<P> 3 . Glass eel: As they enter the continental shelf, leptocephali metamorphose into glass eels (juveniles), which are transparent and possess the typical elongate and serpentine eel shape . The term glass eel refers to all developmental stages between the end of metamorphosis and full pigmentation . Metamorphosis occurs when leptocephali are about 55 to 65 mm long . Mean age at this metamorphosis has been evaluated at 200 days and estuarine arrival at 255 days; giving 55 days between glass eel metamorphosis and estuarine arrival . Young eels use selective tidal stream transport to move up estuaries . As they enter coastal waters, the animals essentially transform from a pelagic oceanic organism to a benthic continental organism . </P> <P> 4 . Elvers: Glass eels become progressively pigmented as they approach the shore; these eels are termed elvers . The melanic pigmentation process occurs when the young eels are in coastal waters . At this phase of the life cycle, the eel is still sexually undifferentiated . The elver stage lasts about three to twelve months . Elvers that enter fresh water may spend much of this period migrating upstream . Elver influx is linked to increased temperature and reduced flow early in the migration season, and to tidal cycle influence later on . </P> <P> 5 . Yellow eels: This is the sexually immature adult stage of American eel . They begin to develop a yellow color and a creamy or yellowish belly . In this phase, the eels are still mainly nocturnal . Those remained in estuarine environment continue to go through their life cycle more quickly than those traveled into freshwater . Those in freshwater, however, tend to live longer and attain much larger sizes . Sexual differentiation occurs during the yellow stage and appears to be strongly influenced by environmental conditions . Krueger and Oliveira (1999) suggested that density was the primary environmental factor influencing the sex ratio of eels in a river, with high densities promoting the production of males . From life history traits of four rivers of Maine, Oliveira and McCleave (2000) evaluated that sexual differentiation was completed by 270 mm total length . </P> <P> 6 . Silver eels: As the maturation process proceeds, the yellow eel metamorphoses into a silver eel . The silvering metamorphosis results in morphological and physiological modifications that prepare the animal to migrate back to the Sargasso Sea . The eel acquires a greyish colour with a whitish or cream coloration ventrally . The digestive tract degenerates, the pectoral fins enlarge to improve swimming capacity, eye diameter expands and visual pigments in the retina adapt to the oceanic environment, the integument thickens, percentage of somatic lipids increases to supply energy for migrating and spawning, gonadosomatic index and oocyte diameter increase, gonadotropin hormone (GTH - II) production increases, and osmoregulatory physiology changes . </P>

How long does it take for eel eggs to hatch