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Fishery Bulletin 93(1). 1995 



large solitary chromatophores on the cleithral sym- 

 physis, gut ventrum, anus, and on the notochord at 

 the point of flexure, and all undergo flexion within a 

 narrow size range of 4.2-5.2 mm SL. 



There are, however, a few distinctive characteris- 

 tics that can be used to separate the larvae of these 

 species. Immediately following flexion at 4.40 mm, 

 larvae of O. chrysurus andi?. aurorubens (flexion at 

 4.7 mm, Laroche, 1977) possess large serrations on 

 both the anterior and posterior margins of the dor- 

 sal spines, but these are not present on larvae of L. 

 campechanus (Collins et al., 1980) or L. griseus 

 (Richards and Saksena, 1980). Preopercular spina- 

 tion is also a useful character in that the longest spine 

 (located at the preopercle angle in each described 

 species) is serrated in R. aurorubens but not in L. 

 campechanus, L. griseus (Laroche, 1977), or O. 

 chrysurus (present study). Lyczkowski-Shultz and 

 Comyns 1 compared small, preserved larval R. 

 aurorubens and L. campechanus , and found that both 

 species had two dorsal spines and 4 or 5 preopercular 

 spines at 3.3 to 3.9 mm SL. Yellowtail snapper differ 

 in having fewer or no dorsal spines and only three 

 preopercular spines at the same preserved sizes (cor- 

 responding to days 7-11, Fig. 2, Aand B). Lyczkowski- 

 Shultz and Comyns 1 also examined pigmentation 

 differences in <4.0 mm larvae and identified a char- 

 acteristic pigment spot in R. aurorubens located on 

 the branchial chamber and visible through the oper- 

 culum; they also observed pigment on the anterior 

 surface of the gut (at the level of the pectoral fin base) 

 inL. campechanus. Larval O. chrysurus of the same 

 size range were devoid of pigment in either of these 

 locations. Larval R. aurorubens (Laroche, 1977) had 

 numerous, dark chromatophores located on both the 

 midbrain and hindbrain regions in all sizes of larvae 

 examined, however, the two species of Lutjanus and 

 O. chrysurus had head pigment only on the hindbrain 

 area. The yellow chromatophores found on live or 

 recently preserved specimens of O. chrysurus are 

 definitive characteristics for identification of this 

 species; unfortunately, this light-colored pigment was 

 not visible after the 30-day preservation period in 

 larvae <7.00 mm SL and would not likely be detected 

 in ichthyoplankton samples preserved in ETOH. The 

 yellow chromatophores were faintly visible on the 

 snout, operculum, and lateral line of the larger pre- 

 served individuals. Larval O. chrysurus can be dis- 

 tinguished from the other described lutjanid species 

 by utilizing combinations of the above characteris- 

 tics including the presence of heavy serrations on 

 both the anterior and posterior margins of the dor- 

 sal spines at the time of flexion, lack of serrations on 

 the longest preopercle spine, reduced number of 

 preopercle spines and dorsal spines at comparable 



sizes, and lack of internal pigment on the anterior 

 surface of the gut or branchial chamber. 



Newly hatched and early developmental stages of 

 larval fishes are rarely collected or retained in net 

 samples. 3 Those larvae that are collected show sig- 

 nificant handling effects (Theilacker, 1980; Hay, 1981; 

 McGurk, 1985), including distortion and size reduc- 

 tion that result in less than optimal depictions of size 

 at critical stages of development. In contrast, labo- 

 ratory-reared specimens provide more realistic size 

 values and information on age and pigmentation not 

 available to studies with field-caught larvae. The 

 shrinkage rates at each age and phase of morpho- 

 logical development in O. chrysurus are conserva- 

 tive measures because field-collected larvae show 

 additional shrinkage from net damage. In small 

 unossified larvae, reduction in SL as a result of net 

 collection alone increased shrinkage rates of labora- 

 tory-preserved northern anchovy by 19% (Theilacker, 

 1980) and in Pacific herring by about 8% (Hay, 1981). 

 From these results it is clear that some additional 

 allowance for net shrinkage should be applied to the 

 laboratory-preserved lengths of O. chrysurus when 

 compared to those of field-caught individuals; how- 

 ever, shrinkage rates may be variable between spe- 

 cies; therefore the value to be used is unclear. Shrink- 

 age rates have been shown to decrease with increas- 

 ing age and size of larvae (Theilacker, 1980; McGurk, 

 1985) and to become equivalent to that of larvae ex- 

 posed to laboratory handling only (e.g. no net dam- 

 age) once larvae are completely ossified. Shrinkage 

 rates of laboratory O. chrysurus also decreased in 

 postflexion larvae, stabilizing at <10% in early juve- 

 niles. Therefore, to make predictions regarding the 

 live size or age of field-collected larval snappers, an 

 additional, though unknown, rate of shrinkage due 

 to net damage should be taken into account in 

 preflexion stages but not in postlarvae and juveniles. 



The nomenclatural status of the yellowtail snap- 

 per has come under review recently. After describing 

 the morphology of the natural hybrid between O. 

 chrysurus and Lutjanus synagris (Loftus, 1992) and 

 the laboratory-produced hybrids of O. chrysurus and 

 L. synagris (Domeier and Clarke, 1992), the authors 

 of these studies concluded that the morphological and 

 meristic data indicated that Ocyurus is probably not 

 a distinct genus from Lutjanus. The larval morphol- 

 ogy described in this study of O. chrysurus also con- 

 firms the very similar size and developmental char- 

 acteristics of this species with the previously de- 

 scribed members of the genus Lutjanus. 



3 Lyczkowski-Shultz, J. Southeast Fish. Sci. Cent. NOAA, NMFS, 

 Pascagoula, MS. Personal commun., Jan. 1994. 



