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Although Pacific white shrimp, Litopenaeus vannamei is a euryhaline shrimp species, when suffering from acute low salinity stress, the survival and physiological status of the shrimp may be affected. This study aimed to investigate whether the dietary yeast hydrolysate (YH) helped Litopenaeus vannamei to respond to acute low salinity stress. Firstly, shrimp (mean weight 15.82 ± 0.08g) were randomly assigned to two groups and fed two diets containing 0% YH (YH0) and 3% YH (YH3) four times daily at a salinity of 28. After a two‐week feeding trial, some shrimp fed the two diets were transferred to salinity 4 and 20 mediums and others were transferred to salinity 28 as control for a low salinity stress. Samples of shrimp were collected at 0 h, 0.5 h, 1 h, 3 h, 6 h and 9 h after transferred. Results showed that Na/K‐ATPase and phenoloxidase (PO) activities were not affected, while alkaline phosphatase (AKP) and acid phosphatase (ACP) activities decreased, but the superoxide dismutase (SOD) activity increased in shrimp fed diet with yeast hydrolysate before the low salinity stress (0 h). The Na/K‐ATPase activity decreased at 1 h, 3 h and 6 h due to the decrease in salinity. The Na/K‐ATPase activity of shrimp fed YH3 diet increased at 1 h and 9 h but decreased at 6 h compared with that fed YH0. The AKP activity decreased at 6 h, while the ACP activity decreased at 1 h and 3 h for the salinity stress. AKP and ACP activities of shrimp fed YH3 diet decreased at 3 h and 6 h compared with that fed YH0. The PO activity decreased at 0.5 h, 1 h, 3 h and 9 h because of the decrease in salinity. However, it increased in shrimp fed YH3 diet at 1 h compared with that fed YH0 diet. The SOD activity decreased at 3 h and 6 h due to the low salinity stress. The SOD activity of shrimp fed YH3 diet decreased at 0.5 h and 9 h compared with that fed YH0. Therefore, it was concluded that the ingestion of the feed containing yeast hydrolysate improved the defence against low salinity stress by modulating the activity of Na/K‐ATPase, PO and SOD enzymes, while the diet factor has less impact on the AKP and ACP activities of the organism compared with the culture salinity. [ABSTRACT FROM AUTHOR]

A 56‐day feeding trial was conducted to study the effects of cottonseed protein concentrate (CPC) as fishmeal (FM) replacement on growth, digestive proteinase, intestinal morphology and microflora in pearl gentian grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu). FM of 0% (FM), 12.00% (R12), 24.00% (R24), 36.00% (R36), 48.00% (R48) and 60.00% (R60) was replaced with CPC, to prepare six diets and feed groupers. Weight gain (WG) and specific growth rate (SGR) were highest in the R24 group, and the lowest feed coefficient rate (FCR) was observed in this group compared with the other groups (p <.05). Pepsin activity of the R12 group and chymotrypsin activity of the R36 group reached significant maximum (p <.05). With increasing CPC replacement, the plica height and width and the lamina propria thickness of intestine decreased significantly (p <.05). 16S rDNA amplicon sequencing suggested dominant intestinal microflora of grouper subjected to different treatments was similar. At the phylum level, the abundance of Proteobacteria, Firmicutes, Verrucomicrobia, Bacteroidetes and Actinobacteria was high, while Photobacterium, Pseudoxanthomonas, Romboutsia, Akkermansia, Vibrio and Bifidobacterium were the dominant taxa at the genus level. The abundance of probiotics (Bifidobacterium) decreased, whereas the abundance of opportunistic pathogen (Proteobacteria, Actinobacteria and Vibrio) increased. These results suggested that CPC replacement affected growth, digestive proteinase activity, intestinal morphology and microflora structure in grouper. Under the conditions of this experiment, the fishmeal replacement with CPC (24% level) yielded the most satisfactory results, providing reference for sustainable aquaculture. [ABSTRACT FROM AUTHOR]

