Fourline Blenny

Description: Overall grey to tan with horizontal stripes black three lateral and one at dorsal-fin base, may be broken or absent sometimes (Ref. 90102). Detailed color description of live and preserved specimens could be found in Ref. 5296. Osprey Reef and Great Barrier Reef fishes differ in size and color pattern (Ref. 5269). Dorsal fin XII.13-15 (usually 14); anal fin 11,14-17 (usually 16); pectoral fin 12-14 (usually 13); caudal-fin segmented rays 13. Vertebrae 10 + 21-23 (usually 22); dentary incisors and canines very similar in appearance, 42-51, posterior canines 4-8 on each side (rarely 8 unilaterally), but less than 4 in specimens less than 20 mm SL. (Ref. 5296). Posterior rim of anterior nostril with cirrus. Lateral line tube series ends between ninth to twelfth dorsal spine. Body depth 5.7 in SL at anal-fin origin (Ref. 90102).

Oviparous, distinct pairing (Ref. 205).

Dorsal spines (total): 12; Dorsal soft rays (total): 13 - 15; Analspines: 2; Analsoft rays: 14 - 17; Vertebrae: 31 - 32

Found in shallow areas.

Adults inhabit coral reefs 2-11 m deep (Ref. 90102). Found in shallow areas. 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).

aquarium: commercial

Ecsenius aequalis

DESCRIPTION.—Dorsal fin XII.13–15 (14 in 85% of specimens). Anal fin II,14–17 (16 in 84% of specimens). Pectoral fin 12–14 (rarely 12 or 14, and only unilaterally). Segmented caudal-fin rays 13. Vertebrae 10 + 21–23 (22 in 87% of specimens). Dentary incisor teeth (includes anterior canine teeth, which differ little, if at all, in appearance from incisors) 42–51; posterior dentary canines (specimens at least 25 mm SL) 4–8 on each side (only two of 52 specimens had 8, unilaterally; specimens 20 mm SL or less have 0–4). Lateral line without pairs of pores, terminating posteriorly at point between vertical from dorsal-fin spine 9 and vertical from interspace between spines 11 and 12 (rarely reaching past vertical from spine 11). Cirrus present on posterior rim of anterior nostril; none on anterior rim.

Preserved Color: In Great Barrier Reef specimens: head varying from generally pale dusky (females and small males) to darkly dusky (large males), ventral surface infrequently with diffuse, faint stripe on each side extending posteriorly from just posterior to lower jaw and curving up along posterior margin of opercle (usually fading out before reaching opercle margin), body usually exhibiting three slender, dark stripes separated by about equal interspaces in region of pectoral-fin axil; stripes often variously interrupted; dorsal stripe originating in region above anterior oblique portion of lateral line or on horizontal portion of lateral line, proceeding posteriorly along lateral line, and terminating at some point below segmented-ray portion of dorsal fin; middle stripe originating no further anteriorly than intersection of oblique portion of lateral line with head and terminating as far posteriorly as caudal-fin base (usually ceasing well anterior to fin base); ventral stripe originating as far anteriorly as pectoral-fin axil and ceasing posteriorly at some point anterior to caudal-fin base; occasional specimens have stripes represented by only a few diffuse, dash-like markings, and one small specimen (21 mm SL) from the Trobriand Islands exhibited ventral two stripes anteriorly, but each appearing as row of 4 or 5 fine, dark spots posteriorly. Specimens from Osprey Reef vary from lacking body stripes to having the stripes restricted to the anterior half of the body, where they are poorly developed and frequently interrupted.

Dorsal fin: spinous portion anteriorly with fine melanophores along spines, posteriorly with melanophores partially filling interradial membranes; segmented-ray portion with slender, immaculate area basally forming stripe, from which melanophores extend dorsally along rays, concentrating ventrally and at ray tips, thus giving appearance of two, somewhat diffuse stripes (Osprey Reef specimens lack concentrations at ray tips); interradial membranes more densely pigmented in males than females. Anal fin generally dusky, but ray tips pale; melanophores often concentrating in membranes just proximal to ray tips, giving appearance of subdistal stripe. Pectoral fin with melanophores along rays. Pelvic fins ranging from immaculate to rays with sparsely distributed melanophores. Caudal-fin rays essentially unmarked except for fine, dusky margining dorsally and ventrally on each ray; membranes varying from almost clear (females) to almost uniformly dusky (large males).

A freshly collected specimen from the Great Barrier Reef, posed underwater, is shown in color on Plate 14: figure 3. The species either has no distinctive color in life or, more probably, this particular specimen has faded. Photographs of living specimens at Osprey Reef (e.g., Plate 14: figure 4), show fishes that are generally cream colored, varying from lacking dark body stripes and pigmentation in the fins to having some dark dash-like marks on body. Most notable in the Osprey Reef specimens is the black pupil of the eye surrounded by a broad, white ring, which is surrounded by a slender, yellow ring. The yellow ring is perimital in lateral view, but the dorsal surface of the eye medial to the ring is black with fine yellow spots.

DISTRIBUTION.—Known only from the northern portion of the Great Barrier Reef off Queensland, Osprey Reef in the Coral Sea, and the Trobriand Islands.

ETYMOLOGY.—The name aequalis is derived from the Latin word for “equal,” and refers to the approximately equal spacing of the dorsal and ventral stripes relative to the middle stripe. The name is here used as a noun in apposition.

HOLOTYPE.—AMS I.22586–076, male, 28.6 mm SL, Australia, Queensland, Escape Reef North, hole in bommie [coral head] in lagoon, 2–6 m, coral sand, 30 October 1982.

PARATYPES.—Australia, Queensland: Escape Reef, AMS I.22586–014 (8 specimens: 15–32 mm SL) and USNM 278048 (3:26–31, collected with holotype); AMS I.22633–017 (18: 18–34), AMNH 55723 (1:24), 55722 (4:18–24), ROM 40449 (3:30–32), 40450 (5:15–30), 40451 (3:15–25); Yonge Reef, AMS I.18740–017 (10:15–32), I.19472–016 (1:20), I.19546024 (5:13–31); Lizard Island, AMS I.19473–065 (1:31). Papua-New Guinea, Trobriand Islands, Kiriwina Island: USNM 217567 (2:21, 28). Coral Sea: Osprey Reef, AMS I.25113 (13:16–28); BPBM 31040 (6:17–26).

Ecsenius aequalis, known commonly as the fourline blenny, is a species of combtooth blenny found in coral reefs in the western Pacific ocean.