The objectives were to assess motility, fertilizing capacity, structural integrity, and mitochondrial function in fresh versus frozen-thawed (15% DMSO was used as a cryoprotectant) sperm from red seabream (Pagrus major). Mean (+/-S.D.) rates of motility, fertilization and hatching of frozen-thawed sperm were 81.0+/-5.4, 92.8+/-1.9, and 91.8+/-5.2%, respectively; for fresh sperm, they were 87.5+/-7.7, 95.8+/-2.4, and 93.8+/-4.2%. Although motility was lower in frozen-thawed versus fresh sperm (P<0.05), there was no effect (P>0.05) of cryopreservation on fertilization or hatching. Based on scanning and transmission electron microscopy, 77.8+/-5.6% of fresh sperm had normal morphology, whereas for frozen-thawed sperm, 63.0+/-7.2% had normal morphology, 20.6+/-3.1% were slightly damaged (e.g. swelling or rupture of head, mid-piece and tail region as well as mitochondria), and 16.4+/-4.2% were severely damaged. Sperm were stained with propidium iodide and Rhodamine 123 to assess plasma membrane integrity and mitochondrial function, respectively, and examined with flow cytometry. For fresh sperm, 83.9% had an intact membrane and functional mitochondria, whereas for frozen-thawed sperm, 74.8% had an intact membrane and functional mitochondria, 12.7% had a damaged membrane, 9.9% had nonfunctional mitochondria, and 2.6% had both a damaged membrane and nonfunctional mitochondria. In conclusion, ultrastructure and flow cytometry were valuable for assessment of frozen-thawed sperm quality; cryopreservation damaged the sperm but fertilizing ability was not significantly decreased.

Highly stereoregulated syndiotactic-polystyrene/polyethylene (s-PS/PE) block copolymers with variable ethylene block lengths are synthesized using the sequential monomer feed scheme with C5H5TiCl3 catalyst. The copolymer, after removing the atactic portion, is separated into two fractions by tetrahydrofuran (THF). The insoluble fraction contains a highly stereoregulated s-PS block linked with PE blocks, while the soluble fraction also contains a highly stereoregulated s-PS block but separated randomly by a shorter or isolated ethylene unit. For the I-fraction, rE=25±5 and rS=1.9±0.3, and for the S-fraction rE=0.4±0.1 and rS=0.34±0.15. These results are compared with prior studies, where mainly random type PS/PE copolymers with low styrene stereoregularity and rigio-irregular styrene and polyethylene are produced. Apparently, both the sequential feed scheme coupled with the use of a lower reactivity metallocene catalyst facilitated the switching of catalytical sites with the majority product being of block nature.