Morphometric of blastomeres in Salmo salar.

For Salmo salar, there is a lack of information on the morphology of the first blastomeres formed during embryonic development and which could be used as a diagnostic tool for the first stages of development. The purpose of this investigation, therefore, was to characterize morphometrically the first blastomeres of S. salar. From a pool of eggs incubated at 7.5°C, 100 microphotographs of blastodiscs were extracted and analyzed at different incubation periods: 12, 14, 16, 20 or 24 h. Blastodiscs were characterized morphologically after 16, 20 or 24 h incubation, and classified into symmetric or asymmetric groups according to their morphology. The ratio of length (L) versus width (W) of each blastomere was determined, to establish its symmetry. In addition, 20 microphotographs of blastodiscs of normal appearance were analysed morphologically (control blastodisc: CB) for comparison (20 or 24 h). Results show that the first cleavage ends after 16 h of development. Seven categories were established during blastomere characterization: 47% normal (G1); 27% with dispersed margins (G2); 10% unequal (G3); 9% 'pie-shaped' (G4); 3% amorphous (G5); 2% three equal blastomeres and one different one (G6); and 2% with eccentric cleavage (G7). Although the incidence of abnormal cleavage in S. salar is uncertain, there is a potential for some asymmetries to be corrected during embryogenesis to generate viable individuals. More studies are necessary to correlate these abnormal cleavage patterns with indicators of quality in the later stages of embryogenesis in this species, to establish a quality assessment tool for gametes and/or embryos in salmonid species.

Morphometric characterization of the first blastomeres of rainbow trout (Oncorhynchus mykiss).

In the following investigation the morphometric characteristics of the first two blastomeres of rainbow trout (Oncorhynchus mykiss) were determined. Embryos were incubated at 9°C and then fixed in a Stockard solution every 30 min starting from 8.5 to 12.5 h of incubation post fertilization. Embryonic discs were extracted and microphotographs were taken with Q Capture Pro 5.0 software using a stereomicroscope Olympus SZX7. The average size of the blastodiscs was 941.22 ± 160.42 µm. The first cleavage finished after approximately 12 h of incubation. The first two blastomeres were regularly symmetrical in their morphology. Blastomere 1 had an average length (L) of 942.68 ± 105.56 µm and width (W) of 467.34 ± 64.33 µm. Blastomere 2 had an average length of 887.60 ± 101.65 and width of 454.49 ± 47.25 µm (n = 91). Significant differences were found between the length and width of blastomeres 1 and 2. The proportion between the length of blastomeres 1 and 2 was 0.94 ± 0.07 (n = 91); between the width of blastomeres 1 and 2 it was 0.88 ± 0.11 (n = 91); and the width/length ratio was 0.51 ± 0.09 (n = 182). It was concluded that rainbow trout blastomeres tend to be asymmetrical in length with a higher dispersion of widths.