Seasonal metabolism and biochemical composition of two unionid mussels, Actinonaias ligamentina and Amblema plicata.

We examined the seasonal patterns of physiology and biochemical composition in two unionid bivalves, Actinonaias ligamentina (subfamily Lampsilinae) and Amblema plicate (subfamily Ambleminae). We found that (i) A. ligamentina and A. plicata displayed different seasonal changes in physiology and biochemical composition, (ii) larval brooding affected the physiology but not the biochemical composition of A. ligamentina, and (iii) A. plicata had a greater carbohydrate content and condition index than A. ligamentina. A. ligamentina and A. plicate had different patterns of ammonia excretion rate, O:N ratio. and clearance rate, while patterns of oxygen uptake rate were similar between the two species. Overall, weight specific metabolic rates were higher in A. ligamentina than in A. plicata. Both species had low protein and high carbohydrate content in early summer. Brooding specimens of A. ligamentina had lower oxygen uptake and ammonia excretion rates and higher O:N ratios than non-brooding specimens. Differences in condition and carbohydrate content between the two species could explain some of the species-specific mortalities observed since the introduction of zebra mussels.