Biology Reference
In-Depth Information
(sand) brook lamprey, Lampetra reissneri (Tsuneki and Ouji, 1984), the
mountain brook lamprey, Ichthyomyzon greeleyi (Beamish and Austin, 1985),
the American brook lamprey, Lampetra appendix (Holmes et al., 1999), and
the Pacifi c lamprey, Lampetra tridentata (McGree et al., 2008).
2.6 Preparation for Metamorphosis
2.6.1 Age
This subject received some treatment in the section on the lamprey life cycle
and the length of larval life. It is important, however, to emphasize that
larval age is an important parameter in lamprey metamorphosis. There are
no reports of larvae entering metamorphosis one year after hatching and
even cases of two-year old larvae entering metamorphosis are relatively rare.
Larvae of non-parasitic species metamorphose at much longer lengths than
parasitic species and likely are at least 5 years of age. As mentioned above, the
most widely used method of determining age in larvae is through defi ning
length modes via the use of length-frequency data from fi eld collections.
Age is unquestionably an important parameter in dictating the end of the
larval growth period, but there is a great deal of variability, even within the
same stream population, of lengths (age?) of metamorphosing animals. The
most extensive studies of age at metamorphosis have been reported on the
landlocked sea lamprey, P. marinus , in the watershed of the Great Lakes of
North America. These studies are part of the ongoing challenge to eliminate
or reduce the predation of parasitic-phase, adult P.marinus on sport and
commercial fi shes. Although there are some newer methodologies directed
at post-metamorphic periods of the life cycle (Twohey et al., 2003; Docker
et al., 2003), the primary target has been the larval phase before they can
enter metamorphosis or at least before the immediately post-metamorphic
animals, the juveniles, can start their downstream migration to a site where
they will commence their parasitic feeding. The control method is the use of
the lampricide, 3-trifl uoromethyl-4-nitrophenol (TFM), on larval populations
on a 3-4 year cycle. This treatment cycle period was initially determined
from length-frequency data. However, it can now be assumed that, with
the exception of a few survivors of the TFM treatment, called residuals,
the age (length) at metamorphosis can be determined from the numbers
of years, post-treatment, that metamorphosing animals fi rst appear. Some
stream populations are treated after three years, whereas others are again
subjected to the lampricide in the fourth year post-treatment. Post-treatment
surveys have revealed, as have general larval population surveys, that not
all animals of the same length (age) enter metamorphosis. The study by
Hollett (1998) used a mark and recapture protocol and age through statolith
analysis to conclude that metamorphosing animals are often one year older
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