Influence of ration level and rearing temperature on hepatic GHR1 and 2, and hepatic and intestinal TRα and TRβ gene expression in late stages of rainbow trout embryos

Abstract

The study examined whether the early life‐history temperature experience of rainbow trout Oncorhynchus mykiss embryos affects subsequent growth and expression of growth‐related genes in the growing‐up juveniles in response to variations in ration levels. Embryos were reared in a Heath incubator at either 8·5° C (E 8·5 ) or 6·0° C (E 6·0 ) until hatching, at which time they were transferred to grow‐up tanks supplied with water at 8·5° C. At swim‐up, the late stage embryos were subsequently fed a salmonid starter diet at levels of 5, 2 or 0·5% of live body mass per day. The body mass and proximate composition of the juveniles was examined when yolk absorbance was complete (21 days after the fish commenced feeding). Quantitative RT‐PCR was used to examine the expression of mRNA encoding for growth hormone receptors 1 and 2 (GHR1 and GHR2) in the liver, and the two isoforms of thyroid hormone receptor (TRα and TRβ) in the liver and intestinal tract. Final body mass and total length, liver and intestinal masses, and total lipid content of the E 8·5 treatment group were directly related to increased ration size. These variables in the E 6·0 treatment group fed the 5% ration were significantly lower than for the comparable E 8·5 treatment group, suggesting an effect of embryo rearing temperature on the subsequent growth of these late stage embryos as they undergo the transition from embryo to early juvenile. Intestinal TRα and TRβ mRNA abundance was directly related to ration size in the E 8·5 treatment group, but not in the E 6·0 treatment group. Conversely, hepatic TRα and TRβ mRNA abundance was significantly affected by ration size only in the E 6·0 group, with TRβ and TRα abundance showing direct and inverse relationships with ration size, respectively. Hepatic GHR1 mRNA abundance was significantly and directly related to ration size in both the E 8·5 and E 6·0 treatment groups, but there were no differences in the abundance of hepatic GHR2 mRNA among any treatments.

Bibliographic Information