This experiment was conducted to assess the effects of antimicrobial peptides at different levels (Diet 1 (0%), Diet 2 (0.1%), Diet 3 (0.2%), Diet 4 (0.4%), Diet 5 (0.6%) and Diet 6 (1%)), on growth, serum biochemical indices and antioxidant effect, feed utilization and disease resistance in Litopeneaus vannamei. There were four replicates in each group in the experiment (mean weight = 0.21 ± 0.00 g) and also fed with their respective diets for 8 weeks. Growth performance compared with the control group (0%) significantly increased at first and then decreased among treatment groups (p <.05) whereas the survival rate ranged from 78% to 96%. No significant differences were observed in terms of moisture, crude protein and ash content, but there was a significant increase in crude lipid (p <.05). In serum, acid phosphatase, alkaline phosphatase, polyphenol oxidase, triglyceride, glucose and total cholesterol changed as compared with 0%. Total antioxidant capacity, glutathione peroxidase, catalase, superoxide dismutase and malondialdehyde were also different from 0%. Disease resistance was increased in shrimp among treatment groups with 0.4% recording the lowest mortality percentage of 37% after the challenge test. The results from the present study suggested that supplementation of AMP at 0.4% in shrimp diet can improve growth performance, antioxidants activities and innate immune response of Pacific whiteleg shrimp. [ABSTRACT FROM AUTHOR]

Golden pompano (Trachinotus ovatus) is an important aquaculture species in China and broadly cultivated in Asia–Pacific region. Our previous study found that T. ovatus had a better tolerance to the high level of carbohydrate in diet (360 g/kg) compared to Micropterus salmoides. Present study investigated the tolerance mechanism of T. ovatus to high level of dietary carbohydrate (PH‐360 g/kg of corn starch) on transcriptome level using Illumina sequencing compared to optimum level of dietary carbohydrate (PM‐240 g/kg corn starch). A total of 208,952,492 reads were obtained and assembled into 62,377 unigenes with an average length of 822 bp and a range of 200–16,206 bp. Transcriptome annotation revealed that 27,636 unigenes with a cut‐off e‐value of 10−5 were functionally annotated. Specifically, 7,903 unigenes were clustered into 24 functional categories by searching against the COG database, 12,161 unigenes to 84 GO terms, 26,835 unigenes to Nr database and 23,681 unigenes to SWISS‐PROT database. In addition, 13,739 unigenes were grouped into 240 KEGG pathways. There are 3,461 differentially expressed genes in PH compared to PM, in which 3,059 unigenes were significantly upregulated and 402 unigenes were significantly downregulated. Twelve key genes related to carbohydrate metabolism were further validated by quantitative real‐time RT–PCR, and the results were consistent with those of transcriptome profile.Under high level of dietary carbohydrate (PH‐360 g/kg), the results indicate that T. ovatus can adapt to the high level of dietary carbohydrate by enhancing glycolysis with the increased heaptic HK enzyme activity (p > 0.05), reducing gluconeogenesis with the decreased trend of PEPCK enzyme activity and maintaining the homeostasis of carbohydrate metabolism‐related hormones and hormone receptor gene expressions. Histopathological examination has shown that liver cavity area was significantly increased (p > 0.05), but no visible nutritional diseases are found in fish. This study provides a valuable understanding of the molecular responses of T. ovatus fed by the high level of dietary carbohydrate (PH‐360 g/kg). [ABSTRACT FROM AUTHOR]

