Lamprey Metamorphosis - Metamorphosis in Fish - page 21

Figure 2. Transverse sections through various regions of the branchial (a) trunk (b, c, d) regions
of immediately pre-metamorphic larvae of P. marinus stained with Sudan Black B for fat. a.
Various regions above the notochord and spinal cord stain positively for fat (F). X25. b. The
fat column (FC) and the surrounding muscle layers possess abundant fat. X540. c. The nephric
fold (NF) is a primary site for fat deposition. X460. d. Fat is present in the myosepta (M) and
as a thick layer in subcutaneous tissue (S). X550. (Modifi ed from Youson et al., 1979).
show signs of metamorphosis. The stream populations represented a good
cross section of the types of habitat occupied by larvae of the landlocked
P. marinus . The three criteria were correct predictors for 30 to 73% of the
recaptured larvae in six study creeks, but it was suggested that specifi c
criteria for each creek may be more reliable (Hollett, 1998). A second fi eld
study supported this observation of stream variability where mass alone
could predict metamorphosis in two streams but, depending on the method
used, sometimes length and CF were better predictors in one stream over the
other (Henson et al . , 2003). The results are mixed, but for the most part there
is little doubt that mass should be considered in selecting pre-metamorphic
larval P. marinus . Whether this is cost effective in the sea lamprey control
program is still in question. The most recent study to provide a predictive
model for metamorphosis in this species concluded that a model that used
criteria such as animal length in the fall, animal density, stream lamprey