Journal of Fish Biology (2006) 68, 1679–1692
doi:10.1111/j.1095-8649.2006.01003.x, available online at http://www.blackwell-synergy.com
Scale formation in selected western North Atlantic
flatfishes
K. W. A B L E *
AND
J. C. L A M O N A C A
Rutgers University, Institute of Marine and Coastal Sciences, Marine Field Station,
800 c/o 132 Great Bay Blvd, Tuckerton, NJ 08087-2004, U.S.A.
(Received 16 February 2005, Accepted 19 October 2005)
Patterns of scale formation (onset, completion and spatial pattern) were examined for five
species of flatfishes in four families (Paralichthyidae: summer flounder Paralichthys dentatus,
smallmouth flounder Etropus microstomus, Scophthalmidae: windowpane Scophthalmus aquosus,
Pleuronectidae: winter flounder Pseudopleuronectes americanus and Soleidae: hogchoker
Trinectes maculatus, to determine if the patterns are a useful indicator for the transition from
the larval to the juvenile periods. In all species (except T. maculatus in which samples were
limited), the ontogenetic pattern was very similar with onset of scale formation occurring on the
lateral surface of the caudal peduncle, then spreading anteriorly along the presumptive lateral
line, then laterally over the body, on to the head, and eventually on to the median fins. The
timing of scale formation, relative to fish size, was late relative to other morphological and
behavioural characters (i.e. fin ray formation, eye migration and settlement). The onset of scale
formation, across all species, occurred at 90–270 mm total length (LT), at the same approximate size as eye migration and settlement. Completion of scale formation on the body occurred
at 22–54 mm LT but completion of scale formation on the fins did not occur until 44–88 mm
LT. Thus completion of scale formation in these flatfishes is apparently the last external
morphological change to occur during the larval to juvenile transition and, as a result, is not
completed until approximately one third (S. aquosus and P. dentatus) to one fourth
(P. americanus) or about the same time (E. microstomus and T. maculatus) as the size at first
reproduction. This character may have relevance to defining the end of the larval period and the
beginning of the juvenile period in flatfishes and other fishes. In addition, the pattern of scale
formation may be useful in enhancing understanding of systematics, functional morphology
# 2006 The Fisheries Society of the British Isles
and habitat use.
Key words: flatfishes; juveniles; larvae; morphology; scales.
INTRODUCTION
Scales of teleosts are flexible, calcified plates lying within shallow envelopes, or
scale pockets, in the upper layers of the dermis (Bullock & Roberts, 1974). Scales
provide multiple functions, including protection of the lateral line, storage area
for minerals and nutrients (van Oosten, 1957), drag reduction (Videler, 1994)
and a useful means of ageing (Jerald, 1983; Busacker et al., 1990), and identifying
*Author to whom correspondence should be addressed. Tel.: þ1 609 2965260 ext.230; fax: þ1 609
2961024 email: [email protected]
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K. W.
ABLE AND J. C. LAMONACA
fishes (Batts, 1964; DeLamater & Courtenay, 1974; Daniels, 1996). Despite these
multiple functions and uses relatively little is known about the patterns of scale
formation in teleosts, especially marine taxa.
It is known that scales have their origin in dermal papilla formed by the
multiplication of fibroblasts (Elson, 1939; van Oosten, 1957) that develop into
papillae (Elson, 1939; Waterman, 1970; Lindsey, 1988) that originate in one or
several loci on the surface of the body (Andrews, 1970; Armstrong, 1973; Sire,
1981; Sire & Arnulf, 1990). For many species, scales originate at a single locus on
the lateral midline of the caudal peduncle (Andrews, 1970; White, 1977) and the
formation of scales often occurs between the larval to juvenile periods (Ahlstrom
et al., 1976; Kendall et al., 1984; Gozlan et al., 1999; Webb, 1999; Urho, 2002).
