Syncomistes rastellus Vari & Hutchins, 1978

Shelley, James J., Delaval, Aurélien & Le, Matthew C., 2017, A revision of the grunter genus Syncomistes (Teleostei, Terapontidae, Syncomistes) with descriptions of seven new species from the Kimberley region, northwestern Australia, Zootaxa 4367 (1), pp. 1-103 : 63-68

Syncomistes rastellus Vari & Hutchins, 1978

( Tables 23 , 24 , S 22 & S 23 ; Figures 22 & 23)

Syncomistes rastellus, Vari & Hutchins 1978: 2 : Allen 1982: 6; Merrick & Schmida 1984: 244; Allen 1989: 170; Paxton et al. 1989: 542; Allen & Leggett 1990: 539; Hutchins & Smith 1991: 23; Hutchins 2001: 31; Unmack 2001: 1063; Allen et al. 2002: 238 (photograph S. butleri ); Hoese et al. 2006: 1341; Moore et al. 2008: 24; Morgan et al. 2011a: 17 ; Davis et al. 2012: 1169; Stoffels 2013: 143; Morgan et al. 2014: 267; Allen et al. 2017: online.

Corresponds to the nominated taxa code ‘ S. rastellus ’ of Shelley (2016).

English vernacular name: Drysdale Grunter.

Holotype (measured): P.25723-001 , 100 mm SL, North Creek, a tributary to the Gibb River, on the road to Drysdale Crossing , Western Australia, exact coordinates unknown, (?) 16° 11' 35.87'' S, 126° 28' 51.95'' E, obtained with rotenone by D. E. Rosen, G. J. Nelson and W. H. Butler, April 25, 1969 .

Paratypes (not measured): 23 specimens, 44–125 mm SL. AMNH 36419 (3), 44.0–95.0 mm SL, taken along with the holotype; WAM P25405-007 (1), 85 mm SL, Mogurnda Creek , about? 0.5 km above its junction with the Drysdale River , (?) 15° 1' 45.62'' S, 126° 54' 44.4456'' E, August 5, 1975, obtained with rotenone in a small flowing pool by J. B. Hutchins; the following paratypes were collected in the same vicinity on the Drysdale River (Hutchins 1977), (?) 15° 17' 8.36'' S, 126° 53' 22.52'' E, AMNH 36420 (5), 72–125 mm SL, August 5, 1975, obtained with rotenone in swift flowing pool by J. B. Hutchins ; WAM P25402-004 (3), 74–84 mm SL, August 3, 1975, obtained with rotenone by J. B. Hutchins; WAM P25404-010 (3), 66–81 mm SL, August 4, 1975, obtained with a seine net in a pool and rapids on the mainstream, by J. B. Hutchins; WAM P25410-004 (8), 72–125 mm SL, August 5, 1975, obtained with rotenone in a swift flowing pool on the Drysdale River mainstream by J. B. Hutchins.

Non-type Material (measured): 10 specimens, 45.0– 127.9 mm SL. NMV A 31704 -001 (1), 85.1 mm SL, NMV A 31704-002 (1), 101.9 mm SL, NMV A 31704-003 (1), 82.1 mm SL, NMV A 31704-004 (1), 84.1 mm SL, NMV A 31704- 005 (1), 45.0 mm SL, Upper Drysdale , Drysdale River, 15° 48' 37.32'' S, 125° 57' 9.21'' E, August 1, 2013, obtained using gill nets in a deep, clear pool below a small waterfall by J. J. Shelley and M. C. Le Feuvre; NMV A 31705 -001 (1), 69.6 mm SL, NMV A 31705 -002 (1), 73.9 mm SL, NMV A 31705 - 003 (1), 60.0 mm SL, Russ Creek , Gibb River, Drysdale River, 16° 2' 44.31'' S, 126° 42' 7.51'' E, August 5, 2013, obtained using backpack electrofisher in a moderately deep, clear, isolated pool below the Gibb River Road crossing by J. J. Shelley and M. C. Le Feuvre; NMV A 31706 - 001 (1), 118.2 mm SL, NMV A 31706 -002 (1), 127.9 mm SL, Miners Pool , Drysdale River, 15° 40' 49.33'' S, 126° 24' 23.67'' E, August 10, 2013, obtained using gill nets in a large, deep pool (Miners Pool) with a sandy base, by J. J. Shelley and M. C. Le Feuvre.

