Morphologic and molecular responses of developing rainbow trout (Oncorhynchus mykiss) to dietary minerals

Silva, Nadia

http://hdl.handle.net/10400.1/799

Use this identifier to reference this record.

Name:	Description:	Size:	Format:
Nadia_Silva_9669_tese.pdf		4.4 MB	Adobe PDF	Download

Send Feedback

Authors

Silva, Nadia

Advisor(s)

Power, Deborah

Abstract(s)

Calcium (Ca) and phosphorus (P) play a critical role in diverse biological processes, and their regulation is essential for organism health. In the present study, the adaptive response to Ca and P dietary availability in trout (Oncorhynchus mykiss) was evaluated taking an integrative approach. The impact of dietary restriction in Ca and P on skeletal ontogeny, morphology and density was assessed. The expression of previously known Pi responsive genes, along with calciotropic hormones STC, CT and extracellular matrix proteins (osteonectin and osteopontin) was evaluated by RT-qPCR. The activity of the ultimobrachial gland and corpuscles of Stannius was determined by morphometry after immunohistochemistry for calcitonin (CT) and stanniocalcin (STC) respectively. P restricted individuals showed decreased whole body P and Ca content throughout the experiment. The restriction of dietary P led to delayed skeletal ontogeny which affected the mineralization level of both endochondral and dermal bones, and was associated with an increase in the incidence of skeletal malformation. Low Ca and increased P in the diet also delayed skeletal development at D11 but this effect was transient. High dietary P caused increased plasma levels of P by D11 and a cumulative mortality rate of 90% by the end of the experiment. These individuals had denser bones and a lower incidence of malformations, possibly due to the effect of “survival of the fittest”. Of the previously identified molecular markers of P deficiency in trout S10011A was found to be significantly downregulated in P deficient trout fry, while INaPiIIb was dowregulated in trout fry on low Ca and high P diets. The calciotropic hormone STC was upregulated in trout fry on low P diets and CT was downregulated in trout fry on high P and low Ca diets. OSN expression was also downregulated in the high P group. The study indicates that modifications in the dietary Ca and P during development significantly modify the ontogeny and density of the skeleton. The availability of Ca and P also led to modification in endocrine factors presumably to ensure maintenance of mineral homeostasis. It seems likely that changes in hormone production may be responsible for changes in transcript abundance of specific transporters/binding proteins of Ca and P although in the present study it was not possible to test this hypothesis.