Growth Hormone Transgenic Common Carp Research Articles

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.

Effects of growth hormone over-expression on reproduction in the common carp Cyprinus carpio L.

To study the complex interaction between growth and reproduction we have established lines of transgenic common carp (Cyprinus carpio) carrying a grass carp (Ctenopharyngodon idellus) growth hormone (GH) transgene. The GH-transgenic fish showed delayed gonadal development compared with non-transgenic common carp. To gain a better understanding of the phenomenon, we studied body growth, gonad development, changes of reproduction related genes and hormones of GH-transgenic common carp for 2years. Over-expression of GH elevated peripheral gh transcription, serum GH levels, and inhibited endogenous GH expression in the pituitary. Hormone analyses indicated that GH-transgenic common carp had reduced pituitary and serum level of luteinizing hormone (LH). Among the tested genes, pituitary lhβ was inhibited in GH-transgenic fish. Further analyses in vitro showed that GH inhibited lhβ expression. Localization of ghr with LH indicates the possibility of direct regulation of GH on gonadotrophs. We also found that GH-transgenic common carp had reduced pituitary sensitivity to stimulation by co-treatments with a salmon gonadotropin-releasing hormone (GnRH) agonist and a dopamine antagonist. Together these results suggest that the main cause of delayed reproductive development in GH transgenic common carp is reduced LH production and release.

Increased food intake in growth hormone-transgenic common carp (Cyprinus carpio L.) may be mediated by upregulating Agouti-related protein (AgRP)

In fish, food intake and feeding behavior are crucial for survival, competition, growth and reproduction. Growth hormone (GH)-transgenic common carp exhibit an enhanced growth rate, increased food intake and higher feed conversion rate. However, the underlying molecular mechanisms of feeding regulation in GH-transgenic (TG) fish are not clear. In this study, we observed feeding behavior of TG and non-transgenic (NT) common carp, and analyzed the mRNA expression levels of NPY, AgRP I, orexin, POMC, CCK, and CART I in the hypothalamus and telencephalon after behavioral observation. We detected similar gene expression levels in the hypothalamus of TG and NT common carp, which had been cultured in the field at the same age. Furthermore, we tested the effects of GH on hypothalamus fragments in vitro to confirm our findings. We demonstrated that TG common carp displayed increased food intake and reduced food consumption time, which were associated with a marked increase in hypothalamic AgRP I mRNA expression. Our results suggest that elevated GH levels may influence food intake and feeding behavior by upregulating the hypothalamic orexigenic factor AgRP I in GH-transgenic common carp.

The hematological response to exhaustive exercise in ‘all-fish’ growth hormone transgenic common carp (Cyprinus carpio L.)

This study examined the hematological profiles and responses to exhaustive exercise in ‘all-fish’ growth hormone (GH) transgenic common carp (Cyprinus carpio L.) compared to non-transgenic controls. Transgenic fish had significantly smaller erythrocytes (length, width, surface area and volume), with a larger surface to volume ratios than non-transgenics. There were no significant differences in hematocrit, blood hemoglobin concentrations, plasma glucose, lactate, cholesterol and protein concentrations between the two strains at rest, but the transgenic fish had significantly lower resting mean corpuscular hemoglobin concentrations (MCHC) or higher plasma triglyceride concentrations than controls. Exhaustive exercise did not induce significant changes in hematocrit, hemoglobin concentrations and MCHC in either strain. The patterns of elevation and recovery in plasma glucose and lactate were the same for transgenic and control fish, although lactate levels were lower in the transgnic fish than controls at 1h and 2h post-exercise. There was a significant elevation in plasma cholesterol and triglyceride concentrations for 1h post-exercise in transgenics but not in non-transgenic controls. Plasma protein concentrations were not altered by exhaustive exercise in transgenics but were lower from 2h post-exercise in non-transgenic controls. These findings suggest that the ‘all-fish’ GH transgene significantly affects the erythrocyte morphology and the patterns in hematological response to exhaustive exercise of common carp, especially for lipid metabolism. The greater reliance on triglycerides and a greater erythrocyte surface to volume ratio may help transgenic carp to recover from exhaustive exercise, but further research on muscle metabolism and aerobic metabolic rate are needed in order to confirm this conclusion.

Acute and chronic un-ionized ammonia toxicity to ‘all-fish’ growth hormone transgenic common carp (Cyprinus carpio L.)

