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R EGU L A R PA P E R

A comparative morphological investigation of otoliths of sixparrotfish species (Scaridae) from the Solomon Islands

Laith A. Jawad

4 Tinturn Place, Flat Bush, Manukau, Auckland

2016, New Zealand

Correspondence

Laith A. Jawad, 4 Tinturn Place, Flat Bush,

Manukau, Auckland 2016, New Zealand.

Email: [email protected]

Funding information

No external funding was used for this research.

A comparative morphological investigation of otoliths from six parrotfish species and two

genera, Scarus and Hipposcarus, was conducted to identify taxonomically diagnostic species-

specific characters. Ontogenetic trends in otolith morphology were evident: Otoliths of small-

sized specimens were most like those of large-sized Scarus oviceps and were least similar to

large-sized Hipposcarus longiceps.

KEYWORDS

morphology, otoliths, parrotfish, Scaridae, SEM, Solomon Islands

1 | INTRODUCTION

Using the morphology of hard structures, such as otoliths, scales and

bones, to identify fish species has proven to be less expensive than

other approaches, such as molecular and genetic markers (Aguirre and

Lombarte 1999; Assis 2003; Jawad, 2008; L'Abée-Lund & Jensen,

1993; Ponton, 2006; Tuset et al., 2003a, 2003b, 2006), yet equally

valuable. Sagittal otoliths are generally the largest of the three otolith

pairs, while the lapillus and asteriscus are smallest (Paxton, 2000), at

least in most teleost families. Nevertheless, in siluriforms, characi-

forms and cypriniforms in general, the lapillus may be larger than the

sagittal otoliths (e.g., Ariidae; Schulz-Mirbach & Reichenbacher, 2006;

Teimori et al., 2012). Despite this variability in size, the sagittal otoliths

are widely used for taxonomic and biological (e.g., age and growth)

studies in non-ostariophysan teleosts for many reasons: their typically

large size, relative ease of access, opaque and translucent seasonal

markings, morphological variation and resistance to digestion in the

alimentary canal of predators (L'Abée-Lund, 1988; Nolf, 1985; Platt &

Popper, 1981; Tuset et al., 2003a). They are located on either side of

the basioccipital bone and are separated by a thin septum arising from

the midventral ridge of the occipital (Jawad, 2008; Jawad et al., 2007;

Ruck, 1976).

For parrotfishes (family Scaridae), which are important within

coral-reef ecosystems as herbivorous bio-eroders, there exists no

comprehensive literature on otolith morphology and any comprehen-

sive treatment of this clade is challenged by its nearly 100 species

(Nelson et al., 2016). Data on parrotfish otolith morphology is cur-

rently distributed across a wide range of sources. Nolf (1985) provided

a line-drawing of the sagittal otolith of Scarus iseri (Bloch 1789).

Weisler (1993) highlighted the importance of otoliths of Scarus perspi-

cillatus (Steindachner 1879) for archaeological studies, while Smale

et al. (1995) provided descriptions for six species of the genus Scarus

Forsskål 1775 as well as for Calotomus spinidens (Quoy & Gaimard

1824), Leptoscarus vaigiensis (Quoy & Gaimard 1824) and Hipposcarus

harid (Forsskål 1775). Rivaton and Bourret (1999) provided images of

otoliths of nine species of the genus Scarus and two species of the

genus Cetoscarus Smith 1956 from the Indo-Pacific region. Tuset et al.

(2008) briefly described the otoliths of Sparisoma cretense (Linnaeus

1758) and Sparisoma rubripinne (Valenciennes 1840). Baremore and

Bethea (2010) provided an image for Nicholsina usta (Valenciennes

1840) from the Gulf of Mexico. Lin and Chang (2012) described the

otoliths of seven species of the genus Scarus and one species each of

the genera Calotomus Gilbert 1890, Chlorurus Swainson 1839, Hippos-

carus Smith 1956 and Leptoscarus Swainson 1839 from Taiwan.

Sadighzadeh et al. (2012) gave short descriptions of two species of

Scarus and Nolf (2013) provided line-drawings for the otoliths of

N. usta and S. iseri. Recently, Jawad et al. (2017) described the mor-

phology of two scarid species, Chlorurus sordidus (Forsskål 1775) and

Hipposcarus harid (Forsskål 1775), from the Egypian coast of the Red

Sea. The present paper provides a morphological analysis of parrotfish

otoliths from the Solomon Islands.

The aim of this study is to find distinguishing features, based on

an extensive description of the sagittal otoliths to provide for the

identification of each species and characterize ontogenic stages

between the initial phase and terminal phase (IP and TP) colouration,

which closely follows the change of sex in this family. This study con-

tributes to methods in parrotfish taxonomy, paleoichthyology and the

taxonomy of coral-reef fish.

Received: 21 March 2018 Accepted: 22 August 2018

DOI: 10.1111/jfb.13787

FISH

1046 © 2018 The Fisheries Society of the British Isles wileyonlinelibrary.com/journal/jfb J Fish Biol. 2018;93:1046–1058.

https://orcid.org/0000-0002-8294-2944

mailto:[email protected]

http://wileyonlinelibrary.com/journal/jfb

2 | MATERIAL AND METHODS

Fifty-four otoliths were collected from Hipposcarus longiceps

(Valenciennes 1840), Scarus dimidiatus Bleeker 1859, Scarus ghobban

Forsskål 1775, Scarus niger Forsskål 1775, Scarus oviceps Valenciennes

1840 and Scarus rivulatus Valenciennes 1840 of various sizes between

2014 and 2015. Fishes were speared at night around the Island of

Ghizo (western Solomon Islands, 8.0833� S, 156.8333� E; Figure 1)

and subsequently measured. The top of the cranium was sliced, the

brain was removed and the otic capsules were exposed and separated

with a sharp scalpel. Sagittal otoliths were gently removed with a pair

of fine tweezers, cleaned with 70% ethanol and stored dry.

