202
P.L. Colin
behind the fi rst group, their gamete release may not be in precisely in the same
location, but close enough to the already present gametes that this usually serves to
expand the overall size of the gamete cloud for a single spawning event. In some
larger species, such as Nassau grouper (Fig. 7.3 ) and cubera snapper, there can be a
succession of several gamete releases as fi sh rush in to join an initial group and start
spiralling upward towards the surface, not breaking off quickly after the initial
release (Heyman et al. 2005 ) . In mass spawning, the entire mass of fi sh ascend,
often slowly, then at the peak start swirling and releasing gametes, continuing for
many seconds (Fig. 7.2b ), and is seen in the spawning of yellow and blueback
fusilier, Caesio teres (Bell and Colin 1986 ) .
There can be variations on this general sequence. In one instance a groupspawn by Nassau groupers was followed just a few seconds later by a single pair
(apparently male and female as only one fi sh was spewing sperm) which arched
through where the group had already released and continued in an upward trajectory
(Fig. 7.3 ). While unusual (it was the only such spawning I observed, photographed
or recorded on video) it does indicate that more than one female might participate
in a given spawning rush. For some large transient aggregators, when there are a
series of individuals spawning near simultaneous bursts over the area of the
aggregation, the individual spawns appear to merge to form a single large massive
gamete cloud.
It is usually diffi cult to see the gametes when released. Eggs are nearly transparent,
and only when copious are the sperm visible. For most pair and small group-spawning fi shes, the gametes appear as a faint burst of particles in the water at the apex of
a spawning rush which quickly diffuses and disappears (Fig. 7.2a , Colin 2010 ) .
Males of some of the larger transient aggregating species have large testes and their
sperm can be seen as milky clouds in the water for a few minutes presumably because
they release so much sperm at one time (Fig. 7.3 ).
Fig. 7.3 The Nassau grouper, Epinephelus striatus , produces a highly visible gamete cloud when
spawning, largely due to massive amounts of sperm being released. ( a ) A mix of males and females
follow a single leading female prior to release. ( b ) The fi sh come together, release gametes in a
limited volume of water, and then radiate outward. ( c ) In this case, a pair of Nassau grouper swam
through the area of the gamete burst, continued upward and released gametes above the initial
cloud. The male was streaming sperm, leaving a visible track of its path upward prior to spawning.
( d ) A few seconds after spawning the fi sh have all moved outward from the site of gamete release
and the cloud is gradually starting to become less visible as it dissipates (Photos: Lori J. Colin)
P.L. Colin
behind the fi rst group, their gamete release may not be in precisely in the same
location, but close enough to the already present gametes that this usually serves to
expand the overall size of the gamete cloud for a single spawning event. In some
larger species, such as Nassau grouper (Fig. 7.3 ) and cubera snapper, there can be a
succession of several gamete releases as fi sh rush in to join an initial group and start
spiralling upward towards the surface, not breaking off quickly after the initial
release (Heyman et al. 2005 ) . In mass spawning, the entire mass of fi sh ascend,
often slowly, then at the peak start swirling and releasing gametes, continuing for
many seconds (Fig. 7.2b ), and is seen in the spawning of yellow and blueback
fusilier, Caesio teres (Bell and Colin 1986 ) .
There can be variations on this general sequence. In one instance a groupspawn by Nassau groupers was followed just a few seconds later by a single pair
(apparently male and female as only one fi sh was spewing sperm) which arched
through where the group had already released and continued in an upward trajectory
(Fig. 7.3 ). While unusual (it was the only such spawning I observed, photographed
or recorded on video) it does indicate that more than one female might participate
in a given spawning rush. For some large transient aggregators, when there are a
series of individuals spawning near simultaneous bursts over the area of the
aggregation, the individual spawns appear to merge to form a single large massive
gamete cloud.
It is usually diffi cult to see the gametes when released. Eggs are nearly transparent,
and only when copious are the sperm visible. For most pair and small group-spawning fi shes, the gametes appear as a faint burst of particles in the water at the apex of
a spawning rush which quickly diffuses and disappears (Fig. 7.2a , Colin 2010 ) .
Males of some of the larger transient aggregating species have large testes and their
sperm can be seen as milky clouds in the water for a few minutes presumably because
they release so much sperm at one time (Fig. 7.3 ).
Fig. 7.3 The Nassau grouper, Epinephelus striatus , produces a highly visible gamete cloud when
spawning, largely due to massive amounts of sperm being released. ( a ) A mix of males and females
follow a single leading female prior to release. ( b ) The fi sh come together, release gametes in a
limited volume of water, and then radiate outward. ( c ) In this case, a pair of Nassau grouper swam
through the area of the gamete burst, continued upward and released gametes above the initial
cloud. The male was streaming sperm, leaving a visible track of its path upward prior to spawning.
( d ) A few seconds after spawning the fi sh have all moved outward from the site of gamete release
and the cloud is gradually starting to become less visible as it dissipates (Photos: Lori J. Colin)