Ammonia is toxic to fish in natural and artificial waters. We evaluated the acute (96 h) and chronic (21 d) toxicity of un-ionized ammonia to GH transgenic common carp (Cyprinus carpio L.) and non-transgenic common carp using a static-renewal bioassay. The 24, 48, 72 and 96 h median lethal concentrations (LC50) of un-ionized ammonia were slightly lower in transgenic carp (2.64, 2.44, 2.28 and 2.16 mg N/L, respectively) than in non-transgenic carp (2.70, 2.64, 2.52 and 2.33 mg N/L, respectively). Similarly, the median lethal time (LT50) was significantly shorter for transgenic carp (1.41, 7.91 and 117.42 h) than for non-transgenic common carp (2.53, 14.06 and 150.44 h) following exposure to 3.86, 3.29, or 2.09 mg N/L, respectively. Moreover, the mortality of transgenic carp was significantly higher than that of non-transgenic carp at all un-ionized ammonia concentrations ((0.91 +/- 0.12), (0.48 +/- 0.06) and (0.12 +/- 0.01) mg N/L) during the 21 d chronic toxicity test. Our results suggest that GH transgenic carp are less tolerant of un-ionized ammonia than non-transgenic carp. Our data are useful for evaluating potential environmental risk, optimizing stocking density in intensive aquaculture and establishing water quality criteria for ammonia in aquaculture.

Elevated ability to compete for limited food resources by ‘all‐fish’ growth hormone transgenic common carp Cyprinus carpio

Food consumption, number of movements and feeding hierarchy of juvenile transgenic common carp Cyprinus carpio and their size-matched non-transgenic conspecifics were measured under conditions of limited food supply. Transgenic fish exhibited 73.3% more movements as well as a higher feeding order, and consumed 1.86 times as many food pellets as their non-transgenic counterparts. After the 10 day experiment, transgenic C. carpio had still not realized their higher growth potential, which may be partly explained by the higher frequency of movements of transgenics and the 'sneaky' feeding strategy used by the non-transgenics. The results indicate that these transgenic fish possess an elevated ability to compete for limited food resources, which could be advantageous after an escape into the wild. It may be that other factors in the natural environment (i.e. predation risk and food distribution), however, would offset this advantage. Thus, these results need to be assessed with caution.

Metabolism traits of ‘all-fish’ growth hormone transgenic common carp ( Cyprinus carpio L.)

Transgenic animals with improved qualities have the potential to upset the ecological balance of a natural environment. We investigated metabolic rates of ‘all-fish’ growth hormone (GH) transgenic common carp under routine conditions and during starvation periods to determine whether energy stores in transgenic fish would deplete faster than controls during natural periods of starvation. Before the oxygen uptake was measured, the mean daily feed intake of transgenic carp was 2.12 times greater than control fish during 4 days of feeding. The average oxygen uptake of GH transgenic fish was 1.32 times greater than control fish within 96 h of starvation, but was not significantly different from controls between 96 and 144 h of starvation. At the same time, GH transgenic fish did not deplete energy reserves at a faster rate than did the controls, as the carcass energy contents of the two groups following a 60-d starvation period were not significantly different. Consequently, we suggest that increased routine oxygen uptake in GH transgenic common carp over that of control fish may be mainly due to the effects of feeding, and not to an increase in basal metabolism. GH transgenic fish are similar to controls in the regulation of metabolism to normally distribute energy reserves during starvation.

Survival of F2 transgenic common carp (Cyprinus carpio) containing pRSVrtGH1 complementary DNA when subjected to low dissolved oxygen.

The survival and tolerance of F2 transgenic common carp (Cyprinus carpio) containing pRSVrtGH1 complementary DNA were compared with nontransgenic (control) common carp when subjected to low dissolved oxygen. The tolerance of low oxygen was evaluated in 8 families of common carp in rectangular tanks (3 x 1 x 1 m). The absolute mean percentage of survival of transgenic common carp subjected to low oxygen (0.4 mg/L) was higher (P <0.05) than that of control carp in 2 of the 8 families of common carp tested; however, the overall means for all families of transgenic and control carp were not different (P > 0.05). When oxygen tolerance was measured in time to death rather than absolute survival or mortality, the growth hormone transgenic common carp had a longer group mean (P <0.05) than did controls. The mean survival time in minutes for the transgenic genotype was greater (P <0.05) in 5 of the 8 families assessed. Transgenic common carp in some families had higher percentage and longer times of survival than control common carp when subjected to low oxygen. The definition of tolerance of low oxygen and how it is measured is important, and can affect interpretation of results. The pleiotropic effect of pRSVrtGH1 cDNA on superior survival of low oxygen in common carp has important implications for intensive fish culture.