Albula esuncula (Garman, 1899)

Eastern Pacific Bonefish

Figure 1 B, Tables 2, 3

Atopichthys esunculus Garman, 1899:327 (type locality: off Acapulco [Guerrero, Mexico]).

Albula vulpes (not of Linnaeus): Alexander, 1961 (in part):38 (table I, station 1203 XV; leptocephalus, Gulf of Panama); Bussing and López, 1993:36; Tapia-García et al., 1998; Morales-Nin, 1994:213.

Albula neoguinaica (not of Valenciennes): Allen and Robertson, 1994:41; Castro-Aguirre et al., 1999:93.

Albula sp.: van der Heiden and Findley, 1990:213.

Albula sp. C: Colborn et al., 2001; Pfeiler et al., 2002; Bowen et al., 2008.

Albula esuncula: Robertson and Allen, 2002, 2008; Pfeiler et al., 2008a (Fig. 1, larval syntypes), 2008b (Fig. 1 b).

The above studies examined specimens, either in whole or in part, of different life history stages of what we recognize here as A. esuncula based on sampling locations (southern Gulf of California to Panama) and mitochondrial DNA sequence data ( Albula sp. C. and A. esuncula, only).

Syntypes. MCZ 28430, two metamorphic leptocephali (39 and 44 mm), off Acapulco, Guerrero, Mexico, Albatross Station 324, 13 April 1891 (see Fig. 1 in Pfeiler et al. 2008a).

Material examined. CIAD 10–03/TB 03.ALE–34, –35 2(194–208 mm), same collection data as holotype of A. gilberti: Isla Venados (exposed side) El Playón, Mazatlán, Sinaloa, Mexico, marine, cast net, obtained from local fisherman Hipólito Olague Sifuentes, 31 January 2009; CIAD 05–3/TB 02.ALE–12, –19, 2(203–205 mm), Isla Venados (exposed side) El Playón, Mazatlán, Sinaloa, Mexico, marine, cast net, depth 2 m, Hipólito Olague Sifuentes, 3 July 2005; CIAD –04–201 to –203, 3(271–279 mm), San Dionisio del Mar, Oaxaca, Mexico, September 2004; CIAD –06–201, –202, 2(258–280 mm), near Laguna Chautengo, 16°31'2''N, 99°16'3''W, Guerrero, Mexico, January 2006 (specimens from Oaxaca and Guerrero accidentally lost).

Diagnosis. Distinguished from A. gilberti by diagnostic nucleotide substitutions at 17 different sites in the 544 bp cyt b gene segment (Table 4). In A. esuncula, the pelvic-fin tip does not surpass the anterior edge of the anus whereas it may reach the posterior edge in A. gilberti . In A. esuncula, the number of pelvic-fin rays is always 10 whereas it varies from 9 to 12 in A. gilberti . Lateral-line scale counts and numbers of rakers on the first gill arch are lower in A. esuncula (68–71 vs. 68–73 and 3–8 vs. 4–10, respectively). Since we examined only four or nine specimens of A. esuncula, according to the characteristic, the diagnostic value of the meristic differences between both species and the position of the pelvic-fin tip should not be considered validated yet and be used with caution.

Description. Meristic and morphometric data are given in Tables 2 and 3. Body fusiform, moderately elongate, slightly compressed; dorsal profile more strongly convex than ventral. Caudal peduncle depth 6.6–8.1% SL, mean 7.4%. Head conical, subquadrangular (25.0–31.0% SL, mean 27.8%); snout bluntly conical, projecting far in advance of mouth (40.8–41.4% HL, mean 41.1%). Eyes with prominent, annular, adipose eyelid (17.2–23.8% HL, mean 20.5%). Interorbital space 20.8–22.7% HL, mean 22.1%. Mouth small, inferior and horizontal; maxilla failing to reach eye by about 50% of horizontal eye diameter. Teeth on premaxillary, anterior portion of maxillary, lower jaw, vomer and palatines villiform. Tooth patches on parasphenoid, mesopterygoids and tongue composed of enlarged, rounded, molariform teeth; patches equally arranged as in A. gilberti (Fig. 2 B). Gill rakers on first arch rudimentary, tubercle-like, covered with tiny spines 3–8 + 10–13 (mode on upper limb = 8 [66.7%], 7–8 in 88.9% of specimens, only one specimen extends lower limit to 3, no specimens with 4, 5 or 6 gill rakers; mode on lower limb = 11 [44.4%]); total number of gill rakers on first arch 15–21 (mode = 18 [33.3%], 18–20 in 77.8% of specimens). Fins without spines. Dorsal-fin rays 17–18 (mode = 18 [77.8%]). Anal-fin rays 8–9 (mode = 8 [88.9%], only one specimen with 9 rays). Dorsal- and anal-fin rays with conspicuous membranous lateral extensions creating a plume-like appearance. Pectoral-fin rays 18–19 (mode = 19 [55.6%]). Pelvic-fin rays 10 in all specimens; tip of pelvic fin not reaching or just reaching anterior edge of vent in 75.0% and 25% of specimens, respectively. Caudal fin broadly forked, upper lobe slightly longer than lower. Scales on body medium-sized, with frilled membranous border; head naked; back with central row of elongate, membranaceous scales, frilled at posterior edge. Lateral line scales pored (68–71; mode = 70 [50.0%]).

Coloration. Color of thawed specimens from Mazatlán, Sinaloa: brilliantly silvery, blue-green to blue-gray above, back and sides with 10 thin, dark lines between the rows of scales; 8 above and 2 below the lateral line; back of smaller specimens with 9 dark bands; very thin, black line along lateral line canal. Outer face of basal portion of paired fins, triangular space between lower jaws, gill membrane, and ventral border of operculum lemon-yellow; branchiostegal rays pale. Belly, lower half of dorsal fin, caudal fin, and base of anal fin faint yellowish. Paired fins often with scattered melanophores on inner face, inner face of basal portion lemon-yellow to bright orange, most obvious in pectoral fin. Color of preserved specimens (alcohol): silvery aspect lost; orange color on inner face of basal portions of paired fins changed to dark brown; lines over back and sides dark; upper margin of dorsal and caudal fins dark, remainder grayish to pale; all other fins grayish to pale.

Remarks. The original description (Garman 1899) was based on larvae (leptocephali, two syntypes) and does not provide characters that can be used for separating Albula esuncula and A. gilberti . Late premetamorphic and early metamorphic leptocephali of the two species are essentially identical (Pfeiler et al. 2008a), as are leptocephali of the more distantly related A. vulpes from the Caribbean (Pfeiler 1996). Therefore, we recognize the need to set aside the existing name-bearing type (syntypes) and select and describe a neotype of A. esuncula . However, since all our available specimens are from Mazatlán, which in our opinion is too distant geographically (~ 1000 km) from the original type locality (off Acapulco) and which is also located at the northern limit of its distributional range, we will start a collecting effort in Acapulco, Guerrero, to obtain fresh specimens and describe the neotype.

Distribution. Southern Gulf of California, Mexico to at least San Pablo, Ecuador. The Ecuador record is based on a specimen collected by P. Béarez on 5 November 2008 which we have recently sequenced. The cyt b haplotype of this individual is identical to that of A. esuncula from Acapulco, Guerrero (haplotype A20; CIAD –06–201; Gen- Bank EF602159) thus confirming its identity. The bonefish species found south of Ecuador to Peru (Hildebrand, 1963) also is assumed to be A. esuncula, but this has not been verified.

Etymology. Unknown.