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A 10-week experiment was conducted to evaluate the effects of dietary lysine levels on growth performance, lipid metabolism, anti-oxidant capacity, mitochondrial biogenesis and immune response of grass carp, Ctenopharyngodon idella. Fish (mean initial weight 51.01 ± 0.17 g) were fed seven diets containing graded levels of lysine (1.69 %, 1.79 %, 1.91 %, 2.01 %, 2.11 %, 2.24 % and 2.31 %). Results showed that fish fed the control diet (1.69 %) showed lower weight gain (WG) and higher feed conversion rate FCR than those fed 2.01–2.31 % lysine (P < 0.05). Viscerosomatic index decreased when dietary lysine increasing from 1.69 % to 2.11 % (P < 0.05). Suitable dietary lysine levels enhanced the lipolysis and mitochondrial biogenesis of grass carp. Total antioxidant capacity (T-AOC) in the liver was higher in fish fed 2.24 % dietary lysine than those fed diets containing 1.69 % and 1.79 % lysine (P < 0.05). The malonaldehyde (MDA) contents in liver decreased when dietary lysine increased from 1.69 % to 2.01 % (P < 0.05). Relative mRNA levels of glutathione peroxidase and catalase in liver and intestine were affected by dietary lysine levels (P < 0.05). B-cell lymphoma 2 (Bcl-2) mRNA level in liver was up-regulated and inhibitor kappa B kinase β (IKKβ) mRNA level in the intestine was down-regulated by increasing dietary lysine levels (P < 0.05). Second-order regression based on WG indicated the suitable level of lysine in feed of grass carp was 2.24 % (6.19 % protein). • Dietary deficiency of lysine would impair the growth performance and feed utilization of grass carp. • The protein synthesis, lipolysis and mitochondrial biogenesis of grass carp might be enhanced by lysine. • Immune response and anti-oxidant defense system of grass carp might be affected by dietary fish lysine levels. [ABSTRACT FROM AUTHOR]

Dietary fish meal (FM) and fish oil (FO) replacement are crucial for the sustainable development of aquaculture. An eight weeks feeding trial was conducted to evaluate the potential replacing FM with soy protein concentrate, and the suitable FO level for a low FM diet of Penaeus monodon. A diet containing 25% FM was used as the control (C diet), and three other diets were formulated to contain 15% FM, and supplemented with 3%, 2%, 1% FO [high FO (HF), medium FO (MF) and low FO (LF), respectively]. The experiment was conducted in quadruplicates (30 shrimp per replicate, average weight 1.00 ± 0.01 g). The results indicated that besides the final body weight, there were no differences in weight gain, feed efficiency and survival rate observed among the four groups. The results of the acute salinity stress showed that shrimp fed the C and MF diets showed a similar survival rate, which was significantly higher than those fed a LF diet. Shrimp that were fed HF, MF and LF diets showed a lower level of fatty acid transport-related mRNA expression in the hepatopancreas, compared with those fed the C diet. Shrimp fed HF, MF and LF diets showed lower expression levels of superoxide dismutase, endoplasmic reticulum protein 57 and immune deficiency (IMD) in the hepatopancreas than those fed the C diet. Shrimp that were fed a LF diet showed the lowest expression levels of inhibitor of apoptosis proteins, Toll and tumor necrosis factor receptor associated factor 6 (TRAF6) in the hepatopancreas, as well as the highest expression levels of Toll, extracellular signal-regulated kinase, Relish and TRAF6 in the intestine among four groups. Intestinal microstructure damage was observed in shrimp that were fed a LF diet, and intestinal endoplasmic reticulum (ER) swelling was observed in shrimp fed MF and LF diets. In conclusion, these results indicated that the growth performance of shrimp was not affected when the FM and FO contents decreased, whereas a low content of FM negatively influenced the immune response in shrimp by modulating IMD and ER stress related gene expression. Under low FM conditions, a suitable dietary FO level would benefit to the lipid transport, hepatopancreas and intestine health, as well as the immune response of shrimp. • Reduce the dietary FM level from 25% to 15% had no negative effect on growth performance of P. monodon. • Low dietary fish oil reduced the acute salinity stress resistance of P. monodon fed low FM diet. • Low dietary fish oil impaired the immune response of shrimp through the IMD and Toll signaling pathways. [ABSTRACT FROM AUTHOR]

