Percorrer por autor "Nunes, Telma Vieira"
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- Improvement of European native clams’ cultivationPublication . Nunes, Telma Vieira; Baptista, Teresa Maria CoelhoIn recent years, clam production in Europe has declined due to various factors, including overfishing, abiotic stress, diseases, and recruitment failure. Seed production in hatcheries has become essential to ensure the sustainability of clam production. Artificial breeding conditioning enables hatcheries to extend their production season, reducing dependency on the specific period when wild bank clams naturally mature. In many bivalve molluscs determining sex and reproductive stage non-lethally is challenging. In bivalve aquaculture, monitoring sexual maturation is crucial for determining the optimal time to induce spawning events for seed production. Anaesthesia is commonly used in aquaculture to facilitate tissue biopsies and for gametogenesis studies. The primary goal of this study was to enhance cultivation methods in commercial farming of native European species like Ruditapes decussatus, particularly during critical phases such as conditioning. Initially, the study evaluated the effect of a sandy substrate on R. decussatus broodstock conditioning. Subsequently, an assay was conducted to develop a non-lethal method for assessing gonad development stage and sex during conditioning, as well as for collecting tissue samples for later laboratory analysis. This methodology was also tested on clams of the species Venerupis corrugata. Adult specimens of R. decussatus were kept in an open system with and without sand during conditioning. Regular samplings were conducted to assess gonadal development, evaluating parameters such as condition index, histological analysis, and biochemical composition (glycogen, protein, and lipids). The results indicated that using sand as substrate did not impact gonadal maturity progression. In terms of biochemical composition, there was an observed increase in protein content during the conditioning period. Significant differences in biochemical composition were noted between the two conditions (with sand/without sand) at the end of the conditioning period. For the method of collecting biological samples, individuals of each species, R. decussatus, and V. corrugata, were anesthetized with c magnesium chloride (MgCl2.6H2O) at a concentration of (50g/L). The percentage of anesthetized clams was assessed every hour to determine the effectiveness of the anesthetic. In a subsequent trial, the optimal dosage of the anesthetic for each clam species was determined based on the initial test. Anesthetized clams were also subjected to gonad biopsies for sex determination. The results showed that at a concentration of 50g/L, it took 5 hours for 80% of V. corrugata individuals to become anesthetized. However, in R. decussatus, a mortality rate of 23.33% was observed among individuals undergoing biopsy procedures. Despite this, gonadal tissue collected via biopsy enabled the determination of an individual´s sex through microscopic examination. The results of this study represent a significant advancement in the conditioning of breeding stock in hatchery units. This study provides valuable insights into how the overall condition of individuals before exposure to experimental conditions influences conditioning success. Additionally, it facilitated the development of a non-lethal method for evaluating sex and collecting biological samples in R. decussatus and V. corrugata. These findings lay a solid foundation for future research and practical applications in bivalve aquaculture management and reproductive studies.