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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

Mussel farming is an important economic resource for Canada, producing 26101 tonnes of mussels in 2019 worth more than 43 million Canadian dollars. A major cause of loss of production for mussel farmers originates from the fall-off of mussels during their growth. This phenomenon is particularly important during the reproduction season, as mussels invest most of their energy in the reproduction and have less energy for byssogenesis. This leads to byssal weakening, which can ultimately end with the fall-off of the mussels. Recently, there has been an increasing interest in the development of mussel hatcheries and more specifcally on the production of triploid mussels. Indeed, it is known that triploidy often reduces the fertility of bivalves and can even produce sterile bivalves that have more energy to invest in their growth and other vital tissues (e.g. byssus). In this study, we compared the production and mechanical properties of byssal threads of diploid and triploid mussels in relation to their energy budget and reproductive investment. To determine the effect of triploidy on byssal threads, diploid and triploid mussels were placed in a recirculating fume to induce production of byssal threads, then their scope for growth were estimated. The threads were counted and collected for tensile testing. Results show that triploid mussels produced up to 40% more threads than diploidfmussels, with triploid threads eliciting better mechanical properties. From May to September, during the reproductive season, diploid and triploid mussels were harvested in Georgetown Harbour, Prince Edward Island. Gonadosomatic index (GSI), gonad volume, gonad maturation, and sex ratio were determined for both groups. Results showed that while triploid mussels do invest a part of their energy in reproduction, they had lower GSI and gonad volume than the diploids. Also, for all tested groups, triploid gonads were less mature than those of diploids, and their sex ratio was signifcantly altere