Diagnosis: A smaller species of Syncomistes (recorded up to 150 mm SL, commonly 70–120 mm SL). Syncomistes rastellus differs from all other species within the Syncomistes complex by a combination of the following characters: lower jaw distinctly pointed when viewed from below, making a ‘V-shape’ in individuals> 65 mm ( Fig. 5d ), rounded in individuals <65 mm; mouth subterminal; teeth flattened, wide and short, ‘paddleshaped’ with anterior and posterior edges widening rapidly from a narrow stem, running straight and parallel, flat to slightly rounded at end ( Fig. 6j ); jaw of adults (> 65 mm) as wide as it is long or slightly longer when viewed from below; dorsal profile straight from dorsal origin to shallow notch on upper jaw; body with 3–4 slightly wavy dark stripes running horizontally along sides (most often in juveniles); restricted to the Drysdale River that drains the northern Kimberley Plateau.

Description: See Table 23 for a summary of meristic variation by type material and other material examined and Table S22 meristic variation across all specimens combined. Dorsal fin spines XII (XII–XIII), rays 11 (11–12); anal fin spines III, rays 8 (6–9); caudal fin rays 12+8+7+12 (11–13+8+7+10–13, n = 6); pectoral fin rays 15 (14– 16); pelvic spines I, rays 5; vertebrae 11 +14 = 25 (10–11+14–15 = 24–26) (n = 6); lateral line scales 47 (45–49); scales above lateral line 9 (8–10); scales below lateral line 16 (15–16); pre-dorsal scales 15 (14–17); cheek scale rows 3 (3–4); caudal peduncle scales 26 (26–28); gill rakers on first arch 10+29 = 29 (9–12+18–21 = 27–33); opercular spines 2; preopercular spines 9 (6–14).

See Table 24 for a summary of morphometric variation by type material and other material examined and Table S23 morphometric variation across all specimens combined. Body slightly compressed, with dorsal profile slightly more steeply angled than ventral profile, which is similarly convex. Dorsal profile begins with concave notch behind upper lip, steep rise, convex to dorsal fin origin, convex to just beyond base of last dorsal ray, then horizontal to caudal fin base. Ventral profile on underside of head straight and horizontal, slightly convex from back of head to last soft anal ray, then horizontal to caudal fin base. Lateral line continuous from behind head to base of caudal fin, and approximately parallel to dorsal profile. Body depth at dorsal fin origin 30.2 (28.0–32.7) % SL; body depth at anal fin origin 28.1 (25.5–29.7) % SL; caudal peduncle length 17.9 (16.5–20.0) % SL; caudal peduncle depth 11.3 (10.8–12.7) % SL; pre-anus length 66.2 (63.6–68.0) % SL. Head length 28.7 (27.5–30.0) % SL; head pointed; snout length 39.3 (36.2–42.4) % HL; upper-jaw length 30.3 (27.3–33.4) % HL; jaws equal throughout development; jaw width 34.1 (30.1–39.2) % SL. Teeth laterally compressed, wide and short relative to Syncomistes , ‘paddle-shaped’ with anterior and posterior edges widening rapidly from a narrow stem, running straight and parallel, flat to slightly rounded at end (Tooth Morphotype 6; Fig. 6j ); teeth fitted closely together and overlapping, laterally pointed in lower jaw, extending beyond outer edge of lip. Outer row of large teeth with 2–4 inner rows of smaller teeth embedded in jelly-like gum, reducing in size towards back rows; teeth on outer row of upper jaw 67 (36–95) number varying with size, 8.9 (7.7–10.0) / mm when standardised with upper jaw length; teeth on outer row of lower jaw 58 (32–64) number varying with size, 6.7 (5.1–8.0) / mm when standardised with upper jaw length; 4 (3–4) tooth rows behind outer row in upper jaw, 3 (2–3) in lower jaw; toothless medial hump present on dorsal surface at symphysis of lower jaw, opposite toothless region of upper jaw; lower jaw pointed V– shape in adults, rounded in juveniles (<65 mm SL) when viewed from below, wider than it is long (Morphotype 4; Fig. 5d ); lower jaw flattened when viewed laterally. Orbital diameter 24.0 (19.9–33.0) % HL; inter-orbital width 31.0 (27.5–32.2) % HL; inter-orbital smooth and not scaled; post-orbital length 40.1 (38.0–43.2) % HL. Lower opercular spine is longer and more robust than upper opercular spine, sometimes extends beyond edge of opercular membrane; Preopercular spines serrate, reducing in size dorsally and anteriorly, anteriormost spine just behind mid-point of orbit. Intestinal pattern of adults highly convoluted; large amount of looping to left of stomach; juveniles with less convoluted pattern.

