Improved reproductive
readiness of pond-reared broodstock Penaeus merguiensis by
environmental manipulation
T. Hoang, S.Y. Lee, C.P. Keenan, G.E. Marsden-2003
Aquaculture, 221(1-4):523-534
Abstract:
Two environmental manipulation protocols were tested
against a current maturation technique (CONTROL) in an 81-day experiment.
PROTOCOL 1 mimicked changes in the natural environment from winter to spring
when ovarian maturation and spawning in Penaeus merguiensis starts.
PROTOCOL 2 evaluated whether a clear improvement of temperature from a
fluctuation period to a stable one could help trigger ovarian maturation. In
phase A (first 30 days) of the experiment, temperature and day length were
gradually increased from 22 to 27 °C and from 10 to 14 h, respectively,
while light intensity was stepwise reduced from 360 to 240, 120 and 5 lx for
PROTOCOL 1. For PROTOCOL 2, light intensity and day length were manipulated
as for PROTOCOL 1, but temperature was cycled from 22 to 27 °C every 3
days. In phase B (the following 30 days) temperature, light intensity and
day length were stably maintained at optimal levels (27 °C, 5 lx and 14 h
light, respectively). During phase B, the proportion of female prawns
reaching stages III and IV was significantly (P<0.05) highest in
PROTOCOL 1 and lowest in the CONTROL. Of the total spawns by unablated
females recorded in this phase, 55.6% was in PROTOCOL 1, 33.3% in PROTOCOL 2
and only 11.1% in the CONTROL. Mass spawning was induced by unilateral
eyestalk ablation on day 60. Spawning performance of prawns were monitored
for a further 21-day period (phase C). Overall, PROTOCOL 1, PROTOCOL 2 and
the CONTROL produced 2.36, 1.96 and 1.53 million eggs, respectively. The
latency period of spawners was shortest (P<0.05), whereas the
proportion of spawners, fecundity, spawning rate and egg production/female
were all improved in PROTOCOL 1. An improvement of prawn growth was observed
in PROTOCOL 2. This study suggested that environmental manipulation could
improve ovarian maturation and spawning rate of pond-reared P.
merguiensis.
(School of Environmental and Applied Sciences,
Griffith University, PMB 50 GCMC, Queensland 9726, Australia, e-mail: Tung.Hoang@dpi.qld.gov.au)