Beautiful Rockskipper

Body of males with several paired bands; spots from mouth to nape and posterior part of body; dusky stripes on segmented portion of dorsal fin (Ref. 4404). Females with dusky bands on body; head, body and fins (except pelvic fins) covered with fine dark specs (Ref. 4404).

Oviparous, distinct pairing (Ref. 205).

Dorsal spines (total): 12 - 14; Dorsal soft rays (total): 20 - 22; Analspines: 2; Analsoft rays: 20 - 22

Adults are found in intertidal flats and rock shores (Ref. 90102). Oviparous. Eggs are demersal and adhesive (Ref. 205), and are attached to the substrate via a filamentous, adhesive pad or pedestal (Ref. 94114). Larvae are planktonic, often found in shallow, coastal waters (Ref. 94114).

Istiblennius bellus (Günther)

Salarias bellus Günther, 1861:256 [type locality: “China seas” or “Chinese seas,” probably erroneous; lectotype, BMNH 1848.3.16.1, 123 mm SL specimen, designated in nomenclatural discussion below].

Salarias kellersi Fowler, 1932:6 [Niuafoou, Tonga Group; holotype, USNM 91944].

Salarias leopardus Fowler, 1938:82 [Nukuhiva, Marquesas Islands; holotype, ANSP 68305].

Salarias personatus Fowler, 1945:71 [Saipan Island, holotype, ANSP 71604].

Istiblennius bellus impudens J.L.B. Smith, 1959:242 [St. Pierre Isl. [Seychelles], holotype, RUSI 270].

DESCRIPTION.—Dorsal fin (Table 38). XII to XIV,20 to 22 = 33 to 35 (XIII in 93% of specimens); males from any locality tending to have higher mean number of total elements than females from same locality (higher for 6 of 7 localities where means for both sexes are available; statistically significantly higher for 4 of the 6 localities); membrane between spinous and segmented-ray portions notched deeper than half length first segmented ray; membrane from posteriormost ray attaching to point ranging from on dorsal edge of caudal peduncle just anterior to caudal-fin base to point <20% caudal-fin length out on dorsal edge of caudal fin (out on caudal-fin >10% fin length in only 1 of more than 125 specimens examined for character).

Anal fin (Table 38). II,20 to 22; males from any locality have higher mean number of segmented rays than females from same locality (higher for all 7 localities where means for both sexes are available; statistically significantly higher for 3 localities); posteriormost ray usually split to base, (posterior element of split ray usually well developed, readily discernible externally); last ray attached by membrane to caudal peduncle in only 4 of 57 specimens examined for character. Skin covering anal-fin spines and distal half of rays scarcely expanded, at most only slightly crinkled along lateral edges in large and/or mature males.

Pectoral-fin rays 13 or 14 (14 bilaterally in 94%, unilaterally in 6% of 103 specimens examined for character).

Pelvic-fin segmented rays 3.

Caudal fin. Dorsal procurrent rays 6 to 8 (7 in 77% of 102 specimens examined for character), ventral procurrent rays 5 to 8 (7 in 66% of specimens), combination of 7 dorsal with 7 ventral procurrent rays in 57% of specimens; segmented rays 13.

Vertebrae (Table 38). 10 to 12+27 to 29 = 38 to 40 (11 precaudal vertebrae in 91% of specimens); males from any locality tending to have higher mean number of total vertebrae than females from same locality (higher for 6 of 7 localities where means for both sexes are available; statistically significantly higher for only 1 of the 6 localities); posteriormost pleural rib on 11th or 12th from anteriormost centrum (about equally divided between these centra); posteriormost epineural on 13th to 17th from anteriormost centrum (rarely on 13th; on 15th in 59% of specimens).

Cirri. Nape cirrus absent. Orbital cirrus slender, usually simple, occasionally with lateral branch or few, tiny branches near tip, length ≤half orbital diameter in females, slightly
Lateral line. Continuous canal anterodorsally with no vertical pairs of pores, extending posteriorly to point between verticals from 5th and 10th dorsal-fin spines (to point between 8th and 9th spines in 77% of specimens examined for character), then descending to midside and continuing posteriorly up to half distance to caudal-fin base (varying with locality, Table 39) as series of 1 to 16 short, disconnected, horizontally bi-pored canals (tubes) in skin (number of tubes varying with locality, Table 28; posteriormost tube lying between verticals from 9th dorsal-fin spine and 13th segmented ray).

Mandibular pores 3 to 7 (rarely 3,4 or 7, and only unilaterally; 5, at least unilaterally, in 16%, and 6, at least unilaterally, in 81% of 117 specimens examined for character).

Five to 7 (commonly 5 or 6, rarely 7) sensory pore positions between 1 o'clock and 5 o'clock on postorbital margin; 0 to 2 positions with paired pores (0 in 58% of specimens, 1 in 36%, 2 in 6% of 163 specimens examined for character).

Posterior dentary canines absent.

Ventral margin of upper lip and dorsal margin of lower lip noticeably crenulate in most specimens >60 mm SL, variably crenulate or entire in smaller specimens (upper lip crenulae granular, visible only on internal surface of lip in some specimens; crenulae scarcely noticeable in some poorly preserved specimens).

Males with fleshy, blade-like crest on head dorsally, definitely noticeable at about 35 mm SL, ridge-like crest precursor noticeable at 33 mm; females without crest, but short, low, rounded ridge (crest precursor) in largest females from Pacific localities.