As a result, the completion of scale formation may be a useful indicator of the
completion of the larval period and the beginning of the juvenile period
(Fuiman, 1997; Fuiman et al., 1998). In order to test this possibility in flatfishes,
the size and variation in size at scale formation (onset, completion and spatial
pattern) were compared in five flatfishes in four families (Paralichthyidae,
Pleuronectidae, Scophthalmidae and Soleidae; Chapleau, 1993) from the western
North Atlantic.
MATERIALS AND METHODS
S O U R C E S O F SP E C I M E N S
Specimens for examination of the patterns of scale formation were collected, with a
variety of techniques (plankton nets, beam trawls, otter trawls and seines), primarily in
Great Bay-Little Egg Harbor estuaries (c. 39 300 N; 74 190 W) and on the adjacent
continental shelf off New Jersey, U.S.A. An effort was made to examine a length series
from prior to eye migration to full coverage of scales as occurs in the adult condition.
Sample sizes examined varied between species (Table I).
SC A L E T E C H N I Q U E S
Because scale formation was examined in wild-caught specimens (Table I), care was
taken during all stages of collection, preservation and examination to prevent damage of
the integument or scale loss. Individuals to be stained were first preserved in 95% ethyl
alcohol (ETOH) for at least 48 h, then treated with a solution containing alizarin red S to
elucidate scales, as adapted from Taylor (1967) and Pothoff (1983). Stock solutions
consisted of alizarin red S powder ad libitum plus a 05% KOH solution diluted 1 : 10
in 50% ETOH solution. Individuals were immersed in alizarin red S solution for c. 30 s
and rinsed with deionized water or ETOH. Stained individuals were then transferred to
95% ETOH for final preservation. These specimens were visually examined with an
Olympus stereomicroscope and patterns of scale formation were illustrated on blank
templates for individual species adapted from illustrations in Able & Fahay (1998).
Additional individual variation was determined for one species [winter flounder,
Pseudopleuronectes americanus (Walbaum)] for which there were a large number of
individuals over the appropriate size range. In all cases, the illustrations were then
transferred to a digital medium via illustration in Adobe Photoshop. The area covered
by scales was calculated from these illustrations using the Image J software package
(Rasband, 2003) and expressed as per cent of body covered relative to the adult condition
of scale coverage (100%). The adult condition was based on the smallest size at which
scales were no longer being formed.
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2006 The Fisheries Society of the British Isles, Journal of Fish Biology 2006, 68, 1679–1692
#
11–12
8 5
80, 121
c. 130
3 8
20?
2 0
24–28
30–35
17–20
9–13
11–16
10–20
?
118–220
LT (mm)
at settlement /
metamorphosis
135
167
270
?
90–110
< 250
342–476
405
520–538
191–221
LT (mm)
at
completion
of scale
formation
on body
250
440
405
570
246
LT (mm)
at onset
of scale
formation
on fins
565
662
885
800
436
LT (mm) at
completion
of adult
complement
of scales
96
83
82
84
82
Per cent
body
covered
by scales
50
200–250
250–280
210–230
599
LT (mm)
at first
reproduction
62
117
49
55
62
Sample
size
for
scale
formation
20–50
and
210–592
98–662
115–885
108–815
90–585
LT (mm)
range
examined
for
scale
formation
5, 6, 3,
7
12, 8, 5,
10, 3, 4
13, 5,
4
11, 2, 3, 4
2,
4,
2,
9,
2,
3,
1, 2, 3, 4
Reference
LT, total length.
1, Richardson & Joseph (1973); 2, Martin & Drewry (1978); 3, Able & Fahay (1998); 4, Collete & Klein-MacPhee (2002); 5, O’Brien et al. (1993); 6, Morse &
Able (1995); 7, Neuman & Able (2002); 8, Able et al. (1990); 9, Keefe & Able (1994); 10, Able & Kaiser (1994); 11, Hildebrand & Cable (1938); 12, Merriman &
Sclar (1952); 13, Laroche (1981).