Dorsal fin origin posterior to vertical plane through pectoral fin origin, anterior to pelvic fin origin; terminates at base of last dorsal ray; dorsal fin sheath scales 1; 6th (5th–7th) dorsal spine longest, length 15.6 (13.0–16.4) % SL; progressively shorter towards first and last spine; last dorsal spine fully joined to first dorsal ray by membrane; 3rd (2nd–4th) dorsal ray longest, length 15.0 (13.5–15.6) % SL; dorsal margin of rayed portion is rounded until tip of last ray; dorsal fin base length 54.1 (53.3–57.4) % SL; dorsal fin length 59.9 (58.6–62.0) % SL; pre-dorsal fin length 38.0 (37.2–40.8) % SL. Anal fin origin immediately posterior to base of last dorsal fin spine; terminates at base of last ray; anal fin sheath scales 3 (2–3) anterior to posterior; 2nd anal spine longest, length 18.5 (14.4–21.5) % SL; 1 st anal ray longest, length 16.4 (15.5–17.4) % SL; rays progressively shorter to last ray; margin of rayed portion is rounded; anal fin base length 15.2 (13.8–16.5) % SL; anal fin length 23.0 (19.9–25.7) % SL; pre-anal fin length 71.2 (68.9–72.4) % SL. Caudal fin slightly emarginate; upper caudal lobe length 24.1 (21.5–26.4) % SL; middle caudal ray 17.9 (16.1–22.2) % SL. Pectoral fin length 20.4 (17.6–22.5) % SL; pre-pectoral fin length 28.5 (26.5– 31.4) % SL. Pelvic spine length 11.8 (9.8–12.6) % SL; 2st (1st–2nd) pelvic ray longest, length 18.7 (17.0–20.9) % SL, then progressively shorter; pelvic fin length 20.6 (18.6–22.4) % SL; pre-pelvic fin length 37.2 (35.4–38.9) % SL.

Colour when fresh: Body greenish-grey overall with a gold sheen. Darker dorsally, fading to white along the ventral surface. A horizontal greenish-gold stripe running below eye to snout, and a dark spot is present on upper edge of gill cover.

Body colouration is sometimes interrupted by 3–4 dark, slightly wavy lines on the body of juveniles and adults, although stripes are more prominent in juveniles: First, running from anterior of nape to below posterior of soft dorsal ray base; second running from posttemporal to dorsal edge of caudal peduncle; third, follows the lateral line, starting at anterior base of dorsal fin and ending at posterior base; fourth, from supracleithrum to middle of caudal base. Lines fade quickly once fish are removed from the water or after death.

Dorsal fin membranes dusky-brown with clear edges. Pectoral and anal fins dusky to yellow. Caudal fin membranes dusky-brown with clear edge. Pectoral fins clear.

Colour when preserved: Juveniles and adults uniformly light to dark brown with hints of pale colouration becoming more dominant towards the ventral region. Mostly pale brown when viewed ventrally. Lateral line is distinctly pale in colouration. All fins uniformly light to dark brown. Overall colouration fades from darker to lighter the longer the specimen is preserved.

Distribution: See Fig. 23 . Occurs throughout the Drysdale River in the northern Kimberley region, Western Australia.

Ecology: Adults prefer deeper, slow flowing sections of creeks and rivers and are often observed shoaling in the middle of the water column, sometimes with S. trigonicus . Juveniles found in shallow, still waters or occasionally in riffle habitat. Found in clear and slightly turbid waters, over rocky substrates, often where algae is abundant. Recorded in water temperature up to 32°C. Individuals sexually mature at 70–80 mm and breed during the wetseason. Appear to wait until a major flood event to spawn. Eggs are medium size (~ 2mm) and non-adhesive. Diet primarily consists of filamentous algae that is scraped off rocks with its modified teeth. Observed actively feeding at night.

Comparison: Broadly similar morphological grouping to Syncomistes holsworthi , Syncomistes dilliensis , and S. versicolor based on the presence of a more pronounced, longer notch behind the upper lip, a more pronounced concave dorsal profile between the notch and the dorsal fin, and a squat V-shaped jaw in adults that is wider than it is long (jaw is U-shaped in juveniles <65 mm).

Broadly resembles S. trigonicus and are often caught together. Sycomistes rastellus is most easily told apart by having 3–4 horizontal stripes compared to 5–6 in S. trigonicus , a deeper body 28.0– 32.7 in SL compared to 23.4– 29.1 in SL in S. trigonicus , fewer teeth (relative to jaw length) on the lower jaw 5.1–8.0 compared to 6.7–16.7 in S. trigonicus , noticeable larger and wider teeth than S. trigonicus , and adults have a V-shaped jaw that is wider than it is long, rather than as long or longer than it is wide as in S. trigonicus . Juveniles of both species (<65 mm) have Ushaped jaws, but each other character listed here can distinguish between juvenile specimens.

Etymology: The name rastellus , from the Greek for rake, refers to the rake-like dentition of the species (Vari 1978).

