MANY vertebrate and invertebrate species

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1 Copeia, 2003(3), pp Aspects of Metamorphosis and Habitat Use in the Conger Eel, Conger oceanicus GEOFFREY W. BELL, DAVID A. WITTING, AND KENNETH W. ABLE The early life history of the conger eel, Conger oceanicus, has been the focus of only a few studies. These have emphasized larval development and distribution; little is known about its metamorphosis and settlement. To quantify changes in body proportions, dentition, and pigmentation of metamorphosing C. oceanicus during these transitions, we collected leptocephali, glass eels, elvers, and juveniles during 1993, 1996, and 1998 (n 166) in coastal ocean and estuarine waters in southern New Jersey. We developed a staging scheme based on morphology, pigmentation, and dentition that categorized the developmental state from the leptocephalus to the juvenile stage. Our study demonstrated that, although the early life history of C. oceanicus occurs over large spatial scales (10,000s of km 2 ), metamorphosis can take place over only a few 10s of km 2. We conclude that selected body proportions (e.g., percent preanal length) are better indicators of developmental state than total length for metamorphosing C. oceanicus. Our results also suggest that certain metamorphic stages are associated with specific habitats. Further, the spatial differences in morphology, dentition, and developmental stage across the ocean to estuary transect suggest that oceanic individuals are earlier in development than those caught within the estuary and that many aspects of metamorphosis (e.g., changes in body morphology, dentition, and habitat use) co-occur with their migration into estuaries. MANY vertebrate and invertebrate species experience a transitional period during which changes occur in morphology, behavior, and habitat use (Yousson, 1988; Benoit et al., 2000). These changes are often referred to collectively as metamorphosis. Among fishes, one of the more dramatic metamorphoses occurs in the Superorder Elopomorpha (eels, tarpons, and bonefishes), members of which share a unique leptocephalus larval stage. Collections of leptocephali of the conger eel, Conger oceanicus, in and around the Sargasso Sea, have been used to describe the size distribution of leptocephali in the region and have confirmed that spawning occurs in this area in the late fall and early winter (Schmidt, 1931; McCleave and Miller, 1994; Miller, 1995). Leptocephali are subsequently found in the Florida Current/Gulf Stream, where they are presumably transported along the east coast of the United States. Later developmental stages of C. oceanicus (e.g., metamorphosing leptocephali, glass eels, and elvers) have been infrequently collected within estuaries ranging from North Carolina to Maine (Pearson, 1941; Moring and Moring, 1986; Able and Fahay, 1998). Little is known about the late leptocephalus through juvenile stages of C. oceanicus because of their rare occurrence in collections (Pearson, 1941; Hauser, 1975; Collette and Klein-Mac- Phee, 2002). The leptocephali grow to approximately 100 mm total length (TL) before metamorphosis (Smith 1989a). During metamorphosis there are changes in dentition (loss or absorption of the euryodontic teeth; Smith, 1989b) and changes in certain body proportions (percent preanal length, predorsal length, body depth, and head length; Able and Fahay, 1998). However, little is known about other morphological changes that occur during metamorphosis, as well as how these may differ among habitats. The purpose of this paper is to provide a morphological staging scheme for this transitional period and determine a general pattern of habitat use, including size and stage at ingress and settlement over the ocean-estuary interface. MATERIALS AND METHODS Identification. Early life-history stages of five species of anguilliform fishes have been collected from the study area (Able and Fahay, 1998). These include the anguillid Anguilla rostrata, a muraenid Gymnothorax sp., the ophichthids Myrophis punctatus and Ophichthus gomesi, and the congrid C. oceanicus. Conger oceanicus is distinguished during its late leptocephalus stage from other leptocephali collected in the study area by its relatively large size ( mm TL vs 80 mm) and the presence of melanophores along the midlateral line and ventral edge of the body during early metamorphosis. As a glass eel, C. oceanicus differs from A. rostrata and oth by the American Society of Ichthyologists and Herpetologists

