Gobiosoma spilotum (Ginsburg 1939)

Van Tassell, James L., Joyeux, Jean-Christophe, Macieira, Raphael Mariano & Tornabene, Luke, 2015, Status of Gobiosoma (Teleostei: Gobiidae) from Brazil: description of a new species, redescription of G. hemigymnum, molecular phylogeny of the genus, and key to Atlantic species, Zootaxa 4007 (4), pp. 451-480 : 469-473

Gobiosoma spilotum (Ginsburg 1939)

Figs. 10 , 11 , 12

Garmannia spilota Ginsburg 1939:62 (type locality: Colon, Panama, in tidepools)

Gobiosoma (Austrogobius) spilotum Böhlke & Robins 1968: 59 (assigned to Gobiosoma , subgenus Austrogobius ).

Material examined. PANAMA (Atlantic): USNM 81828, holotype, Meek and Hildebrand, 12 March 1912, tidepools, Colon, Panama; AMNH 233131, 2 (1 female, 1 male photographed, male missing), J.L. Van Tassell, 0 9 April 2001, Panama Canal, near Fort Sherman; ANSP 108745, 6 of 7, Pillsbury sta. 321, 0 5 July 1966, W shore of Limon Bay, 1400 m S of Pulpit Point, Canal zone, Panama; ANSP 110681, 1, c&s, Pillsbury sta. 321, 0 5 July 1966, W shore of Limon Bay, 1400 m S of Pulpit Point, Canal zone, Panama; UF 222503, 5, R/V Pillsbury, 0 4 July1966, Canal zone, Caribbean Pulpit Point, Limon Bay; GCRL V72: 8698, 10 of 31, Dawson and Jones, 20 March 1972, Canal zone, Gatun Locks, Colon.

Comments on Gobiosoma spilotum . Böhlke and Robins (1968) adequately enhanced the description of Gobiosoma spilotum provided by Ginsburg (1939). We examined many of their specimens and additional collections made by Dawson & Jones (1972). Here we expand on the previous works to enable us to draw clear distinctions between G. hemigymnum and G. alfiei .

Diagnosis. A species of Gobiosoma distinguished from other members of the genus by the following characters: body scaled from caudal peduncle to base of pectoral fin, scales in a wedge shape to under anterior of second dorsal-fin base, then continuing anteriorly in a row of 4–5 scales, row slightly tapering anteriorly; a naked area extending from upper pectoral-fin base to 3rd of 4th ray of second dorsal fin (rarely extending further) and from the lower pectoral-fin base to 3rd or 4th anal-fin ray (rarely extending further); upper jaw 41.5% in head length; lateral scales modally 26; pectoral fin 19 (18–20); maximum size to 27 mm SL.

General morphology. Body is cylindrical, elongate; head rounded in profile; eyes dorsolateral 6.3–8.4% in SL; maxilla generally extending posteriorly to a vertical ventral to mid-eye; upper jaw length 10.6–12.3 % in SL; anterior naris an elongate narrow tube without a flap; posterior naris a raised rim. A very small, wart-like barbel in front of eye, near anterior naris. Males with a triangular, wide, flattened urogenital papilla; female papilla, slightly tapering, not flattened, with large opening at end; juveniles with urogenital papilla similar to that of males but shorter, less flattened and rounder at tip.

Fins. Counts for holotype followed by (range; mode). First dorsal fin VII, none filamentous or elongated; first dorsal connected to second dorsal by low membrane; second dorsal fin I,11 (I, 10–I,11; I,11), the last element a single ray in 30% of specimens examined; anal I,9 (I, 8–I,10; I,9); second dorsal and anal fins not reaching caudal fin when adpressed; pectoral counts for left fin followed by right, 19/19 (18–19/18–20; 19/19), fin ovate, extending to anus when adpressed; caudal segmented rays 16 (16–19; 17), and branched rays 15 (13–15; 14), fin round; pelvic fin I,5 (I,5; I,5), oblong to ovate, extending 3/4 distance to anus.

Scales ( Fig. 4 C). Lateral scale rows 28–29 (26–29); head, nape, abdomen, prepelvic region and belly without scales; body scales ctenoid, with posterior edge pigmented, scales in a wedge shape to under middle of first dorsalfin base, than continuing forward, reducing in width ending under pectoral-fin base; one large cycloid scale, generally present under lower anterior third of pectoral fin; naked area extending from upper pectoral-fin base to 3rd element of second dorsal fin (never extending to end of fin base) and from lower pectoral-fin base to the 3rd element of anal-fin base (never extending to middle of fin base); four basicaudal scales extending on to caudal fin base, the dorsal and ventral-most with elongate ctenii ( Fig. 4 E).

Lateral-line system. Cephalic lateral line system ( Fig. 12 ) with pores B', C(s), D(s), E, F, H' and posterior oculoscapular pores K', L'; preopercle canal with pores M', N and O'. The supraorbital canals are fused between the eyes with only a single canal present.

Sensory papillae in a transverse pattern ( Fig. 12 ). Row 1 extending from orbit to row d; rows 2 and 3, not reaching orbit; row 5 s from orbit to near anterior of b; row 6 not reaching row b; row 7 represented by 1 papilla (rarely 2). Row b short, ending anteriorly before row 5 s; row d continuous; row 5 i under b and extending below level of d by 2–3 papillae. Dorsal row g with 2 papillae; row o reduced to 1 papilla; row m not observed and row n extending from above pore F to beyond pore E (about 4 papillae medial to pore E).

