7724

• UCREFRP Catalog Number: 7724
• Author: Snyder, D. E.
• Title: Contributions to a Guide to the Cypriniform Fish Larvae of the Upper Colorado River System in Colorado.
• USFW Year: 1981.
• USFW - Doc Type: \
• Copyright Material: NO

PrototQPvat Phase - The larval phase of bony fish
development characterized by the absence of distinct
spines or rays associated with the future median fins
(dorsal, anal or caudal fins). Transition to the
mesolarval phase is based on the appearance of at
least one distinct spine or ray in any of the median
fins. Pectoral and pelvic fins or fin buds may be
present.

MesotQPvat Phase - The larval phase of bony fish
development characterized by the morphogenesis of
distinct principal rays in the median fins.
Transition to the metalarval phase is based on the
following two criteria, each of which must be met,
except in species lacking pelvic fins: 1) the full
adult complement of principal rays must be distinctly
formed in the median fins; and 2) the pelvic fins or
fin buds must be evident.

MetatQPvat Phase - The larval phase of bony fish
development characterized by the full adult complement
of principal rays in the median fins and the presence
of pelvic fins or fin buds (except in species lacking
pelvic fins). Transition to the juvenile period is
as specified in the definition for the larval period.

The median fin elements inmost fishes appear
first in the caudal portion of the finfold. For these
species the protolarval phase is essentially synony-
mous with Ahlstrom's preflexion phase (except when a
yolk sac is present) (Ahlstrom et al. 1976) and
Faber's (1963) straight-notochord phase. For the
remaining fishes, those in which the first median fin
elements usually appear in the developing dorsal or
anal fin, the proto1arva1 phase terminates before the
preflexion or notochord phase (e.g., the larvae of
lined sole, Aahipus lineatus, described by Houde
et al. 1970).

The metalarval phase is defined so as to allow
in description and key preparation the use of princi-
pal ray counts of the dorsal, anal and caudal fins,
as well as the relative positions of these fins and
the pelvic fins, assuming the species has pelvic fins.
In some fishes, the pelvic buds form as or after the
full adult complement of distinct principal rays in
the median fins is attained. For these the distinc-
tion between mesolarvae and metalarvae is exceedingly
simple. In other fishes, the pelvic fin buds make
their appearance during the mesolarval phase, prior
to the appearance of the full complement of principal
median fin rays, or they may be even more precocious
and appear during or before the protolarva1 phase
(e.g., the 1anternfish Symbolophopus californiensis
described by Moser and Ahlstrom 1970).

For fishes in which part of the finfold is still
present upon attainment of the other two criteria for
transition to the juvenile period, distinction between
the larval and juvenile periods is particularly easy.
Recently-transformed juvenile fish, based on this
terminology, mayor may not yet resemble the adult.
However, for most fishes, the appearance will be very
adult-like.

In meeting the three criteria suggested for a
standard terminology, this terminology, unlike most
others, avoids the difficulties inherent in using
the transition from endogenous to exogenous nutrition
as a phase or periOd boundary. Although this transi-
tion is of tremendous physiological, ecological and
behavioral significance, the various criteria
previously used for determining a boundary between
intervals based on it are frequently difficult to

LARVAL CHARACTERISTICS 9

discern with precision on preserved material and are
no less arbitrary than criteria for other interval
boundaries. Like hatching or parturition, the
transition from endogenous to exogenous feeding,
largely a physiological change, does not correlate
well with the more obvious morphological features
of larval development such as fin morphogenesis.
In many fishes, yolk absorption is completed during
the protolarva1 phase; in others, such as salmon and
catfishes, yolk is still present in the metalarval
phase. If it is desirable to indicate the presence
of yolk, the phase name can be modified by the
prepositional phrase "with yolk" (as
per Faber 1963; e.g. mesolarva with yolk).

CHARACTERISTICS USEFUL IN THE IDENTIFICATION
OF CYPRINIFORM FISH LARVAE

The identification of fish larvae is in part a
process of elimination. Even before examination of
a single specimen, the range of possibilities can be
narrowed by knowledge of the adult species which
occur within or near the source of the specimens to
be identified (possible incidental transport of the
eggs or larvae from far upstream or distant tribu-
taries must also be considered), Knowledge of
spawning seasons, temperatures, habitats, and
behavior coupled with information on egg deposition
and larval nursery grounds and behavior are also
useful in delimiting the possibilities.

In the following discussions of useful characters,
generalizations with respect to the order Cypriniformes
refer specifically to North American species of the
families Cyprinidae and Catostomidae. The generaliza-
tions might not apply to other members of the order.

"Although species of a genus may vary from one
geographical area to another, generally the larval
forms of closely related species (and sometimes of
genera and even families) look alike. At the same
time, the larvae of distantly related forms may be
closely similar in gross appearance." (Berry and
Richards 1973). Cypriniform larvae as a group are
distinctive and generally easy to distinguish from
larvae of other families. The beginning worker is
advised to become familiar with the general larval
characteristics of each family likely to be encoun-
tered. The various guides and keys cited in the
introduction are most useful in this respect.
Lippson (1976), Lippson and Moran (1974), Wang and
Kernehan (1979) or Drewry (1979) are particularly
recommended for the variety of families covered.
Faber (1963), May and Gasaway (1967), Scotton et al.
(1973) and Berry and Richards (1973), discuss the
types of characters useful in the identification of
larval fishes; the latter, strongly influenced by
the late Elbert H. Ahlstrom, is especially recommended.

In the Upper Colorado River Basin, cypriniform
larvae are readily categorized as cyprinids or
catostomids. But elsewhere, if members of the
cyprinid subfamily Cyprininae (the carps) and the
catostomid subfamily Ictiobinae (the carpsuckers and
buffalofishes) or tribe Erimyzontini (chubsuckers,
Catostominae), are present, identification at the
family level may become more difficult for the
inexperienced.

Within their respective families, and especially
at the subfamily level, cypriniform larvae are very
homogeneous in gross structure and appearance and,
therefore, may be especially difficult to discriminate