2 BELL ET AL. METAMORPHOSIS OF CONGER OCEANICUS 545 Fig. 1. Map of the study site depicting the three ocean sites (LE Buoy, Stations 9 and C), and two estuarine sites (Little Sheepshead Creek Bridge and Schooner Creek) in the vicinity of Little Egg Inlet, New Jersey. er species by its large size (64 80 mm TL vs mm) and the location of the dorsal fin origin over the posterior portion of the pectoral fin. Study sites. The study area was immediately offshore of the Great Bay Little Egg Harbor estuarine system in southern New Jersey (Fig. 1). The offshore portion of the study area occurred over depths of m where a sand ridge (Beach Haven Ridge) formed the outer boundary of the study area. The estuary is polyhaline and is divided by a salt marsh peninsula to the west of Little Egg Inlet, the primary source of ocean water entering the estuary. Several channels, including Little Sheepshead Creek, run through the peninsula between Great Bay and Little Egg Harbor. This system has a broad seasonal temperature range (-2 C to 28 C), a moderate tidal range (approximately 1 m; Able et al., 1992; Able and Fahay, 1998), and a protected, relatively undeveloped watershed surrounded by extensive marshes (Psuty et al., 1993; Able et al., 1996). Collections. All preserved individuals (n 129) used in this study were selected from archived collections at the Rutgers University Marine Field Station (RUMFS). Planktonic individuals from within the Great Bay Little Egg Harbor estuary were selected from samples collected from a bridge that spans Little Sheepshead Creek (Fig. 1). We selected 24 individuals from five dates during 1993 to develop the staging scheme and compare differences in morphology and dentition among different habitats. Little Sheepshead Creek bridge is located approximately 3 km from the creek mouth and is 5.4 km inside Little Egg Inlet. Water depth at the sampling location was approximately 3 4 m. During flood tides, coastal ocean water flows into the estuary through Little Egg Inlet and some of it passes directly into the mouth of Little Sheepshead Creek, located on the Little Egg Harbor side of the peninsula (Charlesworth, 1968; Chant et al., 2000). Therefore, during flood tides the water sampled is, at least in part, coastal ocean water entering the estuary with its complement of larval fishes (Witting et al., 1999). The weekly samples were collected with a 1 m diameter (1 mm mesh) plankton net that was suspended in midwater from the bridge during night flood tides for three sets of 30 min duration each. Upon retrieval of each set, contents of the plankton nets were transported immediately to the laboratory, sorted, preserved in 95% ethyl alcohol, and later measured (months, years) after shrinkage had presumably ceased. The data presented here were not corrected for shrinkage, which can be approximately 7.5% for Conger conger leptocephali preserved in 95% ethanol (Correia et al., 2002). Demersal individuals from within the estuary were selected from an archived series that used demersal habitat trays ( m, 3 mm mesh) filled with oyster shell to collect structure-oriented fish and crustaceans. Metamorphosing specimens of C. oceanicus were frequently collected in these trays (E. J. Duval, unpubl. data), and thus the shell was considered to represent adequate settlement structure for the eels. These trays were located within Schooner Creek, a subtidal marsh creek located approximately 1 km from Little Sheepshead Creek (Fig. 1). A total of 46 specimens were collected on five dates during 1993 and preserved in 95% ethyl alcohol for use in the staging scheme and comparison of stage across habitat. The developmental state of these individuals was compared to pelagic individuals, caught at Little Sheepshead Creek Bridge, to determine when settlement occurs during development. Oceanic specimens of C. oceanicus were collected on three dates in May and June This presented a unique opportunity to describe earlier developmental stages that had not previously been reported and to make comparisons between oceanic and estuarine individuals. However, during 1996, estuarine demersal sampling did not occur and only a few pelagic estuarine individuals were collected, therefore, comparisons among the three habitats were made across two different years. Oceanic specimens were collected approximately 4 5 km outside Little Egg Inlet (Stations 9 and C, and Little Egg [LE] buoy, Fig. 1) with a 1 m (6 mm mesh) beam trawl at depths of m. A total of 59 individuals were preserved in 95%

