has been accidental introductions. Logperch came in
with a shipment of largemouth bass; rainwater killifish first probably arrived as eggs on
oyster shells; and yellowfin gobies apparently were flushed into the Delta from the
bilge of a cargo ship.
The introduced fishes have obviously radically changed the nature of California's fish
fauna since they are now the most abundant fishes in much of the state's waterways.
Nevertheless, the introductions themselves bane been only partially responsible for the
reduction of the native fish fauna. By and large, introduced species are most abundant
in aquatic habitats modified by man while native fishes persist mostly in undisturbed
areas. In the San Joaquin River system, for example, the aggressive, predaceous green
sunfish is widely distributed in foothill streams, In undisturbed regions they occur