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This study was conducted to evaluate the effect of dietary protein levels on growth performance, muscle composition, digestive enzymes activities, hemolymph biochemical indices and ovary development of pre-adult red swamp crayfish Procambarus clarkii (initial weight = 12.86 ± 0.10 g). Six isoenergetic diets (fish meal, soybean meal, gluten, and shrimp powder as main protein sources) were formulated to contain graded levels of 20.70 %, 24.70 %, 30.56 %, 35.77 %, 41.12 % and 44.64 % crude protein. Each diet was assigned to triplicate groups of 15 experimental crayfish (10 female and 5 male) for 8 weeks. Our results showed that weight gain (WG) increased with dietary protein supplementation from 20.7% to 35.77%, and then decreased with further increases in dietary protein. Broken-line regression analysis based on WG showed that the optimal dietary protein level for maximum growth performance of crayfish was 39.60 %. Feed conversion ratio (FCR) exhibited an opposite trend as observed in WG, with the lowest in crayfish fed the 30.56 % or 35.77 % protein diet. Protein efficiency ratio (PER) in crayfish fed the 41.12 % or 44.64 % protein diet was significantly lower than that in crayfish fed the 20.70–30.56 % protein diet. Hepatosomatic index (HSI) value of crayfish decreased with dietary protein supplementation and achieved minimum values at 35.77 % or 41.12 % protein diet. The highest crude protein content of tail muscle was found in crayfish fed the diet containing 35.77 % or 41.12 % protein. Activities of protease and lipase in both hepatopancreas and intestine were significantly affected by dietary protein levels, while amylase activity showed no significant difference. Dietary protein also significantly induced the contents of hemolymph total protein, albumin, globulin, glucose, total cholesterol and low-density lipoprotein, along with aspartate transaminase and alanine transaminase activities. Moreover, histological analysis revealed that the ovary development of most female crayfish fed the 35.77–41.12 % protein diet were at stage V, which had a higher frequency of mature oocytes than that of females fed other protein diets. Thus, these results provide the theoretical basis for feed formulation to determine the appropriate protein requirement of pre-adult red swamp crayfish.

A 10‐week feeding trial was conducted to investigate the effects of dietary raw starch (RS)/gelatinized starch (GS) ratios on the growth, digestive functions, intestinal histology and the growth hormone‐insulin‐like growth factor‐I (GH‐IGF‐I) axis of Megalobrama amblycephala. Fish were randomly fed five diets containing various RS/GS ratios: 100/0, 75/25, 50/50, 25/75 and 0/100. Fish in the 75/25 group obtained the highest weight gain rate, specific growth rate, protein efficiency ratio and nitrogen retention efficiency compared with other groups, whereas the opposite was true for feed conversion ratio. Intestinal activities of amylase, maltase and sucrase all achieved the highest values in the 75/25 group. The highest lipase and α‐glucosidase activities were found in the 25/75 and 50/50 groups respectively. Activities of protease, alkaline phosphatase and Na+,K+‐ATP decreased with the decreasing of RS/GS ratios. The villi length and crypt depth of the 75/25 group were significantly higher than that of the 100/0 group. Furthermore, the transcriptions of GH increased with the decreasing of RS/GS ratios with the highest observed in the 75/25 group. Overall, our findings indicated that a RS/GS ratio of 75/25 could benefit the growth performance of Megalobrama amblycephala by increasing intestinal digestive and absorptive capabilities as well as promoting GH release. [ABSTRACT FROM AUTHOR]

Abstract: In this study, diets containing 5, 10, 15, and 20% Gracilaria lemaneiformis (GL) (D1–D4 diet) were prepared to investigate the effects of GL on growth performance, carcass composition, activities of digestive enzymes, transaminases activities of black sea bream (Acanthopagrus schlegelii) juvenile. Weight Gain (WG) and Feed Efficiency Ratio (FER) of the fish fed D4 diet were significantly lower than that of control group. Fish fed with the D4 diet showed significantly lower crude lipid of both body and liver and Hepato-Somatic Index (HSI) than those fed with the control diet. Activities of pepsin in the stomach, lipase and amylase in the anterior intestine were significantly suppressed in fish which were fed with the D4 diet (P <0.05). On the other hand, the activities of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were significantly higher in fish which were fed with the D4 diet (P <0.05) than that of the control group. These results indicate that incorporation of the GL in the diet at up to 15% level for juvenile black sea bream is feasible in terms of the growth performance and the physiological state. [Copyright &y& Elsevier]