Istiblennius unicolor (Rüppell 1838)

Oviparous, distinct pairing (Ref. 205).

Dorsal spines (total): 13; Dorsal soft rays (total): 17 - 18; Analspines: 2; Analsoft rays: 17 - 19

A rare species endemic to the Red Sea; nothing is known of its habits nor habitat preferences (Ref. 9962). According to traits of family where it belongs, it is 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 unicolor (Rüppell)

Salarias unicolor Rüppell, 1838:136 [Massaua; holotype, SMF 1866].

DESCRIPTION (based on 6 males and 4 females).—Dorsal fin (Table 40). XIII,17 or 18 = 30 or 31; membrane between spinous and segmented-ray portions notched deeper than half length of first segmented ray; membrane from posteriormost ray attaching to point ranging from on dorsal edge of caudal peduncle anterior to caudal-fin base to on dorsal edge of caudal fin very slightly posterior to caudal base.

Anal fin (Table 40). II,17 to 19; posterior element split to base in 4 specimens and not split in 5, of 9 specimens checked for character; posterior element of split ray visible externally; last ray not attached by membrane to caudal peduncle. Skin covering anal-fin spines and distal half of rays not modified in males.

Pectoral-fin rays 14.

Pelvic-fin segmented rays 4, tip of innermost ray not free, but externally visible in all specimens.

Caudal fin. Dorsal procurrent rays 5 to 7, ventral procurrent rays 5 to 7, total procurrent rays 10 to 14 (Table 41), segmented rays 13.

Vertebrae (Tables 40 and 41). 10+25 = 35; posteriormost pleural rib on 11th or 12th from anteriormost centrum (on 12th in only 1 specimen); posteriormost epineural on 12th to 14th from anteriormost centrum (on 13th in 8 specimens).

Cirri. Nape cirrus absent. Orbital cirrus variable, usually shorter than orbital diameter, consisting of central stalk with side branches. Nasal cirrus small, palmate with 4 to 7 separate tips.

Table 40—Frequency distributions for certain characters of specimens of Istiblennius flaviumbrinus. I. unicolor, and I. spilotus from various localties. Underlining indicates significant differences between means of sexes from same locality (p ≤ .05).

Table 41.—Frequency distributions for certain characters of specimens of Istiblennius flaviumbrinus, I. unicolor, and I. spilotus from various localities.

Lateral line (Table 41). Continuous canal anterodorsally with simple pores (no vertical pairs of pores), extending posteriorly to point between vertical from interspace between bases of 6th and 7th dorsal-fin spines and vertical from base of 9th spine (probably only rarely failing to reach posterior to vertical from base of 7th spine), thence continuing posteriorly as series of 9 to 14 short, disjunct, horizontally bi-pored canals (tubes) in skin; posteriormost tube on body in area between verticals from bases of 2nd and 10th segmented dorsal-fin rays.

Mandibular pores 5.

Six sensory pore positions between 1 o'clock and 5 o'clock on postorbital margin (dorsalmost pore somewhat removed from margin); all pore positions with simple pores (no pore pairs).

Posterior canines absent in both sexes.

Ventral margin of upper lip crenulate; dorsal margin of lower lip completely or partially crenulate.

All males, including smallest, 57 mm SL, have small, but well-developed crests; females, including largest, 92 mm SL, lack all evidence of crest formation.

Color pattern (in preservative; Figure 51). Well-preserved specimens of both sexes, with dark, posteriorly rounded blotch (apparently bluish in life), often separated posteriorly by narrow, pale area from paler, anteriorly facing crescent, just posterior to orbit; second crescent variably present just posterior to first; several specimens with small, pale spot just ventral to dark blotch; about 12 more or less evenly spaced fine, dark, bands extending from area below middle of eye around snout to middle of other eye. Very faint indications of similar marks noticeable in most specimens. Both sexes with up to 4 irregular, fine, pale stripes on body coursing through dark, mottled background, each stripe with several darkenings vertically aligned with darkenings of other stripes, giving appearance of bands.

Slender, dark band present on fleshy pectoral-fin base; second band, not as dark, curves around bases of fin rays; 3 or 4 faint-dusky, irregular bands cross fin distal to curving band. Females have dark spots or streaks on dorsal fin, dark spots on caudal fin; males also have dark spots on these fins, but spots may be more diffuse than those of females; vertical pair of prominent dark spots at bases of caudal-fin rays.

Size. Largest specimen, male, 102 mm SL; largest female, 92 mm SL; smallest specimen, male, 57 mm SL.

COMMENT.—Istiblennius unicolor is the least common species of Istiblennius in collections. Nothing is known of its habits or habitat preferences. Such rarity is unexpected, as highly restricted endemic fish species, such as this species, are usually very common (Randall, 1992b:56). Istiblennius rivulatus, which, like I. unicolor is also endemic to the Red Sea, is extremely common.

COMPARISONS AND RELATIONSHIPS.—See discussion in this section under Istiblennius spilotus.

DISTRIBUTION (Figure 69).—Northernmost Gulf of Aqaba south to Dahlak Archipelago, southern Red Sea.

MATERIAL EXAMINED.—G of Aqaba: Israel, Elat, HUJ 12377 (1), TAU 10315 (1). Gulf of Suez: Egypt, Et Tur, HUJ 9553 (1), USNM 325430 (1). Red Sea: NMW 73248 (1 specimen), NMW 73249 (1); Dahlak Archipelago, Romia, HUJ 12779 (3); Ethiopia, Massawa, SMF 1866 (holotype of Salarias unicolor).

Istiblennius unicolor, the pallid rockskipper, is a species of combtooth blenny found on coral reefs in the western Indian Ocean. Males of this species can reach a maximum standard length of 10.2 cm (4.0 in), while females can reach a maximum length of 9.2 cm (3.6 in).