3 546 COPEIA, 2003, NO. 3 ethyl alcohol for use in the development of the staging scheme and for a comparison of morphology and dentition with individuals collected during 1993 in the adjacent estuary. Because later juvenile stages were not preserved during 1993 and 1996, and certain metamorphic traits could not be measured using preserved samples (e.g., development of erythrocytes), we used additional live specimens collected in 1998 to further develop the staging scheme. We examined live metamorphosing leptocephali (n 27, mm TL) to determine when erythrocytes developed during metamorphosis. Because C. oceanicus leptocephali and glass eels are transparent, the presence of erythrocytes was easily determined by observing the ventral aorta under a dissecting microscope. Also live juveniles (n 10, mm total length, TL), collected during 1998 from demersal habitat trays, were measured to obtain body proportions for juvenile stages that were not preserved during 1993 or These live individuals were only used to complete the staging scheme and were not used in the habitat comparison analysis. Morphology, dentition, and pigment. We recorded a suite of morphological measurements, assessed the development of dentition (sensu Able and Fahay, 1998) and illustrated pigmentation patterns for preserved specimens of C. oceanicus that were collected across a series of stations from the ocean to the estuary (Fig. 1). A dissecting microscope was used to obtain length measurements to the nearest 0.1 mm. Total length (TL), preanal length (distance from the tip of snout to the posterior margin of the anus [PAL]), predorsal length (distance from tip of snout to base of first dorsal ray [PDL]), and greatest depth (body depth at the anus [GD]), as described by Smith (1989a), were recorded. We report PAL, PDL, and GD as percentages of total length in this paper because these percentages are most commonly used in studies of leptocephalus development (Kubota, 1961; Smith, 1989a; Correia et al., 2002). A compound microscope was used in conjunction with an image analysis software program to count the total number of euryodontic and juvenile teeth on the right side of the jaw. Pigmentation patterns we describe were based, in part, on a scheme for A. rostrata (Haro and Krueger, 1988). Analysis. The correlation coefficient (r) was calculated between TL and transformed percent PAL (arcsine square root) during three life-history stages (late euryodontic leptocephalus, metamorphosing leptocephalus, and glass eel through juvenile). We tested the correlation coefficients to determine whether a significant stage-specific relationship (positive or negative) existed between these two independent variables (H o :r 0) and used least-squares linear regression to model this relationship. After transformation, PAL was normally distributed for all stages; however, TL was only normal for the late leptocephalus and metamorphosing leptocephalus stages despite the log transformation. Hypothesis tests about correlation coefficients are robust to deviations from the assumption of bivariate normality (Zar, 1984); nonetheless, results for the glass eel to juvenile stage should be interpreted with caution. A multivariate analysis of variance (MANO- VA) was used as an overall test to determine whether individuals collected from within the three locations (coastal ocean, pelagic estuarine, and demersal estuarine) were significantly different based on TL, percent PAL, and the number of euryodontic and juvenile teeth (response variables). To reduce redundancy in the response variables, percent PDL and GD were excluded from this analysis because of their highly significant correlation with percent PAL (Pearson correlation coefficient r 0.98 and 0.91, respectively; P 0.001). Pairwise univariate contrasts were then constructed to establish which locations and response variables contributed most to the overall significant difference among locations. Means for each response variable were calculated for each sampling date and were treated as replicates in the MANOVA (n 3, 5, and 5 for