OSTEOLOGY OF THE FIRST DORSAL FIN IN TWO TERAPONTID FISHES, LEIOPOTHERAPON UNICOLOR (GUNTHER, 1859) AND AMNIATABA CAUDAVITTATA (RICHARDSON, 1845), FROM WESTERN AUSTRALIA EVIDENCE FOR HYBRIDISATION

2006·4.5 MB·English

by  David L Morgan

Recordsofthe WesternAustralianMuseum 23: 133-144 (2006).
Osteology of the first dorsal fin in two terapontid fishes, Leiopotherapon
unicolor (Gunther, 1859) and Amniataba caudavittata (Richardson, 1845),
from Western Australia: evidence for hybridisation?
DavidL. Morganand HowardS. Gill
CentreforFishandFisheriesResearch,MurdochUniversity,SouthStreet,Murdoch,
WesternAustralia6150,Australia;Email: [email protected]
Abstract - Osteological characters, such as number of supraneural bones
anteriorto firstneural spine, numberofspineson first dorsal pterygiophore,
position of insertion of first proximal dorsal pterygiophore and number of
anterior proximal dorsal pterygiophores insertingbetween successiveneural
spines, in conjunction with morphological characters, were used to provide
evidence of natural hybridisation between two species of the Terapontidae:
thefreshwater Leiopotherapon unicolorand themarine/estuarineAmniataba
caudavittata.
INTRODUCTION Western Australia, throughout northern Australia
The Terapontidae (commonly called trumpeters and southern New Guinea to the east coast of
or grunters) consists of small to medium-sized northern Queensland (Vari 1978; Allen etal. 2002).
fishes represented by approximately 46 species WhilstA. caudavittataisconsideredtobeprimarily
from 16 genera in marine and freshwaters of the marine (Vari 1978), in south-western Australia it is
Indo-Pacific region (Vari 1978; Nelson 1994; Allen essentially restricted to estuaries (Potter etal. 1994;
etal. 2002). Of these, about 33 are restricted to the Wise et al. 1994). It is also able to tolerate both
freshwaters of New Guinea and Australia where freshwater and hypersaline conditions (Hutchins
they are often of economic and/or recreational andSwainston 1986;MorganandGill2004).
importance (Allen et al. 2002). The 16 genera Leiopotherapon unicolorandA. caudavittataboth
mm
assigned to the group are separated on the basis of attain total lengths of ca 300 and are
the following features: pigmentation; extrinsic superficially similar, with considerable overlap
swimbladder muscle; swimbladder and intestinal occurring in many of the characteristics often used
pattern; height of dorsal and anal fin sheath; and to differentiatebetween species of fish, e.g., dorsal-
osteological characteristics of the posttemporal, fin spines (XI-XIII in L. unicolor cf. XII-XIII in A.
tabular,dentary, maxilla, premaxilla,spinousdorsal caudavittata); dorsal-fin rays (9-12 cf. 8-10); anal-fin
fin and vertebral column (Vari 1978). The rays (III, 7-10 cf. Ill, 8-9); pectoral-fin rays (15-16cf.
