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This study deals with investigations on how to control off-season maturation and spawning of the Pacific white shrimp Litopenaeus vannamei by using various maturation techniques. For the experiment, the broodstock were separated into five groups (Group 1: Control, Group 2: Serotonin-injected, Group 3: Ablated, Group 4: Temperature-fluctuated, and Group 5: Another ablated groups). Each of the first four groups were stocked into a 2-m diameter round tank at density of 9.44 shrimps per m 2 (2:1, female/male), while Group 5 were stocked into a 3-m diameter tank at density of 5.67 shrimps per m 2 (1:1, female/male). The experiment continued for 2 months until maturation in a recirculation system. Each female was tagged and any ripe female carrying a spermatophore was removed to spawn individually in a spawning tank. The first spawnings occurred on 25-28 th days of the experiment in all the groups. The highest female spawning rate (55-90%) and fecundity (79,778-125,015 eggs) were obtained in the eyestalk-ablated groups (P<0.05). Serotonin (Group 2) induced ovarium development in 35% of the females, generating 60,277 eggs per female. Cyclic temperature fluctuation (Group 4) stimulated ovarium maturation in 39% of the females with a mean fecundity of 28,500 eggs per female (P<0.05). Mean egg fertility rates ranged from 63.08% to 96%, and hatching rates from 8.53% to 31%. Spawning, fecundity and hatching rates were found to be different between the two eyestalk-ablated groups (Group 3 and 5), and the reasons were thought to be due to tank size and/or shrimp stocking density. Our broodstock displayed poor reproductive performance with abnormal egg morphology and low egg hatching rates. The stress caused by off-season reproduction and low genetic variation due to past selective breeding programs might have seriously hampered the reproductive performance of our broodstock. The results of this study has demonstrated that, under M editerranean climatic conditions, the broodstock of this non-indigenous shrimp species can be readily matured and spawned out of season in recirculating systems.

Off-season Maturation and Spawning of the Pacific White Shrimp Litopenaeus vannamei in Sub-tropical Conditions