The present study aims to eva‎luate the viability of reciprocal crosses between Caspian trout (Salmo caspius) and rainbow trout (Oncorhynchus mykiss), and the effect of triploidization on embryonic development, growth and survival of hybrid embryos and larvae. This experiment included six groups of crosses: (1) pure O. mykiss (2nR); (2) pure S. caspius (2nC); (3) diploid and (4) triploid ♀O. mykiss×♂S. caspius hybrids (2nR×C and 3nR×C); (5) diploid and (6) triploid ♀S. caspius×♂O. mykiss hybrids (2nC×R and 3nC×R). Triploidy was induced by a thermal shock after fertilization. Fertilization, hatching, and embryonic development were studied. Hatching rate was more than 90% in 2nR and 2nC, 35% in 2nR×C group, 45% in 3nR×C group, whereas all embryos died before the eyed stage in 2nC×R and 3nC×R groups. Chromosome number ranged between 57-61 and 78-81 in 2nR and 2nC groups, 69-71 in 2nR×C and 99-103 in 3nR×C. The time before blastopore closure was the most important point in the embryonic phases when most deaths occurred in all groups. Hatching occurred earlier in 2nR and 3nR×C groups than in 2nC group. The highest final weight and specific growth rate were observed in 2nR and 3nR×C groups. The highest rate of malformation was observed in the 2nRC group, while triploid induction successfully reduced the preva‎lence of malformed larvae in the 3nRC group. Principal component analysis (PCA), canonical variable (CVA), Procrustes and Mahalanobis distances were used to determine morphometric changes. PCA analysis showed the overlap of hybrid with rainbow trout and CVA analysis grouped all three species into three distinct populations. The greatest differences in appearance between the species were found in the dorsal, anal, abdominal and pectoral fins, gill cover, mouth and eyes at the larval stage. Cartilage-bone ontogeny was examined using the Alcian Blue-Alizarin Red staining method. Two-day-old larvae (R, C, 3nRC) were completely cartilaginous. The onset of ossification was observed in the skull and all fins in R, 3nRC and C, respectively. This study was also carried out again at the University of Göttingen, Germany, to perform gene expression studies, which included 5 groups: O. mykiss (R), Salmo trutta (B), diploid and triploid hybrids (shock induced by two different methods) between female O. mykiss and male S. trutta (2nRB, 3nRB1, 3nRB2). In 3nRB1 a heat shock of 28 ºC was used for 10 min, 10 min after fertilization and in 3nRB2 a heat shock of 26 ºC was used for 20 min, 25 min after fertilization. The expression of four genes related to growth and immunity including (GH, IGF-I, IGF-II and TLR3) and two housekeeping genes (-actinβ and elongation factor 1α) at four different developmental stages (eyed egg, pre-hatch, newly hatched and 21-day-old larvae) was examined. All four target genes (GH, IGF-I, IGF-II and TLR3) were expressed at all stages examined. GH and IGF-I gene expression was significantly higher in group B than in the other groups at all sampling times. Similarly, no significant difference was observed between the 3nRB1 and 3nRB2 groups and the R group. The highest level of IGF-I gene expression in all groups was observed in 21-day-old larvae and IGF-II in the embryonic period. The highest level of TLR3 gene expression was measured in hybrids (2nRB, 3nRB1 and 3nRB2) and the lowest in brown trout (B).

يزدان كيواني , سالار درافشان

فاطمه پيكان حيرتي

اميرحسين جلالي حاجي آبادي , مجيد طالبي , ايرج هاشم زاده سقرلو