coastal ocean, pelagic estuarine, and demersal estuarine, respectively). Although TL and PAL were normally distributed, the number of euryodontic and juvenile teeth were not despite the square-root transformation, which is recommended for count data (Zar, 1984). A plot of model predicted values versus residuals suggested that variances were homogeneous. RESULTS AND DISCUSSION Staging scheme. Based on our observations from live and preserved specimens, and the literature (Schmidt, 1931; Castle, 1984; Smith, 1989a), we assembled a system for identifying a series of early life-history stages through metamorphosis (Table 1). The engyodontic stage has not been described for C. oceanicus; however, Castle (1984) described engyodontic stage anguilliform leptocephali as being elongate, having few needle-like teeth, and having a lower jaw equal to or longer than the upper jaw. Eury-

4 BELL ET AL. METAMORPHOSIS OF CONGER OCEANICUS 547 TABLE 1. LIFE-HISTORY STAGES OF Conger oceanicus INCLUDING CHARACTERISTIC PIGMENTATION, DENTITION TYPE (INCLUDING NUMBER OF TEETH ON RIGHT SIDE OF JAW), AND BODY PROPORTIONS (PERCENT PREANAL LENGTH [% PAL], PERCENT GREATEST DEPTH [% GD]), AS WELL AS OTHER ASPECTS OF MORPHOLOGY. Dentition type follows description by Smith (1989b). NA not available; ** not applicable. Stage Life history Engyodontic leptocephalus Euryondontic leptocephalus Designation TL (mm) Pigmentation (also see Fig. 4) Dentition % PAL % GD Other characteristics Habitat EG N/A Engyodontic N/A N/A Lower jaw equal or longer than upper, nasal capsule unformed, laterally compressed body, total length increasing (assumed based on other species, see Castle, 1984) ER Large individual melanophores along midlateral line and small melanophores along top of gut; crescent patch under eye Transforming M Same but smaller and discrete melanophores may be present in tail region Glass eel M Smaller, discrete melanophores in patches dorsal to midlateral line Glass eel M3 Similar Same but smaller discrete melanophores uniformly distributed dorsal to midlateral line Elver M4 Similar Dark band of pigment formed dorsal to midlateral line Elver M5 Similar Same, with small discrete melanophores forming on ventral side of midlateral line Elver M6 Similar Same, with small discrete melanophores forming dorsal to dark pigment bank Euryodontic Lower jaw shorter than upper, nasal capsule forms, laterally compressed body, total length increasing. In coastal collections, two paired nostrils and change in dorsal profile of head above eye Euryodontic (reduced in size and number) Body laterally compressed, total length decreasing, head has level dorsal profile above eye, lips and nasal tubes present Juvenile (0 4) Body with adult proportions and still laterally compressed, red blood cells develop, internal organs begin development Juvenile (4 20) Same Same Same with body becoming rounder Juvenile (20 30) Same ** Body round in cross-section, internal gelatinous matrix completely broken down Sargasso Sea (pelagic) (Schmidt, 1931) Sargasso Sea to Coastal ocean (pelagic demersal) (Smith, 1989a; this study) Coastal ocean: (demersal) Estuary: (pelagic demersal) Estuary (demersal) Same Same Juvenile (20 40) Same ** Same Same Juvenile (40 80) Same ** Same Same Juvenile J Increasing Fully pigmented Juvenile ( 80) Same ** Same Same

5 548 COPEIA, 2003, NO. 3 Fig. 2. Illustrations of transforming Conger oceanicus at stage ER (85.4 mm TL), stage M1 (114.0 mm TL), and stage M2 (82.8 mm TL). See Table 1 for further characteristics of these stages. odontic leptocephali (i.e., individuals with three series of shorter, broad-based teeth) of C. oceanicus were described by Smith (1989a) as being moderately elongate and with a short head and snout, moderately large melanophores along the midlateral line, and a crescent-shaped patch of pigment under the eye. From our collections, we found that euryodontic leptocephali (stage ER) had increased in size and decreased in some body proportions (percent PAL and PDL) relative to less developed individuals in the same stage collected by Smith (1989a; see later section for detailed discussion). These leptocephali are elongate (Fig. 2), laterally compressed, have a high euryodontic tooth count (Table 1), and have an abrupt change in the dorsal profile of the head above the eye (Fig. 3). Stage M1 begins with the formation of the lips and the