197
7 Aggregation Spawning: Biological Aspects of the Early Life History
could have a negative effect on hatching. While this study and others (Akatsu et al.
1983 ; Watanabe et al. 1995, 1996, 1998 ) , have been conducted in rearing tanks
rather than under natural conditions, they demonstrate that such factors may infl uence survival in the fi eld. Unpredictable weather conditions may result in spawning
under less than optimal conditions and result in failure of a cohort spawned in an
aggregation. Certainly cohort size can vary considerably in aggregating species.
For example, in the leopard coralgrouper, Plectropomus leopardus , a single cohort
was found to dominate in areas closed to fi shing on central the Great Barrier Reef,
Australia (Russ et al. 1996 ) .
First feeding – If physical conditions are acceptable, the critical transition from yolk
feeding to capturing food can occur. Larvae ready to begin feeding lack a caudal
supporting structure and other well-developed fi ns; however they can swim in a
coordinated fashion to orient, approach and strike at potential food items. They are
not capable of swimming well enough for migration purposes, have limited ability
to control their depth and often lack an infl ated swim bladder. It seems likely that
early feeding of aggregation-spawned reef fi sh larvae will be dependent on vision
for feeding and limited to periods of adequate daylight. At fi rst feeding the larvae
capture food items usually by launching themselves at the food item and ingesting
it. Within few days feeding ability develops so they can feed by striking forward
using the pectoral fi ns or an “S” or “C” shaped bend in the body, and engulfi ng prey
with, by now, protrusible jaws.
If the correct type and size of food organisms are present and feeding is initiated
(a “match”) survival may be high, or if the larval state and food available are incorrect (a “mismatch”) the larvae face starvation in a very short time period. This
“match-mismatch” hypothesis (Sinclair 1988 ) has been widely accepted from studies of temperate ichthyoplankton, and is undergoing some revisions to thinking as
more information becomes available (Leis and McCormick 2002 ) . Almost certainly
the limited time between exhaustion of the yolk and starting to feed externally is a
“critical period” but the time limits are poorly known for reef fi sh larvae. The times of
hatching and exhaustion of the yolk after spawning are dependent on temperature;
higher temperatures producing shorter time spans. For larvae of cultured Malabar
grouper, Epinephelus malabaricus , for example, Yoseda et al. ( 2006 ) found the
volume of yolk remaining, representing endogenous energy reserves at time of
opening of the mouth and the onset of feeding, to be higher at 25°C than at 28° and
31°C. By delaying the start of feeding by 6–24 h after mouth opening, they found
only a short period where this delay did not affect survival. Overall the higher
the energy reserves remaining when feeding can begin, the greater the chance of
successfully transitioning to exogenous food. Some results seem contrary, however.
For example, Sugama et al. ( 2004 ) reported highest survival of highfi n grouper,
Cromileptes altivelis (Serranidae), larvae at 28°C (versus 25° and 31°C) although
larvae, fed rotifers (density of 5–10 per litre), held at 31°C ingested more rotifers
and had higher growth rates.
Infl ation of the swim bladder – Most reef fi shes with pelagic eggs, including aggregation species, have swim bladders as juveniles/adults which develop during larval life.
7 Aggregation Spawning: Biological Aspects of the Early Life History
could have a negative effect on hatching. While this study and others (Akatsu et al.
1983 ; Watanabe et al. 1995, 1996, 1998 ) , have been conducted in rearing tanks
rather than under natural conditions, they demonstrate that such factors may infl uence survival in the fi eld. Unpredictable weather conditions may result in spawning
under less than optimal conditions and result in failure of a cohort spawned in an
aggregation. Certainly cohort size can vary considerably in aggregating species.
For example, in the leopard coralgrouper, Plectropomus leopardus , a single cohort
was found to dominate in areas closed to fi shing on central the Great Barrier Reef,
Australia (Russ et al. 1996 ) .
First feeding – If physical conditions are acceptable, the critical transition from yolk
feeding to capturing food can occur. Larvae ready to begin feeding lack a caudal
supporting structure and other well-developed fi ns; however they can swim in a
coordinated fashion to orient, approach and strike at potential food items. They are
not capable of swimming well enough for migration purposes, have limited ability
to control their depth and often lack an infl ated swim bladder. It seems likely that
early feeding of aggregation-spawned reef fi sh larvae will be dependent on vision
for feeding and limited to periods of adequate daylight. At fi rst feeding the larvae
capture food items usually by launching themselves at the food item and ingesting
it. Within few days feeding ability develops so they can feed by striking forward
using the pectoral fi ns or an “S” or “C” shaped bend in the body, and engulfi ng prey
with, by now, protrusible jaws.
If the correct type and size of food organisms are present and feeding is initiated
(a “match”) survival may be high, or if the larval state and food available are incorrect (a “mismatch”) the larvae face starvation in a very short time period. This
“match-mismatch” hypothesis (Sinclair 1988 ) has been widely accepted from studies of temperate ichthyoplankton, and is undergoing some revisions to thinking as
more information becomes available (Leis and McCormick 2002 ) . Almost certainly
the limited time between exhaustion of the yolk and starting to feed externally is a
“critical period” but the time limits are poorly known for reef fi sh larvae. The times of
hatching and exhaustion of the yolk after spawning are dependent on temperature;
higher temperatures producing shorter time spans. For larvae of cultured Malabar
grouper, Epinephelus malabaricus , for example, Yoseda et al. ( 2006 ) found the
volume of yolk remaining, representing endogenous energy reserves at time of
opening of the mouth and the onset of feeding, to be higher at 25°C than at 28° and
31°C. By delaying the start of feeding by 6–24 h after mouth opening, they found
only a short period where this delay did not affect survival. Overall the higher
the energy reserves remaining when feeding can begin, the greater the chance of
successfully transitioning to exogenous food. Some results seem contrary, however.
For example, Sugama et al. ( 2004 ) reported highest survival of highfi n grouper,
Cromileptes altivelis (Serranidae), larvae at 28°C (versus 25° and 31°C) although
larvae, fed rotifers (density of 5–10 per litre), held at 31°C ingested more rotifers
and had higher growth rates.
Infl ation of the swim bladder – Most reef fi shes with pelagic eggs, including aggregation species, have swim bladders as juveniles/adults which develop during larval life.