No abstract

The present study aimed to investigate the effect of dietary astaxanthin (Ast) from Phaffia rhodozyma on growth performance, survival, carotenoid content, the activity of antioxidant and immune-related enzymes, intestinal microbiota comparison, and disease resistance against Vibrio parahaemolyticus in Penaeus monodon. Juveniles (average weight 3.15 ± 0.12 g) were fed with six experimental diets supplemented with 0 (Control), 20.5, 41, 61.5, 82, and 102.5 mg/kg of Ast (defined as diet A–D) in triplicate for 56 days. The results indicated that shrimp fed with Ast supplementation significantly (p < 0.05) improved growth performance compared with the control. Furthermore, significantly (p < 0.05) increased survival and decreased feed conversion ratio (FCR) demonstrated the beneficial effects of dietary Ast on enhancing nutrient utilization and ultimately improving the growth and survival of shrimp. Furthermore, shrimp fed with Ast including diet developed a deeper red color than the control, consistent with the significantly (p < 0.05) increased Ast deposition in the shrimp shell. Hemolymph-immunological parameters [aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (AKP)] and hepatopancreatic antioxidant status [total antioxidant capacity (T-AOC), malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD)] were significantly (p < 0.05) affected by dietary Ast supplementation. Dietary increasing Ast levels significantly (p < 0.05) increased shrimp resistance performance to V. parahaemolyticus according to the LT50 results in the current study, which may be caused by increased total carotenoid contents in shrimp tissues from all the Ast-supplemented treatments. Conversely, intestinal microbiota biodiversity and richness were not affected by dietary Ast. The best performances of growth, antioxidant status, immunological response, and carotenoid deposition were observed in diets E and F among all the Ast-supplemented treatments. Overall, all the data suggested that dietary P. rhodozyma Ast played a critical role in improving growth performance, achieving the desired coloration, increasing carotenoid content, and keeping better health status of shrimp. Based on these positive performances, P. rhodozyma Ast could gain the trust of the consumers as a natural source and provide a potential alternative for synthetic Ast using in the Penaeus monodon culture industry.

To better understand the size differentiation mechanism of adult male prawn Macrobrachium nipponense, transcriptome sequencing was performed from the second pereiopod, hepatopancreas, and muscle of adult male prawn M. nipponense with significant differences in size (large: 1.47 ± 0.12 g; small: 0.28 ± 0.04 g). A total of 46,557 unigenes with an average length of 1,312 bp were obtained. Based on pereiopod of large male (LP) versus pereiopod of small male (SP), muscle of large male (LM) versus muscle of small male (SM), and hepatopancreas of large male (LH) versus hepatopancreas of small male (SH), a total of 805, 473, and 1,037 significantly upregulated DEGs were identified, respectively. The KEGG pathway analysis indicated that pathways such as the PI3K-Akt pathway, the cAMP pathway, the Hippo pathway, and the Ras signaling pathway were enriched in all three comparisons, which may be key size regulators in adult male prawn M. nipponense. Furthermore, as potential candidates for size differentiation in adult male prawns, twenty-eight DEGs involved in these four pathways were screened out, and their expressions were verified by quantitative real-time PCR (qPCR). The results of this study preliminarily elucidate the molecular mechanism of male M. nipponense in size differentiation and provide a theoretical reference for improving the commercial size of cultured male prawn M. nipponense.