Biology Reference
In-Depth Information
recruitment phase, which allows them to colonise the rivers and to grow to
the reproductive adult stage.
Post-larvae migrating upstream provide an important source of food
for local human populations in certain archipelagos (Bell, 1999; Keith et al.
,
2006), where this increasing fi shing activity has a real socio-economic impact
(Delacroix, 1987). However, harvesting of this food resource in estuaries is
highly unsustainable, on account of the complexity of the species' life cycle
and the hydrological specifi cities of these islands.
Keith et al. (2008) described the different post-larval and juvenile stages
of
S. lagocephalus
(Gobiidae, Sicydiinae),
which are fi shed
in Reunion Island
when recruiting back to rivers. The characterisation of the different stages
should improve the biological and physiological knowledge needed to
understand the processes involved in the metamorphosis and recruitment
stages and help managers for a monitoring of stocks (Lord and Keith,
2007).
Taillebois et al. 2011 investigated the hormonal control of
S.
lagocephalus
larval metamorphosis which occurs during recruitment to rivers and
precisely studied the infl uence of thyroid hormones in the metamorphic
changes.
5.2 Metamorphosis: Morphological Changes from a Planktonic
Life to a Benthic One
S. lagocephalus
adults are benthic and rheophile. They live on the bottom
of the rivers, and are herbivorous. Their teeth and their mouth, located
ventrally, are particularly adapted to grazing algae and diatoms that grow
on the rocks. They have a strong pelvic sucker resulting from the fusion of
the pelvic fi ns; it enables them to climb waterfall, to colonise rivers upstream
and to resist to strong currents. When post-larvae enter freshwater from
the sea, they are plankto-pelagic, with a terminal mouth and they are not
adapted to the particularities of insular river habitats. They undergo a
metamorphosis characterised by morphological changes, as described by
Keith et al. (2008) and listed in Table 1. Keith et al. (2008) also characterised
the different post-larval and juvenile stages of this species. Metamorphic
changes start at sea during the transition from larvae to post-larvae. As
fi sh recruit to the estuary, more metamorphic changes are observed as fi sh
change through several post-larval stages, which allow them to colonise
the river. As for the transformation of eel leptocephalus larva to post-
larval glass eel (Chapter 3), these larval and post-larval transformation
events in
S. lagocephalus
are a continuum, constituting the entire larval
metamorphosis.
Several morphological characters are highly modifi ed during the
environmental shift from a plankto-pelagic larval life to a benthic one.
