BULLETIN OF MARINE SCIENCE, 40(2): 330-375,1987 CORAL REEF PAPER DESCRIPTION OF LARVAL AND JUVENILE YELLOWTAIL DAMSELFISH, MICROSPATHODON CHRYSURUS, POMACENTRIDAE, AND THEIR OSTEOLOGICAL DEVELOPMENT Thomas Potthoff, Sharon Kelley, Vishnu Saksena, Martin Moe and Forrest Young ABSTRACT Eggs were collected from nests of yellowtail damselfish, Microspathodon chrysurus. on a south Florida reef and hatched in the laboratory. Hatched larvae were reared, with some killed and preserved at time intervals. A series of 109 larvae and juveniles 2.0 mm NL-19.8 mm SL (3 to 79 days old) were measured for morphometric changes and examined for pigment development. Ninety of these laboratory-reared larvae (2.1 mm NL to 19.8 mm SL) and three wild-caught juvenile and adults (54.4 to 116 mm SL) were cleared and stained to study osteological development. Larvae of M. chrysurus can be distinguished from other known damselfish larvae by their large pigmented pectoral fin and by a number of large melanophores over the hind brain and on the dorsal and ventral tail margin. Re (1980) described early larvae of Abudefduf /uridus. which are strikingly similar to the larvae of M. chrysurus. Osteological development of the vertebral column and ribs, the paired and unpaired fins and their supports, the hyoid arch, the branchial skeleton and the opercular series were studied. Cartilaginous neural arches and spines first appeared anteriorly on the notochord; addition was in a posterior direction. Cartilaginous hypurals appeared before all neural and haemal arches and spines had developed. Notochord flexion started in a 3.7 mm NL 16-day-old larva. Pleural ribs first developed as cartilage and then ossified, whereas epipleural ribs originated directly from ossification of connective tissue. Four or five anterior haemal arches of the caudal centra supported epipleural ribs. The vertebral column ossified from anterior to posterior. The coracoid bone of the pectoral girdle had one or two foramina, a feature not observed in perciforms except pomacentrids. In M. chrysurus. the second dorsal and anal fins and supports probably started development before the first dorsal fin. There were three predorsal bones, and the first dorsal pterygiophore supported two fin spines. The first anal pterygiophore supported two spines and one ray. Middle radials were absent in the dorsal and anal fin supports, but one stay was associated with the posteriormost pterygiophore of both fins. In the caudal complex only one uroneural developed, which fused with the urostyle forming a neural canal. Principal caudal rays were 8+ 7 compared to the most common perciform count of9+8. The ceratohyal bone of the hyoid arch had the primitive beryciform foramen, and the fifth ceratobranchials fused during ontogeny forming the lower pharyngeal jaw. Recently, the pomacentrids have been removed from the percoids and placed with the labroids. Our findings support this placement because of the fused fifth ceratobranchials and the reduced principal caudal ray count. The yellowtail damselfish Microspathodon chrysurus belongs to the large per- ciform family Pomacentridae. Recently, Kaufman and Liem (1982) removed the Pomacentridae from the suborder Percoidei and placed it in the suborder Labro- idei. This family has 4 subfamilies, about 25 genera and about 235 species (Allen, 1975; Nelson, 1984). Most damselfish species occur on reefs of the Indo-Pacific. Microspathodon (subfamily Pomacentrinae) has two other species, the giant blue damselfish, M. dorsalis, found in the eastern Pacific, and M. frontatus from the Gulf of Guinea (Emery, 1970). In the western Atlantic, M. chrysurus is a very common species on coral reefs and occurs from Bermuda, the Bahamas, Florida and the Gulf of Mexico across the Caribbean to the coast of South America, as 330 POTTHOFF ET AL.: M/CROSPATHODON LARVAL DEVELOPMENT 331 far as Brazil (Ciardelli, 1967; Bohlke and Chaplin, 1968; Randall, 1968). Juveniles of this species are commonly known as jewelfish and are of considerable value in the aquarium trade. The behavior, reproduction and ecology of damselfishes are well known (Reese, 1964; Breder and Rosen, 1966; Emery and Thresher, 1980; Sale, 1980). Fewer studies, however, have dealt with the description of the eggs and larvae of dam- selfishes and these are summarized by Leis and Rennis (1983), Thresher (1984) and Richards and Leis (1984). Leis and Rennis figured and described develop- mental series of about four genera. At present, only one comprehensive osteo- logical study of one pomacen trid species (Lepidozygus tapeinosoma) exists (Emery, 1980). Another study by Emery (1973), which is not comprehensive and does not include M. chrysurus, treats the functional osteology of 14 species of damselfish. Emery and Allen (1980) examined the insertion sequence of predorsal bones and anterior pterygiophores in adults of 21 damselfish genera, including Microspa- thodon. Developmental osteology has not been examined within the family. There