Etropus
microstomus
Scophthalmus
aquosus
Paralichthys
dentatus
Pseudopleuronectes
americanus
Trinectes
maculatus
Species
LT (mm)
at hatch
LT (mm)
at completion
of adult complement
of fin rays
LT (mm)
at onset
of scale
formation
on body
TABLE I. Scale formation characteristics in representative flatfishes from the Middle Atlantic Bight. Observations of onset and completion of
scale formation on the body and fins are original observations; the other information is based on the literature sources provided
SCALE FORMATION IN FLATFISHES
2006 The Fisheries Society of the British Isles, Journal of Fish Biology 2006, 68, 1679–1692
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ABLE AND J. C. LAMONACA
The illustrations of representative stages of scale formation were standardized across
all species. For example, the location of the lateral line is shown with a thin line, even
before it is formed, to provide a local landmark. In addition, the margin of the dorsal and
anal pterygiophores is also noted with a thin line. The area behind the pectoral fins is not
shaded to indicate the location of the pectoral fins in order to provide another local
landmark. The darkly shaded areas indicate scale formation on the body; the grey shaded
areas indicate where scales occur on the fins. For selected species [P. americanus and
windowpane Scophthalmus aquosus (Mitchill)] both sides of the fishes were compared
because blind and ocular side scale formation can differ in some flatfishes (Ahlstrom
et al., 1984). For all species, no differentiation was made between ctenoid (typically on
the ocular side) and cycloid (typically on the blind side) scales (Norman, 1934; Ginsburg,
1952; Gutherz, 1967). Neither were occurrences of accessory scales noted, which typically
occur later in development on summer flounder Paralichthys dentatus (L.) and smallmouth flounder Etropus microstomus (Gill) (Ginsburg, 1952; Gutherz, 1967).
RESULTS
P A T T E R N S O F SC A L E F O R M A T I O N
In all flatfish species examined, the onset of scale formation began after eye
migration and attainment of the general asymmetrical, flattened shape of the
adult. Scale formation, as generally depicted for the ocular side, shared the same
general sequence in scale formation. For all species that could be examined,
progression of scale formation began on the caudal peduncle, and extended
anteriorly and then laterally, with no obvious differences between bothid, paralichthyid, pleuronectid and scophthalmid species (Figs 1–3). Specimens of the
appropriate size were lacking to determine the pattern for hogchoker Trinectes
maculatus (Bloch & Schneider). In the adult condition scales covered 82–84% of
the entire body and fins (Table I). The exception was T. maculatus, in which the
scales covered 96% of the body. There are some species specific differences in the
size at onset and completion of scale formation. The patterns depicted in Figs 1–3
are representative of the larger sample sizes examined for this study (Table I).
Etropus microstomus
Scale formation occurs over the size range of c. 33 mm (Figs 1 and 3). The
onset of scale formation probably occurs between 90–110 mm because specimens slightly larger (113 mm) have a fully scaled lateral line (Fig. 1). By
c. 13 mm the area covered by the scales has expanded laterally both above and
below the lateral line and this continues at 15 mm. By 17–18 mm the body is
completely covered and other scales have begun to develop on the operculum. By
c. 22 mm scales cover the head, except for the snout, (as in the adult condition)
and small areas of the operculum. At larger sizes, scales begin forming on the
dorsal, anal and caudal fins and they reach the adult condition, i.e. scale formation is complete, by c. 43 mm LT, when the scales cover all except the tips of the
median fins. This size is very close to the size at first reproduction (599 mm LT)
(Table I).