Australian terapontid fauna consists of 25 species 13-17); pelvic-fin rays (both 1-5); lateral line scales
which are restricted to freshwaters and a further (45-57cf. 46-54); scales above lateral line (both 7-9);
eight species that are considered predominantly scales below lateral line (16-20 cf. 17-19); caudal
marineorestuarine(Vari 1978;Allen etal. 2002). scales (3-6 cf. 4-6); and predorsal scales to occiput
Two of the most common and widespread (15-20 cf. 14-17) (Vari 1978). Notwithstanding the
terapontids in Australia are the Spangled Perch above similarities in these species, L. unicolor is
Leiopotherapon unicolor (Gunther, 1859) and the readily distinguished from A. caudavittata as the
Yellowtail Trumpeter Amniataba caudavittata fins of the former species are a uniform pale,
(Richardson, 1845). The former is the most silvery-grey colour, whereas those of the latter
widespread freshwater fish species in Australia, speciesareyellow and, inthecaseofthe2nd dorsal-
occurring in major rivers, isolated drainages and fin and caudal-fin, bear prominent black bands
ponds throughout the northern two thirds of (Vari 1978). Furthermore, in L. unicolorthe row of
Australia, includingmostriversystemsnorthofthe spots running from the eye to the upper jaw and
Murchison River in Western Australia, the the row below the eye from the preopercle to the
Northern Territory, Queensland, the Lake Eyre/ upper jaw are represented by distinct spots,
Bulloo drainage systems and those rivers north of whereas in smaller specimens of A. caudavittata
the Murray-Darling River in New South Wales thesespotscoalesce to form two distinctbands (see
(Vari 1978; Allen et al. 2002). Amniataba Figure 1 and photographs on pages 227 and 241 in
caudavittata occurs from the lower west coast of Allenetal. 2002).
134 D.L.Morgan,H.S.Gill
Figure1 A, Amniataba caudavittata. B, Leiopotherapon unicolor and C and D, intermediate forms (note bars on
caudalfinsandroundedsnout).
Hybridisationof L. unicolorandA. caudavittata 135
In addition to the clear distinction in coloration Hybridisation between fish species is not
between L. unicolorand A. caudavittata, members uncommon and Schwartz (1972, 1981) compiled
of the genus Leiopotherapon can be differentiated almost 4000 references reporting either natural or
from those of Amniataba using the following artificial hybridisation between various species.
osteological criteria: one supraneural bone in front Historically, themain methods ofdetectinghybrids
of the first neural spine in Leiopotherapon have been through the comparison of
compared to two in Amniataba; one spine on first morphological characters (e.g., morphometric and
dorsal pterygiophore cf. two; the insertion of the meristic data), with the assumption that the hybrid
first proximal dorsal pterygiophore between the has characters that are intermediate between the
second and third neural spines cf. its insertion parent species (Campton 1987, 1991). In this paper
between the first and second; two of the anterior wedescribetheosteologyofthefirstdorsal finand,
proximal dorsal pterygiophores inserting between bycomparison with thedescriptions and diagnoses
successive neural spines cf. one (Figure 2) (Vari of the two genera provided by Vari (1978), provide
1978). evidence of natural hybridisation in the
Duringa recent surveyofthe freshwaterfishes of Terapontidae. In addition, we provide evidence to
the Pilbara (Morgan and Gill 2004) L. unicolorand suggestthatthehybridsarereproductivelyviable.
A. caudavittata were often observed schooling
together up to 300 km inland in the Murchison
River. On closer examination, it became apparent MATERIALSANDMETHODS
that many individuals from these mixed schools
possessed combinations of coloration and pattern
characteristic of both species. Thus, some MurchisonRiver, WesternAustralia
individuals had distinct spots that had not The Murchison River is located in the Pilbara (or
Indian Ocean) Drainage Division of Western
coalesced into bands on the snout and cheek
(characteristicof L. unicolor)buthad yellowish fins Astuasntdraarldisa,adnrdainisinglaragpeprboyximWaetsetleyrn12A0us0t0r0alkiman2
(characteristicofA. caudavittata) andeitherhadno,
or one or two weak or strong band(s) on their a(Fpipgruorxeim3)a.teIltsyh5e0a0dwkamterisnlaarnidsefnreoamrtMheeekmaotuhatrhraa,t
cAa.udcaauldalvoibtetsat(ac,haroarctienrtiestrimcesdioafteeitbheetrwLe.enunitchoelotrwoo)r Kalbarri. Precipitation near the river mouth is
(see Figure 1). It was suspected that these rmeml/atainvneluym)l,owwiatnhdlohwigshulymmseerasaonndalme(mdeiaunmcwaint37e5r
individualswerehybrids.
falls, while the inland reaches receive relatively
marginal and unpredictable rainfall (ca 238 mm/
annum) throughout the year (data provided by the
Western Australian Bureau of Meteorology). The
riverismarginallysalinethroughoutitslength.