Color pattern (in preservative). Males (Figure 48). Head dark dusky, usually with darker spots on snout, bordering eye and upper lip, along preopercular pore series, and on opercle (position of each spot apparently consistent among all specimens, although all positions not spotted in all specimens, spots of variable darkness; males from Christmas Island, Indian Ocean, usually lack dark spots, possibly artifact of preservation). Body dark dusky with up to 7 irregular bands (4 anteriormost bands each variably split vertically into band pair), bands variably restricted to mid-longitudinal axis of body or continuing dorsally into basal portion of dorsal fin; faint-dusky spots or rings scattered on body, spots most apparent posteriorly (spots may fade completely in long-preserved specimens; not present on Christmas Island males). Fins dark dusky, dorsal fin occasionally with pale streaks, anal occasionally with pale spots. Body more or less uniformly pigmented, head without spots at 35 mm SL; body faintly spotted at 33 mm SL.

Table 38.—Frequency distributions for certain characters of specimens of Istiblennius bellus from various localties. Underlining indicates significant differences between means of sexes from same locality (p ≤ .05).

Females. Head faint to dark dusky with densely distributed, small, diffuse dark spots variably present; spots occasionally appearing to occupy positions similar to those on heads of males. Body with up to 7 dusky bands; body and fins, except uniformly pale-dusky pelvics, densely covered with dark spots (see section on geographic variation for modification of this description). Pattern recognizable in specimens at least as small as 38 mm SL.

Two smallest available specimens, both 22 mm SL (Éfaté, New Hebrides), sex indeterminate, with diffuse spots on body; spots relatively larger in 1 specimen than in other, possibly indicating sexual difference, but specimens not otherwise sexually differentiated.

Table 39.—Frequency distributions for lateral-line characters in specimens of Istiblennius bellus from various localities.

Live or fresh color. Springer (1986, pl. 114: figs. 235.21 (A),(B)) illustrates colored paintings prepared by M.M. Smith from large, fresh specimens (male holotype from St. Pierre Island; female from southern Mozambique): Male. Dark spots and streaks on body and fins of preserved males appear blue, segmented-rayed fins pinkish; spinous dorsal fin, head, and body with dark dusky-brown markings, body pale ventrally.

Female. Yellowish overall, with fine, reddish spots. Fine spots in spinous dorsal, anal, and pectoral fins, contrasting somewhat with pattern of western Indian Ocean females; see section on geographic variation. We could not verify the accuracy of the painting as the specimen upon which it is based was not available; P.C. Heemstra, in litt., wrote that no [female] specimens from Mozambique are present in the RUSI collection.

Size. Largest male, 128 mm SL; largest female, 131 mm SL; specimens >100 mm uncommon.

GEOGRAPHIC VARIATION.—Geographic variation is expressed primarily in color-pattern differences among females (no differences among males, except possibly Christmas Island males; see color pattern description above) and secondarily by the position of the posteriormost lateral-line tube relative to a dorsal-fin element (both males and females, Table 39), which is related to the number of lateral-line tubes (Table 39).

In females from the western Indian Ocean (Figure 49c,d), the pectoral fins are more or less uniformly dusky (not spotted), the spinous dorsal fin is variable: with fine, dark spots, or dusky with indistinct, irregular, pale streaks or diffuse dark spots that can be seen only with transmitted light; the anal fin of large females, at most, bears faint spots (but heavily spotted in small females), and the spots on the body maintain their integrity even in the largest females. In females from Christmas Island (eastern Indian Ocean) and the Pacific (Figure 49a,b), the pectoral, spinous dorsal, and anal fins are distinctly dark spotted (but fewer spots in Christmas Island females than in others). In females from Christmas Island and the New Hebrides (Figure 49a), the body spots also maintain their integrity, but in females from Pacific-plate islands (Figure 49b), the spots on the body begin to fuse and form vermiculations at sizes over 70 mm SL, and the pattern is completely vermiculated at about 85 mm SL.

Specimens from Niuafo'ou, Samoa, and possibly the Marquesas, tend to have the posteriormost lateral-line tube positioned further posteriorly than in specimens from other localities.

COMPARISONS AND RELATIONSHIPS.—Istiblennius bellus subjectively appears to us to be most closely related to I. zebra, endemic to the Hawaiian Islands, with which it falls into a weakly supported polytomous clade, which also includes I. muelleri (Figure 60, see Phylogenetic Analysis section). The two species differ most obviously in that the females of Istiblennius bellus do not have a crest on the head and have a strikingly different color pattern from that of males (crest present and color pattern more or less similar to that of males in I. zebra and I. muelleri). Additionaly, means for numbers of dorsal- and anal-fin elements and total vertebrae are lower for I. bellus than for I. zebra.

DISTRIBUTION (Figure 66).—Western Indian Ocean from 3 miles (5km) north of Muqadisho, Somalia, south to Balito Bay, Natal, South Africa; St. Pierre (SW Seychelles); Nossi Be, Madagascar, Juan de Nova Island; Mauritius; Eastern Indian Ocean only from Christmas Island; Pacific Ocean from New Hebrides, Niuafo'ou (but not more southern islands of Tonga), Samoa, Niue, Marquesas, Saipan islands. The large distributional gap between the Indian Ocean and islands on and along the western margin of the Pacific plate appears to be real (as do other large gaps in its Indian and Pacific oceans distributions), and is evidence favoring extinction of I. bellus in the gap area (Springer and Williams, 1990). Saipan, Mariana Islands, is well removed from all other known occurrences of I. bellus, which is otherwise known essentially only from south of the equator. Large shorefish collections are available from, at least, nearby Guam, but no specimens of I. bellus have been taken at the other Mariana Islands.

NOMENCLATURAL

Istiblennius bellus, the imspringer, is a species of combtooth blenny found in coral reefs in the Pacific and western Indian ocean. It is also known as the beautiful rockskipper or the dusky blenny. Males of this species can reach a maximum of 16 cm (6.3 in) SL, while females reach a maximum of 13.1 cm (5.2 in) SL.