Effect of sub-chronic dietary L-selenomethionine exposure on reproductive performance of Red Swamp Crayfish, (Procambarus clarkii).

The effect of selenium (Se) on the reproductive system has been investigated in both humans and vertebrates, but few studies of female fertility and reproduction in invertebrate have been reported. This study is aimed to investigate the effect of SeMet on growth performance and reproductive system after crayfish were fed with graded levels of dietary SeMet (0, 1.49, 3.29, 10.02, 30.27 or 59.8 µg Se/g dry weight) for 60 days. Crayfish treated with the high levels of SeMet (10.02, 30.27 and 59.76 µg Se/g) exhibited decreasing FW and CL in both male and female. Interestingly, Se accumulation was higher in ovary than in other tissues, suggesting that ovary may serve as a target organ for Se accumulation. We found that dietary Se concentration of 10.02 µg Se/g significantly improved the spawning rate, promoted the synchronized spawning, and up-regulated the expressions of mRNA of cdc2 and vitellogenin, with significantly increased E2 and VTG concentrations in hemolymph of female crayfish. However, a marked decrease of the E2 contents and spawning rate was observed in the groups treated with 30.27 and 59.76 µg Se/g diets. In conclusion, the results of this study indicated that the Se had maximum accumulation in ovary, affecting the reproductive capacity by intervening the expression of cdc2 and vitellogenin in the reproductive system. The LOAEL to induce FW was observed in crayfish fed with 10.02 µg Se/g diet, and its value can cause toxicity within the range of natural concentration, so the addition of Se in the feed should be within 10.02 µg Se/g.

Sequence, genomic organization and expression of ghrelin receptor in grass carp, Ctenopharyngodon idellus.

The growth hormone secretagogue-receptor (GHS-R) is an endogenous receptor for the gut hormone ghrelin. Here we report the identification and characterization of GHS-R1a in grass carp, Ctenopharyngodon idellus. The full-length GHS-R1a cDNA contained a 1803-bp coding domain sequence which encoded a peptide of 360 amino acid residues. Comparison analysis revealed that the amino acid sequences of GHS-R1a were highly conserved in vertebrates and shared 97% amino acid identity with zebrafish (Danio rerio), 96% with jian carp (Cyprinus carpio var. Jian) and 93% with goldfish (Carassius auratus). The GHS-R1a showed the highest level of mRNA expression in the pituitary, followed by the brain and liver, and the lowest expression was observed in the hindgut. Intraperitoneally injected with grass carp ghrelin (50, 100 and 150ng/g body weight (BW)), grass carp showed greater mRNA expression of GHS-R1a in the pituitary compared with saline injected at 0.5h postinjection. It was observed that food deprivation could promote the expression of ghrelin and GHS-R1a in the pituitary, demonstrating that nutritional status can influence the expression of both ghrelin and GHS-R1a in the pituitary. After a 2- or 4-week fast, plasma growth hormone (GH) increased, was positively correlated with ghrelin and GHS-R1a mRNA expression levels in the pituitary. These results suggested that the involvement of ghrelin/GHS-R1a systems in mediating the effects of nutritional status and ghrelin on growth processes in grass carp.