Samplinglocalitiesandenvironmentalvariables
Thirteen sites on the lower, middle and upper
Murchison River were sampled using a variety of
seine nets and rod and line. The seine nets were
comprised of either 3 or 6 mm woven mesh. The
main study sites (3 and 4) were situated at the
easternend oftheKalbarri National Park(Figure3)
and the water temperature and conductivity were
recorded in each month between December 2000
and November 2001 at site 4. Other sites were
sampled on a single occasion and the numbers of
each species (that superficially resembled either L.
unicolororA. caudavittata)wererecordedandthey
supraneurals, anterior proximal
pterygiophores, anterior neural spines and were then released immediately. Fish that were
anterior Is' dorsal spines in A, keptwereeuthanased inaniceslurry.
Leiopotheraponand B, Amniataba. N.B.One
supraneural anterior to first neural spine in Morphologyandosteology
Leiopotherapon(versus2 in Amniataba)', one Each fish retained from theMurchison River was
sdLoeercisooapnlodtsphaiennredapootnnhif(rirvdsetraasnnuttseer2riiooinrrApptmteneriryaygtgiaiobpoahpo)h;roaerneidsn msuebajseucrteivdetoastsheesnsemaernetstm1amdem a(stottaol lwehnegtthh)erandthea
insertingbetween successiveneural spines in individual superficially resembled more closely L.
Leiopotherapon(fromVari1978). unicoloror A. caudavittata; based on fin and body
136 D.L.Morgan,H.S.Gill
coloration and patterning, and also overall shape dorsal-fin pterygiophore; the position of the
(in L. unicolor the body is slender and the snout insertion of the first proximal dorsal-fin
rounded, whereas the body of A. caudavittata is pterygiophore (between second and third or first
moderately deep and the snout pointed and and second neural spine); and number of anterior
relatively shorter than that of L. unicolor). The proximal dorsal-fin pterygiophores inserting
vertebral column, and associated supraneurals, betweensuccessiveneuralspines (oneortwo) (Vari
pterygiophores and dorsal spines, below the 1978, and Figure 2). The vertebral column and
anterior-most section of the first dorsal-fin were associated structures werethen drawn with the aid
then displayed by dissection and the following of a dissecting microscope and compared to those
characteristicsdetermined: numberofsupraneurals that comply with either L. unicolor or A.
in front of the first neural spine (one or two for caudavittata (Vari 1978, and Figures 2 and 4).
Leiopotherapon and Amniataba, respectively); Dissection, rather than radiography, was used to
number of dorsal-fin spines (one or two) on first determine the osteolgy of the first dorsal-fin as a
Figure3 The rivers and embayments (Shark Bay) in Western Australia from which terapontids were examined. The
mainstudysitesontheMurchisonRivers,andthemajortowns,KalbarriandMeekatharra,arealsogiven.
HybridisationofL. unicolorandA. caudavittata 137
preliminary investigation demonstrated that Reproductivebiology
radiographs were often difficult to interpret, The gonads of each fish retained from the
whereas dissection provided unambiguous and Murchison River were examined, and the sex and
accuratedescriptions. stage of gonadal development determined
The osteology of individuals of presumptive L. macroscopically.Thestageofgonadaldevelopment
unicolorfrom the Gascoyne (5 specimens), Minilya was based on the following criteria adapted from
(4), Cane (5), Yule (5), De Grey (5) and Fitzroy (5) Laevastu (1965): stage I/II (immature); stages III/IV
rivers, andA. caudavittatafrom theSwanRiver(5), (maturing); stage V (mature); stage VI (spawning)
Shark Bay (25) and Cape Keraudien (33) were also andstageVII(spentorrecentlyspawned).