Scophthalmus aquosus
Scale formation occurs over a relatively large size range from 27–80 mm
(Figs 1 and 3). Scale formation begins with a few scales on the midline of the
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2006 The Fisheries Society of the British Isles, Journal of Fish Biology 2006, 68, 1679–1692
SCALE FORMATION IN FLATFISHES
(a)
(b)
1683
(c)
9·0–11·0 mm
27·6 mm
17·0 mm
11·3 mm
33·8 mm
19·8 mm
13·8 mm
36·5 mm
20·5 mm
15·5 mm
41·1 mm
31·0 mm
22·1 mm
46·5 mm
48·0 mm
43·6 mm
80·0 mm
88·5 mm
FIG. 1. Description of scale formation relative to total length in selected flatfishes: (a) Etropus microstomus, (b) Scophthalmus aquosus and (c) Paralichthys dentatus.
caudal peduncle where the lateral line will eventually form (Fig. 1). By 33 mm
scale formation has extended along the lateral line to the posterior edge of the
operculum and has also expanded laterally. By c. 36 mm scales have extended
anteriorly beyond the pectoral fins but not on the operculum or head. By 41 mm,
the lateral extent of scale formation has continued with new locations for scale
development occurring at the dorsal and ventral margins of the body near the
middle of the dorsal and anal fins. By c. 46–54 mm the body is completely scaled
and scales are beginning to form on the operculum. Between sizes of 57–76 mm,
scales are beginning to form on the median fins. By 80 mm scales have formed
on the dorsal, anal and caudal fins and scale formation has reached the adult
condition. This size is a little more than approximately one third of the size at
first reproduction (Table I). In an attempt to determine if the extent or rate of
development differed between the ocular and blind sides of this species, scale
formation on both sides were examined (Fig. 3). Based on these observations,
the blind side may have lagged slightly behind the eyed side at sizes between
35–55 mm LT but at larger sizes they appear similar.
Paralichthys dentatus
Scale formation occurs over a larger size range than the other species, i.e. 17–88 mm
(Figs. 1 and 3). By 17–19 mm, scales are present along the lateral line from the
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K. W.
ABLE AND J. C. LAMONACA
(a)
13·5 mm
16·1 mm
18·1 mm
(b)
23·3 mm
25·0 mm
33·0 mm
46·2 mm
66·2 mm
58·1 mm
FIG. 2. Description of scale formation relative to total length in (a) Pseudopleuronectes americanus and (b)
Trinectes maculatus.
origin of the caudal fin to behind the pectoral fin. By c. 20 mm, the scales have
expanded laterally but not anteriorly. By 22 mm the scales have expanded
further laterally and also anteriorly to the posterior margin of the operculum.
By 31 mm scale formation has extended to the dorsal and ventral limits of the
body and extended anteriorly, to the dorsal portion of the head behind the eyes.
By 40 mm all the scales are formed on the body and some are beginning to form
on the median fins. By c. 88 mm all the scales are formed on the dorsal, anal and
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SCALE FORMATION IN FLATFISHES
100
(a)
80
60
40
20
*
0
100
(b)
80
60
40
20
* * *
Adult scale coverage (%)
0
100
(c)
80
60
40
20
*
0
100
(d)
80
60
40
20
*
0
100
(e)
80
60
40
20
90·0–94·9
80·0–84·9
70·0–74·9
60·0–64·9
50·0–54·9
40·0–44·9
30·0–34·9
20·0–24·9
10·0–14·9
*
0–4·9
0
LT (mm)
FIG. 3. Variation in areal coverage of scales (means S.E., where the sample size is sufficient) by length
during development presented as per cent of the adult condition of scale coverage in (a) Etropus
microstomus (n ¼ 62 ocular), (b) Scophthalmus aquosus (n ¼ 55 ocular and n ¼ 17 blind), (c)
Paralichthys dentatus (n ¼ 49 ocular), (d) Pseudopleuronectes americanus (n ¼ 117 ocular and n ¼ 22
blind) and (e) Trinectes maculatus (n ¼ 62 ocular). *, size examined in which scales have not formed.
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ABLE AND J. C. LAMONACA
caudal fins and scale formation has reached the adult condition. This size is
approximately one third of the size attained at first reproduction (Table I).
