Establishment of environmental and biological bases to optimise the production of the European clam Ruditapes decussatus (Linnaeus, 1758)

Dissertação para obtenção do Grau de Doutor em AmbienteIn Portugal, aquaculture is greatly supported by the production of Ruditapes decussatus that represents 80 % of the total shellfish production. However, the culture of R. decussatus is clearly limited by the availability of seed, which proceeds exclusively from natural recruitment. In the last few years, the production of this species has clearly decreased due to recruitment failures and to severe mortalities. The development of hatchery technology that will provide an alternative reliable source of clam spat, will allow to overcome this constrain. Production of R. decussatus seed in hatcheries is however a relatively new industry for which most methods have been developed using empirical approaches. Due to the scarcity of information on this species production, the main objective of the present work was the evaluation of the biological and ecological processes involved in the different culture phases (broodstock conditioning, larval culture and on-growing). Concerning broodstock conditioning, the reproductive cycle of the two main Portuguese populations of R. decussatus, as well as its nutrient storage and exploitation strategy were characterized. Moreover, the best broodstock origin and timing of collection were determined, as well as the most adequate conditioning temperature and food to achieve maturation, spawning success and larval viability, limiting factors for the reproduction of this species. In order to optimize the larval management, important information on the energetic utilization during oogenesis and metamorphosis was obtained, contributing to the design of the most suitable diet for the larval phase. Concerning the on-growing phase, the response of R. decussatus to local and seasonal environmental factors was evaluated, aiming to define ecological and production management strategies. Finally, the overall information gathered in the present study allowed the development of a successful R. decussatus production program