Saprolegnia - The iLumina Digital Library

determinations) of isolates was not useful in separating the species that had been
recognized classically on morphological grounds.
In evaluating his observations and experimental data, Neish (1976) defined the
Saprolegnia diclina-S. parasitica complex as one consisting of specimens with
predominantly diclinous antheridial branches, and thin-walled, unpitted or
inconspicuously pitted oogonia. He proposed (Neish, 1976:118) that the name parasitica
be discarded as a nomen ambiguum, and a much-broadened interpretation of S. diclina be
adopted.
Detailed morphological analyses by Willoughby (1968b, 1969 1970, 1971a),
Willoughby and Pickering (1977), and Pickering and Willoughby (1977) of watermolds
associated with fish led to a decision that isolates could be grouped into types.
Willoughby (1978) recognized three types of Saprolegnia diclina (parasitic forms from
salmonids and perch, and strictly saprophytic ones) based upon the ratio of oogonium
length to diameter. He concluded that it was impossible to maintain a two-species
concept consisting of S. diclina and S. parasitica, and conserved the former name. We
agree with his decision and are herewith formally reducing S. parasitica to synonymy.
In his study on salmonid fish saprolegnians, Willoughby (1978) called attention
to the fact that some isolates of the diclina-parasitica complex produced very extensive
antheridial branches that closely invested the oogonia to which they were attached.
Much earlier, Tiesenhausen (1912) had referred to profuse antheridial branch
development, and illustrated clearly what Willoughby (1978: fig. 2e-h) was to refer to as
a “bird nest” condition. We find the heavily enwrapped oogonia to be produced (Fig.
99 F, G) in some specimens of S. diclina recovered from water and mud samples.
Willoughby also discovered that the oospheres did not mature consistently. This
condition recalls immediately the infrequency of mature oospores in S. australis, and
strengthens the view that R. F. Elliott’s (1968) species might prove to be only a variant
of S. diclina.
In sum, it may be stated that a broadened, flexible interpretation of Saprolegnia
diclina emerges from an analysis of all the data at hand. Specimens isolated from fish
may show profuse antheridial development, but sparse development is characteristic of
other specimens. The same may be said for “saprophytic” (saprotrophic) forms of the
species, as is shown by Willoughby’s (1978: fig. 4) S. diclina Type 3, and our own isolates
from water (Fig. 99 G). With respect to oospore size -- Willoughby (1978) analyzed this
character thoroughly in his specimens -- there is noticeable overlap and intergrading
among isolates. It may be recalled, however, that the oospores of S. parasitica sensu
Kanouse (1932) were smaller than those of S. diclina (sensu Seymour, 1970). This
distinction fades when additional isolates are examined (see Willoughby, 1978, fig. 5).
There remains the troublesome matter of a name to be applied to the nonsexual
specimens of Saprolegnia associated with fish. To these, of course, Coker (1923) had
applied the name parasitica, and this subsequently was widely adopted even after
Kanouse (loc. cit.) had discovered the sexual stage of individuals she chose to identify
with Coker’s species. There is no way to be certain that the watermolds studied by
Kanouse were indeed identical to Coker’s specimens. In the final analysis, it appears to
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