Apogon phenax Böhlke and Randall

Baldwin, Carole C., Brito, Balam J., Smith, David G., Weigt, Lee A. & Escobar-Briones, Elva, 2011, Identification of early life-history stages of Caribbean Apogon (Perciformes: Apogonidae) through DNA Barcoding, Zootaxa 3133, pp. 1-36 : 12-15

Apogon phenax Böhlke and Randall

Identification. Sixteen adult specimens of A. phenax provided the basis for genetic identification of larvae and juveniles (Appendix 1, one adult is shown in Fig. 10 ). Adult A. phenax can be distinguished from other Apogon by the combination of eight segmented anal-fin rays, body and lateral-line scales of similar size, body with two distinct dark markings (one wedge-shaped bar below and just behind second dorsal fin and a bar on the posterior part of caudal peduncle—the distance between the two bars larger than the width of the posterior bar), and 11 to 14 (usually 13–14) gill rakers ( Böhlke & Chaplin 1993, Gon 2002).

Juveniles ( Fig. 11 ). Eight juveniles, 16.0–22.0 mm SL, are present in our material. The body is pale orange. The head, abdomen, first dorsal fin, bases of second dorsal and anal fins, and posterior portion of the caudal peduncle are darker pink/orange. There are melanophores on the head, gut, outer rays of the caudal fin and on the distal portions of the second dorsal and anal fins. Two dark bars are present on the trunk in all juveniles. The anterior bar is somewhat wedge shaped (slightly broader dorsally than ventrally) and extends ventrally to a point slightly below mid body or slightly above the anal-fin base. This bar is confluent with a stripe of melanophores along the second dorsal-fin base and separated by a gap from a similar stripe along the anal-fin base. The bar on the caudal peduncle extends from the dorsal to the ventral margins of the body. As in adults, the distance between the two bars is greater than the width of the posterior bar. There are 13–14 lower-limb gill rakers on the first arch in the juveniles, which is consistent with values for adults ( Table 2 ).

Comparisons Among Juveniles. Juvenile A. phenax can be distinguished from other juvenile Apogon by the same characters that separate adults.

Larvae ( Fig. 12 ). Apogon phenax larvae genetically analyzed in this study range from 9.5 to 11.0 mm SL. The smaller specimens are bright orange in life, and the fins are clear ( Fig. 12 a). Much of the snout is transparent, but there is a conspicuous orange spot above the upper lip. The upper and lower jaws have scattered orange chromatophores. A nearly solid line of orange pigment extends along the base of the anal fin and ventral midline of the caudal peduncle. A 10.0–mm SL specimen ( Fig. 12 b) is paler orange in general, has more pale areas on the snout and jaws, and has a large pale area on the dorsal portion of the caudal peduncle. There are a few orange chromatophores at the bases of the central and ventral rays of the caudal fin. In one 11.0 mm SL specimen ( Fig. 12 c), the dark bars characteristic of juveniles and adults are beginning to form posteriorly, and the area between the bars is pale. In all larvae there are melanophores on top of the head, in the temporal region, and over the swim bladder and gut. The caudal-peduncle length ranges from 32–36% SL.

Comparisons Among Larvae. The smallest larvae of A. phenax resemble larvae of A. aurolineatus and A. maculatus in usually having a bright orange body color, but they differ in lacking orange/yellow ( A. aurolineatus ) or orange ( A. maculatus ) pigment on the first dorsal fin; A. aurolineatus also has orange second dorsal, anal, and pelvic fins, which are clear in A. phenax larvae. Additionally, larvae of A. phenax have more melanophores on top of the head than A. aurolineatus and a longer caudal peduncle than that species and A. maculatus (caudal-peduncle length 32% SL or larger in A. phenax , 27–29% SL in A. aurolineatus , 30% in A. maculatus ). Larger Apogon phenax larvae are very similar to those of A. binotatus , and somewhat similar to those of A. townsendi , but they differ from both in having a conspicuous orange spot above the upper lip (vs. small and pale, if present). Larval A. phenax can be separated from larval A. planifrons by the absence of bright yellow pigment on the head and from larval A. mosavi by the absence of a distinctive pattern of chromatophores on the median fins. We have identified no morphological features to separate preserved A. phenax , A. binotatus , A. townsendi , and A. planifrons larvae.

Apogon lachneri Böhlke

Identification. Four adult specimens of A.lachneri provided the basis for genetic identification of seven juveniles (Appendix 1; one adult is shown in Fig. 13 ). The combination of characters that distinguishes A. lachneri adults from other Apogon species is eight segmented anal-fin rays; 16–17 gill rakers on the lower limb of the first arch; lateral-line and body scales of similar size; a small dark saddle behind the second dorsal fin, followed by a white spot (white spot may not be apparent in preserved specimens); a large dark area on the first dorsal fin posterior to the second spine; and anterior portions of the second dorsal and anal fins dark to dusky distally ( Böhlke & Chaplin 1993, Gon 2002).

Juveniles ( Fig. 14 ). Juveniles examined range from 18.0–22.0 mm SL. In all specimens, the body is pale orange, and the dark pattern of pigment on the dorsal and anal fins typical of adults is conspicuous. The caudal-fin rays are densely covered with melanophores. There are scattered melanophores on the head in the smallest juveniles. The posterior margins of the scales on the dorsal portion of the trunk and caudal peduncle are covered with melanophores, forming roughly diamond-shaped patterns of pigment on the body. The dark saddle behind the second dorsal fin characteristic of adults is beginning to develop or fully present in all specimens. There are 16 gill rakers on the lower limb of the first gill arch.

Comparisons Among Juveniles. Juvenile A. lachneri can be distinguished from all Apogon juveniles by the conspicuous dark pigment on the dorsal and anal fins. It resembles A. aurolineatus in lacking dark markings on the caudal peduncle, but it is easily separated from that species by the dark saddle behind the second dorsal fin (vs. no distinguishing marks on the body in juvenile A. aurolineatus ). Apogon lachneri juveniles most closely resemble those of A. maculatus and A. pseudomaculatus in having a dark spot of pigment associated with the base of the second dorsal fin, but the position of the spot distinguishes them (behind the last ray of the second dorsal fin in A. lachneri ; on the posterior base of that fin in A. maculatus , and well below the posterior base of the second dorsal fin in A. pseudomaculatus ). Juvenile A. lachneri can further be distinguished from A.maculatus and A. pseudomaculatus by lacking a dark blotch of pigment on the caudal peduncle.

Figures

FIGURE 10. Apogon phenax, adult, 32.0 mm SL, DNA # BLZ 5268, photograph by J. Mounts.

FIGURE 11. Apogon phenax, juvenile, 16.0 mm SL, DNA # BLZ 8166, photograph by C. Baldwin and L. Weigt.

FIGURE 12. Apogon phenax a) larva, 9.5 mm SL, DNA # BLZ 6335; b) larva, 10.0 mm SL, DNA # BLZ 6361; c) larva, 11.0 mm SL, DNA # BLZ 6359; photographs by J. Mounts and C. Baldwin.

FIGURE 13. Apogon lachneri, adult, 36.0 mm SL, DNA # BLZ 5118, photograph by J. Mounts and C. Baldwin.

FIGURE 14. Apogon lachneri, juvenile, 21.0 mm SL, DNA # BLZ 5265, photograph by J. Mounts.