Is it possible to keep the exoskeleton of the crab Callinectes ornatus soft for several days?

Abstract

Soft-shell crab is considered a gastronomic delicacy, reaching high values in the international market. The process of hardening of the crabs exoskeleton after moulting takes approximately two days to complete; however, the duration for which the shell remains at the consistency of high commercial value is only 3 hours on average. After this period, the shell assumes a consistency classified as \"paper\", later becoming \"hard\" again. The goal of this work was to evaluate the use of the crabs themselves to alter the chemical characteristics of the water and thereby increase the amount of time during which they can be marketed as \"soft-shell crab\". In this work, 241 individuals of Callinectes ornatus were used in two experiments. In the first experiment, the animals were maintained in a collective system with filtration and partial daily water renewal. In the second experiment, the crabs were maintained in a collective system with filtration but no water renewal. In Experiment 1, the chemical characteristics of the water remained unchanged over time (p > 0.05), and the median time to hardening of the exoskeleton to the paper consistency after moulting was 3 hours. Over the course of Experiment 2, there was a significant reduction (p < 0.05) in pH and significant increases in the ammonia and nitrite concentrations. When moulting occurred in water with a pH below 7.3 and total ammonia concentrations above 6.0 mg/L, the crabs shells did not harden, and it was possible to keep them soft for up to 5 days.