Genomic polymorphisms at the crhr2 locus improve feed conversion efficiency through alleviation of hypothalamus-pituitary-interrenal axis activity in gibel carp(Carassius gibelio)

Improvement in fish feed conversion efficiency(FCE)is beneficial for sustaining global food fish supplies.Here,we show that a set of polymorphisms at locus of the corticotropin releasing hormone receptor 2(crhr2),which is involved in hypothalamuspituitary-interrenal(HPI)axis signaling,is associated with improved FCE in farmed allogynogenetic gibel carp strain CAS Ⅲ compared with that in the wild gibel carp strain Dongting(DT).This set of polymorphisms downregulates the expression levels of crhr2 mRNA in the brain and pituitary tissues in gibel carp strain CAS Ⅲ compared with those in strain DT.Furthermore,compromised HPI axis signaling is observed in gibel carp strain CAS Ⅲ,such as decreased α-melanocyte stimulating hormone protein levels,plasma cortisol content,and stress responses.Moreover,enhanced activation of protein kinase B/mammalian target of rapamycin complex 1 signaling observed in the muscle tissue of strain CAS Ⅲ in comparison to that in strain DT indicated elevated anabolic metabolism in strain CAS Ⅲ.Thus,these studies demonstrate that the genetic markers associated with compromised HPI axis signaling,such as crhr2,are potentially useful for genetic selection toward improvement in farmed fish growth and FCE,which would reduce fishmeal consumption and thereby indirectly facilitate sustainable fisheries.