A growth experiment was conducted to determine the optimal dietary carbohydrate-to-lipid (CHO : L) ratio for the Australian redclaw crayfish, Cherax quadricarinatus (von Martens). Specimens were divided into five treatment groups and fed twice a day to apparent satiation with isonitrogenous and isoenergetic diets with dietary CHO : L ratios of 10.75:1, 5.99:1, 3.60:1, 2.18:1, or 1.33:1. Over the 8-wk growth trial, redclaw crayfish fed the 2.81:1 and 3.60:1 diets exhibited better weight gain (WG), specific growth rate (SGR), and feed conversion ratio (FCR) than specimens fed the other diets (P < 0.05). Activities of hexokinase and pyruvate kinase were stimulated by elevated levels of dietary carbohydrate, whereas activities of lipase and alkaline phosphatase were stimulated by elevated levels of dietary lipid. Dietary CHO : L ratios significantly affected digestive enzyme activities (P < 0.05), except for trypsin (P > 0.05). On the basis of the analysis of growth, FCR, and costs of culturing redclaw crayfish, the optimal growth and costs occurred when the dietary carbohydrate and lipid levels were 290.10 g/kg and 80.70 g/kg, respectively, corresponding to a CHO : L ratio of 3.60:1. These results indicate that a CHO : L ratio of 3.60:1 is optimal for rearing redclaw crayfish and that this species uses carbohydrate more efficiently than lipid.

Heat shock proteins (HSPs) are molecular chaperones and have an important role in the refolding and degradation of misfolded proteins, and these functions are related to aging. Rotifer is a useful model organism in aging research, owing to small body size (0.1-1 mm), short lifespan (6-14 days), and senescence phenotypes that can be measured relatively easily. Therefore, we used rotifer as a model to determine the role of four typical hsp genes on the aging process in order to provide a better understanding of rotifer aging. We cloned cDNA encoding hsp genes (hsp40, hsp60, hsp70, and hsp90) from the rotifer Brachionus calyciflorus Pallas, analyzed their molecular characteristics, determined its modulatory response under different temperatures and H 2 O 2 concentrations and investigated the changes in expression of these genes during the aging process. We found that Bchsp70 mRNA expression significantly decreased with aging. In addition, we also studied the effects of dietary restriction (DR) and vitamin E on rotifer lifespan and reproduction and analyzed the changes in expression of these four Bchsp genes in rotifers treated with DR and vitamin E. The results showed that DR extended the lifespan of rotifers and reduced their fecundity, whereas vitamin E had no significant effect on rotifer lifespan or reproduction. Real-time PCR indicated that DR increased the expression of these four Bchsps. However, vitamin E only improved the expression of Bchsp60, and reduced the expression of Bchsp40, Bchsp70, and Bchsp90. DR pretreatment also increased rotifer survival rate under paraquat-induced oxidative stress. These results indicated that hsp genes had an important role in the anti-aging process.

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Rotifers are useful model organisms for aging research, owing to their small body size (0.1–1 mm), short lifespan (6–14 days) and the relative easy in which aging and senescence phenotypes can be measured. Recent studies have shown that antioxidants can extend the lifespan of rotifers. In this paper, we analyzed changes in the mRNA expression level of genes encoding the antioxidants manganese superoxide dismutase (MnSOD), copper and zinc SOD (CuZnSOD) and catalase (CAT) during rotifer aging to clarify the function of these enzymes in this process. We also investigated the effects of common life-prolonging methods [dietary restriction (DR) and resveratrol] on the mRNA expression level of these genes. The results showed that the mRNA expression level of MnSOD decreased with aging, whereas that of CuZnSOD increased. The mRNA expression of CAT did not change significantly. This suggests that the ability to eliminate reactive oxygen species (ROS) in the mitochondria reduces with aging, thus aggravating the damaging effect of ROS on the mitochondria. DR significantly increased the mRNA expression level of MnSOD, CuZnSOD and CAT, which might explain why DR is able to extend rotifer lifespan. Although resveratrol also increased the mRNA expression level of MnSOD, it had significant inhibitory effects on the mRNA expression of CuZnSOD and CAT. In short, mRNA expression levels of CAT, MnSOD and CuZnSOD are likely to reflect the ability of mitochondria to eliminate ROS and delay the aging process.

Superoxide dismutase (SOD) is an important antioxidant enzyme that protects organs from damage by reactive oxygen species. We cloned cDNA encoding SOD activated with manganese (Mn-SOD) from the rotifer Brachionus calyciflorus Pallas. The full-length cDNA of Mn-SOD was 1,016 bp and had a 669 bp open reading frame encoding 222 amino acids. The deduced amino acid sequence of B. calyciflorus Mn-SOD showed 89.1, 71.3, and 62.1 % similarity with the Mn-SOD of the marine rotifer Brachionus plicatilis, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster, respectively. The phylogenetic tree constructed based on the amino acid sequences of Mn-SODs from B. calyciflorus and other organisms revealed that this rotifer is closely related to nematodes. Analysis of the mRNA expression of Mn-SOD under different conditions revealed that expression was enhanced 5.6-fold (p < 0.001) at 30 °C after 2 h, however, low temperature (15 °C) promoted Mn SOD temporarily (2.5-fold, p < 0.001) and then decreased to normal level (p > 0.05). Moderate starvation promoted Mn-SOD mRNA expression (p 12 < 0.01, p 36 < 0.05), which reached a maximum value (15.3 times higher than control, p 24 < 0.01) at 24 h. SOD and CAT activities also elevated at the 12 h-starved group. These results indicate that induction of Mn-SOD expression by stressors likely plays an important role in aging of B. calyciflorus.