Metabolomic and transcriptomic profiling reveals the effect of dietary protein and lipid levels on growth performance in loach (Paramisgurnus dabryanus).

The subject of this study was to explore the optimum requirements of loach (Paramisgurnus dabryanus) regarding dietary proteins and lipids and discuss the underlying mechanism. We designed nine diets to determine the effects of different levels of dietary crude protein (CP: 30%, 35%, and 40%) and ether extract (EE: 6%, 10%, and 14%) on the growth performance and metabolism of P. dabryanus. In total, 2160 healthy P. dabryanus (5.19 ± 0.01 g) were divided into nine groups with four replications at 60 fish per barrel stocking density. The trial lasted for eight weeks. Serum and liver samples were gathered for metabolomic and transcriptomic analyses. The results showed that the specific growth rate of P. dabryanus in the CP40EE10 group was the fastest and notably higher than that in other groups (P< 0.05). Analysis of the metabolome results found that the mTOR signaling pathway, glycerophospholipid metabolism, D-arginine and D-ornithine metabolism were significantly enriched pathways in the CP40EE10 group compared with the other groups (P< 0.05). Moreover, the transcriptomic analysis of differentially expressed genes (DEGs) showed that the expression of ARG (arginase) involved in protein synthesis was significantly upregulated in the CP40EE10 group compared to the slowest growing group (P< 0.05). Additionally, the expression of SPLA2 (secretory phospholipase A2) involved in lipid metabolism and FBP (fructose-1,6-bisphosphatase) involved in glucose metabolism were all significantly downregulated in the CP30EE6 group compared with the CP40EE10 group (P< 0.05). Furthermore, the analysis of differentially expressed metabolites (DEMs) and DEGs co-enriched in the KEGG pathway revealed that the significantly enriched pathways were arginine and proline metabolism, glycerophospholipid metabolism, and glycolysis/gluconeogenesis in CP40EE10 compared with other groups (P< 0.05). We conclude that including 40% CP and 10% EE in the P. dabryanus diet could result in a better growth rate. We hypothesized from metabolomic and transcriptomic analyses that the CP40EE10 diet might promote the growth of P. dabryanus by promoting protein synthesis, lipid metabolism, and energy production.

Dietary Macroalgae Saccharina japonica Ameliorates Liver Injury Induced by a High-Carbohydrate Diet in Swamp Eel (Monopterus albus).

A high-carbohydrate diet lowers the rearing cost and decreases the ammonia emission into the environment, whereas it can induce liver injury, which can reduce harvest yields and generate economic losses in reared fish species. Macroalgae Saccharina japonica (SJ) has been reported to improve anti-diabetic, but the protective mechanism of dietary SJ against liver injury in fish fed a high-carbohydrate diet has not been studied. Therefore, a 56-day nutritional trial was designed for swamp eel Monopterus albus, which was fed with the normal diet [20% carbohydrate, normal carbohydrate (NC)], a high carbohydrate diet (32% carbohydrate, HC), and a HC diet supplemented with 2.5% SJ (HC-S). The HC diet promoted growth and lowered feed coefficient (FC), whereas it increased hepatosomatic index (HSI) when compared with the NC diet in this study. However, SJ supplementation increased iodine contents in muscle, reduced HSI, and improved liver injury, such as the decrease of glucose (GLU), total bile acid (TBA), and alanine aminotransferase (ALT) in serum, and glycogen and TBA in the liver. Consistently, histological analysis showed that SJ reduced the area of lipid droplet, glycogen, and collagen fiber in the liver (p < 0.05). Thoroughly, the underlying protective mechanisms of SJ supplementation against HC-induced liver injury were studied by liver transcriptome sequencing coupled with pathway analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the differentially expressed genes (DEGs), such as the acetyl-coenzyme A synthetase (acss1), alcohol dehydrogenase (adh), interferon-induced protein with tetratricopeptide repeats 1 (ifit1), aldo-keto reductase family 1 member D1 (akr1d1), cholesterol 7-alpha-monooxygenase (cyp7a1), and UDP-glucuronosyltransferase (ugt), indicated that the pathway of glycolysis/gluconeogenesis was the main metabolic pathway altered in the HC group compared with the NC group. Meanwhile, hepatitis C, primary BA biosynthesis, and drug metabolism-cytochrome P450 were the three main metabolic pathways altered by SJ supplementation when compared with the HC group. Moreover, the BA-targeted metabolomic analysis of the serum BA found that SJ supplementation decreased the contents of taurohyocholic acid (THCA), taurochenodeoxycholic acid (TCDCA), taurolithocholic acid (TLCA), nordeoxycholic acid (NorDCA), and increased the contents of ursocholic acid (UCA), allocholic acid (ACA), and chenodeoxycholic acid (CDCA). In particular, the higher contents of UCA, ACA, and CDCA regulated by SJ were associated with lower liver injury. Overall, these results indicate that the 2.5% supplementation of SJ can be recommended as a functional feed additive for the alleviation of liver injury in swamp eel-fed high-carbohydrate diets.