• Based on survival, the optimal dietary protein level for post larval white shrimp was 49.58 %. • Shrimp fed the optimal dietary protein obtained the highest expression of TOR gene. • Shrimp fed the optimal dietary protein obtained the highest expression of two important initiation factors: eIF4E and eIF3k. A 25-days experiment was conducted to evaluate the effect of dietary protein levels on growth, survival, digestive enzymes and protein synthesis of post-larval Litopenaeus vannamei. Post-larval white shrimp (mean initial weight 2.1 mg) were fed five isoenergic diets containing gradient levels of protein (456, 469.9, 484.6, 501.4, 512.9 g/kg). Results indicated that 501.4 g/kg dietary protein increased the survival of post-larval white shrimp. Special growth rate (SGR) and weight gain (WG) showed no difference among each group. Whole body protein contents increased with the dietary protein increased to 484.6 g/kg. The relative mRNA levels of trypsin and chymotrypsin also increased with the dietary protein increased to 484.6 g/kg. Target of Rapamycin (TOR) and eukaryotic translation initiation factor 4E-binding protein (4EBP) mRNA expressions were significantly higher in shrimp fed the 484.6 g/kg dietary protein than other groups. The mRNA expression of two important translation initiation factors eukaryotic translation initiation factor 4E (eIF4E) and eukaryotic translation initiation factor 3k (eIF3k) were increased with the increasing dietary protein levels. Three endoplasmic reticulum (ER) stress related genes (eIF2α, XBP1 and ATF4) expression also increased with the dietary protein increased to 484.6 g/kg. These results clearly indicated that proper dietary protein improved the survival, and enhanced the protein synthesis of post larval white shrimp. Quadratic regression analysis based on survival indicated that the optimal dietary protein level of post-larval white shrimp was 495.8 g/kg. [ABSTRACT FROM AUTHOR]

Plant protein sources are the main alternative to fish meal (FM), but excessive substitution can induce inflammatory responses and oxidative stress in aquatic animals. In this study, the antioxidant capacity, endoplasmic reticulum stress (ERS), apoptosis and intestinal health of Litopenaeus vannamei at the different stages of feeding trial were evaluated after replacing FM with soy protein concentrate (SPC). Two diets were designed: HF diet (25% FM) and LF diet (15% FM + 10% soy protein concentrate), respectively. The samples were collected at 7d, 14d, 28d, 42d, 56d of the feeding trial. The results showed that the antioxidant capacity of the hepatopancreas of shrimp fed the LF diet gradually decreased after 28d. The glutathione peroxidase (GSH-PX) activity, superoxide dismutase (T-SOD) activity and total antioxidant capacity (T-AOC) showed a decreasing trend with the went on of the feeding trial and were lower than those of shrimp fed a HF diet. The length of microvilli and height of mucosal folds in shrimp fed the LF diet were significantly lower than those fed the HF diet after 42d (P <0.05), and the endoplasmic reticulum and mitochondria were swollen, and the mitochondrial matrix showed irregular structure and even almost complete dissolution at 56d. The expression of hepatopancreatic endoplasmic reticulum stress (ERS)-related genes was highest at 14d, and the hepatopancreatic endoplasmic reticulum-related genes were overall higher in shrimp fed the LF diet than those fed the HF diet after 28d. The expression of apoptosis-associated genes in hepatopancreatic cells showed an overall decreasing trend. However, the relative expression of intestinal ERS and apoptosis related gene was in the opposite trend. ERS was enhanced and apoptosis was inhibited in shrimp since 7d of the feeding trial when the dietary FM level was reduced. In conclusion, the antioxidant capacity and immune response of shrimp would be reduced as the feeding trial went on, ERS and apoptosis in the intestine of shrimp fed a LF diet would be earlier to be induced compared to those fed the HF diet. • Soy protein concentrate reduces the antioxidant capacity of shrimp hepatopancreas. • Soy protein concentrate causes stress in the intestinal endoplasmic reticulum. • Soy protein concentrate causes apoptosis of intestinal cells. [ABSTRACT FROM AUTHOR]

