The increased feeding motivation and enhanced growth found in growth hormone (GH)
transgenic coho salmon, Oncorhynchus kisutch, raises questions regarding the hormonal changes
regulating growth and feed intake. These fish exhibit increased circulating GH and insulin-like
growth factor I (IGF-I) and GH mRNA expression resulting from the GH transgene, but the role
of the other hormones in the GH-axis and appetite control are unknown. Transgenic and non-transgenic
coho salmon pre-smolts were fed diets with 15, 17, 19 and 21 MJ of digestible
energy/kg for 84 days and they were analyzed for growth, feed intake and protein utilization.
Gene mRNA expression of the major regulators in the GH-axis: growth hormone, growth
hormone receptor (GHR), insulin-like growth factor I, growth hormone-releasing hormone
(GHRH) and somatostatin (SS) as well as the appetite hormone, cholecystokinin (CCK), were
analyzed with quantitative PCR in the brain of fish from this experiment and in six brain regions
(telencephalon, hypothalamus, pituitary, optic tectum, midbrain, cerebellum) and muscle and
liver of size-matched (55g) full-ration transgenic, restricted-ration transgenic (pair-fed to nontransgenic
fish) and full-ration non-transgenic fish. Transgenic fish had greater feed intake and
growth which were respectively negatively and positively correlated with the digestible energy
content of the diet. Protein use was more efficient in transgenic fish when fed the 15 and 17
MJ/kg diets only and diet had no effect on gene expression. Plasma IGF-I was greater in
transgenic fish but did not correlate with weight as in the non-transgenic coho salmon. In the
size-matched study, GH expression was highest in transgenic fish, except in the pituitary where
there were no differences. GHR expression generally followed that of GH but was tissue
specific. Transgenic fish has higher IGF-I expression but hepatic IGF-I levels in ration-restricted
transgenic fish were reduced to that of non-transgenic fish. GHRH, SS or CCK expression did
not differ between groups. It is concluded that transgenic fish, with enhanced growth, feed
intake and protein utilization, ingested feed to meet a caloric demand that was possibly set by
increased GH, GHR and IGF-I whereas the other GH regulating hormones and the CCK satiety
signal showed little change. / Science, Faculty of / Zoology, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/17748 |
| Date | 05 1900 |
| Creators | Raven, Peter Andrew |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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