determined (Figure 3). Specimens of
Leiopotherapon unicolor in the collections of the
Western Australian Museum were also examined RESULTS
mm
(P4336, 4, 56-83 TL, Murchison River, 12
mm Environmentalvariables
ORicvteorb,eGral1e9n58a;,P2573S6e2,pt3e,m7b5e-r1019061). TL, Murchison The mean water temperature at the main study
A(F.Iingcuaorureddae4vr)ittmtooatrdaeettechrleomsimenileyniwrhmeesutemhmebnrlueamdbveLa.rriuaonnfitccpohalatontrgeerosnr sFAieutbgersuusaftroyl(lc(aocwa1e6d2°7C°a)C)s2e0aa0n1sd.onTarlehaecphacitontngedrunac,tmivpiientaiykmiounfmgthiienn
required to transform each individual pattern to main study sites throughout the year of the study
that of L. unicolor and A. caudavittata was ranged from 1.6-26.8 mScnr1, but averaged ca 13.2
mScnr'.
estimated. In these transformations the following
assumptions were made. Firstly, in general, dorsal
spines and pterygiophores were not independent, Distributionofterapontidsinthe Murchison
thus the loss, gain, or movement of an individual River
pterygiophore included a corresponding loss, gain Terapontids were captured at 13 sites in the
or movement of the associated spine. Secondly, in Murchison River. Forms that superficially more
the case of the first pterygiophore, it was closelyresembled L. unicolorwerefoundatallsites
considered that the loss of a second spine on that except the two most downstream locations (Figure
pterygiophore could occur without losing the 3). Those resembling more closely A. caudavittata
pterygiophore and other spine, and that gaining a were captured at nine sites, ranging from the two
second spine on the first pterygiophore did not downstream sites to the most inland sites. Both
require gaining an additional pterygiophore 'forms' co-occurred atsevensites.
bearing two spines. It is worth noting that if this
second assumption is not made, and Morphologyandosteology
transformations require the loss (or gain) of the Ofthe231 terapontidsexaminedforvertebraland
whole pterygiophore they contain either the same first dorsal osteological comparison during this
number of steps or require additional steps. study, 32different patterns were evident(Figures2
Finally, wherethere aretwoor moreequallyshort and4,Table1).
transformations, the one presented in Table 1 In the Murchison River samples collected during
maximises movements rather than losses and the current study, only 24 (30%) of the 80
gains, e.g., in Type 19 the transformation to individuals that superficially more closely
Leiopotherapon presented is: Step 1, move resembled L. unicolor had an osteological
supraneural 2 to between neural spines 1 and 2; configuration that complies with Vari's (1978)
Step 2, move supraneural 3 to between neural description for Leiopotherapon (see also Figures 2
spines 1 and 2; Step 3, remove 1st pterygiophore; and4). Intheremaining56individuals,20different
Step 4, remove 2nd or 3rd pterygiophore; Step 5, osteological patterns unlikethosedescribed forany
move new pterygiophore 1 to between neural other terapontid, were found (Figure 4, Table 1).
