Biology Reference
In-Depth Information
Branchionus plicatilis
, and water fl eas,
Daphnia
sp. The process of
E. hawaiensis
metamorphosis that occurred in the reared fi sh was essentially similar to
that of
E. saurus
except for the body length and the number of myomeres.
However, the metamorphosis of
E. hawaiensis
was divided into two
phases. The fi rst and second metamorphic phases generally corresponded
to the early and mid metamorphosis proposed by Gehringer (1959). The
following period when the length again increased was classifi ed as the
juvenile phase. Under these captive conditions, the larvae passed through
the fi rst and second metamorphic phases in seven days, and six to eight
days, respectively.
Fully-grown leptocephali of the Pacifi c tarpon,
M. cyprinoides
, were
captured at Ohara harbor in Boso Peninsula, Japan and were maintained
in the laboratory (Tsukamoto and Okiyama, 1997). Metamorphosis was
examined in these cultured fi sh. The maximum size of the leptocephalus of
this species was about 3 cm and was the smallest among the Elopomorpha.
The morphological changes during metamorphosis were principally similar
to those of
Elops
. The prominent characteristic of metamorphosis of this
species was a relatively long delay between the metamorphic shortening and
the subsequent growth in length. Thus, as shown in Fig. 5, metamorphosis
was divided into three phases; leptocephalus negative growth phase (32-16
mm in length), sluggish growth phase (16-20 mm), and juvenile growth
phase (20-40 mm). Although the body length was nearly constant during
the sluggish phase, marked changes in body proportions took place similar
to those in the mid metamorphosis of
E. saurus
. Ossifi cation and intense
pigmentation also commenced during this phase. The sluggish phase lasted
about one month.
A unique feature of elopiform metamorphosis is that at the end of
metamorphic shrinkage the larva is still quite immature and is still far from
achieving juvenile morphology. Tsukamoto and Okiyama (1997) suggested
that the most shrunken larvae of the elopiforms are similar to whitebait,
larvae of the clupeiforms (herrings), gonorynchiforms (milkfishes),
osmeriforms (freshwater smelts) and aulopiforms (lizardfi shes), and that the
subsequent growth pattern of the these larvae resembles that of whitebait-
type larvae. On the basis of this style of metamorphosis, they regarded the
Elopiformes as the most primitive among the Elopomorpha.
3.4.2 Albuliforme metamorphosis
This group of fishes possesses two different morphological types of
leptocephalus with either a forked-tail (bonefi shes) or a fi lamentous tail
(halosaurs and spiny eels), as shown in Fig. 3. Only the metamorphosis of
bonefi shes is introduced in this section because no information is available
on the metamorphosis of the fi lamentous-tailed leptocephali.
