Search

Simple Summary: The shortage of fishmeal is currently a pressing issue for the aquaculture industry, as it increases the cost of aquatic product production and contributes to overfishing in the oceans. To solve this problem, Chlorella sorokiniana has started to be used in recent years as a major protein source in aquatic animal diets. However, differences in dietary protein sources will result in different optimal protein requirements. Accordingly, this study determined the growth performance, body composition, intestinal digestion and microbiota of Litopenaeus vannamei fed with five isolipid diets using C. sorokiniana as the main protein source but in different protein levels. The results showed that a dietary protein level of 40.81% resulted in the best weight gain rate when C. sorokiniana was used as the main protein source. Additionally, the optimal nutritional composition, digestibility and intestinal microbiota stability of L. vannamei occurred at a 40% dietary protein level. Higher dietary protein levels increased the colonisation of beneficial bacteria and inhibited the colonisation of pathogenic bacteria. These data inform the scientific application of C. sorokiniana in L. vannamei diets and promote the sustainable development of L. vannamei farming. This study investigated the effect of dietary protein levels on Litopenaeus vannamei. Five isolipid diets with protein levels of 32%, 36%, 40%, 44% and 48% were prepared using C. sorokiniana as the main protein source. L. vannamei (initial body weight 0.83 ± 0.02 g) were fed these five diets for 8 weeks and referred to as the CHL32, CHL36, CHL40, CHL44 and CHL48 groups, respectively. When the feeding trial was finished, the growth performance, body composition, intestinal digestion and microbiota of L. vannamei were studied. The results showed that the maximum weight gain rate (WGR) of L. vannamei was in the CHL40 group while the lowest feed conversion ratio (FCR) was in the CHL48 group. According to the regression analysis using WGR as the evaluation index, the best growth performance of L. vannamei was obtained when the dietary protein level was 40.81%. The crude protein content of whole shrimp showed an increasing and then decreasing trend with increasing dietary protein levels. Furthermore, the L. vannamei muscle amino acid composition was relatively stable and, to some extent, independent of dietary protein levels. Trypsin, lipase and amylase (AMS) activity increased and then decreased with increasing dietary protein levels and, significantly, peaked in the CHL44 group. Analysis of the alpha diversity of the intestinal microbiota showed that the Chao1 index peaked in the CHL40 group and was significantly lower in the CHL48 group. Additionally, the relative abundance of pathogenic bacteria decreased significantly while the relative abundance of beneficial bacteria increased significantly in the intestine of L. vannamei as the dietary protein levels increased. The functional prediction of the intestinal microbiota revealed that dietary protein levels may influence the growth of L. vannamei by regulating various metabolic activities, and the highest WGR in the CHL40 group may have been related to the significant enrichment of nicotinate and nicotinamide metabolism and biotin metabolism functions. In summary, the optimal protein requirement for L. vannamei was around 40% when C. sorokiniana was used as the primary protein source. Too high or too low dietary protein levels could adversely affect shrimp body composition, intestinal digestion and microbiota. [ABSTRACT FROM AUTHOR]

The type of protein source in diets has many effects on shrimp. In this study, Litopenaeus vannamei with an initial body weight of 3.68 ± 0.002 g were fed for 8 weeks on three experimental diets (isoproteic: 41.00%; isolipidic: 7.61%) that were formulated using fish meal (FM), Chlorella sorokiniana (CHL), and Clostridium autoethanogenum protein (CAP) as the primary protein sources, respectively. This study examined the growth, non-specific immunity, intestinal digestion, and microbiota of L. vannamei after the feeding experiment concluded. Compared to the FM group, the findings indicate that the weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) of L. vannamei were notably enhanced via dietary CAP. The CHL group exhibited the highest levels of catalase (CAT), phenoloxidase (PO), and superoxide dismutase (SOD) activities in the gills of L. vannamei, whereas the FM group had the lowest levels. Conversely, the malondialdehyde (MDA) content showed the opposite trend. Both dietary CHL and CAP promoted the digestive enzyme activities of L. vannamei, with dietary CAP having a more pronounced promotional effect. An analysis of alpha diversity indicated that the consumption of dietary CHL substantially enhanced the abundance and diversity of microbiota in the intestinal tract of L. vannamei. Furthermore, the dietary CHL significantly increased the colonization of immune-associated beneficial bacteria and inhibited the colonization of pathogenic bacteria in the intestinal tract of L. vannamei, whereas dietary CAP mainly increased the colonization of growth-associated beneficial bacteria. Functional predictions showed that different dietary protein sources affect various metabolic activities and signaling pathways of L. vannamei, and some functions, including signal transduction, cell motility, and the immune system, were significantly enhanced in the CHL group. In summary, both dietary CHL and dietary CAP promoted growth and immunity in L. vannamei compared to dietary FM. The results of this study could be helpful for the sustainable development of shrimp farming. [ABSTRACT FROM AUTHOR]

