Biology Reference
In-Depth Information
Figure 5.
Metamorphic processes in the Pacifi c tarpon (
Megalops cyprinoides
). Reproduced
from Tsukamoto and Okiyama (1997) with permission.
The report by Rasquin (1955) is the first detailed study of the
metamorphosis of the bonefi sh (
Albula vulpes
). This author classifi ed
metamorphosing fi sh from Stage I (the largest leptocephalus, 55 mm) to
Stage VII (completion of metamorphosis) based on observations of the
sequence of morphological changes in the external appearance of reared
fi sh, although the criteria for each stage were obscure. A series of studies by
Pfeiler (reviewed by Pfeiler, 1986 and 2008) further examined physiological
and biochemical changes during metamorphosis of the bonefi sh (
Albula
sp.
A, undescribed species). In this study, the metamorphic period was simply
divided into two stages termed Phases IIa and IIb (Fig. 6). Stages I to IV
and Stages IV to VII of Rasquin (1955) appear to correspond to Phase IIa
and IIb, respectively. The maximum size of the leptocephalus of
Albula
sp.
A (>70 mm) was larger than that of
Albula vulpes
.
Histochemical examination revealed that the gelatinous matrix consisted
of acid mucopolysaccharides and neutral fats (Rasquin, 1955). This tissue
gradually disappeared as metamorphosis progressed and was considered
to be utilized as a nutritive reserve. The rate of shrinkage of body length
and the loss of wet mass were more rapid during Phase IIa than Phase IIb
(Pfeiler, 2008). Despite the rapid reduction of body mass, the leaf-like body
shape was mostly maintained during Phase IIa and then rapidly changed
into the juvenile style during Phase IIb. By the end of metamorphosis, the
body length had been reduced to about 40%, its dry mass had decreased
to about half, and wet mass to 24% (Pfeiler, 1984a). Metamorphosis was
complete within about 10 days (Rasquin, 1955; Pfeiler, 1984a). Unlike
elopiforms, the body shape of albuliformes is juvenile-like when their body
length was minimal at the end of metamorphosis.
