Effects of Dietary Protein Levels and Processing Techniques on the Growth Performance, Digestibility, and Antioxidant Capacity of Red Swamp Crayfish (Procambarus clarkii)

Abstract

The red swamp crayfish (Procambarus clarkii) is the largest freshwater shrimp cultured in China. Protein is a critical factor affecting red swamp crayfish growth performance and feed cost. Too high or too low protein levels in feed negatively affect crustaceans. However, the results of the optimal dietary protein content of red swamp crayfish identified in different studies vary considerably. There are mainly two types of feed for red swamp crayfish on the market: extruded and pellet feed. There have been few reports on the impact of processing technique on red swamp crayfish. Many studies have shown that the growth-promoting effects of extruded and pellet feed on diverse aquatic animals differ considerably. Moreover, there have been few studies on the impact of different protein levels and processing techniques on the growth of aquatic species. This study aimed to investigate the effects of dietary protein levels and processing techniques on the growth performance, digestibility, and antioxidant capacity of red swamp crayfish. The two-factor experiment (4×2) with four different protein levels (28%, 30%, 32%, and 36%) and two processing techniques (expanded feed [EF] and pellet feed [PF]) was conducted for 13 weeks as a feeding trial, aiming to provide theoretical support for optimizing the feed formula and processing technique of red swamp crayfish. The results showed that the protein levels and processing technique significantly influenced the weight gain rate (WGR) and hepatosomatic index of red swamp crayfish (P<0.05). The main effects showed that 28% protein could significantly increase the WGR of red swamp crayfish. The WGR and SGR (specific growth rate) of the EF group were significantly higher than those of the PF group (P<0.05). There was an interaction between the protein level and processing technique and the trypsin and amylase activities in the hepatopancreas of the red swamp crayfish (P<0.05). The activities of trypsin and amylase in the hepatopancreas and intestine were highest, with 28% of dietary protein. Trypsin and amylase activities in the hepatopancreas and trypsin activity in the intestine of red swamp crayfish from the EF group were higher than those from the PF group (P<0.05). The impact of dietary protein levels and processing technique on the malondialdehyde (MDA) content and alkaline phosphatase (AKP) activity in the hepatopancreas of the red swamp crayfish was observed (P<0.05). The results revealed that AKP activities in the hepatopancreas, and AKP and acid phosphatase activities in the serum were significantly lower at 28% dietary protein (P<0.05). The MDA content in the hepatopancreas of the PF group was significantly lower than that in the EF group, respectively (P<0.05). The AKP activity in the hepatopancreas of the PF group was significantly lower than that of the EF group (P<0.05). Logistic, Gompertz, von Bertalanffy, and Brody models could be suitable for fitting the growth curves of body weight and body length of red swamp crayfish with a R2 value of no less than 0.97. The Logistic model was the most suitable for fitting the body weight and length, and the power function could reflect the relationship between the body weight and length. Overall, a dietary protein level of 28% and expanded processing could optimize the growth performance and digestibility of red swamp crayfish, and supplementation with a 28% dietary protein level and pellet processing could improve their antioxidative ability.

Keywords

• procambarus clarkii
• protein levels
• processing technique
• growth curve
• digestibility
• antioxidant