are a limited number of papers dealing with Microspathodon. Montgom- ery (1980) reported on the impact of grazing on algal communities by M. dorsalis, the giant blue damselfish. MacDonald (1973) and Pressley (1980) studied repro- duction and behavior in M. chrysurus. Ciardelli (1967) studied food habits and the anatomy of the feeding mechanism in M. chrysurus. Cummings (1968) ob- served yellowtail damselfish behavior and measured 100 eggs, which averaged 1.1 mm in diameter. Emery (1973) studied yellowtail damsel fish ecology on a Florida reef. Richards and Leis (1984) presented a lateral view drawing ofa 3.7 mm NL flexion stage larva of M. chrysurus, which is a specimen used in this study. Moe and Young (1981) initially reported on the successful laboratory- rearing of yellowtail damselfish, and showed photographs of eggs, larvae and juveniles. In this study we describe the development of morphometrics and pig- mentation of cartilaginous and bony structures and of the paired and unpaired fins. This information will aid identification of M. chrysurus larvae and future studies of labroid and percoid relationships. MATERIALS AND METHODS Nests of yellowtail damselfish eggs were collected from reefs of the Coffins Patch reef complex for experimental rearing on 28 and 29 August 1978 and 17 August 1981, 4 March and 8 June 1982. The nests were located by observing the territorial behavior of the damselfish and then searching the center of the indicated area. Nests were also easily found when spawning activity was intense by examining blades of fire coral, Millepora complanata, on the reef top in areas where numerous damsel fish were observed. The nests were almost always found on the flat sides of dead blades of fire coral and rarely on the more massive encrusting portions of fire coral growth. Collected nests varied in age from newly spawned to actively hatching. The incubation period from spawn to hatch was about 3 days. An effort was made to obtain nests that were close to hatching to shorten laboratory incubation. They were collected by carefully breaking off the dead blade of fire coral at the base. The collected nests were transported back to the hatchery in a bucket. The nests were maintained in the laboratory by suspending them above a vigorous air release and allowing the rising bubbles to rush past the developing eggs. Nests were successfully maintained from several hours to several days with this technique. Hatching usually occurred at night; however, eggs close to hatching would often hatch during the day if disturbed. Hatching and rearing of larvae were under identical conditions as described for Anisotremus vir- ginicus by Potthoffet al. (1984). At 8 to 9 weeks of age the young yellowtail damselfish were transferred to 1,361 liter grow-out tanks supplied with a constant flow of filtered seawater. One hundred and nine larvae from 2.0 mm NL to 19.8 mm SL were preserved in 5% Formalin,' 3,4,6,8,9,11, 12, 13, 16, 18,25,29,33,34,50 and 79 days after hatching; three wild-caught specimens 54.4, 114 and 116 mm SL were also used in this study. Four laboratory-reared specimens I Mention of any product in this paper docs not imply endorsement by the National Marine Fisheries Service, NOAA. 332 BULLETIN OF MARINE SCIENCE, VOL. 40, NO.2, ]987 10.5-10.7 mm SL (50 days) were used in the morphometric section only. Fifteen of the laboratory- reared specimens (2.0-3.3 mm NL, 3 to 6 days old) were used for pigment and morphometric de- scriptions only; the remaining 96 specimens were used for pigment and osteological descriptions. The preserved larvae hatched in 1978 were examined by us three years later in 1981. The larvae hatched in 1982 were examined about three months after preservation. No specimens were preserved between 4.5 (18 days) and 7.3 mm SL (25 days). We found that this represented a critical gap for which developmental data were not available. The following measurements were made on M. chrysurus larvae and juveniles. Notochord length (NL): Tip of snout to tip of notochord before and during notochord flexion. Standard length (SL): Tip of snout to distal margins of hypurals after notochord flexion. Body depth: Vertical height of body measured at transverse level of pectoral-fin origin. Snout length: Tip of snout to anterior margin of eye. Eye diameter: Horizontal distance between anterior and posterior edges of fleshy orbit. Predorsal length: Distance along midline from tip of snout to origin of spinous dorsal fin. Preanus length: Distance along midline from tip of snout to anus. In clearing and staining we followed the method ofPotthoff(1984). Most drawings were made using a camera lucida. For the caudal complex we used a composite terminology following Gosline (1961 a; 1961b), Nybelin (1963) and Monod (1968). For the terminology of the branchial and hyoid arches we followed McAllister (1968), Nelson (1967; 1969) and Rosen (1973). PIGMENTATION Figures 1-6, Table 1 Pigmentation of Formalin preserved larvae is described here.