As a highly conserved serine/threonine kinase with catalytic and regulatory subunits distributed ubiquitously in eukaryotic organisms, casein kinase 2 (CK2) is involved in multiple cellular functions, including immune regulation. In this study, two variants of the catalytic subunit (designated PvCK2α-1 and PvCK2α-2) and the regulatory subunit homologs (designated PvCK2β-1 and PvCK2β-2) in Penaeus vannamei were cloned and characterised. PvCK2α-1 and PvCK2α-2 shared the same genomic sequence consisting of six exons and five introns and encoded the same protein of 350 amino acids with an S_TKc domain, although there was a sequence deletion in 3′-UTR in PvCK2α-2 when compared with PvCK2α-1. Because of the sequence deletion in the ORF, PvCK2β-1 and PvCK2β-2 encoded different proteins with a CK_II_beta domain. The gene structures of PvCK2β-1 and PvCK2β-2 were identical and consisted of four exons and three introns. Semi-quantitative RT-PCR analyses revealed that PvCK2α and PvCK2β were constitutively expressed in all P. vannamei tissues tested, with higher levels detected in the immune-related tissues including hemocytes, hepatopancreas, gills and intestine. In these four tissue types, all variants of PvCK2α and PvCK2β were induced upon challenge with white spot syndrome virus (WSSV), Vibrio parahaemolyticus and Staphyloccocus aureus. The inhibition of PvCK2α, PvCK2β-1 and PvCK2βComb (the amount of PvCK2β-1 and PvCK2β-2) significantly reduced the survival rates of P. vannamei after WSSV infection and significantly increased the WSSV viral loads. Knockdown of PvCK2 by RNAi could distinctly decrease the expression of NF-κB related genes. All of these results suggest that PvCK2 plays an important role in the innate immune response to pathogen challenges in P. vannamei , with a positive role in anti-WSSV response which may be mediated through regulating the expression of NF-κB drived antimicrobial peptide genes. • Two variants of the catalytic (CK2α) and regulatory subunit (CK2β) in P. vannamei were cloned and characterized. • PvCK2α and PvCK2β were constitutively expressed and induced by pathogens challenge in P. vannamei. • Inhibition of PvCK2α and PvCK2β significantly reduced the survival rates of P. vannamei after WSSV infection. • Knockdown of PvCK2α and PvCK2β significantly increased the WSSV viral loads. • Knockdown of PvCK2α and PvCK2β significantly decreased the expression of NF-κB related genes. [ABSTRACT FROM AUTHOR]

With the increasing price and demand for fishmeal (FM) in aquaculture feeds, Tenebrio molitor (TM), an insect species known as yellow mealworm, is becoming an attractive alternative to FM in the aquaculture industry. This study investigated the effect on growth, enzyme activity, resistance to Vibrio parahaemolyticus , intestinal microbiota, and hemolymph transcriptome in Litopenaeus vannamei (Pacific white shrimp) of replacing up to 45% of FM with TM. L. vannamei (initial weight: 0.42 ± 0.01 g) were fed with diets that replaced FM with TM at 0% (TM0, control), 15% (TM15), 30% (TM30), and 45% (TM45). The results showed that dietary TM30 significantly increased the final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) of L. vannamei (P < 0.05) when compared with TM0. For the enzyme activity of serum, alkaline phosphatase (AKP), catalase (CAT), superoxide dismutase (SOD), phenoloxidase (PO), and lysozyme (LZM) differed significantly in TM45 compared with TM0 (P < 0.05), and malondialdehyde (MDA) decreased. The trypsin in the intestine significantly increased in TM45 compared with TM0 (P < 0.05). In the shrimps challenged with V. parahaemolyticus (1.3 × 107 CFU/mL), survival rates were not significantly different between groups. The alpha diversity indicators were significantly affected by feeding different levels of TM (P < 0.05), and beta diversity analysis showed that the four groups differed significantly (P < 0.05). Based on IndVal values, eight families were distinguished. RNA-seq analysis showed that the most enriched pathway was 'Metabolism of xenobiotics by cytochrome P450'. Some DEGs (differentially expressed genes) of the cytochrome P450 pathway correlated with the abundance of intestine bacteria at the family level. This study provides an insight into the mechanisms associated with molecular and microbiota responses to the effects of substituting TM for FM on L. vannamei , as well as suggests that TM is a potential protein source for farmed L. vannamei , possibly improving its antioxidant capacity, immunity, and resistance to disease via the cytochrome P450 pathway. • Replacement of 30% of dietary fishmeal by T.molitor meal significantly improved L. vannamei growth performance. • Dietary contained T. molitor meal improved non-specific immunity and antioxidant capacity of L. vannamei. • Dietary T. molitor improves L. vannamei growth and immunity, probably associated with Akkermansiaceae and CYP450 pathway. [ABSTRACT FROM AUTHOR]

