Cryptic Female Choice (CFC) is a form of sexual selection operated by the female through chemical and physical mechanisms. In some fish species, CFC has been associated to the Major
Histocompatibility Complex (MHC) and the presence of specific MHC alleles has been associated with a higher survival of the offspring. The present study aims to investigate the CFC phenomenon associated with the MHC-IIB gene in the rainbow trout (Oncorhynchus mykiss) by evaluating the reproductive performance of specific matings.

The study were carried out at the “Azienda Agricola Canali Cavour” fish farm (Italy). 100 rainbow trout were selected on the basis of MHC-IIB gene. MHC-IIB gene was amplified and sequenced.
Haplotypes were estimated through Bayesian statistics, considering 23 Single Nucleotide Polymorphisms (SNPs). The rainbow trout were monitored to assess the reproductive status and to perform artificial reproductions based on the three haplotypes (2/2, 2/x and x/y) according to a full-factorial design. Parameters monitored: morpho-physiological parameters  of the females, fertilized and unfertilized eggs, hatching mortality, skeletal deformity larvae, irregular absorbing yolk sac rate and healthy larvae at the end of incubation. Finally the overall survival rates were estimated.

The results of the reproductive performance indicate a better output for the matings performed with 2/2 females. Furthermore, the GLM indicate a greater survival during the incubation phase for the mating F 2/2 + M 2/2 if compared with other matings. Despite these encouraging findings, the results of this study are not able to confirm the presence of CFC in the rainbow trout (O. mykiss) associated with the mating among similar haplotypes (F 2/2 + M 2/2).

Poster at aquaculture 2022 congress