Effect of reproduction on escape responses and muscle metabolic capacitiesin the scallop Chlamys islandica Muller 1776

In scallops, gametogenesis leads to mobilization of glycogen and proteins f rom the adductor muscle towards the gonad. This mobilization is likely to d iminish the metabolic capacities of the adductor muscle and thereby the sca llops' escape response. We examined the escape response in terms of number of valve claps until exhaustion, rate of clapping and the recovery during a nd after valve closure in adult scallops, Chlamys islandica, sampled at dif ferent stages in the reproductive cycle (immature, mature, before and after spawning). In parallel, we measured muscle glycogen, protein and phosphoar ginine contents, the oxidative capacity of mitochondria isolated from the a dductor muscle and levels of muscle enzymes which are active during exercis e and recovery. The number of claps (24-26), rate of clapping (similar to 1 3 claps min(-1)) and phosphoarginine and arginine kinase levels were simila r 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 Is , 12 and 18 h, respectively. Overall phasic adductor muscle from mature, pr espawned and spawned animals showed decreased glycogen phosphorylase, phosp hofructokinase, pyruvate kinase (except for prespawned), octopine dehydroge nase and citrate synthase levels, a deterioration of the oxidative capacity of mitochondria and a marked decrease in glycogen content compared to imma ture scallops. Therefore, during gonadal maturation and spawning, C. island ica did not change its clapping capacity, bur slowed its recuperation from exhausting burst exercise, both during and after valve closure, likely due to the decreased metabolic capacity of the adductor muscle. (C) 2000 Elsevi er Science B.V. All rights reserved.