The effects of cottonseed protein concentrate (CPC) in place of fishmeal on the growth performance, immune response, digestive ability and intestinal microbiota of Litopenaeus vannamei were investigated in this study. L. vannamei (initial body weight: 0.42 ± 0.01g) was fed for 8 weeks by four isonitrogenous and isolipid feeds with CPC replacing fishmeal (FM) at 0% (control), 15% (CPC15), 30% (CPC30) and 45% (CPC45), respectively. At the end of the study, the final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR) and protein efficiency ratio (PER) of L. vannamei in CPC15 and CPC30 groups were significantly increased, while the feed conversion ratio (FCR) of L. vannamei in the CPC30 group was significantly reduced when compared with the FM group (P < 0.05). After Vibrio parahaemolyticus infection, the cumulative mortality of L. vannamei in CPC15 within 24 hpi was significantly lower than that of the control group (P < 0.05). When compared with the control group, the activities and expression of the immunity-related enzymes in the hepatopancreas had almost the same obvious change trend in the CPC-containing groups, which indicated that the replacement for fishmeal by CPC led to significant immune response in L. vannamei. Besides, significant up-regulation of the digestive enzyme activities were observed in the CPC-containing groups. Analysis of intestinal microbiota showed that significant difference in alpha diversity existed between the CPC-containing groups and the control group. The relative abundances of several top 10 dominated species at the phylum and genus levels were significantly changed in the CPC-containing groups compared with the control group (P < 0.05). Functional prediction of the microbiota indicated that the pathway of protein digestion and absorption was significantly more abundant while the pathways of nitrotoluene degradation, aminobenzoate degradation, atrazine degradation, dioxin degradation and xylene degradation were significantly less abundant in the CPC-containing groups than the FM group (P < 0.05). In summary, optimal dietary CPC replacement of FM could improve the growth, immunity, digestive capacity and the diversities of the intestinal microbial flora of L. vannamei. However, parts of the functions of the intestinal microbial flora were decline. • The FM replaced by CPC no higher than 30% significantly improved the growth of Litopenaeus vannamei. • The activities and expression of the immune enzymes were induced in the hepatopancreas. • The activities of digestive enzymes in the intestine could be increased when the FM was replaced by CPC. • Replacing FM with CPC had an important impact on the diversity, profiles, and function of the intestinal microbial flora. [ABSTRACT FROM AUTHOR]

This study explored the use of Chlorella vulgaris (CHL) in Litopenaeus vannamei under varying salinity conditions. Juvenile L. vannamei (initial weight 0.38 ± 0.01 g) were fed experimental diets for 8 weeks at different salinity levels: low (15‰), moderate (30‰), and high (45‰). The control diet contained 589 g/kg fishmeal (FM) as the sole protein source, while experimental diets included 150 g/kg FM and 492 g/kg CHL as protein sources. Results revealed that shrimp fed with CHL showed a robust survival rate even at higher salinities. Following a Vibrio parahaemolyticus infection challenge, shrimp fed with CHL exhibited higher survival rates than those fed with FM at equivalent salinities. Enzyme activity and gene expression analyses indicated that CHL enhanced immune response and digestion in L. vannamei compared to the FM, even under similar salinity conditions. Additionally, shrimp fed with CHL outperformed those fed with FM under varying salinity stress. Microbiota analysis revealed increased diversity and beneficial bacteria in the intestines of shrimp fed with CHL at the same salinity levels. Transcriptomic sequencing identified genes with differential expression (DEGs) related to immune and metabolic pathways. Furthermore, a combined analysis of microbiota and DEGs revealed that CHL also had a beneficial impact on the composition of the intestinal microbiota and controlled the expression of genes related to immune and metabolic pathways. In summary, CHL as a primary protein source improved survival rate, disease resistance, immune response, and digestion in L. vannamei , positively impacting intestinal microbiota and gene expression, and enhancing adaptability to salinity changes. • Dietary CHL boosts L. vannamei immunity, optimizes microbiota, and activates immune/metabolic pathways at the same salinity. • Within the salinity range of 15‰ to 45‰, L. vannamei fed CHL showed greater benefits than FM. • Adding 49.2% of CHL to the feed can serve as a safe and effective alternative protein source in shrimp feed. [ABSTRACT FROM AUTHOR]

