February 15-18, 2009 Washington State Convention Center Seattle ...

SPERM MOTILITY ACTIVATION IN THE ESTUARINE FISH Fundulus grandis
CONDITIONED IN DIFFERENT SALINITIES
Shaunna N. Harris*, Rafael Cuevas-Uribe and Terrence R. Tiersch
Aquaculture Research Station
Louisiana State University Agricultural Center
Baton Rouge, LA 70820 USA
snharris@agcenter.lsu.edu
Sperm motility in externally fertilizing fishes typically responds
to levels of specific ions and the difference in osmotic pressure
between the surrounding water and the body tissues. Usually,
the sperm of marine fish are activated by an increase in osmotic
pressure (hypertonic salinity), and that of freshwater species by a
decrease (hypotonic). These species exist in relatively stable environments.
Estuarine fish, however, are exposed to wide salinity
ranges, often resulting in external osmotic pressures that include
those of the body (isotonic).
To assess the ability of F. grandis sperm to adapt to changes in
salinity, groups of five adult males were acclimated to salinities
of 0, 5, 10, 20, 35, or 50 ppt for one month. Testes were dissected
from the fish and sperm were activated with various osmolalities
of Hanks’ balanced salt solution (HBSS) and calcium-free HBSS
(Ca-F HBSS). The osmolality eliciting the highest motility was
significantly different (P < 0.01) among acclimated groups (Figure
1). It was also evident that calcium or other ions play a role
in motility which peaked after 30 sec exposure to HBSS, and decreased
over 10 min (Figure 2, top). Motility exhibited a similar
initial pattern when exposed to Ca-F HBSS. However, sperm
gained motility at lower osmolalities over 10 min, exhibiting multiple
peaks (Figure 2, bottom). This may aid in explaining apparent
contradictions in research and be of importance in spawning and
cryopreservation of estuarine fishes.
FIGURE 2. Sperm motility after exposure to HBSS
or Ca-F HBSS. Solid lines indicate motility at 30
sec after exposure, dashed lines at 2 min, and dotted
lines at 10 min. These males were acclimated to 35
ppt.
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FIGURE 1. Osmolality of HBSS (circles) eliciting
highest sperm motility in males acclimated to
various salinities. Points sharing letters were not
significantly different. There was no difference
among blood plasma osmolality (squares) of the
males.