Pseudopleuronectes americanus
The duration of scale formation occurred over c. 53 mm (Figs 2 and 3). Scale
formation begins with a few small scales in the middle of the caudal peduncle at
c. 13 mm. By 14–17 mm scales are formed along the entire lateral line. By
16–20 mm the scales rows have expanded dorsally and ventrally but not to the
ventral margin of the body. At c. 23 mm the scales have expanded to cover a
broader area extending to the base of the dorsal and anal pterygiophores. Scales
begin to form on a small area of the operculum between 22–29 mm. Between
27–37 mm new scales begin forming at several locations over the base of the
dorsal and anal pterygiophores. By 44 mm, scales are forming on the median
fins. By 66 mm scale formation has reached the adult condition because scales
extend midway on to the dorsal and anal fins and slightly further on the caudal
fin. This size is approximately one fourth the size of first reproduction (Table I).
In a comparison between the eyed and the blind sides, the blind side seemed to
lag slightly behind the eyed side at sizes between 20–40 mm and at sizes
<60 mm. The latter may be the adult condition for the blind side.
There were a large number of specimens of this species, of the appropriate
sizes, to examine scale formation in more detail and as a result it was possible to
determine how much variation occurs at similar sizes. As an example, specimens
that ranged from 170–172 mm (n ¼ 5) varied in areal coverage of scales from
3–13%. In another example, individuals ranging from 200–205 mm (n ¼ 4)
varied from 13–40%. At larger sizes, an individual at 316 mm had new scales
forming over the dorsal and anal pterygiophores while an individual at 318 mm
did not.
Trinectes maculatus
There is an incomplete series for scale formation of this species and thus less is
known of the pattern of scale formation especially between sizes of 5–20 mm
(Figs 2 and 3). Individuals <5 mm have no scales. By 25 mm the scales cover
almost all of the body with the exception of a patch just anterior to the
approximate location of the pectoral fin. At this same size some scales are
beginning to form on the proximal portions of the dorsal, anal and caudal
fins. By 25–35 mm scales on the body are complete and the scales on the fins
are more extensive. This pattern continues until 55–60 mm at which size the
scales almost completely cover the fins, more so than any of the other flatfishes
examined (Figs 1–3), and achieve the adult condition. The size is approximately
the same size as that at first reproduction (Table I).
DISCUSSION
D E V E L O P M E N T A L C O N SI D E R A T I O N S
The onset of scale formation is variable for the western North Atlantic flatfishes examined here. It occurs at the same length or at greater lengths than that
at which most major morphological features have been completed (Table I). For
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SCALE FORMATION IN FLATFISHES
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example, while the onset of scale formation occurs at approximately the same
length as completion of the adult complement of fin rays for some species
(E. microstomus and P. americanus) for others it occurs at larger lengths
(S. aquosus and P. dentatus) (Table 1). This difference is especially marked for
S. aquosus in which the fin rays are complete at 85 mm while the onset of scale
formation does not occur until 270 mm. The onset of scale formation on the
body occurred at sizes of 90–270 mm for the five species for which data are
available (Table I). This is at the same approximate size (E. microstomus) or
larger than the size (S. aquosus, P. dentatus and P. americanus) at which the
general adult body forms (flattened and asymmetral) and eye migration occurs
for these species (Table I). Thus, all median fin rays have already been formed
(Martin & Drewry, 1978), a common character for discerning the end of transformation and metamorphosis (Kendall et al., 1984; Fuiman, 1994; 1997;
Fuiman & Higgs, 1997; Fuiman et al., 1998; Urho, 2002). The completion of
scale formation in these flatfishes occurs at larger sizes in development, relative
to other morphological changes, than is typically considered for most fishes
(Table I). Scale formation of these same flatfishes was not complete until
22–54 mm LT, depending on the species. Completion of the adult complement
of scales, including on the fins, did not occur until 44–88 mm LT. The sizes at
completion of the adult complement of scales, including the fins, are overlapping
or one third to one quarter the size at first reproduction, another indication that
completion of scale formation occurs relatively late in development.