The effects of different stocking densities on Litopenaeus vannamei were investigated from the aspects of growth performance, immune response and transcriptome in this experiment. L. vannamei (initial body weight: 0.30 ± 0.02 g) were reared for 8 weeks at three stocking densities of 100 (LSD), 200 (MSD) and 300 (HSD) shrimp/m³, respectively. The results showed that the survival rate (SR), final body weight (FBW), weight gain rate (WGR), specific growth ratio (SGR) and protein efficiency ratio (PER) of L. vannamei significantly decreased, while the feed factor (FCR) significantly increased with the increase of stocking density. After Vibrio parahemolyticus infection, the SR of L. vannamei in the HSD group was significantly lower than that in the LSD and MSD groups. Increasing stocking density significantly increased the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lysozyme (LYS) while significantly decreased the activities of catalase (CAT) and phenol oxidase (PO) in the serum of L. vannamei. Similar changes of the gene expression as the activities of immune enzymes were found in the hemocytes. Pairwise comparison between the LSD, MSD and HSD group in the transcriptome analysis identified that there were 304, 1376 and 2083 differentially expressed genes (DEGs) in LSD vs MSD, MSD vs HSD and LSD vs HSD, respectively. Among them, most of the immune-related DEGs were down-regulated and metabolism-related DEGs were up-regulated with the increasing stocking density. In addition, KEGG enrichment pathway analysis revealed that several immune and metabolic related pathways including PI3K-Akt signaling pathway and AMPK signaling pathway were significantly enriched. Of these, the PI3K-Akt signaling pathway had the most DEGs and was also the most significantly enriched pathway. Furthermore, 16 DEGs (such as FOXO, PCK2 and CTSC, etc.) and partial immune enzyme activity (such as AST, CAT and PO, etc.) changes were closely correlated with the increase of stocking density when partial immune-related DEGs and immune-related enzymes were analyzed jointly. All these results indicated that changes in stocking density had a significant effect on the growth performance, immunity and transcriptome of L. vannamei. • High stocking density significantly reduced the growth performance of Litopenaeus vannamei. • High stocking density reduces survival rate after Vibrio parahaemolyticus infection. • High stocking density stimulates the secretion of metabolic enzymes. • The PI3K-Akt signaling pathway possessed most DEGs and was the most significantly enriched pathway. • 16 DEGs and partial immune enzyme activity changes were closely correlated with the increase of stocking density. [ABSTRACT FROM AUTHOR]

In this study, the effects of dietary lipopolysaccharide (LPS) on Litopenaeus vannamei were investigated to determine whether LPS could play a role as a potential immunostimulant in shrimp. L. vannamei with an initial body weight of 0.30 ± 0.02 g were fed a diet containing LPS at doses of 0, 0.2, 1, 5, 25 or 125 mg kg−1 for eight weeks (groups LPS0, LPS0.2, LPS1, LPS5, LPS25 and LPS125, respectively). After eight weeks of feeding, the growth performance, immunity and transcriptome response of L. vannamei were analysed. Only dietary LPS at 0.2 and 1 mg kg−1 resulted in a significant increase in the growth of L. vannamei (P < 0.05). According to the weight gain rate (WGR) and specific growth rate (SGR), the optimum dietary LPS level was 2.462 and 2.455 mg kg−1, respectively. When compared with the control group, the survival rate (SR) of L. vannamei in the LPS0.2 group was significantly increased after white spot syndrome virus (WSSV) infection and the SR of L. vannamei in the LPS1 group was significantly increased after Vibrio parahaemolyticus infection (both P < 0.05). Compared with the LPS0 group, immune enzyme activity in the serum of L. vannamei could be significantly increased and the content of maleic dialdehyde (MDA) significantly decreased by dietary LPS. Transcriptome analysis of the haemocytes of L. vannamei identified 399 up-regulated differentially expressed genes (DEGs) and 5000 down-regulated DEGs in the LPS0.2 compared to the control group. Most of the DEGs were significantly enriched in the following pathways: phosphatidylinositol signalling, Wnt signalling, Jak-STAT signalling and inositol phosphate metabolism. In conclusion, this study revealed that diets supplemented with low-dose LPS had positive effects on the growth and immunity of L. vannamei. • Dietary low dose LPS had positive effect on the growth of L. vannamei. • Dietary low dose LPS could enhance the ability of L. vannamei to resist WSSV and V. parahaemolyticus infection. • Dietary low dose LPS could significantly affect several immunity and metabolism related signaling pathways in L. vannamei. [ABSTRACT FROM AUTHOR]