Growth variation in bivalves: New insights into growth, physiology and somatic aneuploidy in the carpet shell Ruditapes decussatus

The carpet shell, Ruditapes decussatus is a species with a high commercial importance in Portugal and other Southern European countries. However, high growth rate variability is a major problem in the aquacultural production of this species. The objective of this work was then to study the possible differences between fast-, medium- and slow-growing individuals at three times of sampling, of a same cohort of R. decussatus in terms of eventual numerical chromosomal changes, aneuploidy, but also the level of physiological capacity, by assessing the condition index and the biochemical composition: proteins, total lipids, neutral lipids, phospholipids, carbohydrates, free reducing sugars, polysaccharides and total energy. Hypoploid cells of 2n = 37, 36, 35 or 34 were observed in all groups of individuals. The aneuploidy values observed ranging from 19% to 79%, were substantially higher than those observed in previous studies for other bivalve species. The differences in the observed aneuploidy between fast- and slow-growing clams were highly significant and a negative correlation was also observed between the level of aneuploidy and length. In general, the synthesis of the evaluated biochemical components showed no significant differences among groups suggesting that this synthesis could be related to extrinsic factors or that the analyzed biochemical components were not specific to detect the lack of certain aminoacids and enzymes involved in growth. The only exception was for total lipids, which were significantly lower in the medium and slow growing groups relative to the fast growing group. The evaluation of the relationships between all the studied parameters was performed through a principal component analysis (PCA). The results of this study demonstrate the existence of a negative correlation between somatic aneuploidy and growth in the carpet shell, as previously reported for other bivalve species. Moreover, for the first time in this study, this negative correlation is confirmed over time in a same cohort of the clam R. decussatus.

Research highlights
► Evidence of a negative correlation between aneuploidy and growth in R. decussatus.
► Study for the first time, of the evolution of the aneuploidy level in bivalves.
► New fields for research for a better understanding of aneuploidy in bivalves.
► Evidence that synthesis of biochemical components is related to extrinsic factors.