Fishes were aggregated in length groups, which were determined

by species (Tables 1–6). It is important to note that the species stud-

ied can attain larger lengths than the specimens speared (Randall,

2005), but no fishes of the maximum reported size were caught during

this study. The data gathered, however, are sufficient to draw first

conclusions and waiting for the ideal situation, in which specimens of

all sizes become available for study, is not justified. Otoliths were

placed in their respective length groups by species so that species-

specific ontogenetic changes in otolith shape could be followed. Spec-

imens of all species except S. rivulatus were divided into three group-

ings (H. longiceps: group 1,100–200 mm, group 2,201–300 mm,

group 3,301–400 mm; S. dimidiatus: group 1,100–150 mm,

group 2:151–200 mm, group 3:201–300 mm; S. ghobban: group

1:100–200 mm, group 2:201–300 mm, group 3:301–400 mm;

S. niger: group 1:100–150 mm, group 2:151–200 mm, group

3:201–250 mm; S. oviceps: group 1:100–150 mm, group

2:151–200 mm, group 3:201–250 mm). Specimens of S. rivulatus

were placed in four groups (group 1:100–150 mm, group

2:151–200 mm, group 3:201–250 mm, group 4:251–300 mm).

Otoliths from each size class of all six species were examined with

scanning electron microscopy (SEM), which allowed observation of

morphological characteristics on the mesial face of the otoliths. In

preparation for SEM, otoliths were air cleaned and mounted on an alu-

minium stub using double-sided carbon tape. Stubs were sputter-

coated with gold in a vacuum of about 4,061,023 Torr. Otoliths were

viewed in a Hitachi SU-70, EM (www.hitachi.com), at 5.0 kV.

Terminology of otolith morphology follows Smale et al. (1995)

(Figure 2(a), (b)).

3 | RESULTS

The following characters are shared by small and large parrotfishes:

otolith width, otolith depth, shape of mesial and lateral surface, shape

of sulcus acusticus, ostio-caudal differentiation and rostrum thickness.

The otoliths of small (group 1) H. longiceps (Figure 3) differed from

those of larger (group 3) specimens in 14 out of the 22 characteristics

studied. Detailed descriptions of the otoliths from three size classes

are shown in Table 1. The otolith shape is oval–oblong in small and

oblong–ovate in larger H. longiceps (Figure 3). The dorsal margin is cre-

nate, sinuate and dentate in smaller fish (groups 1 and 2), becoming

irregular in larger ones (group 3). The shape of the dorsal margin

shows an increasing trend in irregularity from group 1 to group

3, including the presence of lobes and ridges. The ventral margin can

be flattened, gently irregular, indented, crenate and lobed in group

3. The posterior margin is usually not uniform in group 1 and group

3 and can be rounded, slightly or deeply indented, lobed and elon-

gated. In group 2, it is lobed with a shallow indentation or elongated

with a large indentation. The ostium in otoliths of different length

groups is flared and lumps of different sizes cover their floor. In smal-

ler specimens (group 1), it is straight in its anterior part, but curved in

group 2 and straight again in larger specimens (group 3). The ostium is

deep in group 1 and group 2, but shallow in group 3. The cauda is

flared in otoliths of all length groups and circular or oval in group

1 and group 2, becoming oblong in group 3. The floor is either smooth

or covered with lumps of different sizes in all three length groups. A

deep groove is present in otoliths of large fish (group 3). The crista

superior is usually ridge-like or well developed in smaller fishes (group

1 and group 2) and may be absent or have a ridge-like shape in larger

fish (group 3). The crista inferior is well developed in smaller fish, but

poorly developed in some large ones (group 3). The dorsal depression

is elongated in all length groups, but shallow in group 1 and group

3. The rostrum is blunt and oblique, short or long in group 1 and group

2, but irregular and long in group 3. The antirostrum in large fish

(group 3) is long and lobed. The collum is either low or absent in all

length groups. The latter two characteristics could not be used to

identify the relative size of H. longiceps. The antirostrum, if present, is

either small, moderate, large, broad, or pointed. In general, the larger

specimens appear to have a well-developed antirostrum (Figure 3).

Solomon Islands(a)

(b) SolomonIslands

Kolombangara

New

GeorgiaGhiza

Randova Island

Vanguru

Vella laVella

N

N

FIGURE 1 Map showing (a) the geographical position of the Solomon

Islands and (b) the collection localities

JAWAD 1047FISH

http://www.hitachi.com

The otoliths of small (group 1) S. dimidiatus (Figure 4) differ from

larger ones (group 3) in 11 out of the 22 characteristics studied.

Detailed descriptions of the otoliths from the three size classes are

shown in Table 2. The following characters did not vary between indi-

viduals of group 1 and group 3: the shape of both crista superior and

crista inferior, the rostrum thickness, the dorsal depression and the

shape of vexcisura. In group 1, the shape varies between oval and

elliptic, becoming oval and oblong in group 2 and oval in group 3. The

dorsal margin gradually changes from lobed to irregular in group 1 and

group 2, to entirely irregular in group 3. The ventral margin is crenate,

serrated or lobed in group 1 and group 2, but lobed at the middle in

group 3. The posterior margin is broad in all three length groups, with

a pointed, rounded or straight rim, but irregular in larger fish (group 3).

The ostium is flared and shallow in all specimens examined with lumps

on the floor. The lumps change to a longitudinal ridge in medium and

larger sized specimens (group 2 and group 3). The anti-rostrum in

group 3 is very poorly developed. In group 1 and group 2, the cauda is

flared, shallow or deep and the floor covered with lumps, ridges or

smooth. In adult fish of group 3, it is flared, shallow, or a longitudinal

ride and the floor is smooth. The rostrum is usually long in the smaller

specimens, but very short and blunt in the larger specimens. The

antirostrum is short in all specimens examined, but pointed in group

1, poorly developed in group 2 and rounded and poorly developed in

group 3. The collum is a solid ridge in group 1 and group 2, but absent

in group 3.

