Biology Reference
In-Depth Information
Monogenea and eel parasites in the Atlantic and Indo-Pacific
Oceans
Monogeneans are ectoparasitic flatworms inhabiting the gills, fins, and
body surface of fish (and occasionally other sites and other hosts). They
range in size from less than a millimeter to several centimeters long and
are therefore easily detected under the microscope, permitting rapid
examination of large numbers of fish. They are thus good models for
ecological studies. Rohde (
1980c
,
1986
) demonstrated that relative species
diversity (number of parasite species per host species) of monogeneans
infecting the gills of marine fish increases from high to low latitudes
both in the Atlantic and Pacific Oceans, but diversity is significantly
greater in the latter. He suggested that the older age of the Indo-Pacific
is responsible for its greater diversity, because numbers of species of
Gyrodactylidae, which are predominantly cold-water species and are
therefore unlikely to have immigrated from warmer southern waters,
are much more numerous in the northern Pacific than Atlantic, and this
in spite of the fact that the area of the northern Pacific is not greater than
that of the northern Atlantic. Structural complexity, as indicated by the
length of the coastline and the number of islands, is also not greater in the
northern Pacific, and the lengths of major rivers draining into the north-
ern Pacific and their discharge rates and annual discharge volumes are
actually smaller than those of the northern Atlantic, indicating that more
gyrodactylids could have immigrated from freshwater into the northern
Atlantic than the Pacific, which - however - did not happen.
Another example is parasites of eels. Eels (Anguilla spp.) spawn in the
ocean, but migrate into rivers and lakes, where they spend much of their
lives before returning to the sea. Their parasites may be acquired in
freshwater or the sea, although most parasites are acquired in freshwater.
Parasites of eels have been studied in detail by Hine (
1978
,
1980a
,
1980b
),
Hine and Francis (
1980
), Kennedy (
1985
,
1990
,
1992
,
1995
), Gosper
(
1992
), Kennedy and Gu´gan (
1994
,
1996
), Kennedy et al.(
1997
), and
Marcogliese and Cone (
1993
,
1996
,
1998
). The long association of eels
with the oceans (Aoyama and Tsukamoto
1997
; Tsukamoto and Aoyama
1998
; Aoyama et al.
2001
; Tsukamoto et al.
2002
) permits conclusions
concerning the effects of history, geographical region, etc. on parasite
diversity. Protistans and myxoxoans were not examined by all authors and
are therefore not included in this discussion.
Data in Kennedy and Gu´gan (
1996
) show that infracommunity rich-
ness of intestinal parasites in 1175 Anguilla anguilla at one locality in