The completion of scale formation has been identified as a useful ontogenetic
index for the end of the larval period and the beginning of the juvenile period
[although Balon (1999) considers scales ‘less vital characters’]. This length based
character (Armstrong, 1973; Fuiman 1997) undergoes transition late in development and after the completion of the last sensory system to be developed, i.e. the
lateral line (Webb, 1989, 1999; Fuiman et al., 1998; Higgs & Fuiman, 1998). The
length based nature of scale formation was not specifically examined in the
present study but in other groups of fishes (cyprinodontid and fundulids) the
length at scale formation was similar in field captured and laboratory reared
specimens (Sakowicz, 2003, K.W. Able, unpubl. data). Further considerations
for S. aquosus (Neuman & Able, 2002), based on a comparison of a variety of
morphological characters, has also suggested the completion of scale formation
as a good indicator for the end and beginning of the larval and juvenile periods,
respectively. This has been suggested for non-flatfish species as well (Copp &
Kovac, 1996; Fuiman & Higgs, 1997; Fuiman et al., 1998; Urho, 2002). Thus,
one possibility to consider, as an ontogenetic index for flatfishes and perhaps
other fishes, is that the larval period ends when scale formation begins and the
juvenile period begins when scale formation, on the body, is complete. Those
individuals in the intervening period could be defined as ‘transitional’ or ‘transforming’ (Kendall et al., 1984) individuals. This approach may be an advantage
to those working on development and ecology of the early life history of flatfishes and other fishes. The benefit would be that instead of using the numerous
terms that have been applied to individuals that have not completed development including postlarvae, pterygiolarvae, prejuveniles (Kendall et al., 1984) and
metalarvae (Snyder, 1976) the single term ‘transforming’ could be applied. A
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K. W.
ABLE AND J. C. LAMONACA
potential difficulty in the broad use of this metric is that some species and
families of fishes lack scales (van Oosten, 1957).
P A T T E R N S O F SC A L E F O R M A T I O N
Variation in scale formation within species was relatively small, based on the
small measures of S.E. about mean values at different sizes based on the data for
some species (Fig. 3). Most often the highest variability occurred for the smallest
specimens examined. Some of this variation may simply be due to variability in
shrinkage upon preservation, which commonly occurs in many small fishes
(Fowler & Smith, 1983; Kruse & Dalley, 1990). Some variations may also be
due to type of preservative. This may be especially important when assembling a
length series from multiple sources.
There are few accounts of scale formation for flatfishes in the literature with
which to compare with the present observations. For one species, however, the
patterns in timing appear different but these differences in timing are the result
of different approaches. A prior examination of scale formation in S. aquosus
divided up the surface of the ocular side into regions and determined the onset
and end of scale formation in each region separately based simply on the
presence or absence of scales in each region (Neuman & Able, 2002). The
approach used here (Figs 1 and 2), in general, provides a more accurate description of the pattern of scale formation. In another study of scale formation for
Paralichthys olivaceus (Temminck & Schlegel), completion was reported at a
relatively large size (540 mm) (Seikai, 1980). In the present examination of a
congener, P. dentatus, scale formation on the body was completed at 405 mm
LT but scale formation on the fins was not complete until 885 mm LT.
Curiously, Seikai (1980) did not mention or illustrate scale formation on the
fins of P. olivaceus. Perhaps the focus on scales on the body, and not the fins
accounted for this. A similar reason may account for the description of a ‘fully
scaled’ T. maculatus of 18 mm (Hildebrand & Cable, 1938) while the present
observations indicate that scale formation, on the fins, is not complete until
much larger (Fig. 2). Prior studies of P. olivaceus noted that anomalously
coloured individuals appeared to form scales at a slower rate than normally
coloured individuals raised in a hatchery (Seikai, 1980).
