Effect of reproduction on escape responses and muscle metabolic capacities in the scallop Chlamys islandica Müller 1776.

In scallops, gametogenesis leads to mobilization of glycogen and proteins from the adductor muscle towards the gonad. This mobilization is likely to diminish the metabolic capacities of the adductor muscle and thereby the scallops' escape response. We examined the escape response in terms of number of valve claps until exhaustion, rate of clapping and the recovery during and after valve closure in adult scallops, Chlamys islandica, sampled at different stages in the reproductive cycle (immature, mature, before and after spawning). In parallel, we measured muscle glycogen, protein and phosphoarginine contents, the oxidative capacity of mitochondria isolated from the adductor muscle and levels of muscle enzymes which are active during exercise and recovery. The number of claps (24-26), rate of clapping ( approximately 13 clapsmin(-1)) and phosphoarginine and arginine kinase levels were similar during the different reproductive stages. All immature scallops responded to restimulation immediately after opening their valves, while only 62% of mature, 82% of prespawned and 38% of spawned scallops responded. Immature animals completely recovered their initial swimming capacity within 4 h of opening their valves, but mature, prespawned and spawned scallops needed 18, 12 and 18 h, respectively. Overall phasic adductor muscle from mature, prespawned and spawned animals showed decreased glycogen phosphorylase, phosphofructokinase, pyruvate kinase (except for prespawned), octopine dehydrogenase and citrate synthase levels, a deterioration of the oxidative capacity of mitochondria and a marked decrease in glycogen content compared to immature scallops. Therefore, during gonadal maturation and spawning, C. islandica did not change its clapping capacity, but slowed its recuperation from exhausting burst exercise, both during and after valve closure, likely due to the decreased metabolic capacity of the adductor muscle.