Assessment of depuration system and duration on gut evacuation rate and mortality of red swamp crawfish

Abstract

Two depuration, or purging, systems were examined for their effect on survival and evacuation rate of intestinal contents of the hindgut of crawfish ( Procambarus clarkii). In the immersion system, crawfish were held in baskets suspended in the water column and subjected to profuse aeration and low water exchange. Crawfish in the water spray system were maintained in shallow pools (1.3-cm deep water) and in a constant mist environment. Loading rate for each system was 14.5 kg crawfish/m 2 surface area. Similar mortality was observed from the two systems and averaged 9% and 12% for 24 and 48 h of purging, respectively. Cannibalism occurred in both purge systems; however, the mean net hindgut evacuation rate for crawfish was similar for the two systems and averaged 57%, 63%, 78%, and 81% for 12-, 24-, 36-, and 48-h purge durations, respectively. Evacuation efficiency after 12 and 24 h was positively correlated with water temperature. Of the total amount of intestinal contents excreted during 48 h of purging, 70%, on average, was excreted within the first 12 h. Mortality increases as purge duration increases; therefore, the shortest and most practical duration that results in a product acceptable by the consumer will be the most cost effective. A 12-h (or overnight) duration in well-managed systems may be sufficient for most markets in Louisiana.