Aspects of the physiology of decapod crustaceans with particular reference to the live marketing of Cancer pagurus (L) and Necora puber (L)
The crabs Cancer pagurus (L) and Necora puber (L) are exported live, in bulk, from the UK to various continental countries. The success of this relatively new trade is marred by the incidence of mortalities and impaired quality of the delivered product. These studies addressed various causes - procedural and biological - of these events.Descriptions are given of detailed examinations of handling and other marketing protocols for both species from point of capture to arrival at continental dealer's premises. Such examinations were made with the help of a number of major dealers in the UK, Spain and France and included studies of handling, packing, holding and transportation methods, physical damage assessments before and after consignment, and chemical and biochemical analyses of seawater and blood samples.Dissolved ammonia levels were found to increase greatly in the fixed volume water of vivier tanks and this was found to be matched by correspondingly high blood ammonia values of the contained animals. The measurement of both free ammonia and ionic ammonia efflux rates of juvenile and adult Cpagurus and Npuber in media with high dissolved ammonia levels was investigated and was found to be related to concentration gradients between the internal and external media. The fluxes could be explained on the basis of diffusion down concentration gradients. When animals were transferred to media with higher ammonia levels than those in blood, a cessation of efflux, or even a net influx of ammonia (NH4+) occurred.During emersion, blood ammonia concentration rose. Such accumulated ammonia was very rapidly off loaded when the animals were re-immersed.The data produced has been discussed in the context of crustacean physiology and of improving the expectations of delivering a live, quality product after journeys of several days.