Long photoperiod delayed spawning and increased
somatic growth in gilthead seabream (Sparus aurata)
G.W. Kissil, I.
Lupatsch, A. Elizur, Y. Zohar-2001
Aquaculture, 200(3-4): 363-379
Abstract:
The
effects of extended photoperiods, mimicking the longest day of the year,
were studied in 1- and 2-year seabream. The photoperiod regimes started in
late July, 36 and 39 days after the summer solstice and continued for 11
months, well beyond the natural reproductive season of December¯March.
Regime 1 (long day, 15.5L:8.5D), which used natural and fluorescent light,
reduced the incidence of maturity in both year classes and females did not
spawn although some gonadal development was observed. Among all 1-year
sampled fish of regime 1, a maximum of 5% became spermiating males (March)
and 5% reached the yolk granule stage of vitellogenesis (VO3; 250¯400
µm diameter) by May. Among 2-year sampled fish of regime 1, 45% became
spermiating males and 25% were females, which reached the advanced
vitellogenesis stage (VO4; 400¯600 µm) by April. Regime 2
(skeleton photoperiod), consisting of natural light and a 1.5-h pulse of
fluorescent light during the period 14¯15.5 h after sunrise,
postponed gonadal development and spawning for up to 3 months. In this
regime, a maximum of 80% of 1-year sampled fish were spermiating males in
February and a maximum of 10% were VO3 stage females in March. In the
sampled 2-year fish, the maximum levels were 50% spermiating males in
February and 25% VO3 stage females in March. Control fish, which were
exposed to the natural photoperiod (29°34'N), spawned during their natural
season. The maximum levels for 1-year sampled control fish were 95%
spermiating males and no females in December, while among 2-year sampled
fish, maxima of 75% males in February and 45% VO4 stage females in November.
Final average weights of photoperiod treated fish (1-year=430 g¯¯regime
1, 400 g¯¯regime 2; 2-year=582 g¯¯regime 1, 518 g¯¯regime
2) were significantly greater (p<0.05) than control fish
(1-year=341 g; 2-year=476 g). Daily feed consumption (g/100 g fish) dropped
from an average of 1.83 to 0.93 g for 1-year fish during August¯December
and from 0.88 to 0.54 g for 2-year fish during the same period. This was
correlated with reduced autumn and winter water temperatures (26¯20°C
summer to winter change) and increased fish weight in all treatments. Daily
feed consumption was also affected by the onset of spawning in the control
and regime 2 (skeleton photoperiod) treatments of both 1- and 2-year fish.
The efficiency of feed utilization (FCR) and protein and energy retention
were all affected by the photoperiod regimes and followed the same pattern
of decrease as weight gain, regime 1 (long day)>regime 2 (skeleton
photoperiod)>control.