Remarks: Syncomistes rastellus is found in sympatry with S. bonapartensis and S. trigonicus . The description here is based on material examined for analysis in this paper. A more comprehensive description of S. rastellus can be found in Vari & Hutchins (1978).

Figures

FIGURE 5.

FIGURE 6.

FIGURE 22.

FIGURE 23.

Tables

TABLE 23. Summary of meristic variation in Syncomistes rastellus (values for number of teeth of upper and lower jaw are per mm of jaw length).Dashes indicate measurements that could not be made.

	Holotype	Non-type Material (N = 10)
Character		Mode	Mean		Min.	Max.	S.D.
DS	12	12	12.1		12	13	0.32
DR	11	11	11.4		11	12	0.52
AS	3	3	3.0		3	3	0.00
AR	8	8	7.8		6	9	0.79
PecR	15	15	14.9		14	16	0.88
PelS	1	1	1.0		1	1	0.00
PelR	5	5	5.0		5	5	0.00
UUCR	12	12	12.0		11	13	0.63
UBCR	8	8	8.0		8	8	0.00
LBCR	7	7	7.0		7	7	0.00
LUCR	12	12	11.7		10	13	1.03
LLSc	48	47	47.2		45	49	1.32
LD	8	9	8.9		8	10	0.57
LA	15	16	15.7		15	16	0.48
PDSc	15	15	15.3		14	17	0.87
DSSc	1	1	1.0		1	1	0.00
ASSc	2	3	2.5		2	3	0.53
CScR	3	3	3.2		3	4	0.42
CPSc	27	26	26.5		26	28	0.71
GRup	-	10	9.8		9	12	0.97
GRlow	-	20	19.5		18	21	1.27
GRtot	-	29	29.4		27	33	1.67
PcV	11	11	10.8		10	11	0.41
CV	14	14	14.2		14	15	0.41
TV	25	25	25.0		25	25	0.00
LDR	2	2	2.5		2	4	0.71
LDS	6	6	5.9		5	7	0.57
LAR	1	1	1.0		1	1	0.00
LAS	2	2	2.0		2	2	0.00
LPR	2	2	1.8		1	2	0.42
Tup	6.5	9	9.0		7.7	10.0	0.78
Tlow	5.1	7	6.7		5.1	8.0	1.06
TRup	4	4	3.7		3	4	0.48
TRlow	3	3	2.7		2	3	0.48
OS	2	2	2.0		2	2	0.00
PS	9	9	9.2		6	14	2.49

TABLE 24. Morphometric variation in Syncomistes rastellus (values are percentages of denominators in ratios, except for SL).

	Holotype	Non-type Material (N = 10)
Character		Mean	Min.	Max.	S.D.
SL (mm)	99.5	83.1	84.8	45.0
BDd / SL	30.2	30.2	30.3	28.0	32.7
BDa / SL	28.6	28.0	27.5	25.5	29.7
CPL / SL	19.4	17.9	17.9	16.5	20.0
CPD / SL	12.1	11.3	11.5	10.8	12.7
HL / SL	28.9	28.7	28.9	27.4	30.0
OD / HL	21.2	24.0	24.6	19.9	33.0
IoW / HL	33.3	31.0	30.5	27.5	32.2
PoL / HL	41.7	40.1	40.4	38.0	43.2
SnL / HL	41.8	39.3	39.2	36.2	42.4
JLup / HL	33.0	30.5	30.4	27.3	33.4
JW / HL	35.2	34.1	34.6	30.1	39.2
PDFL / SL	39.1	38.0	38.4	37.2	40.8
PPecL / SL	28.2	28.5	28.7	26.5	31.4
PPelL / SL	38.3	37.2	37.3	35.4	38.8
PAL / SL	67.4	66.2	66.1	63.5	68.0
PAfL / SL	70.3	71.2	71.0	68.9	72.4
DFBL / SL	53.4	54.1	54.4	53.3	57.4
DFL / SL	58.8	59.9	60.0	58.6	62.0
DFRL / SL	13.7	15.0	14.8	13.5	15.6
DFSL / SL	13.7	15.5	15.1	13.0	16.4
AFBL / SL	13.6	15.2	15.1	13.8	16.5
AFL / SL	20.6	23.0	22.9	19.9	25.7
AFSL / SL	14.3	18.5	18.0	14.4	21.5
AFRL / SL	15.9	16.4	16.3	15.5	17.3
PecL / SL	19.3	20.4	20.4	17.6	22.5
PelL / SL	21.1	20.6	20.5	18.6	22.4
PelSL / SL	10.9	11.8	11.6	9.8	12.6
PelRL / SL	18.1	18.7	18.8	17.0	20.9
CLLup / SL	29.0	24.1	23.9	21.5	26.4
CLLmid / SL	17.1	17.9	18.1	16.1	22.2