Dietary fucoidan extracted from macroalgae Saccharina japonica alleviate the hepatic lipid accumulation of black seabream (Acanthopagrus schlegelii).

The use of an artificial diet often leads to the increase of risk factors for the development of liver diseases, such as hepatic lipid accumulation (HLA) in commercially cultured fish species. Our previous study showed that dietary Saccharina japonica could effectively alleviate HLA in black seabream (Acanthopagrus schlegelii), which may be linked predominantly to S. japonica fucoidan. Thus, a 56d nutritional trial was designed to investigate the effects of dietary fucoidan (CTRL, 0 g kg-1; ASJ1, 0.75 g kg-1; ASJ2, 3.00 g kg-1) on growth performance, fillets nutritional values, and HLA of black seabream. Results showed that dietary fucoidan significantly improved the growth and the contents of n-3 polyunsaturated fatty acids (n-3PUFA) in fillets of black seabream. Moreover, dietary fucoidan improved HLA-related parameters, including reducing serum and liver lipid contents and the activity of aminotransferase. Meanwhile, histological analysis showed that dietary fucoidan reduced the area of hepatic lipid droplets in black seabream (P < 0.05). In addition, the transcriptomic analysis of differentially expressed gene (DEG) showed that all DEG in fatty acid metabolism, primary bile acid biosynthesis, and fatty acid biosynthesis were down-regulated, and all DEG in the regulation of autophagy were up-regulated in the ASJ1 group compared with CTRL group. Moreover, the metabolomic analysis of differentially expressed metabolite (DEM) found that lipid metabolism was the main type of KEGG pathway altered by fucoidan supplementation. Furthermore, the combined transcriptomic and metabolomic analysis found that dietary fucoidan mainly modified the lipid metabolic pathway of primary bile acid biosynthesis, glycerophospholipid metabolism, and arachidonic acid metabolism in the liver. In general, dietary fucoidan effectively alleviated HLA of black seabream, and the underlying mechanism may be ascribed to promoting the autophagy and inhibiting the synthesis of lipids and bile acids.

Effects of dietary hydroxyproline on collagen metabolism, proline 4-hydroxylase activity, and expression of related gene in swim bladder of juvenile Nibea diacanthus.

This study was conducted to investigate the effects of dietary hydroxyproline (Hyp) on tissue collagen level, proline 4-hydroxylase (P4H) activity as well as transcript levels of COL1As (COL1A1 and COL1A2) and P4Hαs (P4Hα(I), P4Hα(II), and P4Hα(III)) in juvenile Nibea diacanthus. A total of 450 fishes were randomized to six equal groups and fed the diet with graded supplementary Hyp-0, 5, 10, 15, 20, and 25 g kg-1 of dry matter for 8 weeks. Results showed that fish fed diets with 10 g kg-1 Hyp had significantly higher acid-soluble collagen (ASC) and total collagen (TC) concentrations in swim bladder than fish fed with the other diets (P < 0.05). The activity of P4H in liver and swim bladder showed a similar trend, showing first increase and then decrease with increasing dietary Hyp (P < 0.05). The mRNA expression of COL1As in swim bladder and muscle were significantly higher than those in the liver and intestines. Meanwhile, with increasing dietary Hyp, the relative expression of COL1As genes in swim bladder showed a similar pattern with the TC concentrations of swim bladder, increased significantly initially followed by a decrease. Increased dietary Hyp content corresponded with significant decrease in the mRNA level of P4Hαs in swim bladder. These results indicated that the dietary Hyp promotes the collagen accumulation of swim bladder to some extent, and the promoting action may be related to the expression of COL1As. The optimum supplement of dietary Hyp was estimated from TC of swim bladder with piecewise regression analysis to be 9.66 g kg-1.