Spontaneous spawning, fecundity and spawning periodicity in the donkey's ear abalone Haliotis asinina Linnaeus 1758
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Spontaneous group spawning was monitored in wild-caught (WC) and hatchery-bred (HB) abalone broodstock (Haliotis asinina) held in duplicate tanks at 1:3 (male: female) ratio from June 1997 to January 1999. Abalone breeders (mean SL, wild = 69-79 mm, HB = 68-71 mm) were kept in perforated plastic baskets and fed red alga, Gracilariopsis bailinae, to excess given at weekly intervals. Abalone spawned spontaneously year-round. Water temperature during the study ranged from 26-29 degree C. A total of 139 and 128 spawning episodes were recorded for WC and HB group respectively. Spawning in WC group (mean: 7 ± 0.8) were more frequent in September (1998) and from February to April. Spawning frequency in the HB group (mean: 6.4 ± 1) was generally high during September (1998) until April. Likewise, egg production was highest during these months. Pooled mean survival from trochophore to veligers stage ranged from 7 to 30% (n=36). Potential fecundity was determined in sacrificed group of HB females (n=21) varied from 6,741-11,902 oocytes g -1 BW. Mean oocyte diameter ranged from 136 to 150 mu m. Bigger females had higher potential fecundity (range: 6.2 to 11 x 105 oocytes individual -1 than smaller females (range: 2.8 to 3.3 x 105 oocytes individual -1). The time interval between successive spawning among animals that spawned more than twice during a 5-month period ranged from 13 to 34 days for the small-size group and from 18 to 37 days for large-size group. In separately stocked HB females (without male), instantaneous fecundity was shown to range between 1,500 and 12,300 eggs g -1 BW (n=16). In contrast to potential fecundity, smaller and younger individuals gave higher 68-71 instantaneous fecundity (range: >3,000 >12,000 oocytes g -1 BW) than the bigger and older individuals (1,500-6,500 oocytes g -1 BW).
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