Color in life. Based on photographs of two fresh specimens from AMNH 233131 ( Fig. 10 ). Background color of body light grayish brown in males, somewhat lighter yellowish pale in females; body with eight bars faint in males, apparent in females; bars with light centers extending width of body, forming, in heavily pigmented specimens, a double bar. Anterior of first bar under second spine of D1, second bar under posterior of D1, third between D1 and D2, fourth, fifth, sixth under D2, seventh on mid-caudal peduncle, eight a thin bar on base of caudal fin. Sides of body, in both sexes, with a series of eight black spots along mid-line. In both, the first dot approximately below the 3rd spine of the first dorsal (D1) spine, the second spot below the origin of the 6th D1 spine, the third spot (may be doubled) below the origin of the second dorsal (D2) fin, the fourth spot below the 5th element of D2, the fifth spot (may be doubled) below the 7th element of D2; sixth spot under last element of D2, seventh on mid-caudal peduncle, and eighth spot, frequently a forward anteriorly directed triangle, on mid-caudal fin base; spots in males often separated by a narrow pale area along lateral midline. Posterior edge of scales pigmented, more heavily pigmented in females.

Background color of head yellowish brown, brighter yellow ventrally in males. Three dark spots located between the posterior of the eye and upper pectoral fin base; first directly behind eye, second above the preopercle, third above posterior edge of opercle. Side of head with two dark bars below eye; anterior bar extending from anterior margin of eye ventrally across the jaw, continuing under the lower jaw, pigment on jaw much lighter in males than females. Posterior bar in both sexes, wider than anterior, nearly as wide as pupil diameter, originating below middle of eye, extending ventrally slightly below posterior margin of lower jaw. Two thin lines of pigment one near the posterior edge of the preopercle, the other along the anterior of the opercle.

First dorsal fin with dark lateral band near base of fin, dark band broken or mottled in females, dorsal half of fin pale or whitish. Second dorsal-fin base with dark marks continuous with bars on body; two bands formed by scattered melanophores, middle band lighter and narrower, upper band with light spotted pattern. Pectoral-fin base background yellowish with scattered melanophores; spot formed by larger melanophores on lower third of fin base, more distinct in males; base of fin rays with two pigmented areas on upper and lower thirds, each covering 5–6 rays; lower pigmented area extending on to fin base. Anal and pelvic fins with scattered melanophores, darkest at base, edges of fins with thin, light to whitish band. Caudal fin uniformly covered with melanophores on anterior half of in males, mottled or with broken vertical bars in females, posterior half of fin lightly pigmented to pale in both sexes.

Preserved color ( Fig. 11 ). Preserved specimens body and head background color light brown only. Body and head markings as above; anal and pelvic fins tend to lose pigmentation.

Distribution and habitat. We can document this species only from the Panama Canal, Gatun locks and Limon Bay in the Atlantic. Three specimens from Columbia (INVEMAR PEC-1108) and one specimen from Costa Rica (UCR 276516), near the border with Panama exist but we have not yet been able to obtain these specimens in order to confirm the identification. The species is found in brackish coastal areas with a rock and algae substrate. Gobiosoma spilotum was collected in large numbers, 30–80 per lot by Dawson in 1972 and 1974, from the Gatun locks of the Panama Canal and Limon Bay, the Atlantic entrance to the canal. Recent collections in the same area, by one of us (JVT) in 2001, have yielded only two specimens AMNH 233131.

Conservation status. If the species only occurs in the Limon Bay and Gatun locks area, then it would be critically endangered. Construction of the new canal and pollution from shipping will impact the habitat. Specimens inhabiting Gatun Locks and the surrounding Gatun Lake are subject to predation by the introduced cichlid, Cichla ocellaris Bloch & Schneider 1801 , which has eliminated seven of the eleven most common fish species within the lake (Zaret & Paine 1973).

Figures

FIGURE 4. Scale patterns of A) Gobiosoma hemigymnum, B) G. alfiei, C) G. spilotum, D) G. grosvenori. Shaded areas in A-D indicate distribution of scales on body. E) Distribution of basicaudal scales, including modified basicaudal scales on dorsal and ventral caudal peduncle.

FIGURE 10. (A) JVT- 01 - 105, Gobiosoma spilotum, an adult breeding male photographed shortly after capture, collected with AMNH 233131; (B) AMNH 233131, Gobiosoma spilotum, a female photographed shortly after capture. Photographs by J. L. Van Tassell.

FIGURE 11. (A) ANSP 108745, Gobiosoma spilotum, a male photographed after fixation, 18.03 mm TL; (B) GCRL V 72 8698, Gobiosoma spilotum, a male photographed after fixation, 31.75 mm TL; (C) GCRL V 72 8698, Gobiosoma spilotum, a female photographed after fixation, 23.29 mm TL. Photographs by J. L. Van Tassell.

FIGURE 12. Sensory papillae patterns of Gobiosoma spilotum, from specimen GCRL V 72 8698 # 7.