Aspects of Metamorphosis and Habitat Use in the Conger Eel, Conger oceanicus

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 km²), metamorphosis can take place over only a few 10s of km². 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.

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

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

Fig. 3.

Illustrations of the head of transforming Conger oceanicus at stage ER, stage M1, and stage M2

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

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 = 0.01 + 37.8). Regression equations calculated using the arcsine-square-root transformation for percent preanal length. Arrows indicate direction of development during metamorphosis

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

Accepted: 03 Feb 2003