spines 2 and 3; Step 6, move new pterygiophore 2 The most common of these variant configurations
to between neural spines 3 and 4. The alternative (Type 4, 20 individuals) differs from the
is: Step 1, move supraneural 2 to between neural configuration diagnostic of Leiopotherapon only in
spines 1 and 2; Step 2, move supraneural 3 to having the second pterygiophore arising from
between neural spines 1 and 2; Step 3, remove 1st between thesecond and third, ratherthan thethird
pterygiophore; Step 4, remove 2nd pterygiophore; and fourth, neural spines (Figure4,Table 1). Ofthe
Step 5, remove 3rd pterygiophore; Step 6, gain remainingconfigurations present in specimens that
additional pterygiophore between nemal spines 3 resembled L. unicolor, types 1, 2, 3, and 5 alsovary
and 4. Thus, the first transformation comprises from the pattern diagnostic of Leiopotherapon in
four movements and two losses, whereas the only requiring the addition or movement of a
alternativecomprisestwomovements, threelosses supraneural or pterygiophore and its spine, whilst
and oneaddition. Type 7 only requires the addition of a supraneural
138 D.L.Morgan,H.S.Gill
Type 1 -Lu
Type2-Lu
ywy
y
Type3-Lu Type 13 -Lu Type23 - Lu
w/
v y
Type4-Lu Type 14-Lu Type24-Ac
w/
r/wi
y y
Tffl'V/l
Type 15 -Lu Type25 -Lu
Type29-Lu&Ac
w/M
Type 10-Lu
v/ttf
Figure4 Diagramatic representationofthe osteology oftheanterior sectionofthe first dorsal fin for the teraponids
examinedandwhethertheysuperficiallyresembled Leiopotheraponunicolor(Lu)orAmniatabacaudavittata
(Ac).
, ; ,
Hybridisationof L. unicolorandA. caudavittata 139
and a slight increase in the size of the first description, two were Type 4 (one step) and one
supraneural. The remaining patterns (types 8, 10, was Type 11 (two steps). Of the five L. unicolor
12, 13, 15, 17-23, 25 and 29) require between two examined from theFitzroy River one followed Vari
and six transformation steps. Of these patterns, (1978), while the others were types 4 (two, one
types 1-5, 7,8, 10, 12and 13areclosertothepattern step), 11 (oneindividual, two steps) or 15 (one, two
diagnostic of Leiopotherapon, types 18-23, 25 and steps).TheType11 pattern wasalsofound ina fish
29areclosertothatofAmniataba,and types 15and from the Murchison River, but in that case the
17areequidistantbetween thetwo. individual more closely resembled Amniataba
Of the 52 individuals that superficially more (Figure 4, Table 1). All of these patterns are equal
closely resembled A. caudavittata, 42 (ca 81%) had (Type 15) or closer to that diagnostic of
theosteological patterncharacteristicforthatgenus LeiopotheraponratherthanthatofAmniataba.
(Figure 2) (Vari 1978), however, the remaining 10 All A. caudavittata examined from the Swan
(ca 19%) displayed nine different osteological River(5) andSharkBay(25), and30of33examined
configurations unlike those described for any other from Cape Keraudien had a dorsal osteology that
terapontid (types 6, 11, 16, 24 and 26-30 in Figure conformed to Vari's (1978) description for
4). Three patterns (28-30) are only one Amniataba. The three individuals that differed in
transformation step from that diagnostic of osteological formula from Vari's (1978) description
Amniataba whilst the remainder are either two were either types 28 (1) or 30 (2). Both of these
(types 16, 24, 26 and 27) or three (types 6 and 11) patterns only require the movement of a single
steps away. Of these patterns, types 24 and 26-30 supraneural to conform to the Vari's (1978)
are closer to the pattern diagnostic of Amniataba, diagnosisforAmniataba(Figures1 and4,Table1).
types 6and 11 arecloser to thatof Leiopotherapon, Based on comparisons of the minimum number
andType16isequidistantbetweenthetwo. of steps required for a pattern to transform into
Of the L. unicolorexamined from the collections thosediagnosticofLeiopotheraponandAmniataba,
of the Western Australian Museum, and that all thefishthatsuperficiallymorecloselyresembled L.
