Biology Reference
In-Depth Information
The biometrical parameters measured allowed replacing the different
morphological changes of
S. lagocephalus
observed in the stages scale defi ned
by Keith et al. (2008). Fish were collected at PL1 stage where the sucker is
already formed. According to changes in the corner of mouth angle, PL1
stage was observed until day 2 when the corner of mouth angle is less than
67°. After day 2, fi sh entered PL2 stage, which lasted until day 10. This
stage corresponds to the phase where the changes in the cranium and the
changes in the corner of mouth angle are the most striking. After day 10, fi sh
entered J1 stage when the mouth has reached its ventral position. The corner
of mouth angle quickly increased during the metamorphosis, the mouth
moving from a terminal position to an almost ventral one as reported in
Keith et al. (2008). Standard and total lengths continuously decreased during
the entire monitoring period (37 days) and the most important decrease in
body length occurred during the post-larval stages. For the fi rst time, weight
and factor of condition (Fulton's
K
factor of condition was calculated as
followed:
K
=100 (standard length
3
/body mass)) were monitored and both
parameters decreased progressively during the metamorphic event (Fig. 4).
The fi sh stops feeding when it enters freshwater; it is facing an ecological
changeover due to the diet transition. No feeding behaviour was observed
before day 7; after day 7 fi sh started grazing on pebbles that had been placed
on the bottom of the fl uvarium. According to this observation, fi sh seem
Figure 4.
Evolution of biometrical parameters and hormonal levels during metamorphosis
in fl uvarium on
S
.
lagocephalus
post-larvae. (No. Days: number of days spent in fl uvarium
after capture).
