Blue Dashed Rockskipper

Blenniella periophthalmus (Valenciennes)

(See geographic variation section for discussion of color-pattern types indicated in synonymy.)

Salarias periophthalmus Valenciennes in Cuvier and Valenciennes. 1836:311 [Ticopia, archipel de Santa Cruz; lectotype designation by inference, MNHN 857, Vanikoro, Santa Cruz Islands, in Bauchot, 1967:30; see nomenclatural discussion below]. [Color-pattern Type la.]

Salarias biseriatus Valenciennes in Cuvier and Valenciennes, 1836:316 [archipel des Indes; putative holotype, MNHN A.2150, designated neotype in nomenclatural discussion below]. [Color-pattern Type la.]

Salarias percophthalmus Swainson, 1839:274 [misspelling of periophthalmus].

Salarias schultzei Bleeker, 1859b:345 [Karangbollong, Java; holotype lost]. [Type la.]

Salarias muscarus Snyder, 1908:109 [Naha, Okinawa; holotype USNM 62245]. [Type la.]

NOMENCLATURAL VARIATION.—Several color-pattern and meristic characters vary geographically. Pigmentation pattern on the chin (Figure 27) and spinous-dorsal fin vary among, and sometimes within, populations (Table 19). Although most mature males from all localities have a uniform distribution of melanophores over the chin, young males and most females have either small spots or narrow bars in this area.

Females and about one-fourth of the males from Midway, Hawaiian, and Johnston islands (MHJ) have small, dark spots, which are most prominent in females, on the chin. The only other incidence of chin spots is in a single Phoenix Islands male, which has small, white spots on the chin, but all other specimens from this locality have either barred or uniform chin pigmentation. None of the MHJ specimens have bars.

Non-MHJ females typically have 2 or 3 bars on the chin, but some have uniformly pigmented chins. Occasionally melanophores fill the space between the 2 anterior bars to form a single broad band. Some non-MHJ males also have the chin barred.

Variation in pigmentation of the spinous-dorsal fin is most pronounced in males (Table 19, Figures 23, 24). Marquesas Islands males have a distinctive, broad, dark stripe extending along the complete distal edge of the fin; females have 2 large, black spots, 1 each on the 2 anteriormost interspinous membranes. Some males from the Hawaiian Islands have a faintly dusky spinous dorsal-fin stripe faintly similar to that of Marquesas males, but most Hawaiian males (and females) are characterized by having 1 (sometimes 2), black, anterior interspinous dorsal-fin spot. Males from Marcus, Wake, Caroline, and Marshall islands (71%), and from the western Indian Ocean (98%), typically lack anterior interspinous dorsal-fin spots (none have more than 1 spot). At these same localities, females typically have 2 spots (1 or 3 in about 4% of specimens). Both sexes at other Pacific localities have at least 1 dorsal-fin spot and females often have 2 spots, but no locality has the distinctive dichotomy of males with no spots and females with 2 spots.

The Johnston, Hawaiian, Midway, Marcus, Wake, and Marquesas islands specimens have the highest modal and mean numbers of total dorsal-fin elements and total vertebrae (Mariana Islands specimens have only high vertebral counts, Table 16). The same islands, less the Marquesas, tend to have the highest modal and mean numbers of segmented anal-fin rays (Table 16).

The presence or absence of nuchal cirri varies both within and among the various populations, with a strong tendency to lack cirri exhibited by the Hawaiian, Johnston, Midway, Marcus, Wake, Mariana, Marquesas, Caroline, and Marshall islands and the Western Indian Ocean populations (Table 17).

Mean numbers of lateral-line pores (Table 18) tend to be similar in certain geographic areas. The lowest means occur among specimens from Midway, Hawaiian, and Johnston islands. The highest means occur among the southern Oceania populations (Niue, Cook, Tuamotu, Pitcairn islands), on the one hand, and the northwestern populations (Marcus, Wake, Mariana islands), on the other. Means for the more central Pacific island populations and that from the Western Indian Ocean, tend to be intermediate.


