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Recently, there is a greater interest for the development of mussel Mytilus edulis hatcheries, particularly for the production and commercialization of triploid bivalves. The aims of this study were to examine the efficiency of inducing triploid mussels by various treatments and to determine the effect of triploidy on larval development. To produce triploids, extrusion of the second polar body of fertilized eggs was inhibited by 6-(dimethylamino)purine (6-DMAP), cold-shock, or heat-shock treatments. Triploidy was detected by flow cytometry for all the treatments. Treatment with 6-DMAP was the most efficient with a rate of triploidy of 90%, followed by heat-shock (56%) and cold-shock (30%) treatments. No survival differences were observed between diploids and 6-DMAP-induced triploid larvae from the D-shape stage up to their settlement. Moreover, increased growth was observed in triploid larvae compared to diploid larvae. Overall, this study showed that 6-DMAP is a highly efficient method to induce triploidy in mussels, with triploid larvae having faster growth compared to diploid. [ABSTRACT FROM AUTHOR]

The production of triploid bivalves has elicited great interest because their reproductive investment is known to be lower than that of diploids. Reduced reproductive investment is expected to improve the survival and growth of triploid bivalves compared to diploids as the energy spared from reproduction could be used for other metabolic needs. However, the reduction of triploid fertility varies among species, therefore, its impacts on survival and growth are variable. In this study, we compared the reproductive investment of diploid and triploid mussels between two age and size groups (1-year-old ˂ 30 mm, and 2-years-old ˃ 50 mm). We measured gonadosomatic index (GSI), gonad volume fraction (GVF), gonad maturation, and sex ratio. Results demonstrated that while triploid mussels do invest part of their energy in reproduction, they had lower GSI and GVF than diploids. In all tested groups, triploid gonads were less mature than those of diploids, and their sex ratio was significantly altered, with the absence of female triploids. Furthermore, triploid gonads showed signs of gamete resorption, suggesting that the gametes of triploid mussels could serve as energy reserves. This study reveals that triploid mussels invest less energy in reproduction which suggests that the spared energy could be used to improve other metabolic need and survival. We conclude that triploid mussels could be of great interest for aquaculture because they may have better resistance to post-spawning weakness and better recovery due to gametes resorption. • Triploid mussels invest less in reproduction than diploids do. • Triploid mussels have reduced gonadosomatic index and gonad volume. • Gametes of triploid mussels do not show full maturation. • Triploid mussels have an altered sex ratio, with the absence of females. [ABSTRACT FROM AUTHOR]

A major problem in mussel farming is mussel fall-off from mussel socks due to weakened byssal threads. This weakening is particularly prevalent following spawning events. During the last decades, significant work has been devoted to the production of triploid bivalves, which have a lower reproductive investment. In this study, we compared the byssal properties and energetic rates of triploid and diploid 1-year-old mussels (˂30-mm). To determine the effect of triploidy on byssal threads, diploid and triploid mussels were placed in a recirculating flume to induce the production of byssal filaments. Our results showed that triploid mussels produced up to 65% more threads than the diploids. Furthermore, tensile measurements showed that byssal threads from triploid mussels had higher Young's modulus values (45% increase) and had multiple yield points. Energetic rates and metabolic investments were measured through food assimilation and oxygen consumption. The results showed that triploid mussels had a higher clearance rate (40% increase) and scope for growth (260% increase) when compared to diploids. Morphological comparisons showed variations between the two groups, with triploid mussels having a larger shell height than diploids of the same length. • Triploid mussels produce more byssal threads than diploids. • Byssal threads from triploid mussels have a higher Young's modulus than diploids. • Byssal threads from triploid mussels have more yield points than diploids • Triploid mussels have a higher scope for growth than diploids • Triploid shells have a larger shell height than diploids of the same length [ABSTRACT FROM AUTHOR]