The otoliths of small (group 1) S. ghobban (Figure 5) differ from

the larger (group 3) ones in 12 out of 22 characteristics studied. The

following characters do not vary between individuals of group 1 and

group 3: the ostio-caudal differentiation, the ventral depression, the

thickness of the rostrum and the excisura. Detailed descriptions of

otoliths of the three size classes are shown in Table 3. The shape of

the otoliths is either oblong or ovate in smaller fish (group 1 and group

2), but ovate in all larger (group 3) specimens. There is a tendency

toward irregularity in the dorsal margin, which is serrated, lobed and

emarginated in group 1 and group 2, but irregular in group 3. This also

is the case for the ventral margin. The shape of the posterior margin

varies from oblique, to sinuate, lobed and rounded with an extension

in group 1 and group 2, becoming irregular with an indentation in

group 3. The ostium is of a similar shape (flared and shallow) in small

and large individuals; its floor has a ridge in adults. The cauda is flared,

shallow and smooth or with a ridge in group 1 and group 2, but also

deep in group 3. The crista superior has a similar shape and is less

TABLE 1 Otolith characteristics of three size classes of Hipposcarus longiceps from the Solomon Islands

Characters Group 1 (100–200 LT mm) Group 2 (201–300 LT mm) Group 3 (301–400 LT mm)

Otolith shape Raised oval, oval Oval, oblong, raised oval Oblong, ovate

Otolith width Very thick Very thick Very thick

Otolith depth Deep Deep Deep

Mesial surface Convex Convex Convex

Lateral surface Concave Concave Concave

Dorsal margin Slightly crenate, sinuate Sinuate, irregular, dentate Irregular

Ventral margin Smooth with slight irregularity,coarse indentated

Coarsly indentated, dentate, crenate,irregular, lobed

Lobed

Posterior margin Rounded with slight indentation,irregular with deep indentation

Lobed, irregular with wide indentation,irregular, rounded, broadly elongated,lobed with medium indentation, coarselobed

Lobed with shallow indentation, elongatedwith wide indentation

Sulcus acusticus Ostial, homosulcoid Ostial, homosulcoid Ostial, homosulcoid

Ostium Circular, oval, shallow, flared, floorcovered with fine lumps

Flared, shallow, deep, upper and lowermargins straight, floor covered with fewlumps or smooth

Shallow, upper and lower margins staright,floor covered with coarse lumps

Cauda Upper and lower margins notcurved, shallow, floor coveredwith coarse lumps

Circular, oval, oblong, flared or not, floorcovered with coarse and fine lumps orsmooth, shallow

Oblong, flared, lobes at posterior end, floorcovered with coarse lumps or smooth,presence of deep fissure

Ostio-caudaldifferentiation

With dorsal and ventral ridges,poorly developed

With dorsal and ventral ridges, poorlydeveloped

With dorsal and ventral ridges, poorlydeveloped

Crista superior Ridge-like, well deveoped Ridge-like Ridge-like or absent

Crista inferior Well developed Well, poorly developed or absent Well or poorly developed

Dorsal depression Elongated, shallow Elongated, deep Elongated, shallow, wide

Ventral depression Absent Absent Absent

Rostrum shape Rounded Rounded with lobes Irregular

Rostrum size Short Short or long Long

Rostrum thickness Broad Broad Broad

Antirostrum Short, with fine tip or absent Short with broad or pointed tip, absent,with lobes

Long, broad with lobes

Collum Low Low or absent Low or absent

Excisura Absent Shallow, narrow notch, narrow angle orabsent

Shallow, narrow notch, narrow angle orabsent

Note. LT: Total length.

1048 JAWADFISH

pronounced in younger specimens. This is also the case for the crista

inferior in those otoliths of group 3 where it is developed, although it

is poorly developed in some specimens of group 1. There is a ten-

dency toward a poorly developed dorsal depression, which is shallow

and narrow in smaller specimens, but poorly developed in otoliths of

larger fish. The rostrum is usually short and blunt in all otoliths exam-

ined, it is irregular in some otoliths of group 2 and in all otoliths of

group 3. The antirostrum is mostly short and poorly developed in

group 1 and in some specimens of group 2, but long and pointed in

group 3. The collum becomes more developed as the otoliths grow

larger. It is either absent or poorly developed in specimens of group

1 and group 2 but has a ridge-like shape in group 3.

The otoliths of small (group 1) S. niger (Figure 6) differ from those

of group 3 in eight of 22 characteristics studied. The following charac-

ters do not vary between individuals of group 1 and group 3: the

ostio-caudal differentiation, the shape of the crista superior and crista

inferior, the shape of the rostrum, the size and thickness, the collum

and the excisura. Detailed descriptions of otoliths from the three

length groups are shown in Table 4. In specimens of group 1, the oto-

lith is oval, becoming elliptic in group 2 and either ovate or oval in

group 3. There is a tendency toward a lobed dorsal margin, slightly in

individuals of group 1 and group 2, but raised in group 3. The ventral

margin varies from lobed, crenated and irregular in group 1 and group

2 to irregular in group 3. The posterior margin is broad in all otoliths

examined, pointed in group 1 and group 2, but mainly oblique in group

3. In all otoliths examined the ostium and cauda are flared and deep,

the floor is covered with lumps in group 1 and group 2 but covered

with a ridge in group 3. The dorsal depression is elongated and narrow

in all length groups, deep in individuals of group 1, but gradually shal-

lowing as the fish grows larger (group 3). The rostrum is short, blunt

and oblique. The antirostrum appears to be short and pointed or

absent.

The otoliths of small (group 1) S. oviceps (Figure 7 and Table 5) dif-

fer from larger (group 3) ones in 6 out of 22 characteristics studied.

