Biology Reference
In-Depth Information
Figure 5.
A comparison of the number of observed (August, open bars) and predicted (based
on size and condition factor in June) of
P. marinus
metamorphosing/tank following treatment
in one of fi ve different water temperature regimes. The asterisk (*) above the prediction bar
indicates a signifi cant difference (P ≤ 0.05) from observed at each temperature. The data
indicate that 21ºC is near optimum for metamorphosis, whereas between 9 and 13ºC water
temperature has an inhibitory effect. (From Holmes and Youson, 1998).
and this feature, given the potential for sexual maturation in post-larval
life, is critical for the perpetuation of the species.
2.7.2 Animal density
It is well established that high density among larval lampreys increases the
length of the larval growth phase and reduces growth rates (Mallatt, 1983;
Morman, 1987; Murdoch
et al
.
, 1992; Rodriguez-Munoz
et al
.
, 2003). It might
be expected then that metamorphosis might occur earlier (at a younger age)
in low-density populations of larva where growth rates may be enhanced
relative to a high-density population. This feature of metamorphosis has
been shown in
P. marinus
(Purvis, 1979; Morman, 1987) and in the northern
brook lamprey,
Ichthyomyzon fossor
(Purvis, 1970) over several consecutive
years in wild populations. Growth in length, an indicator of larval age and
preparation for metamorphosis, slows as density increases and, therefore,
increases the duration of larval life. In contrast, however, a more closely
controlled laboratory study (Fig. 3) of 9-month duration on immediately
pre-metamorphic larval
P. marinus
(appropriate CF and size) showed no
signifi cant difference in the incidence of metamorphosis between high-
density (164 larvae/m
2
) and low-density (66 larvae/m
2
) populations in
three temperature regimes (Holmes and Youson, 1997). In a more recent