straightening of the dorsal profile of the head (Fig. 3). During this stage the body depth decreases (Fig. 2), and the anus and dorsal fin moves anteriorly (percent PAL and PDL decrease (Table 1, Fig. 2). These individuals possess a pigmentation pattern that is similar to the description provided by Smith (1989a; Fig. 4). However, additional smaller melanophores may appear near the tail region later in this stage. Some of these leptocephali may have some smaller euryodontic teeth but they disappear before the end of this stage. During the first glass eel stage (M2) the dorsal fin and anus have reached their final positions on the body (Table 1, Fig. 2), erythrocytes develop, and the juvenile teeth begin to appear. The smaller melanophores, which first appear during the M1 stage, develop from the tail toward the head, and can be found in clusters along the midlateral line (Figs. 2, 4). Pigmentation is the primary characteristic that is used Fig. 3. Illustrations of the head of transforming Conger oceanicus at stage ER, stage M1, and stage M2. to distinguish between the remainder of the glass eel, elver, and juvenile stages (Fig. 4). A spotted pigment band of smaller melanophores develops above the midlateral line during stage M3. By stage M4 (the first elver stage) the melanophore density above the midlateral line becomes more concentrated and gives the appearance of a solid black band of pigment when viewed with the naked eye; however, there is no pigment immediately above and below the band. In stage M5, melanophores develop along the ventral portion of the dark band (see illustration in Able and Fahay, 1998). Similar melanophores appear on the dorsal side of the band during stage M6. Individuals are classified as juveniles (Stage J) once the melanophores appear in a uniform, dark pattern over the whole body. It appears that C. oceanicus leptocephali may increase in size and decrease in some body proportions during the premetamorphic euryodon-

6 BELL ET AL. METAMORPHOSIS OF CONGER OCEANICUS 549 Fig. 5. Relationship between total length versus percent preanal length for preserved specimens (n 129). The developmental stage for each individual is indicated using a specific symbol; stage ER closed squares, M1 open circles, glass eels (M2 M3) closed triangle, elvers (M4 M6) open diamond, and juveniles ( J) open squares. Lines represent linear regression trends for the ER (y 0.16x 75.7), M1 (y 0.36x 15.5) and glass eel through juvenile stages (y ). Regression equations calculated using the arcsine-square-root transformation for percent preanal length. Arrows indicate direction of development during metamorphosis. Fig. 4. Illustrations depicting the changes in lateral pigmentation at the origin of the anal fin for transforming Conger oceanicus at stages ER and M1, M2, M3, M4, M5, M6, and juveniles ( J). See Table 1 for further characteristics of these stages. tic stage. Euryodontic stage leptocephali collected in this study (TL range mm) had percent PAL and PDL measurements (range 59 85% and 40 62%, respectively) that were less than those reported by Smith (1989a) for smaller (SL range mm) euryodontic leptocephali (range 88 97% and 61 69%) collected from locations closer to the Sargasso Sea spawning grounds (e.g., Gulf Stream, Straits of Florida, Bahamas, etc.). Thus, the ER stage leptocephali collected within our study site are likely further developed than those reported by Smith (1989a). This comparison also suggests that premetamorphic leptocepahli development occurs over large spatial scales (100s to 1000s of km 2 ) and may involve an increase in size as the anus and dorsal fin move to a more anterior location on the body. This pattern of development is characteristic of euryodontic leptocephali (Smith, 1989b) and is supported somewhat by the negative correlation r 0.29, n 45) between TL and percent PAL for ER stage leptocephali (Fig. 5). Although the correlation was not significant (P 0.06), our inability to detect significance may be in part based on the large variability in size (Fig. 5) that is characteristic of other premetamorphic congrid leptocephali (Correia et al., 2002) and sampling across spatial scales that are smaller (10s of km 2 ) than the spatial scales at which body proportions change in premetamorphic leptocepahli. Relative to the ER stage, body proportions changed considerably during later stages