A 9-week study was conducted to evaluate the potential of processed animal protein (PAP) in comparison with soybean meal (SM) to replace fish meal (FM) in practical diets for European catfish, Silurus glanis, on growth performance, liver transaminase activities and expression of growth-related genes. Seven isonitrogenous (440 g kg -1 crude protein) and isoenergetic (16.70 MJ/kg) practical diets were formulated by replacing 0 (control), 30%, 60% and 100% FM with either SM or PAP. Each diet was randomly assigned to triplicate groups of 25 fish per cages fixed in the pond. Fish fed the diet substituted 100% FM from SM or PAP had lower (p < .05) growth performance, feed efficiency and protein retention compared to control and other groups. The decreased growth performance occurred concomitant with a decline in the expression level of liver GHR/IGF-I axis genes. The gene expression and activity of liver protein metabolism enzymes also positively correlated with growth performance. Findings of this study indicated that both SM and PAP were equally effective in replacing FM up to 60% in the practical diet of Silurus glanis. Total replacement of FM either with SM or PAP induced negative influences on growth and feed utilization. K E Y W O R D Sgene expression, growth, processed animal protein, protein metabolism, Silurus glanis, soybean meal

Two species from the families Acipenseridae and Polyodontidae, Russian sturgeon (Acipenser gueldenstaedtii, Brandt and Ratzeberg, 1833; functional tetraploid) and American paddlefish (Polyodon spathula, Walbaum 1792, functional diploid) were hybridized. The hybridization was repeated using eggs from three sturgeon and sperm from four paddlefish individuals. Survival in all hybrid family groups ranged from 62% to 74% 30 days after hatching. This was the first successful hybridization between these two species and between members of the family Acipenseridae and Polyodontidae. Flow cytometry and chromosome analysis revealed two ploidy levels in hybrids. The chromosome numbers of the hybrids ranged between 156–184 and 300–310, in “functional” triploids and “functional” pentaploids, respectively. The hybrid origin and the ploidy levels were also confirmed by microsatellite analyses. In hybrids, the size and the number of dorsal and ventral scutes correlated with the ploidy levels as well as with the calculated ratio of the maternal and paternal chromosome sets. An extra haploid cell lineage was found in three hybrid individuals irrespective of the ploidy level, suggesting polyspermy. Although the growth performance showed high variance in hybrids (mean: 1.2 kg, SD: 0.55), many individuals reached a size of approximately 1 kg by the age of one year under intensive rearing conditions.