The following characters do not vary between individuals of group

1 and group 3: the ostio-caudal differentiation, the crista superior and

the crista inferior, the dorsal and ventral depressions, the shape of the

rostrum, the size and thickness, the collum, the shape of the antiros-

trum and the excisura. The shape of the otoliths varies between oval,

ovate and elliptic in the three length groups studied. The dorsal mar-

gin is emarginated, lobed or irregular in group 1 and group 2, but

mostly lobed or sinuate in group 3. Lobes and serrations are charac-

teristics of the ventral margin in fish of group 1 and group 2 but

diminishing in group 3. Lobes and occasional notches are found in oto-

liths of group 1 and group 2. The posterior margin is broad and has

two notches in group 3. The ostium and cauda are flared and shallow

and their floors are covered with lumps or ridges in all otoliths

examined.

The otoliths of small (group 1 and group 2) S. rivulatus (Figure 8)

differ from the larger (group 3 and group 4) ones in 10 out of 22 char-

acteristics studied. The following characters did not vary significantly

between small and large individuals: the shape of ostium, the

TABLE 2 Otolith characteristics of three size classes of Scarus dimidiatus from the Solomon Islands

Characters Group 1 (100–150 mm LT) Group 2 (151–200 mm LT) Group 3 (201–300 mm LT)

Otolith shape Oval. elleptic Elleptic, ovate, oblong Oval





Dorsal margin Lobed, straight with central lobe Irregular Entire

Ventral margin Crenate, coarse crenate Serrate, lobed Lobed at the middle

Posterior margin Rounded, blunt Broadly irregular, straight Broadly irregular

Sulcus acusticus Ostail homosulcoid Ostail homosulcoid Ostail homosulcoid

Ostium Flared, shallow or deep, floor covered withlumps

Flared, shallow withlongitudinal ridge

Flared, shallow with longitudinal ridge

Cauda Flared, shallow, floor covered with lumps,presence of horizontal ridge

Flared, deep, floor with alongitudinal ridge or smooth

Flared, shallow floor smooth

Ostio-caudal differentiation Well developed Well developed Well developed

Crista superior Ridge-like Ridge-like Ridge-like

Crista inferior Ridge-like Ridge-like Ridge-like

Dorsal depression Deep, elongated with edge ventrally Deep, elongated withshelve ventrally

Deep, elongated with shelve ventrally


Rostrum shape Lobed Lobed Lobed

Rostrum size Short Short Short

Rostrum thickness Broad Broad Broad

Antirostrum Short, pointed Short Short, rounded

Collum Solid-bridge Solid-bridge, developed Absent

Excisura Could be absent Could be absent Absent


JAWAD 1049FISH

TABLE 3 Otolith characteristics of three size classes of Scarus ghobban from the Solomon Islands


Otolith shape Obong Oblong, ovate Ovate





Dorsal margin Sinuate, lobed, irregular Irregular, emarginate, raised irregular Irregular

Ventral margin Sinuate Emarginate, crenate, serrate Irregular

Posterior margin Straight with indentation,pointed, irregular

Sinuate, irregular, lobed,rounded with extension

Irregular with indentation

Sulcus acusticus Ostial, heterosulcoid Ostial, homosulcoid Ostial, homosulcoid

Ostium Flared, shallow, floor coveredwith lumps or smooth

Flared, shallow, floor covered withlumps, ridges or smooth

Flared, shallow, floor coveredwith lumps, ridges or smooth

Cauda Flared, shallow, floor coveredwith ridges or smooth

Flared, shallow, floor covered withridges or smooth

Flared, deep, floor coveredwith ridges or smooth

Ostio-caudal differentiation Well or poorly developed Well or poorly developed Well or poorly developed

Crista superior Ridge-like, not developed, developed Ridge-like, developed Ridge-like

Crista inferior Ridge-like, poorly developed Ridge-like, poorly developed Well developed

Dorsal depression Narrow, deep or shallow, elongated Narrow, shallow, elongated, developed Developed


Rostrum shape Broadly pointed, absent With staright end or irregular Irregular

Rostrum size Short Short Short

Rostrum thickness Thick Thick Thick

Antirostrum Short, broad Short, broad, absent, pointed Long pointed

Collum Absent, poorly developed Absent, poorly developed, solid-bridge Solid-bridge

Excisura Absent Present Present


TABLE 4 Otolith characteristics of three size classes of Scarus niger from the Solomon Islands


Otolith shape Oval Elliptic Ovate, oval





Dorsal margin Slightly lobed Lobed, raised lobed Flat or raised lobed

Ventral margin Lobed Lobed, crenate, irregular Irregular, slightly irregular anteriorly,slightly crenate at the middle

Posterior margin Broadly pointed Broadly pointed, irregular Irregular, broadly pointed


Ostium Flared, deep, floor covered with lumps Flared, deep, floor covered with ridges Flared, deep, floor covered with ridges

Cauda Flared, shallow, floorcovered with lumps

Flared, shallow, floor coveredwith lumps or ridges, smooth

Flared, shallow, floor coveredwith lumps or ridges




Dorsal depression Elongated, narrow, deep Elongated, narrow, shallow Elongated, narrow, shallow


Rostrum shape Broadly pointed Broadly pointed Broadly pointed

Rostrum size Short Long Long


Antirostrum Short, broad Short or long, broad Long, broad

Collum Solid-ridge Solid-ridge Solid-ridge

Excisura Absent Absent Absent

Note. LT, Total length.

1050 JAWADFISH

ostio-caudal differentiation, the shape of dorsal margin, the shape of

the rostrum shape and the size and thickness. The shape of the oto-

liths is either elliptic or ovate in small individuals, but elliptic in larger

fish (group 4). The dorsal margin is either emarginate, irregular or

lobed in group 1 to group 3, it is lobed in group 4. The ventral margin

is emarginate, lobed or crenated in group 1 and group 2, but serrated

in group 3 and group 4. Small otoliths tend to develop a mid-ventral

angle on the ventral rim (see also S. dimidiatus). The posterior margin

is characterized by a notch, which varies between narrow and wide in

specimens of group 1 to group 3. In some individuals this margin is

pointed, but in group 4 it is pointed with a deep notch. In the four

length groups studied, the cauda is flared and shallow and the floor

either smooth or covered with lumps or ridges. In specimens of group

4, those lumps change to ridges. The crista superior has a ridge-like

structure in group 1 and group 2, becomes less marked in group 3 and

has a ridge-like structure again in group 4. The crista inferior is poorly

developed and not always along the full length in the four length

groups studied. The excisura is either absent or shallow in groups 1 to

3, but medium or medium-angled in group 4 (Table 6).