of metamorphosis. At about 110 mm TL (after preservation and presumed shrinkage; Correia et al., 2002), C. oceanicus leptocephali appeared to stop increasing in length, and stage M1 begins. This length is similar to the maximum size for C. oceanicus leptocephali (about 100 mm SL) reported by Smith (1989a). There was a highly significant positive correlation between TL and percent PAL during the M1 stage (r 0.54, n 52, P 0.001; Fig. 5), which suggests that metamorphosing leptocephali decrease in length as the anus continues to move anteriorly. By the end of metamorphosis TL decreased to about 70 mm and the anus reached its final position on the body (percent PAL 38 45%). Although a significant positive correlation existed between TL and percent PAL during the glass eel, elver, and juvenile stages (r 0.32, n 44, P 0.04; Fig. 5), we do not believe this trend to be biologically significant because glass eels, elvers, and juveniles possess adult body proportions (Smith, 1989b; Able and Fahay,

7 550 COPEIA, 2003, NO ). Furthermore, this significance may have resulted from a type I error, which is more likely when the assumption of bimodality in correlation analysis is violated, as was the case for these later stages (see analysis section in Materials and Methods). The stage-specific relationships between percent PAL and TL that we observed for developing C. oceanicus are somewhat similar when compared to studies of metamorphosis in Conger myriaster. For example, the premetamorphic stage of C. myriaster (Yamano et al., 1991) corresponds with our euryodontic stage leptocephali (ER) in that TL increases before metamorphosis (Fig. 5); however, these stages differ in that percent PAL remains constant throughout the premetamorphic stage for C. myriaster. Our M1 stage is similar to the metamorphic stages of C. myriaster in that there is a drastic reduction in size and percent PAL (Fig. 5); however, C. myriaster metamorphosis is further subdivided into two phases that differ with respect to the intensity of change in percent PAL (i.e., the relationship between TL and percent PAL during this stage is best described by two lines with differing positive slopes (Kubota, 1961; Yamano et al., 1991). A change in the slope between percent PAL and TL during metamorphosis was not evident for C. oceanicus from this study or from Able and Fahay (1998); therefore we describe only one phase. Total length has long been used as a measure of ontogeny and growth for fish because most fish increase in length as they develop. Previous studies on Brevoortia tyrannus, Sciaenops ocellatus (Fuiman et al., 1998), and Scophthalmus aquosus (Neuman and Able, 2002) suggest that TL is the most accurate measurement of ontogenetic state; however C. oceanicus, as well as other elopomorphs, decrease in size during metamorphosis. This suggests that TL measurements are not as useful an indicator for level of development in elopomorphs. Because percent PAL declines consistently during the transition from leptocephalus to glass eel stage, this measure would be a better indicator of developmental state than TL. Other studies of congrid metamorphosis have successfully used this criterion to classify different stages of metamorphosis (Kubota, 1961; Yamano et al., 1991; Correia et al., 2002). Fig. 6. Comparison of (A) percent preanal length and (B) total length for individuals caught in the coastal ocean (LE Buoy and Stations 9 and C during 1996) (closed circles), estuarine pelagic individuals collected at Little Sheepshead Creek during 1993 (open circles), and estuarine demersal specimens caught at Schooner Creek during 1993 (open triangles). See Figure 1 for location of sampling sites. Habitat relative to morphology, dentition, and developmental stage. There was a significant overall difference in dentition, body proportions, and total length among the three sampling locations (Manova; Wilk s Lambda: P 0.001); however, univariate pairwise contrasts suggest that individuals do not differ among habitats with respect to all characteristics. For example, coastal ocean leptocephali differ from estuarine pelagic individuals with respect to dentition, body proportions, and developmental stage, but not for length. Coastal ocean leptocephali (mostly Stage ER) possessed a greater mean number of euryodontic teeth (mean SE) than pelagic estuarine individuals (mean ); the difference between the two was significant (P 0.02). Also mean percent PAL for oceanic leptocephali (mean , range ) was greater than and significantly different (P 0.001) from pelagic estuarine specimens (mean , range ; Fig. 6A). There was no significant difference (P 0.66) in total length between estuarine, pelagic ( ) and ocean specimens ( ; Fig 6B). There were also distinct differences in developmental stage between coastal ocean and pelagic individuals from the estuary. A greater percentage of the earlier, stage ER individuals were caught in the coastal ocean (93%) than in the