superficially resembled thatspecies,twospecimens unicolorbore 13 patterns thatwere more similar to
from 1958 (P4336) conformed to the diagnostic the diagnostic configuration for Leiopotherapon
pattern ofthegenus andtheremainingtwo wereof (i.e., types 1-5 and 7-14), eight that were more
theType2pattern, i.e.,onestepfrom thediagnostic similar to that diagnostic for Amniataba (i.e., types
pattern, whilst two specimens from 1961 (P5362) 18-23, 25 and 29), whilst two are equidistant
were Type 4 and the other was Type 10, i.e., one between the two diagnostic patterns (i.e., types 15
and two steps from the diagnostic pattern, and 17)(Figures2and4,Table1). Inthecaseoffish
respectively (Figures 1 and 2, Table 1). All of these resemblingA. caudavittata therewerefivepatterns
patterns are closer to that diagnostic of that more closely resembled that diagnostic for
LeiopotheraponratherthanthatofAmniataba. Amniataba (i.e., types 24, 26-28 and 30), two were
Of the five L. unicolor examined from the moresimilar to thatof Leiopotherapon (i.e., types6
Gascoyne River, one conformed to Vari's (1978) and 11) and the remaining pattern was equidistant
description,whilsttheothersweretypes4 (2)and2 between the two (i.e., Type 16) (Figures 2 and 4,
(2), patterns that are both only one transformation Table1).
step away from the diagnostic pattern. All four of Vari (1978) noted that Leiopotherapon and
thepresumptive L. unicolorfrom the Minilya River Amniataba can be distinguished by the following
had a dorsal osteological pattern unlike that osteological criteria: one supraneural bone in front
described by Vari (1978), oneof thesehad a Type2 of the first neural spine in Leiopotherapon versus
pattern (one step from the diagnostic pattern) that two in Amniataba one spine on the first dorsal
was also found in fish from the Murchison and pterygiophore versus two; the insertion ofthe first
Gascoyne Rivers, one had a Type 9 pattern (two proximal dorsal pterygiophore between the second
steps) and the remaining two individuals had a and thirdneuralspinesversusitsinsertionbetween
Type 14 configuration (three steps), these latter the first and second; two of the anterior proximal
patterns were unlike any of the other individuals dorsal pterygiophores insertingbetween successive
examined (Figure 4, Table 1). One of the five neural spines versus one. In the current study, of
individuals from the Cane River conformed to L. the individuals that superficially most closely
unicolor, whilsttheremainingfourall exhibitedthe resembled L, unicolor, six had two supraneurals in
Tyne 4 pattern (one step). In the specimens from front of the first neural spine (types 15 (3), 20, 23
the Yule River, three individuals had the pattern and29),fivehadtwospines(types 14(2), 18,25and
diagnosticof L. unicolor, onehad aType4and one 29), seven had the first proximal dorsal
a Type 12 pattern, i.e. one and three steps away pterygiophore inserting between the first and
from the diagnostic pattern, respectively (Figures 2 second neural spines (types 20, 21 (4), 22 and 23)
and 4, Table 1). Of the five L. unicolorexamined in and six individuals had only one of the anterior
the De Grey River, two conformed to Vari's (1978) proximal dorsal pterygiophores inserting between
, , ^ T
140 D.L. Morgan,H.S.Gill
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142 D.L.Morgan,H.S.Gill
successive neural spines (types 5 (2), 9, 14 (2) and specieswithinthesetwogenera, Variradiographed
17). Inthecaseofindividuals thatsuperficiallymost or cleared and stained for osteological examination
A
closelyresembled caudavittata,fivehad onlyone (Vari personal communication), given such a high
supraneural in front ofthe firstneural spine (types occurrenceofdifferent pterygiophore patterns (i.e.,
6, 11, 16 and 28 (2)), four had the first proximal 54% were unusual), it could be expected that he
dorsal pterygiophore inserting between the second would havenoticed someexceptions.However, our
and third neural spines (types 6, 11, 16 and24) and preliminary use of radiographs suggested that it
four individuals had two of the anterior proximal was often difficult to discern minor variations in
dorsal pterygiophores insertingbetween successive pattern usingthismethod.Thus,althoughnotnoted
neural spines (types 6, 16, 26 and 27). All by Vari (1978), it is likely that some minor natural
individuals that superficially resembled A. variations in pterygiophore pattern occur in these
caudavittata had two spines on the first dorsal species. For example, of the 63 specimens of A.