4 | DISCUSSION

There are several landmark features of the sagittal otolith that assist

in taxonomic studies (Figures 1 and 2). Such features have been docu-

mented in the works of several authors since the early 20th century

(Chaine & Duvergier, 1934; Frizell & Dante, 1965; Nolf, 1985, 2013).

The teleost sagittal otolith is the most widely used anatomical feature

in comparative taxonomic studies, because of its large size and degree

of inter-specific variation (Jawad, 2008; Jawad et al., 2007). In this

study, we examined a wide range of otolith characteristics, of which

only a few turned out to be taxonomically important. It was possible

to recognize two groups of characteristics that can be used to distin-

guish small and large specimens: characteristics that are consistent in

the otoliths of fish across different length groups, which can be used

to identify individual species; characteristics that vary due to ontoge-

netic changes, but may be useful to define certain developmental

stages.

Many parrotfish species are recognized based on morphology and

phenotypic characteristics (e.g., coloration) and these traits are con-

gruent with the phylogenetic evolution of the Scaridae (Bellwood,

1994; Parenti & Randall, 2011). The otoliths of parrotfishes are gener-

ally small, most likely to avoid the background noise produced by

rough seas in shallower regions of coral reefs (Cruz & Lombarte, 2004;

Paxton, 2000; Volpedo & Echeverría, 2003). The small size of otoliths

was clearly noticed in the six parrotfish species studied here, illustrat-

ing the relationship of ecology and otolith size. Relationships between

otolith size, habitat and behavior are also seen in other groups, such

as some notothenioids (Klingenberg & Ekau, 1996; Lombarte et al.,

2003). Sadighzadeh et al. (2014) found a relationship between varia-

tion in the anterodorsal area of the sagittal otoliths and certain behav-

iors in snappers. The anterodorsal area is extended in Lutjanus

argentimaculatus (Forsskål 1775), a species that is active at night

(Martinez-Andrade, 2003); however, results of that study cannot be

TABLE 5 Otolith characteristics of three size classes of Scarus oviceps from the Solomon Islands

Characters GI (100–150 mm LT) GII (151–200 mm LT) GIII (201–300 mm LT)

Otolith shape Oval, ovate Elliptic, oval Elliptic, ovate, oval





Dorsal margin Emarginate, lobed Lobed, irregular Lobed, sinuate

Ventral margin Lobed, coarse serrate Lobed, sinuate Slightly serrate, slightly lobed

Posterior margin Lobed, broadly straight Lobed, broadly pointed Broad with notchs


Ostium Flared, shallow, floorcovered with lumps

Flared, shallow, floorcovered with lumps

Flared, shallow, floorcovered with ridges

Cauda Flared, shallow, floor coveredwith lumps and ridges


Flared, shallow, floor coveredwith lumps and ridges




Dorsal depression Elongated, shallow Elongated, shallow Elongated, shallow


Rostrum shape Lobed Lobed Broadly pointed

Rostrum size Long Long Long


Antirostrum Long or short, broad Long or short, broad Long or short, broad

Collum Solid-ridge Solid-ridge Solid-ridge

Excisura Absent Absent Absent


JAWAD 1051FISH

applied to the six parrotfish fishes studied, because they all have a

lobed anteriodorsal area and they all are day feeders. This study also

shows that the overall morphology of otoliths varies from small to

larger individuals. Out of 22 characters studied, H. longiceps has

14 that differ between small and larger invididuals. The fewest onto-

genetically variable characters were noticed in S. oviceps with only six.

In general, the present study has shown the presence of ontogenetic

changes such as the lengthening of the otolith, the disappearance of a

mid-ventral angle, the ventral rim becoming straighter and generally

less lobed or crenulated, the development of pronounced ridges and

lumps in the colliculi, the more pronounced cristae.

The six species studied share consistent characters from smaller

to larger individuals (Tables 1–6), but these characters cannot be used

as a tool to separate individual species within one genus or between

genera of the Scaridae. The ostial shape of the sulcus acusticus in

Scarus is shared by members of Hipposcarus (this study; Lin & Chang,

2012) and of Nicholsina (Baremore & Bethea, 2010). It cannot be used

either as a characteristic feature to separate the five species of the

genus Scarus studied here. Moreover, it is similar in nine species of

the genus from Taiwan (Lin & Chang, 2012) and one species from

Pacific islands (Weisler, 1993). Furthermore, Smale et al. (1995)

described the sulcus acusticus of 10 parrotfish species, including

seven species belonging to the genus Scarus, as ostio-caudal. Among

those seven species S. ghobban and S. niger were highlighted. Finally,

Sadighzadeh et al. (2012) described the sulcus acusticus of S. ghobban

as homosulcoid. This shows a great geographical variance between

these studies and my findings. Scarus ghobban is one of the most

widespread parrotfish species circumtropically and is generally

believed to be a species complex. Therefore, the characters described

cannot be reliably used to identify any of the six scarid species from

the Solomon Islands elsewhere, as there appears to be too much intra-

specific geographic variability in parrotfish otoliths.

In each of the six species studied, there are certain characters that

are conservative in the different length groups (Tables 1–6): three in

H. longiceps, five in S. dimidiatus, three in S. ghobban, eight in S. niger,

eight in S. oviceps and four in S. rivulatus. The consistency of these

characters can perhaps, with a degree of doubt, be used as a tool to

separate these species from other members of the family Scaridae in

the Solomon Islands, which is a task for future studies. Otolith shape

varies ontogenetically in all species studied. From small to large,

S. dimidiatus shows the highest degree of variability with four shapes,

H. longiceps and S. niger with three shapes and the least variable were

S. ghobban and S. rivulatus with only two shapes. Among the five spe-

cies of Scarus studied here, it was not possible to describe a uniform

shape for the genus. The general trend is oval–ovate–oblong–elliptic.

