Biology Reference
In-Depth Information
wide range of ectoparasites of marine fishes. Important taxa infecting the
gills, mouth cavity, fins and body surface of marine fish are, in order
of importance, copepods, monogeneans, isopods, and trematodes.
Comparison of the numbers of ectoparasite species infecting different
fish species leaves no doubt that many vacant niches exist, even in fish that
are heavily infected with a great number of parasite species (e.g., Rohde
1979a
,
1998a
). Thus, the gills and head of Lethrinus miniatus, a fish of
medium size from the Great Barrier Reef, Australia, is heavily infected
(up to about 3500 parasites of all species per host) with about 25 species of
metazoan ectoparasites, mainly monogeneans and copepods. Fish were
examined at three localities. Maximum prevalence of infection with a
particular parasite species reached 100%, and the number of parasite
species per host was 5-11. But the bony gill arches, infected with various
parasites in other fish species, were never infected (Rohde et al.
1994
).
5666 fish of 112 species had an average of 4.3 species of metazoan
ectoparasites on the heads and gills per fish species (Rohde
1998a
). The
maximum number was 27 on Acanthopagrus australis, a small fish from
warm-temperate waters in southeastern Australia. The vast majority of
fish species had fewer than 7, and 16 had none (Figure
2.6A
). Assuming
that 27 species is the maximum a host species can support (and there is no
reason for this assumption: pathological effects are minimal) and that
other fish species could support the same number (and there is no reason
why they should not), maximally only 15.9% of all niches are filled.
Similarly, considering abundances (the total number of all parasites of all
species per number of fish of a particular species examined), maximum
abundance was about 3500, but most fish had an abundance of fewer
than 5 (Figure
2.6B
). The mean abundance of 54.68 represented 1.82 %
of the maximum, again indicating that many more parasites could
be accommodated.
Different parasite species may be dominant, either by intensity of
infection or biomass (volume), on different host individuals, probably
depending on which infective stages are most common in particular
habitats, or on behavioral differences between fish which determine
contact with particular parasite species (e.g., Rohde et al.
1994
)
(Figure
8.1
). There is no evidence that the dominance pattern is some-
how determined by a hierarchy of interactions, although the occurrence
of some interactions cannot be excluded.
Microhabitats of parasites may be relatively large (e.g., all gills) or very
narrow (e.g., a small portion of the gills). Microhabitat preferences are
genetically determined,
i.e., even in the absence of competitors and
