Growth, metabolism and lipid peroxidation in Mytilus edulis: age and size effects

The age dependence of growth, metabolic rate, the degree of lipid peroxidation and antioxidative defence was studied in 3 different size groups of White Sea (Russia) blue mussels Mytilus edulis L.: small (S, wet tissue weight = 0.23 g, length 20–25 mm), medium (M, wet tissue weight = 0.52 g, length 30–35 mm) and large (L, wet tissue weight = 1.05 g, length 40–50 mm). S group mussels were 2–8 yr old, M group mussels 2–9 yr old, and L group mussels 3–10 yr old. Absolute and weight-specific growth rates were determined from the beginning of the growth season (May) to the time of sampling (August). Respiration rates were measured in individuals from all size groups. Net growth efficiency coefficients were calculated. Malondialdehyde (MDA) and fluorescent age pigment (FAP) concentrations were determined as a measure of lipid peroxidation. The level of antioxidant defence was estimated from superoxide dismutase (SOD) and catalase (CAT) activities in whole body homogenates. Metabolic performance was found to be a function of both age and body size. Weight-specific growth rates and net growth efficiencies decreased with age until mussels reached a ‘critical’ age, beyond which growth virtually stopped. Respiration rates were size dependent, but did not show a clear correlation with age. MDA levels remained unrelated to both age and body size, whereas FAP accumulation increased exponentially with age. However, FAP levels correlated negatively with size (growth rate). At constant body size, SOD and CAT activities did not display clear age-related changes; however, CAT activity decreased significantly with increasing body size. As a corollary, size effects potentially mimic age effects on key physiological functions of continuously growing species, and this needs to be considered in physiological studies of the ageing process.