Such a variation through ontogeny is also reported by Smale et al.

TABLE 6 Otolith characteristics of three size classes of Scarus rivulatus from the Solomon Islands

Characters Group 1 (100–150 mm LT) Group 2 (151–200 mm LT) Group 3 (201–250 mm LT) Group 4 (251–300 mm LT)

Otolith shape Elliptic Ovate Ovate Elliptic

Otolith width Very thick Very thick Very thick Very thick

Otolith depth Deep Deep Deep Deep

Mesial surface Convex Convex Convex Convex

Lateral surface Concave Concave Concave Concave

Dorsal margin Slightly emarginate Raised emarginate, lobed Raised irregular Lobed

Ventral margin Emarginate Emarginate, lobed, crenate Sinuate Sinuate

Posterior margin Broadly pointed,with notch

Lobed with notch Broadly pointed with notch Irregular, with notch

Sulcus acusticus Ostial, homosulcoid Ostial, homosulcoid Ostial, homosulcoid Ostial, homosulcoid

Ostium Flared, shallow, floorcovered with lumps




Cauda Flared, shallow,floor smooth

Flared, shallow, floor coveredwith lumps or smooth

Flared, shallow, floorcovered with lumpsor ridges


Ostio-caudaldifferentiation

Well developed Well developed Well developed Well developed

Crista superior Ridge-like Ridge-like Ridge-like Ridge-like

Crista inferior Absent Absent Absent Absent

Dorsal depression Elongated, shallow Elongated, shallow Elongated, shallow Elongated, shallow

Ventral depression Absent Absent Absent Absent

Rostrum shape Lobed Lobed Lobed Lobed

Rostrum size Short Long Long Long

Rostrum thickness Thick Thick Thick Thick

Antirostrum Short, broad Long or short, broad Long or short, broad Long, broad

Collum Bridge-like Bridge-like, poorly developed Bridge-like, poorlydeveloped

Bridge-like

Excisura Absent Absent or narrow, shallownotch, narrow angle

Absent Medium, shallow notch,medium angle


1052 JAWADFISH

(1995), which suggests that it is impossible to provide a key for the

genera based on the shape of the otoliths for the Scaridae. The ante-

rior margin has an anterodorsal angle, which is high in the scarids. The

anterior margin cannot be described as one unit compared with the

other margins; its different components, rostrum, excisura and anti-

rostrum, were described separately. The three other margins of the

otolith, dorsal, ventral and posterior, show a low range in variation.

There were grades of lobation and irregularities across the different

length groups. Similar findings were reported for triplefin species by

Jawad et al. (2007) and for the greater lizardfish Saurida tumbil (Bloch

1795) by Jawad (2008).

The ostium and cauda in all six species studied are flared shape,

mostly shallow and their floor is covered with either lumps of differ-

ent sizes or ridges. The shape of the sulcus acusticus, the crista supe-

rior and crista inferior is also very variable. Shape and nucleus location

result from the release of soluble Ca2+ on the proximal side (Ibsch

et al., 2004), which in turn precipitates as CaCO3 crystals due to an

increasing alkaline gradient, from the sulcal area towards the otolith

edge (Gauldie & Nelson, 1990). As a result, the growth of the crista

superior and crista inferior is preferred and there is a more important

development on the mesial side. The macula is elongated and narrow

in teleosts and the crista superior and inferior are proportionally more

important than the colliculum (Ladich & Popper, 2001; Lombarte &

Fortuno, 1992; Popper & Hoxter, 1981). The macula faces the collum

and prevents otolith growth at this level (Lombarte & Fortuno, 1992;

Pannella, 1980; Popper & Hoxter, 1981). This is clear in some species

where the collum is either poorly developed or absent. Lombarte et al.

(2003) showed that the variability in the shape of the sagittal otolith is

related to genetic, ontogenetic and environmental factors in Merluc-

cius Rafinesque 1810. Previous studies on fossil and extant otoliths

Crista superior(a)

(b)

Posterior

An�rostrum

Anterrior

1·0 mm

Excisura

5.0kV 15.7 mm x30 (SE(M) 1.00 mm

Sulcus

Ventral

Os�um

Dorsal

Cauda

Crista superior

FIGURE 2 (a) The mesial surface of the left otolith of Hipposcarus

longiceps, 187 mm total length (LT), illustrating various features foundon the otolith and described in the text. (b) the mesial surface of theleft otolith of Scarus oviceps, 230 mm LT, illustrating excisura

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) 1 mm

FIGURE 3 Otoliths of Hipposcarus longiceps taken from fish of

different total lengths: (a) 187 mm (right-side otolith), (b) 196 mm(right), (c) 209 mm (left), (d) 220 mm (right), (e) 230 mm (left), (f )245 mm (right), (g) 255 mm (right), (h) 266 mm (left), (i) 274 mm (left),(j) 328 mm (right), (k) 360 mm (right)

(a) (b) (c)

(d) (e) (f)

(g) (h) 1 mm

FIGURE 4 Otoliths of Scarus dimidiatus taken from fish of different

total lengths: (a) 114 mm (left-side otolith), (b) 115 mm (left),(c) 150 mm (left), (d) 160 mm (left), (e) 178 mm (left), (f ) 187 mm(right), (g) 195 mm (left), (h) 211 mm (right)

JAWAD 1053FISH

have demonstrated that the sulcus morphology usually is consistent

among the species of a single genus (Nolf, 1985, 2013), which sug-

gests that this feature is probably genetically controlled

(Gauldie, 1988).