Feed intake is a crucial factor in promoting aquatic animals' robust and accelerated growth. Recently, plant protein has been used extensively as a replacement for fishmeal in aquaculture diets, potentially causing adverse effects on both feed palatability and animal health. However, incorporating suitable quantities of feed attractants into the diet can enhance feed palatability, stimulate the appetite of aquatic animals, and potentially augment both growth and overall health. A study was conducted to assess the efficacy of various feeding attractant combinations on Penaeus monodon. In this study, these seven diets were formulated consisting of a positive control (labeled as P) based on commercial feed, a negative control (labeled as N) with a low level of feed attractants, and five diets (labeled as A, B, C, D, and E) containing 8% compositional feed attractants. Each of the five attractants (yeast extract, squid visceral powder, fish soluble, squid paste, and shrimp paste) was added in equal amounts to A-E diets. The results showed that compared to the E diet, the A diet significantly improved the final body weight, specific growth rate, weight gain, and feed intake of shrimp and upregulated the expression of pi3k , eif4ela , and raptor in hepatopancreas. Compared to the P diet, the C diet feed significantly increased the activities of glutamate oxaloacetate transaminase and acid phosphatase and upregulated the expression of pi3k , myd88 , and tor in the intestine. In comparison to the N diet, the D diet feed increased the activity of alkaline phosphatase in hemolymph, total superoxide dismutase activity in hepatopancreas, and malondialdehyde content. Additionally, it upregulated the expression of myd88 , pi3k , tor , and ror. Compared to the control group, the feed in the E diet increased the total superoxide dismutase activity in the hemolymph and upregulated myd88 , pi3k , tor , and imd expression levels. Furthermore, C, D, and E diets increased the width of the shrimp's intestinal folds. Regression analysis showed that the weight gain and feed intake increased with the increasing amount of squid paste in the feed and decreased with the addition of shrimp paste. Feed intake increased with the addition of fish-soluble protein and decreased with the addition of yeast extract in the feed. In conclusion, adding attractants (yeast extract, squid viscera powder, fish soluble, and squid paste) to the feed is beneficial for the growth and feeding of shrimp, and it can promote the expression of shrimp intestinal immune-related genes and histological changes, thus promoting shrimp intestinal health. [Display omitted] • The effect of combined feed attractants on growth performance, feed utilization, intestinal organization and immunity of Penaeus monodon. • Dietary A (yeast extract+squid visceral powder+fish soluble+squid paste) positively influenced feed intake and protein synthesis of shrimp. • The addition of squid paste to the diet increased weight gain rate and feed intake, while increasing shrimp paste additions decreased these. [ABSTRACT FROM AUTHOR]

Bile acids have an important role in the growth and sterol metabolism of shrimp. The aim of this study was to elucidate the effects of bile acids supplementation in the low fishmeal diets on sterol metabolism, bile acids enterohepatic circulation, bile acid profile, and apoptosis in Pacific white shrimp Litopenaeus vannamei. Six diets were formulated in this experiment, HFM diet (25% fishmeal), LFM diet (10 % fishmeal), and LFM supplemented with four levels (0.15, 0.3, 0.6, 0.9 g kg−1) of bile acids, which were LBA1, LBA2, LBA3, LBA4, respectively. Soy protein concentrate and cottonseed protein concentrate blend was used to replace fishmeal of 60 %. After 50 days of feeding trial, the shrimp fed the LBA4 diet showed significantly increased final body weight than that fed the LFM diet (P < 0.05). In the sterol metabolism, the shrimp fed the LBA1 diet was significantly increased the HMG-CoA reductase membrane form (hmgcr) and Niemann-Pick type C-2-like protein (npc2) expression compare with that fed the LFM diet, shrimp in LBA2 group was significantly increased the related genes expression [ hmgcr and NPC intracellular cholesterol transporter 1-like (npc1)] than those in the LFM group of hepatopancreas (P < 0.05). In the lipid metabolism, the shrimp in LBA2 group was significantly increased the carnitine palmitoyltransferase-1 (cpt-1) and AMP-activated protein kinase (ampk) expression than that in the LFM group, shrimp in the LBA3 group was significantly increased the fatty acid binding protein fatty acid (fabp) expression than that in the LFM group (P < 0.05). In the bile acids metabolism, the multidrug resistance-associated protein 1-like (mrp2), multidrug resistance-associated protein 2-like (mrp3) and solute carrier family 22 member 7-like (oatp) expressions were significantly increased in LBA1 and LBA2 groups than those in the LFM group of hepatopancreas, organic solute transporter subunit alpha-like (ostα), mrp2 , and acyl-coenzyme A thioesterase 1-like (baat) expressions were significantly up-regulated in LBA4 group than those in the LFM group of intestine (P < 0.05). Supplementary bile acids in the diet could decrease the apoptosis-related protein expression (BCL-2 and CASPASE3) compare with the shrimp fed low fishmeal diet (P < 0.05). The concentration of beta MCA in hemolymph bile acids profile increases with bile acids supplementation. The results showed that bile acids enhanced growth performance, promoted sterol metabolism, enhanced enterohepatic circulation, and reduced apoptosis in shrimp on low fishmeal diets. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical. [Display omitted] • Dietary bile acids supplementation improved growth performance of shrimp. • Dietary bile acids supplementation improved promoted lipid metabolism of shrimp. • Bile acid levels were measured by bile acid-targeted metabolomics and feed supplementation was found to improve the composition of the bile acid pool in the hemolymph of shrimp. • Bile acids alleviate apoptosis in shrimp induced by low fishmeal diets. [ABSTRACT FROM AUTHOR]