The Midway, Hawaiian, and Johnston islands populations, as a group, are the most distinctive. They exhibit only one character, however, that separates them from the other populations: the spotted chin pigmentation pattern of most females and some males. Specimens with uniform chin pigmentation from these three localities, therefore, may not be recognizably different from similarly pigmented specimens from other localities where B. gibbifrons occurs. Somewhat similarly, males from the Marquesas Islands are distinguished from all other males by the broad, dark stripe in the spinous dorsal fin (faintly suggested in some males from the Midway, Hawaiian, and Johnston islands). Females from the Marquesas, however, are undistinguished, and cannot be localized based on morphology. There is considerable overlap among the various populations in all the other characters. For these reasons, we recognize only one taxon for all the populations of B. gibbifrons.

COMPARISONS AND RELATIONSHIPS.—Blenniella gibbifrons appears to be most closely related to B. chrysospilos, with which it alone shares in having numerous vertical pairs of pores in the lateral line and numerous multipored infraorbital pore positions (see Phylogenetic Analysis section). In B. chrysospilos there are many fewer paired pores and there is a dark spot at the tip of each dorsal-fin spine. The 2 species differ most prominently in the presence of upper-lip crenulae and bifurcated tips of the orbital cirri in B. chrysospilos and their absence in I. gibbifrons. These 2 species, together with B. periophthalmus and B. paula, share, to the exclusion of the other species of Blenniella, in having strongly modally 12 precaudal vertebrae and the terminal pleural rib strongly modally or commonly on the 13th vertebra.

Possible confusion may occur in distinguishing the ophioblennius stages of Blenniella gibbifrons and the endemic Istiblennius zebra, the only species of these genera that occur in the Hawaiian Islands. Blenniella gibbifrons usually has lower total numbers of dorsal-fin elements (32 to 34, uncommonly 34), segmented anal-fin rays (20 to 22, uncommonly 22), and total vertebrae (37 to 39—rarely 39, except at Midway) than I. zebra (34 to 36, 21 to 23—uncommonly 21, and 39 to 41, respectively; not known to occur at Midway). Furthermore, B. gibbifrons has 12 precaudal vertebrae (over 99% of specimens) and I. zebra has 10 or 11 (usually 11). The unique condition of joined tips of pairs of pectoral-fin rays of the larger I. zebra ophioblennius stages is unequivocal for recognition of that species.

DISTRIBUTION.—Blenniella gibbifrons occurs in shallow, subtidal areas and, with the exception of the east African coast, is limited in distribution to islands. It has a disjunct distribution pattern including the Pacific plate and the western Indian Ocean (Figure 62). It is found at most Pacific plate islands, east to Ducie Atoll, but appears to be conspicuously absent from Samoa, which has been sampled intensively over the past 30 years. It has a spotty distribution in the western Indian Ocean, where it appears to be absent from the Red Sea, Persian Gulf, and other localities north of the equator, many of which have been intensively sampled (this distributional pattern will be discussed further in the Biogegographic Discussion section. Springer and Williams (1990) have proposed that Recent, glacially influenced extinction of populations in the Indo-Malaysian area accounts for disjunct distribution patterns such as that exhibited by B. gibbifrons. Although this may be true, and Recent glacial sea-level changes probably did influence distribution patterns (see discussion in account of Istiblennius meleagris and Biogeographic Discussion section), we now believe that its distribution pattern probably is the result of influences that existed prior to the Recent.

It is, perhaps, noteworthy that Blenniella gibbifrons is the only species of Blenniella or Istiblennius that occurs at Johnston Island (Randall et al., 1985). Johnston Island is geographically intermediate in position between the Hawaiian Islands and other islands on the Pacific plate. One species each of Istiblennius and Blenniella occur in the Hawaiian Islands and at least 2 of each genus occur at the islands closest to Johnston on the Pacific plate. Few, if any, other localities more or less surrounded by localities harboring several species of these 2 genera harbor only 1 species of the 2 genera. Randall et al. (1985) discussed the depauperate nature of the Johnston Island fish fauna, which they attributed, in part, to the small size of the island and its low diversity of habitats.

NOMENCLATURAL