8 BELL ET AL. METAMORPHOSIS OF CONGER OCEANICUS 551 estuary (7%). Although M1 stage individuals were collected in the coastal ocean and both pelagic and demersal estuarine habitats, no glass eel, elver, or juvenile stages were collected in the ocean or as pelagic individuals in the estuary. Although the relatively large mesh used in oceanic collections might not easily capture the narrower, more cylindrical glass eels, other collections with small mesh (0.5 mm in the vicinity of Beach Haven Ridge; K. W. Able, M. P. Fahay, D. A. Witting, unpubl. data; M. J. Neuman, unpubl. data) have failed to capture them as well. These spatial differences in morphology, dentition, and developmental stage across the ocean to estuary transect suggest that oceanic individuals are earlier in development than those caught within the estuary and that many aspects of metamorphosis (e.g., changes in body morphology, dentition, and habitat use) cooccur with their migration into estuaries. We also observed consistent differences in dentition, body proportions, length, and developmental stage between individuals collected in the pelagic and demersal habitats inside the estuary. The pelagic individuals possessed a greater mean number of euryodontic teeth (mean ) than demersal individuals at Schooner Creek (mean ). Also, these pelagic individuals possessed fewer mean number of juvenile teeth (mean ) than those at Schooner Creek, (mean ). In addition, percent PAL was greater for pelagic individuals (mean , range ) than for those caught in the demersal habitat (mean , range ; Fig. 6A). Individuals with a PAL less than 45% could only be found in the demersal habitat. Pelagic estuarine individuals were also larger (mean ) than demersal estuarine specimens (mean ; Fig. 6B). These differences were significant for the number of juvenile teeth, total length, and PAL, but not for the number of euryodontic teeth (P 0.02, 0.01, 0.003, and 0.09, respectively). Although M1 stage individuals were caught in the estuarine pelagic and demersal habitats in relatively equal proportions (35.7% and 33.9%, respectively), glass eel, elver, and juvenile stages were restricted to the demersal habitat traps. Therefore, changes in morphology, dentition, and developmental stage continue to occur after ingress into estuaries and during the transition to the demersal habitat. Also, because postmetamorphic stages were only caught in demersal samples from within the estuary, it is clear that C. oceanicus takes up permanent residence in the demersal habitat once inside the estuary, at the beginning of the glass eel stage. In summary, the comparison of individuals across the ocean-estuary transect suggest that certain metamorphic stages of C. oceanicus are associated with specific habitats and that metamorphosis and settlement coexist during estuarine ingress. Our results also demonstrate that the metamorphosis of C. oceanicus occurs over small spatial areas (10s of km 2 ) relative to the rest of its early life history, which spans 10,000s of km 2. ACKNOWLEDGMENTS We would like to thank N. A. McGehee and S. O Donnell for providing the illustrations, and M. Neuman for supplying the oceanic specimens. Several individuals offered helpful comments on earlier drafts including M. Miller, M. Fahay, and three anonymous reviewers. This project was begun as an undergraduate internship (GWB) with financial support from Tropical Fish Hobbyist Publications, Inc., and the Rutgers University Institute of Marine and Coastal Sciences (IMCS). This paper is IMCS contribution LITERATURE CITED ABLE, K.W.,AND M. P. FAHAY The first year in the life of estuarine fishes in the Middle Atlantic Bight. Rutgers Univ. Press, New Brunswick, NJ., R. HODEN, D. A. WITTING, AND J. B. 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