Small
fishes constitute a remarkable assemblage with their own unique life history
traits. Their biology and ecology sets them apart from their larger and better-
studied counterparts. They also pose some particular problems from an invasion
biology perspective. Small fishes are typically much more abundant than larger
fishes, and tend to have shorter generation times and higher rates of increase (Munday
and Jones, 1996).
These are qualities that may allow them to establish and spread more easily than
larger fishes. Small fishes also tend to be more diversified, as smaller body
size allows them to associate with smaller elements of the habitat, resulting in
a finer level of habitat partitioning and offers them increased habitat
opportunities (Munday and Jones 1996). This diversification increases the likelihood that a small fish
may be better able to find a place for itself in a native community. Finally,
and of extreme importance, is the fact that small fishes tend to be overlooked
and ignored in many studies. It is harder to identify and estimate abundance of
smaller fishes, and many sampling techniques are also biased against them.
Because of this, small invaders may not be noticed, or may be ignored as
insignificant until they have become extremely successful in the invaded
community.
Although fish invasions tend to be much more common in freshwater systems than in marine systems (Baltz, 1991), small fishes have successfully invaded both marine and freshwater communities. The modes of introduction are extremely variable. Several gobies have been transported into the Great Lakes though ballast water and into San Francisco Bay and the surrounding marshes and estuaries by the same means, as well as into Sydney Harbor in Australia. Mosquito fishes, Gambusia holbrooki and Poecilia reticulata, have been purposefully introduced as biocontrol agents on mosquito larvae to many locations, including the U.S. and Australia where they have had particularly severe effects on native frog populations because they prey on the tadpoles (Morgan and Buttemer, 1996; Webb and Joss, 1997). Movement through canals is another means of introduction. The only fishes to successfully traverse the Panama canal have been small blennies and gobies (McCosker and Dawson, 1975).
The effects that small fishes have on the systems they invade are as diverse as the fishes themselves. In many communities these effects they are unknown because the native community of small cryptic fishes is also unstudied. This is certainly the case in Hawaii, where a new species of small goby was just described from a type locality right outside the main lab at the Hawaii Institute of Marine Biology (Greenfield and Randall, 1999). This little native goby, Eviota susanae, shares the fouling community with a cryptogenic, probably invasive, blenny, Omobranchus rotundiceps obliquus. And just across South Kaneohe Bay, at the Kaneohe Bay Yacht Club, is a second introduced blenny, Parablennius thysanius, reported in the 1970's (Springer 1979). A third blenny, Omobranchus ferox, has just been reported from Halawa estuary (Englund and Baumgartner, in press). Because no one has looked extensively at these small invaders in Hawaii, we have no idea how they have affected the native community. Certainly this situation is not limited to Hawaii.
Sadly, as we become aware of the effects that small fish invasions are having on native communities, we realize that rarely are those effects innocuous. Native fish populations suffer through competition and predation, like the endangered tidewater goby, Eucyclogobius newberryi has in the San Francisco Bay drainage due to the presence of an invasive gobies Tridentiger bifasciatus (Matern and Fleming 1995; Swenson, 1996).
It is important that we consider the role that small fishes play not only in their native communities but also in communities they have invaded. We must also closely examine them as potential or recent invaders and not treat the prospect of invasion or spread by small fishes lightly.
REFERENCES
Baltz,
D.M. 1991. Introduced fishes in marine systems and inland seas. Biological
Conservation. 56: 151-177.
Greenfield,
D.W. and J. E. Randall. 1999. Two new Eviota
species from the Hawaiian Islands (Teleostei:
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Matern,
M.S. and K.J. Fleming. 1995. Invasion of a third asian goby, Tridentiger
bifasciatus, into California. California Fish and Game. 81(2): 71-76.
McCosker,
J.E. and C.E. Dawson. 1975. Biotic passage through the Panama Canal, with
particular reference to fishes. Marine Biology. 30: 343-351.
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L.A., and W.A. Buttemer. 1996. Predation by the non-native fish Gambusia
holbrooki on small Litoria aurea and L. dentata
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