The present study was designed to assess the effects of fish oil with different oxidation degree on growth performance, serum biochemistry parameters and expressive abundance of oxidative stress and fat metabolism genes of orange spotted grouper Epinephelus coioides. The oxidized fish oil was conducted as follows: storage temperature: 4°C, ambient temperature (AT, [31.5 ± 3.5]°C); storage time: 45, 90, 135 days; antioxidant contents: 30 mg/kg (ethoxyquin [EQ]), 300 mg/kg Higher EQ (HEQ). According to the different treated conditions, 14 kinds of fish oil with different oxidation degree were obtained: TF+EQ [positive control (fresh oil + EQ)], TF (negative control [fresh oil]), T4°C+45d+EQ, T4°C+45d+HEQ, T4°C+90d+EQ, T4°C+90d+HEQ, T4°C+135d+EQ, T4°C+135d+HEQ, TAT+45d+EQ, TAT+45d+HEQ, TAT+90d+EQ, TAT+90d+HEQ, TAT+135d+EQ, TAT+135d+HEQ. Groupers were fed isonitrogenous and isolipidic diets containing 14 kinds of fish oil for 8 weeks, respectively. The results showed that survival, weight gain rate and thermal growth coefficient decreased as oxidation degree of dietary fish oil increased (p < 0.05). Higher serum total protein, triglyceride and glucose were observed with ascending oxidation degree of fish oil (p < 0.05). The genes expression levels of catalase, superoxide dismutase and glutathione peroxidase were up‐regulated with dietary oxidized level increasing (p < 0.05). In addition, the similar status also appeared in expression of peroxisome proliferator‐activated receptor gamma (PPARγ), hormone‐sensitive lipase (HSL) and fatty acid synthase (FAS) genes. In conclusion, the fish oil would show negative influence on the fish health until peroxide value and p‐anisidine value in oil exceed 12.96 meq/kg and 20.89. The best storage condition for fish oil is 4°C, 45 days and 30 mg/kg EQ which could keep fish oil available property to grouper. [ABSTRACT FROM AUTHOR]

Abstract: Three groups of juvenile golden pompano, Trachinotus ovatus (54.75 ± 0.25 g), were each fed one of three diets containing different lipid sources: fish oil (FO), soybean oil (SO) and lard oil (LO). Fish were reared in sea cages for 8 weeks, and the fish fed the FO diet had significantly higher specific growth rate (SGR) but lower condition factor (CF) than the other treatments. The fatty acid (FA) composition of whole‐body lipids was closely correlated with those in the diets. Although no differences can be found in hepatic fatty acid synthase (fasn) activity, the carnitine palmitoyl transferase 1 (cpt1) activity in fish fed the FO diet was significantly higher compared with other treatments. In addition, the relative gene expression of lipid metabolism‐related enzymes, such as cpt1, fas, apolipoprotein B100 (apoB100), delta‐6 fatty acyl desaturase (fadsd6) and fatty acid‐binding protein 1 (fabp1), was also influenced by the different dietary lipid sources. Serum triglyceride (TG) and glucose content in fish fed the LO and FO diets were significantly higher than those in the SO group. Accordingly, it can be concluded that FO could not be completely replaced by SO or LO in golden pompano diets. The lipid sources of a diet could impose significant influence on body condition factor and hepatic lipid metabolism of golden pompano. [ABSTRACT FROM AUTHOR]

The synchronous effects of aqueous Na/K and dietary potassium (K+) on growth and physiological characters was studied on the Pacific white shrimp ( Litopenaeus vannamei) reared in low-salinity well water (4 ppt) for 8 weeks with initial weight of 0.28 ± 0.01 g. Three practical diets were formulated with supplement of 0, 0.3%, 0.6% K+ which contained 1.29 g/100 g, 1.60 g/100 g, 1.93 g/100 g K+ respectively. The supplement of K+ to the low-salinity well water was 10, 20, 40 mg L−1 which formed Na:K ratios of 42:1, 33:1, 23:1 respectively. Results showed that when the aqueous Na:K ratio was 42 and dietary K+ was 1.93 g/100 g K+, the WGR and PER of L. vannamei were the highest and the FCR was lower than that of others ( P < 0.01). Supplement of K+ into well water and diets did not showed significant effects on haemolymph ammonia-N, uric acid, urea content ( P > 0.05), but had a extremely significant effect on arginase activity and Cl− concentration ( P < 0.01). Moreover, similar results were observed in alkaline phosphatase (ALP), bacteriolytic activity (LSZ) and respiratory burst activity (O2−) ( P < 0.05). These results suggested that aqueous Na/K in the low-salt well water and dietary K had significant synergistic effect on the growth, osmoregulation and immunity of L. vannamei. Concluded from the growth performance, nitrogen metabolism, osmoregulation and immunity, as the Na/K in the low-salinity well water descended from 42 to 23, the requirement of dietary K+ was also decreased. [ABSTRACT FROM AUTHOR]