Interspecific variation in sulcus morphology has previously been

recorded for only a few other genera. For example, the Euro-African

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k)

(l)1 mm

FIGURE 5 Otoliths of Scarus ghobban taken from fish of different

total lengths: (a) 163 mm (right-side otolith), (b) 185 mm (left),(c) 194 mm (left), (d) 205 mm (right), (e) 215 mm (right), (f ) 227 mm(right), (g) 231 mm (right), (h) 245 mm (right), (i) 271 mm (right),(j) 283 mm (right left), (k) 283 mm (left), (l) 319 mm (right)

(a) (b) (c)

(d) (e) (f)

(g) (h) 1 mm

FIGURE 7 Otoliths of Scarus oviceps taken from fish of different total

lengths: (a) 115 mm (right-side otolith), (b) 133 mm (left), (c) 149 mm(right), (d) 156 mm (right), (e) 208 mm (right), (f ) 214 mm (right),

(g) 215 mm (left), (h) 230 mm (right)

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) 1 mm

1 mm

FIGURE 8 Otoliths of Scarus rivulatus taken from fish of different

total lengths: (a) 126 mm (right-side otolith), (b) 138 mm (right),(c) 144 mm (right), (d) 155 mm (right), (e) 168 mm (right), (f ) 175 mm(left), (g) 182 mm (left), (h) 191 mm (left), (i) 204 mm (right),(j) 217 mm (left left), (k) 261 mm (right)

(a) (b) (c)

(d) (e) (f)

(g) (h) (i) 1 mm

FIGURE 6 Otoliths of Scarus niger taken from fish of different total

lengths: (a) 140 mm (right-side otolith), (b) 151 mm (left), (c) 161 mm(left), (d) 172 mm (right), (e) 183 mm (right), (f ) 197 mm (left right)(g) 202 mm (left), (h) 211 mm (right), (i) 215 mm (right)

1054 JAWADFISH

TABLE

7Geo

grap

hicalvariationin

themorpho

logy

oftheotolithofHippo

scarus

longiceps,Scarus

ghob

ban,

Scarus

niger,an

dScarus

rivulatus

SolomonIsland

sArabian

–Persian

gulf

SouthAfrica

New

Caled

onia

Taiwan

Present

stud

ySa

digh

zade

h&

Tuset,2

012

Smaleet

al.,1995

Rivatonan

dBourret,1

999

Linan

dChan

g,2012

Hippo

scarus

longiceps

201mm

L T–

––

–203mm

L T

Oval

––

––

Shap

e:Ovate

Coarsely

lobe

d–

––

–Posteriormargin:S

traigh

t

Short

––

––

Rostrum:L

ong

Smooth,p

resenc

eofinde

ntation

––

––

Ostium:F

loorwithco

arse

lumps,noinden

tation

anteriorly

Scarus

ghob

ban

194mm

L T215mm

L T245mm

L T319mm

L T191mm

L T210mm

L T241mm

L T375mm

L T

Oblong

Oblong

Oval

Pointed

Shap

e;cu

neiform

-elliptic

Shap

e:Circu

lar

Shap

e:Oblong

Rostrum:R

ounded

Long

Lobe

dLo

bed

–Rostrum:S

hort

Posteriormargin:

With

notch,

nearly

smooth

Dorsalmargin:E

marginate

–

Absen

tEmargina

teSlightly

emargina

te–

Excisura:

Nono

tch

Ven

tralmargin:

Crena

teVen

tralmargin:L

obed

–

Welld

evelope

dLo

ng,p

ointed

Lobe

d–

Cristasupe

rior

andinferior:

Poorlyde

velope

d

Rostrum:S

hort,b

road

Rostrum:E

marginate

–

–Bridg

e-like

Lobe

d–

–Collu

m:A

bsen

tPosteriormargin:P

ointed

–

–W

elld

evelope

dOstial

––

Cristasupe

rior:Poorlyde

velope

dSu

lcusacusticus:Ostio-cau

dal

–

–Dee

pDev

elope

d–

–Dorsalde

pression:

Shallow

Collu

m:A

bsent

–

–245mm

L TW

elld

evelope

d–

–245mm

L TCristasuperior:Absent

–

–Slightly

emargina

teW

ithridg

es–

–Ven

tralmargin:

Crena

teOstium:S

mooth

–

–Pointed

––

–Rostrum:B

road

––

–Bridg

e-like

––

–Collu

m:A

bsen

t–

–

–W

elld

evelope

d–

––

Cristasupe

rioran

dinferior:

Poorlyde

velope

d–

–

–Dee

p,floorwithridg

es–

––

Cau

da:S

hallo

w,smooth

floor

––

–Dee

p,floorwithridg

es–

––

Ostium:S

hallo

w,floorwithlumps

––

–319mm

––

–430mm

––

–Oblong

––

–Sh

ape:

Circu

lar

––

–Coarse

lobe

d–

––

Dorsalan

dve

ntralm

argins;

fine

cren

ate

––

–Lo

bed,

long

––

–Rostrum:B

road

,veryshort

––

–W

elld

evelope

d–

––

Cristainferior;po

orlyde

velope

d–

–

–Bridg

e-like

––

–Collu

m:A

bsen

t–

–

JAWAD 1055FISH

TABLE

7(Continue

d)

SolomonIsland

sArabian

–Persian

gulf

SouthAfrica

New

Caled

onia

Taiwan

–Dee

p,floorwithridg

es–

––

Cau

da:S

hallo

w,floorsm

ooth

––

–Dee

p,floorwithridg

es–

––

Ostium:S

hallo

w,floor

Withfine

lumps

––

–W

elld

evelope

d–

––

-–

–

Scarus

niger

161mm

L T161mm

L T202mm

L T157mm

L T158mm

L T206mm

L T

Oval

Welld

evelope

dW

ithseve

rallobe

sSh

ape:

Circu

lar

Collu

m:A

bsent

Posteriormargin:

Withonelobe

Lobe

dBridg

e-like

Broad

lypo

inted

Dorsalmargin:

Withinde

ntation

above

caud

aCristainferior:Poorly

dev

eloped

Antirostrum;finepointed

Coarse

lobe

dDee

p,floorwithridg

esW

ithco

arse

ridge

Ven

tralmargin;

fine

cren

ate

Ostium

andcauda:

Shallow

withsm

ooth

floor

Ostium

andcauda:

Smooth

withoneridge

Coarse

lobe

dAbsen

tW

elld

evelope

dPosteriormargin:

Curve

dVen

traldep

ression:S

hallow

Collu

m:P

oorlydev

eloped

Long

,lobe

d215mm

–Rostrum;sho

rt,roun

ded

220mm

–

Dee

p,floorwithridg

esSlightly

cren

ate

–Cau

da:S

hallo

w,floorsm

ooth

Ven

tralmargin:C

oarsely

lobed

–

Floorwithlumps

and

ridg

esat

bottom

Broad

lypo

inted

–Ostium:F

loorwithcentralridge

Posteriormargin;straigh

t–

215mm

L TBroad

lypo

inted

–286mm

L TRostrum:W

ithtw

osm

all

projections

–

Withbroad

fissure

Poorlyde

velope

d–

Posteriormargin:

Pointed

Antirostrum:S

hort,p

ointed

–

Long

,sha

llow

Floorwithlumps

–Dorsalde

pression:

Absen

tCau

da:

Floorwithridge

s–

Floorwithco

arse

lobe

san

dridg

es–

–Cau

daan

dostium:F

loorsm

ooth

––

Welld

evelope

d–

–Cristasupe

rior:Poorlyde

velope

d–

–

Scarus

rivulatus

217mm

L T261mm

L T291mm

L T225mm

L T

Shap

e:Domed

withlobe

sElliptic

Shap

e;oblong

Dorsalmargin:E

marginate

Dorsalmargin:

Withde

epfissure

Finecren

ate

Dorsalmargin:C

oarse

lobed

Posteriormargin:

Withshallow

fissure

Rostrum:N

arrow,

fine

pointed

Long

,broad

lylobe

d,lower

edge

coarsely

lobe

dRostrum:S

hort,b

oard,lower

edge

emarginate

Rostrum:B

road

lypointed

Ecisura:W

ith

deve

lope

dprojection

Widewithwideno

tch

Ecisura:N

arrow

with

narrow

notch

Antirostrum:S

hort,b

road

Floorwithlumps

and

ridg

esCau

daan

dostium:

Floorsm

ooth

1056 JAWADFISH

species of Merluccius (Merlucciidae) can be separated from the

American ones, based on the variation of the sulcus; therefore, the

variation in sulcus runs parallel to zoogeography and phylogeny

(Torres et al., 2000). However, the variation in sulcus is also the result

of an acoustic specialization and thus interspecific sulcus variation

may also result from ecomorphological adaptations (Ramcharitar et al.,

2004; Popper et al., 2005). The shape of the sulcus is important in

sciaenid otoliths (Nolf 1985). Apart from sulcus morphology, the cor-

relation between particular otolith features (e.g., the proportions of

rostrum and antirostrum) and biological functions (e.g., swimming abil-

ity, feeding, or other activities) has not yet been established (Popper

et al., 2005). Considering the variety of teleosts, there may be some

correlation between the length of the rostrum and the swimming abil-

ity (Nolf, 1985; Volpedo & Echeverría, 2003), but this correlation is

not significant in the discrimination of closely related species

(Reichenbacher et al., 2007). In this study, the general morphology of

the rostrum in the six species examined is broad, short and lobed and

such a consistency agrees with Reichenbacher et al. (2007).

Selective pressures can sometimes act on sagittae so that their

morphology meets specific auditory needs (Gauldie, 1988; Platt &

Popper, 1981; Popper & Coombs, 1982). Constraints in terms of phys-

ical packing of sagittae within the skull have also been cited in several

studies, especially those examining closely related species with large

sagittae (Arellano et al., 1995; Gaemers, 1984; Smith, 1992). Otolith

growth has long been shown to have a positive relationship to fish

age (Sabetian et al., 2015), but otoliths in very large fishes can be

much smaller than those in small fishes and vice versa (Campana,

2004). A limited comparison made by Friedland and Reddin (1994)

suggests that the shape of otolith is also influenced by genetics. Dif-

ferent morphologies in otoliths of a species obtained from different

localities have been observed. The otoliths of the six scarid species

were compared with those of similar size from other localities and this

comparison is given here (Table 7). Rivaton and Bourret (1999) pro-

vided an image of an otolith from a S. rivulatus of 470 mm length, no

comparable length group was available for the present study. The oto-

lith described by Rivaton and Bourret (1999) is oblong with dorsal

margins nearly smooth and ventral margins crenulated. The rostrum is

long and lobed, there is no collum, the cauda is deep with a smooth

floor and the crista superior extends over the whole length of the

ostium. The largest otolith of S. rivulatus obtained for the present

study is elliptic and there are more differences in several morphologi-

cal aspects. The description of the otolith by Rivaton and Bourret

(1999) complements our knowledge of the otoliths of S. niger.

The results of this study highlight a degree of intraspecific varia-

tion in the shape of the otolith for each species, such as the angle of

the rostrum (straight v. oblique), or the shape of the excisura

(Tables 1–6). This study was unable to highlight enough variability in

otolith shape to use as a key for individual species from the Solomon

Islands, but there is enough variability to distinguish small–juvenile

from large–adult individuals provided the species has been rigourously

identified upon capture. Further investigation is required, including a

comparative study of the shape and geometry of the sagittal otolith,

to add further taxonomic characters for the identification of these

species from the Solomon Islands.

ACKNOWLEDGEMENTS

My sincere thanks are due to those people who collected the fish

specimens and extracted their otolith. Also to the Auckland University

of Technology (AUT) for the SEM imaging of the otoliths and for edit-

ing them in Photoshop.

ORCID

Laith A. Jawad https://orcid.org/0000-0002-8294-2944

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How to cite this article: Jawad LA. A comparative morpho-

logical investigation of otoliths of six parrotfish species (Scari-

dae) from the Solomon Islands. J Fish Biol. 2018;93:

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http://www.horizon.documentation.ird.fr/exl-doc/pleins_textes/divers09-06/010021515.pdf

https://doi.org/10.1111/jfb.13787