Embryonic and larval development of reciprocal diploid and triploid hybrids of Caspian trout (Salmo caspius) and rainbow trout (Oncorhynchus mykiss)

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 9O. mykissx male S. caspius hybrids (2nR x C and 3nR x C); (5) diploid and (6) triploid 9S. caspiusx male O. mykiss hybrids (2nC x R and 3nC x 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 x C group, 45% in 3nR x C group, whereas all embryos died before the eyed stage in 2nC x R and 3nC x R groups. Chromosome number ranged between 57 and 61 and 78-81 in 2nR and 2nC groups, 69-71 in 2nR x C and 99-103 in 3nR x 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 x C groups than in 2nC group. The highest final weight and specific growth rate were observed in 2nR and 3nR x C groups. We have demonstrated that triploidy induction can increase the survival rate of distant hybrid (9O. mykissx male S. caspius) and identified the key embryonic stages that could help introduce this hybrid into aquaculture. The hybrid could be easily commercialized if they show significant improvement in growth, survival and disease resistance.