Protein requirements of juvenile freshwater crayfish Cherax quadricarinatus, with initial mean weight of 1.08 ± 0.34 g, were studied. Juveniles were fed experimental diets containing seven levels of crude protein (CP) (20, 25, 31, 37, 43, 49, and 55%) and 18.73–21.45 kJ g−1 of gross energy.
The highest mean weight and specific growth rate (SGR) (P < 0.05), with values of 9.6 g, and 3.64% day−1, respectively, were achieved by feeding a diet of 31% CP. This diet resulted in a survival rate of 80% over 60 days of culture at 27 °C. The higher protein level tested (55% CP), yielded a significantly (P < 0.05) lower mean weight of 6.4 g. However, there were no significant differences in SGR among the 20, 25, and 49% CP diets. Feed Conversion Ratio (FCR) was close to 1 for all treatments except the lowest (20%) and highest (55%) CP. Optimum protein requirements were estimated by fitting mean weight gain data to a quadratic model (y = 1.142+0.484 − 0.0071x2, r2 = 0.952, P < 0.05). Optimal growth occurred with 34.2% CP, but the results suggest that optimum protein level for 1‐g juvenile C. quadricarinatus is 31% in least‐cost diets. The information obtained will contribute to the formulation of diets that will enhance production of C. quadricarinatus.
A feeding trial was conducted to determine digestive enzyme activity in Cherax quadricarinatus in response to diet composition. Eight experimental diets, each containing one of squid, red crab, sardine (600 and 650 g kg−1 crude protein), sorghum, wheat meal, soy paste and the reference diet were evaluated over 30 days in terms of amylase, lipase, and protease activities in the hepatopancreas. The diet containing wheat meal produced the highest amylase activity. Lipase activity was not significantly different among treatments. Protease activity was higher in animals fed fish meal (60 g kg−1 protein), soy paste and reference diet. Results suggest that C. quadricarinatus can modify hepatopancreatic enzyme levels in response to different compounds in the diet and can digest a broad variety of ingredients, particularly starch.
Organic acids or their salts are promising feed additives for aquatic animals to improve growth performance. We determined the effect of supplementing diets with sodium salts (formate, acetate, lactate, propionate, butyrate, fumarate, succinate and citrate) on trypsin and chymotrypsin activities, in vitro digestibility and zootechnical performance in the whiteleg shrimp (Litopenaeus vannamei). Shrimp trypsin and chymotrypsin activity increased in the presence of acetate and propionate and decreased in the presence of lactate and citrate. The highest in vitro protein digestibility of the experimental diets, using shrimp enzymes, was obtained for diets containing fumarate and succinate, which was significantly greater than the control diet (no supplements). In a growth trial, the highest final weights were in shrimp fed diets supplemented with fumarate, succinate, butyrate and propionate, increasing 53%, 46%, 38% and 29%, respectively, compared to the control. Shrimp that were fed diets with fumarate digested more feed and had a feed conversion ratio 23% higher than the control shrimp. Shrimp survival did not differ among treatments. We concluded that organic salts in the diet modify digestive enzymatic activity and in vitro protein digestibility of whiteleg shrimp. Fumarate, succinate, butyrate and propionate have potential as feed additives for L. vannamei.
Two trials were conducted to determine the e⁄cacy of ¢sh fed live yeast Debaryomyces hansenii strain CBS 8339 on immune and antioxidant systems in leopard grouper Mycteroperca rosacea infected with Aeromonas hydrophila. Juveniles (12 AE 0.5 g) were fed with a control diet or a D. hansenii-supplemented diet (10 6 colony-forming units per gram) for 5 weeks. The live weight of ¢sh was registered on a weekly basis. After 4 weeks, ¢sh from each treatment were immunocompromised with pathogenic A. hydrophila and further fed for1week in order to evaluate the e¡ect on immunological and antioxidant parameters. Generally, the results showed enhanced growth performance in ¢sh fed the diet containing yeast compared with the control. Addition of live yeast had no signi¢cant e¡ect on the immunological parameters after 4 weeks of feeding. However, post infection with A. hydrophila ¢sh fed the yeast-supplemented diet resulted in a sig-ni¢cant increase in the levels of plasmatic immunoglobulin M. Superoxide dismutase and catalase (CAT) activities were signi¢cantly higher in the yeast group. In this ¢sh, CAT and heat shock protein 70 genes were up-regulated before and after infection of A. hydrophila. The present study is the ¢rst one reporting that yeast (D. hansenii) can enhance immunity and resistance against A. hydrophila.
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