Apogon townsendi (Breder)

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 : 16-17

Apogon townsendi (Breder)

Identification. Twelve adult specimens of A. townsendi provided the basis for genetic identification of larvae and juveniles (Appendix 1, one adult is shown in Fig. 15 ). Adult A. townsendi can be distinguished from other Apogon by the combination of eight segmented anal-fin rays, body and lateral-line scales of similar size, the anterior body bar narrow and entirely beneath the second dorsal fin, the posterior body bar with black lateral margins, 12 circumcaudal-peduncle scales, and 17 gill rakers on the lower limb of first gill arch ( Böhlke & Chaplin 1993, Gon 2002).

Juveniles ( Fig. 16 ). Thirteen juveniles of A. townsendi (12.0 to 21.0 mm SL) were identified in our material (Appendix 1). The body is pale orange with more intense orange and some yellow coloration on the head. There is a line of distinctive orange pigment extending along the ventral portion of the body from the base of the pelvic fin posteriorly to the base of the caudal fin. Orange chromatophores are mixed with melanophores in the bar of pigment beneath the second dorsal fin and in the blotch of pigment on the caudal peduncle. The fins are mostly clear, but there are usually a few chromatophores at the bases of the anterior rays of the first dorsal fin and on the bases of the pelvic and anal fins. There are two roughly vertical lines of orange at the base of the caudal fin, one on the upper lobe and one on the lower. There are melanophores on top of the head and internally above the swimbladder and gut. Both body bars typical of adults are present, but the peduncular bar lacks the diagnostic dark lateral margins. The juveniles have 16–18 gill rakers on the lower limb of first gill arch.

Comparisons Among Juveniles. The absence of dark lateral margins on the dark bar on the caudal peduncle in juvenile A. townsendi could result in confusing this species with juveniles of A. pillionatus , A. phenax , and, presumably, A. robinsi and A. planifrons (juveniles of the last two species not present in our material). It can be separated from juvenile A. pillionatus and A. phenax in having at least some yellow coloration on the head (vs. pale orange in A. pillionatus and A. phenax ). It can also be separated from those species, and presumably A. robinsi , by having the anterior bar entirely beneath the second dorsal fin (vs. behind the second-dorsal fin in A. pillionatus and A. robinsi ; beneath and just behind the second-dorsal fin in A. phenax ). Additionally, there are no teeth on the lateral surface of the premaxilla in A. townsendi as there are in A. robinsi . It seems likely that juvenile A. planifrons will exhibit some yellow coloration on the head and may be difficult to distinguish from juvenile A. townsendi . Both species have the anterior dorsal bar entirely beneath the second dorsal fin. In the absence of the diagnostic dark lateral margins on the peduncular bar in juvenile A. townsendi , gill rakers are the best way to separate juveniles of the two species: there are usually 17 (16–18) lower-limb rakers in A. townsendi , and usually 15 (14–16) in A. planifrons ( Böhlke & Chaplin 1993, Gon 2002; Table 2 ).

Larvae ( Fig. 17 ). The two Apogon townsendi larvae genetically analyzed in this study are 11.0 mm SL. In both specimens much of the snout is transparent, but the anterior portion of the snout and the jaws are pale orange. The rest of the head is darker orange, and there appear to be some yellow chromatophores mixed in. Posterior to the head there are extensive pales areas on the body, an orange bar beneath the posterior end of the second dorsal fin, and a darker orange blotch on the posterior end of the caudal peduncle. There is a line of orange pigment on the ventral portion of the body from the base of the pelvic fin to the base of the caudal fin. The fins are mostly clear, but there are a few orange chromatophores on the bases of the pelvic and anal fins. There are two roughly vertical lines of orange on the caudal-fin base, one on the upper lobe and one on the lower. There are melanophores on top of the head and internally over the swimbladder and gut. The caudal peduncle length is 34–35% SL.

Comparisons Among Larvae. Apogon townsendi larvae are similar to those of A. planifrons , A. binotatus , A. phenax , and Apogon sp. 1 in the pattern of chromatophores on the body. They are most easily distinguished from A. planifrons in having primarily orange vs. yellow chromatophores on the head. Larval A. townsendi differs from A. phenax in lacking a prominent orange spot on the snout. From A. binotatus and Apogon sp. 1, larval A. townsendi may differ in having more prominent orange pigment on the caudal-fin base—in two roughly vertical lines, but there is considerable variation in pigment in this region among larval Apogon . From A. maculatus and A. aurolineatus , larval A. townsendi differs in lacking orange or yellow pigment on the first dorsal fin and in having a longer caudal peduncle (peduncle length 34–35% SL in A. townsendi , 30% in A. maculatus , 27–29% in A. aurolineatus ). Caudal-peduncle length also is useful in separating preserved specimens of those species, and preserved larval A. townsendi also have more melanophores on the top of the head than A. aurolineatus .

Figures

FIGURE 15. Apogon townsendi, adult, 34.0 mm SL, DNA # BLZ 7833, photograph by C. Baldwin and L. Weigt.

FIGURE 16. Apogon townsendi, juvenile, 13.0 mm SL, DNA # BLZ 4542, photograph by L. Weigt.

FIGURE 17. Apogon townsendi, larva, 11.0 mm SL, DNA # BLZ 6329, photograph by J. Mounts and C. Baldwin.