Intestinal genomic adaptations induced by dietary phosphorus (P) deficiency differ when rainbow trout are raised in freshwater (FW) or seawater (SW)

Abstract

Because environmental ions composition, including that of phosphate, vastly differs between SW and FW, we hypothesized that trout will use different strategies to cope with dietary P-deficiency and adapt its intestinal P metabolism when FW- or SW-raised. Using 16K salmon microarray, we identified genes whose intestinal expression levels change in FW and/or SW-adapted trout after 5 d of feeding a low P (LP) relative to a high P (HP) diet. Expect for a consistent over-expression of cytochrome P450-2K5 and Ileal Lipid Binding Protein, two completely different populations of genes, mainly involved in intermediary metabolism, regulation of transcription and cell cycle, proteolysis and immune response, were discovered in FW and SW-raised trout challenged with dietary P-deficiency. MRNA levels of most of the genes, quantified by real-time PCR, highly correlate with conventional P-deficiency indicators such as plasma P levels. Their P-response was also sustainable after 20 d of dietary P-deficiency. None of the FW-specific genes changed in expression when examined in the intestine of SW-adapted trout, and inversely. Salinity affects how the small intestine responds to changes in dietary P, as indicated by the different populations of genes identified in SW and FW. Genes that differ throughout the duration of LP consumption are potentially excellent biomarkers, able to detect early stages of P deficiency, prior to advent of clinical symptoms(USDA 04-35206-14154; 03-35102-13520).