Asymmetry in the general morphology of the ocular v. the blind side in
flatfishes, including scales, is not uncommon (Norman, 1934; Ginsburg, 1952;
Ahlstrom et al., 1984) but the differences in the areal coverage of scales do not
appear to be large in the two species examined in this study. While the pattern of
scale formation on the blind side occasionally lags behind that of the ocular side,
the pattern is generally similar, at least for S. aquosus. In P. americanus, the areal
extent of the scales on the blind side seems to lag behind late in development.
Larger fish would need to be examined to determine if the blind side achieves the
same amount of areal coverage of scales as occurs on the ocular side.
The general pattern of scale formation between flatfish species was similar
with scales first forming at a single locus on the caudal peduncle and then
extending anteriorly to cover the lateral line, then laterally and on to the head
and fins until the adult condition was achieved, although Fukuhara & Fushimi,
(1984) described an exception for a non-flatfish species. The pattern of onset of
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SCALE FORMATION IN FLATFISHES
1689
scale formation on the caudal peduncle is similar to that for other fishes in other
families although the number of species for which there is detailed information is
small and is biased toward freshwater families (Andrews 1970, White 1977). As a
further example of the limited information available, of the 66 marine species
with scales on the east coast of the U.S. treated in Able & Fahay (1998), only 31
(47%) species have information on either onset or completion of scale formation
and none describe the pattern of scale formation as completely as is provided
here for the flatfishes. All flatfishes examined have scales on the fins (dorsal, anal
and caudal) (Figs 1 and 2), a pattern shared with all known Pleuronectiformes
(Norman, 1934). This observation and differences between flatfishes and other
families suggest that the pattern of scale formation (number of loci at onset, size
at onset, duration and size at completion) and per cent body coverage may
provide some insights into the taxonomy and phylogeny of fishes as has been
observed for scale morphology (Roberts, 1993; Daniels, 1996) and lateral line
development (Webb, 1989, 1999). The value of the pattern of scale formation will
only become apparent as this information becomes available for a larger number
of species and from other families of fishes.
ECOLOGICAL CORRELATES
The functional significance of teleost scales is largely unknown although it has
been suggested that they play a role in protection and a storage area for minerals
and nutrients (van Oosten, 1957) and drag reduction (Videler, 1994). In the
species of flatfish examined here, the onset of scale formation begins at or
after settlement (Table I), thus scales may play a role in the movement from
the water column to the benthos and interactions with the substratum. Prior
studies with S. aquosus lead to the suggestion that the timing of complete scale
formation on the body (46–54 mm LL) corresponded with the ability to bury
(462 38 mm LT) (Neuman & Able, 2002). This correspondence between
completion of scale formation and burial does not apply to other flatfishes.
For P. dentatus, size at first (partial) burial in laboratory experiments occurred
at 174 mm LT, a size at which eye migration is complete (Keefe & Able, 1994)
but scales are just beginning to form (Fig. 1). Complete burial (all parts of body
except head) occurs at >22 mm LT (Keefe & Able, 1993, 1994) although completion of scale formation does not occur until 405 mm (on body) to 885 mm
(on fins) (Table 1). Scale formation in flatfishes also may correspond to habitat
use such that completion of scale formation may be related to the selection of
habitats in general (Gibson, 1994). Clearly, more details of scale formation
relative to behaviour are required for a better understanding of how this change
in morphology influences the behavior and ecology of flatfishes and other fishes.
We thank the staff at the Rutgers University Marine Field Station many of whom
assisted in making collections of fishes for this analysis. M.P. Fahay and G.P. Sakowicz
provided comments on an earlier draft. Support for this project was provided by Rutgers
University Marine Field Station. This paper is Rutgers University Institute of Marine
and Coastal Sciences Contribution No. 2006–3.
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2006 The Fisheries Society of the British Isles, Journal of Fish Biology 2006, 68, 1679–1692
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ABLE AND J. C. LAMONACA
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