No abstract

The effects of replacing dietary microalgae with artificial diet on pearl production traits and biomineralization‐related gene expression were investigated in pearl oyster (Pinctada fucata martensii). Three experiment groups (EG1, EG2 and EG3) were set. EG1 and EG3 were separately fed Platymonas subcordiformis and artificial diet (D4), respectively, and EG2 was fed with mixed P. subcordiformis and D4. A control group (CG) was cultured in natural sea. All groups were continuously fed for 150 days. The results showed that the survival rates of EG1, EG2 and EG3 were significantly higher than that of CG. No significant differences in retention rate and pearl thickness were observed among the four groups, but CG had the lowest values of both parameters. The relative expression levels of EGFR and FGF18 mRNA did not significantly differ among EG1, EG2 and EG3. Moreover, the relative expression levels of GHITM and TβR I mRNA significantly varied among the groups and EG3, and EG1 had the highest and lowest relative expression levels of GHITM and TβR I mRNA respectively. The relative expression levels of nacrein and chitin‐binding mRNA significantly differed among the groups, and EG1 had the lowest expression levels of nacrein and chitin‐binding mRNA. No significant differences in the relative expression levels of MSI60 and TIMP mRNA were observed among the groups. The results suggested that D4 can replace part of microalgae, which is helpful for further studies on developing artificial diet of pearl oyster.

Pearl oyster Pinctada fucata martensii is widely recognized for biomineralization and has been cultured for high-quality marine pearl production. To ascertain how dietary vitamin D3 (VD3) levels affect the features of pearl production by P. f. martensii and discover the mechanisms regulating this occurrence, five experimental diets with variable levels of VD3 were used with inclusion levels of 0, 500, 1,000, 3,000, and 10,000 IU/kg. The distinct inclusion levels were distributed into five experimental groups (EG1, EG2, EG3, EG4, and EG5). All the experimental groups were reared indoors except the control group (CG) reared at the sea. Pearl oysters, one year and a half old, were used in the grafting operation to culture pearls. During the growing period that lasted 137 days, EG3 had the highest survival rate, retention rate, and high-quality pearl rate. A similar trend was found for EG3 and CG with significantly higher pearl thickness and nacre deposition rates than other groups, but no significant differences were observed between them. A metabolomics profiling using GC–MS and LC–MS of pearl oysters fed with low quantities of dietary VD3 and optimal levels of dietary VD3 revealed 135 statistically differential metabolites (SDMs) (VIP > 1 and p < 0.05). Pathway analysis indicated that SDMs were involved in 32 pathways, such as phenylalanine metabolism, histidine metabolism, glycerophospholipid metabolism, alanine aspartate and glutamate metabolism, arginine and proline metabolism, glycerolipid metabolism, amino sugar and nucleotide sugar metabolism, and tyrosine metabolism. These results provide a theoretical foundation for understanding the impacts of VD3 on pearl production traits in pearl oyster and reinforce forthcoming prospects and application of VD3 in pearl oyster in aquaculture rearing conditions.

Environmental microbiota plays a vital role in the intestinal microbiota of aquatic organisms. However, data concerning the association between the intestinal microbiota of pearl oyster Pinctada fucata martensii and the surrounding seawater are limited. The existing bacterial communities in pearl oyster intestine and surrounding water from two sites (D and H, within Liusha Bay in Guangdong, China) were investigated using 16S rRNA-based sequencing to explore the relationship among the two. D located in the inner bay, and H located in the open sea area outside bay. Results revealed the richness and diversity of pearl oyster intestinal microbiota to be less than those of the surrounding water, with 38 phyla and 272 genera observed as a result of the classifiable sequence. The microbiota compositions in the intestine and the surrounding water were diversified at the phylum and genus levels, with the sequencing data being statistically significant. However, the functional prediction of microbiota emphasized the overall similarity in the functional profile of the surrounding seawater and intestinal microbiomes. This profile was associated with metabolism of cofactors and vitamin, carbohydrates metabolism, amino acids metabolism, metabolism of terpenoids, and polyketides, metabolism of other amino acids, lipids metabolism, and energy metabolism. Seven common operational taxonomic units (OTUs), which belonged to phyla Tenericutes, Cyanobacteria, and Planctomycetes, were noted in the intestines of pearl oysters from two different sites. These OTUs may be affiliates to the core microbiome of pearl oyster. Significantly different bacterial taxa in the intestines of pearl oysters from two different sites were found at the phylum and genus levels. This finding suggested that the bacterial communities in pearl oyster intestines may exhibit some plasticity to adapt to changes in the surrounding water-cultured environment. This study generally offers constructive discoveries associated with pearl oyster intestinal microbiota and provides guidance for sustainable aquaculture.