Improved liver lipid catabolism and utilization in growth hormone transgenic common carp (Cyprinus carpio L.) through enhanced lipolytic and fatty acid β-oxidation pathways

Growth hormone (GH) transgenic common carp (Cyprinus carpio L.) show desirable aquaculture traits. Their specific growth rate (SGR) and feed efficiency (FE) are approximately 12% and 17% higher than the wild-type (WT) common carp, respectively. However, the mechanisms of lipid catabolism (lipolysis and fatty acid β-oxidation) and utilization in GH transgenic common carp are still unclear. In this study, we firstly compared the lipid metabolism of GH transgenic (initial weight 3.72 ± 0.32 g) and WT (initial weight 3.30 ± 0.28 g) common carp fed with a normal fat level diet (6% lipid, 33% protein) for two months, then compared the growth performance of GH transgenic (initial weight 3.65 ± 0.33 g) and WT (initial weight 3.27 ± 0.26 g) common carp fed with different fat levels diets (6% lipid and 12% lipid, 33% protein) for two months. We found that the lipid content in serum, liver and whole body was significantly reduced in GH transgenic common carp, the hepatic activities of the lipolytic enzymes hormone-sensitive lipase and adipose triglyceride lipase were enhanced, and the hepatic expression level of hormone-sensitive lipase was upregulated. In addition, the mitochondrion numbers were increased, and the expression level of carnitine palmitoyltransferase-1a and carnitine palmitoyltransferase-1b was upregulated in the liver of GH transgenic common carp. GH transgenic common carp showed higher weight gain and SGR than that in WT carp when fed with a normal-fat diet as they did when fed with a high-fat diet, and GH transgenic common carp showed higher FE than that in WT carp when fed with a high-fat diet. These results suggested that the lipid catabolism and utilization was improved in the GH transgenic common carp liver through enhanced lipolytic and fatty acid β-oxidation pathways. Our study provides new insights into improving lipid utilization in some aquaculture fish species.

Overexpression of growth hormone improved hepatic glucose catabolism and relieved liver lipid deposition in common carp (Cyprinus carpio L.) fed a high-starch diet

Growth hormone (GH) is important for regulating insulin secretion and carbohydrate metabolism, and its role in mammalian models of diabetes is relatively worked out. Although some fish species were used as models for diabetes research, the effects of GH on insulin and glucose catabolism and anabolism in these models remain to be clarified. In this study, we investigated the effect of GH on insulin and glucose catabolism and anabolism in an omnivorous fish using GH transgenic (T) common carp that consistently overexpressed GH and wild-type (WT) common carp. We compared the intestinal morphology, and digestive and absorptive capacity of fish fed commercial feed. We also analyzed the growth performance, insulin level, glucose catabolism and anabolism, lipid deposition, and lipid catabolism and anabolism in T carp and WT carp fed diets containing either 30% or 40% starch. In the intestine of T carp, α-amylase activity was enhanced, the number of goblet cells and intestinal villi surface area was increased, and the expression level of glucose transport protein-related genes (glut2 and sglt1) was upregulated when compared to these indicators in WT carp. When fed either a normal or high-starch diet, the growth performance of T carp was better than that of WT carp. Compared with WT carp, serum insulin was increased and glucose was decreased, hepatic expression level of igf-1 and glycolysis-related genes was increased, and the activity level of a hepatic enzyme related to glycolysis was enhanced in T carp. When fed with a high-starch diet, the serum alanine aminotransferase activity, hepatic lipid content, and malondialdehyde content were significantly lower in T carp than in WT carp. These results indicated that overexpression of GH (1) enhanced carbohydrate digestion and absorption in the carp intestine, (2) did not induce insulin resistance and improved glucose catabolism and utilization in carp, and (3) relieved liver lipid deposition. Our data might provide new insights into potential ways to improve glucose utilization in fish and diabetes treatments.

Molecular characteristics, pathogenicity and medication regimen of Aeromonas hydrophila isolated from common carp (Cyprinus carpio L.)

Aeromonas hydrophila causes disease in fish known as Motile Aeromonas Septicemia (MAS), also named as bacterial hemorrhagic septicemia. In this study, a pathogenic A. hydrophila strain was isolated from common carp Cyprinus carpio L., which were suffering from severe hemorrhagic septicemia. According to the phylogenetic analysis derived from 16S rDNA sequence, the isolate formed a single branch in the A. hydrophila group, named AhHN1. Artificial infection results indicated that AhHN1 showed strong pathogenicity in C. carpio and the LD₅₀ was 1.38 × 10⁶ CFU/fish, the clinical symptoms and pathological features of infected fish were similar to those observed in natural infections. The antimicrobial susceptibility testing revealed that AhHN1 resistance to more than 13 kinds of antimicrobial agents. However, the AhHN1 strain exhibited an extremely sensitivity to enrofloxacin, the in vitro activities of enrofloxacin were subsequently investigated and drug selection window (MSW) was 0.0016–0.0125 µg/ml. Pharmacokinetics data showed that plasma concentration of enrofloxacin was 0.0016, 0.0148 and 0.0282 µg/ml at 24 hr after orally administered with 2.5, 5 and 10 mg/kg enrofloxacin. Moreover, dosing once a day of 2.5, 5 and 10 mg/kg enrofloxacin, which the relative protection ratio (RPS) was amounted to 33.3, 66.7, and 83.3%, respectively. Therefore, 5 mg/kg enrofloxacin was considered to be the rational regimen for controlling AhHN1 infection in C. carpio in the countries where the use of enrofloxacin is permitted in aquaculture. The aim of this study was to establish a scientific medication regimen for the prevention and therapy of the mutidrug-resistant A. hydrophila infection.