7195

• UCREFRP Catalog Number: 7195
• Author: Nesler, T. P., R. T. Muth and A. F. Wasowicz
• Title: Evidence for Baseline Flow Spikes as Spawning Cues for Colorado Squawfish in the Yampa River, Colorado
• USFW Year: 1988
• USFW - Doc Type: American Fisheries Society Symposium
• Copyright Material: YES

American Fisheries Society Symposium 5:80-88, 1988
© Copyright by the American Fisheries Society 1988
Variation in Pigment and Nape Morphology of
Larval Tidepool Sculpin
JEFFREY B. MARLIAVE
Vancouver Public Aquarium, Post O„~'ice Box 3232
Vancouver, British Columbia V6B 3X8, Canada
Abstract.-Key characters for the identification of yolk-sac larvae of the tidepool sculpin
Oligocottus maculosus include [he presence of a nape bubble and the count of postanal ventral
midline (PVM) melanophores. However, both of these features vary among larvae of this species,
limiting their taxonomic utility. In addition, previously undescribed pigment patterns on the ventral
and lateral gut are polymorphic, being present or absent in different geographic regions and in
different clutches. Precocial development of cranial pigment occurs by the time of hatching in some
larvae. Clinal geographic variation occurs in counts of PVM melanophores. Certain combinations
of these pigment and nape variants make identification of such larvae on the basis of previous
descriptions very difficult. Unusual pigment patterns of reared larvae appear more likely attribut-
able to limited sources of animals for culture than to artifacts of the culture environment.
Identification of fish larvae requires integration
of diverse information, yet it ultimately involves
the matching of available, recognizable" similar-
ities between specimens (Powles and Markle
1984). Such unique character states tend to be
fewer among larvae than among adult fishes. Of
the characters most often used for larvae, pigment
is the only type that has been used for all early life
history stages and at all taxonomic levels in sys-
tematic investigations (Kendall et al. 1984). Ken-
dall et al. (1984) discussed the problems of using
pigment as a taxonomic character, and they sug-
gested that the most serious difficulties involve
convergence of pigment patterns in unrelated spe-
cies and the physiologically variable state of me-
lanophore contraction. Although Powles and
Markle (1984) indicated that regional variation in
appearance of larvae can cause problems with
identification, there appears to be little published
documentation of polymorphic or clinal variation
in pigment patterns or in other features indicated
as diagnostic characters. One exception is a study
of myomere-count variation among Mississippi
River fish larvae (Bosley and Conner 1984). The
pragmatic requirement for usable key characters
to identify fish larvae appears to have resulted in
rather broad acceptance of pigment patterns as
conservative diagnostic characters, especially
with marine species. Although generally correct,
such acceptance causes problems when pigment
variants exist within a species. Similar confusion
can result from polymorphism of other types of
diagnostic characters as well, especially when
several of such features can vary.
The present study provides evidence for extreme
variability in a number of the diagnostic characters
cited for identification of yolk-sac larvae of the
tidepool sculpin Oligocottus tnaeulosus. Most of
these variable characters are pigment patterns such
as cranial, lateral, and ventral gut melanophores
that had not been observed on specimens from the
open Pacific coast from California to Washington
(Stein 1973; Washington 1981). In addition, the
unusual nape bubble described by Washington
(1981) for preflexion tidepool sculpin larvae varies
from being prominent on some larvae to absent on
others. An analysis of these features indicates pa-
rental effects within a locality, as well as geographic
patterns of variation.
Methods
Yolk-sac larvae were obtained from locations in
southwestern British Columbia from the outer
coast of Vancouver Island around to the inland
waters surrounding the city of Vancouver (Figure
1). Eyed-egg masses were collected from the
Mytilus Balanus intertidal zone in most areas and
incubated in running seawater. Larvae were killed
in 1% fotmalin in seawater upon hatching, then
fixed in 3% fotmalin. In certain localities, larvae
were collected in plankton tows in rocky near-
shore areas (Marliave 1986). Tows were limited to
3-5 min duration, so that larvae were alive on
completion of a tow, then larvae were killed and
fixed as for cultured ones. Field-caught larvae
were sorted and identified with dissecting stereo-
microscopes,which were also used for counts and
measurements.
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