Dietary Protein And Phosphorus Requirement Of Red Swamp Crayfish, Procambarus Clarkii

The red swamp crayfish, Procambarus clarkii, a prolific species native to south-central USA, has been successfully introduced worldwide for commercial purposes. The dietary requirement of protein and the effects of total phosphorus on growth and physiology of juvenile red swamp crayfish were conducted in indoor tanks for70d. Results of the present study are presented as follows:1. A growth experiment was conducted to investigate dietary protein requirement of red swamp crayfish (initial mean weight:6.49±0.58g, mean±SD). Eight practical diets were formulated containing the same energy but graded levels of protein (26.14%,28.23%,30.02%,31.98%,33.95%,36.08%,37.95%and40.37%) with fishmeal, soybean meal and rapeseed meal as protein source. Each diet was randomly assigned to triplicate groups of30shrimp in indoors tanks (70cm×50cm×45cm). The results showed that the growth was significantly affected by dietary protein (P<0.05). The weight gain (WG) and specific growth rate (SGR) were both significantly increased by dietary protein up to33.95%(P<0.05) and then leveled off beyond this level. The values of feed conversion ratio (FCR) showed decreasing trend with increasing dietary protein level from28.23%to36.08%(P<0.05). There was no significant difference on survival rate (SR) between the groups. The protease, lipase and amylase activities in the hepatopancreas were much more than that in intestine in red swamp crayfish and effected significantly by dietary protein level (P<0.05). The protease and lipase activities increased, while the activity of amylase decreased with the increase in dietary protein levels. Muscle protein content was positively correlated with dietary protein levels, but inversely correlated with muscle lipid content. No significant differences in the muscle ash and moisture content were found among dietary treatments. Regarding WG and SGR as index, the protein requirement of red swamp crayfish was estimated to be33.44%and34.08%, respectively. Based on the results such as the WG, SGR. FCR, muscle composition and digestive enzyme activities, it was reasonable to recommend33.44%-37.95%as the optimum protein level in the diet for sub-Procambarus clarkii.2. A growth trial was conducted to estimate the optimum requirement of dietary total phosphorus for juvenile red swamp crayfish, Procambarus clarkii. Triplicate groups of juvenile freshwater crayfish (initial mean weight:5.02±0.51g, mean±SD) were fed diets containing graded levels (0.83%,1.07%、1.25%、1.38%、1.59%、1.82%and2.03%) of total phosphorus for70d. The results showed that the WG and SGR were both significantly increased by dietary total phosphorus up to1.82%(P<0.05) and then leveled off beyond this level. FCR significantly decreased with dietary total phosphorus level up to1.82%(P<0.05). No significant differences in SR were found among dietary treatments (P>0.05). Body composition analysis showed that the whole-body ash and total phosphorus contents were significantly affected by dietary total phosphorus concentration (P<0.05); Dietary total phosphorus levels also had distinct effects on hepatopancreas alkaline phosphatase activity. Broken-line analysis based on WG and SGR indicated that the total phosphorus requirement for the optimal growth of juvenile freshwater crayfish were1.84%and1.80%, respectively. Based on the results such as the WG, SGR, FCR, whole-body and muscle composition and alkaline phosphatase activity, it was reasonable to recommend1.80%-2.03%as the optimum total phosphorus level in the diet for sub-Procambarus clarki.