pterygiophore. caudavittataexamined from theSwan River, Shark
Bayand Cape Keraudien, i.e., estuarineand marine
Reproductivebiology sites at which L. unicolordoes not exist, the three
Individuals exhibiting characteristics of both that did not conform to the pattern diagnostic for
species had lengths ranging from 39-253 mm TL, that genus only differed in the position of the
while those representing L. unicolor and A. secondorthirdsupraneural.Furthermore, although
caudavittata ranged in length from 47-211 and 29- variations in pterygiophorepatternwere evident in
206 mm, respectively. Of the 13 fish greater than some specimens of L. unicolorexamined from the
200 mm TL, 11 exhibited characteristics of both Western Australian Museum, these variations were
species. minorand all specimens exhibited the coloration of
Fromthemacroscopicstagingofthegonadsofall thatspecies.
fish dissected, including those with characteristics Notwithstanding that some minor differences in
of both species, it was evident that many were the anterior dorsal-fin pterygiophore pattern occur
either mature, spawning or had recently spawned. naturally, the level of variation in the first dorsal/
The peak spawning period for the two species and neural spine patterns and the fact that many
the fish exhibiting characteristics of both species in specimens exhibited coloration and shape
theMurchisonRiverappeared tobein latesummer/ characteristics of both L. unicolor and A.
earlyautumn. caudavittata suggests that in the Murchison River
The sex ratio in the individuals that exhibited these two species can readily hybridise. This is
both characteristics was ca 1.8 females:l male, further highlighted by the fact that in many
whereas for L. unicolorand A. caudavittata it was instancesitwasverydifficulttodecidewhetherfish
2:1 and 1.6:1, respectively. superficially resembled L. unicolor or A.
caudavittata. Furthermore, as only seven of the 25
presumptive L. unicolor examined from the
DISCUSSION Minilya, Cane, Yule, De Grey and Fitzroy Rivers
Ofthe 161 terapontids collected from the riverine were actually L. unicolor as described by Vari
sites during thecurrent study, thecharacteristicsof (1978), andaseach riverhad at least twospecimens
the first dorsal/neural spine matrix resembled L. that did not conform to the diagnostic pattern, it is
unicolorin about 20% of cases and A. caudavittata possible that hybridisation between terapontids is
in about 26% of cases. The remaining 54% of fish not restricted to the Murchison River. It is also
had first dorsal/neural spine osteological worth noting that the related barred grunter
characteristics unlike any of those described for (Amniataba percoides) is present in some of these
terapontids by Vari (1978). Whilst many of the rivers and that Dr Barry Hutchins of the Western
novel patterns described in the current study are Australian Museum believes that hybridisation
very similar to those described by Vari (1978) as between terapontids may be quite common in the
diagnostic for the two genera, others bear little rivers of the Kimberley (Hutchins pers. com., see
resemblance to the diagnostic patterns. Vari (1978), alsoHutchins 1981).
who examined 10 specimens from the Murchison In addition to proposing that much of the
River,76fromtheDeGreyRiverand over 100from variation in coloration and anterior pterygiophore
the Fitzroy River, made no mention of the patterns described in the current study is the result
osteological variability evident in thecurrentstudy of hybridisation, we also suggest that, in the
for these species. Furthermore, he noted no Murchison Riveratleast, (1)hybridisationhas been
variation in the patterns of other members ofthese occurring for at least the last few breeding seasons,
genera considering the two patterns to be (2) hybrids are reproductively viable and (3) some
diagnostic for Leiopotherapon and Amniataba. individuals may have been hybrids of hybrids.
Although it is not known how many individual L. Thesefurtherhypothesesarebasedonthefactsthat
unicolor or A. caudavittata, or specimens of other fish from the Murchison River that exhibited such