There is a lack of information on the morphology of the first blastomeres that could be used as a diagnostic tool for the first stages of embryonic development for Coho salmon. The purpose of this investigation, therefore, was to characterize morphometrically the first blastomeres of Coho salmon (Oncorhynchus kisutch). In total, 660 embryonic discs from a pool of eggs that had been fertilized and incubated at 5°C and after 19 h of incubation were extracted and photographed. Of these, 20 microphotographs of blastodiscs of normal appearance were analyzed morphologically (control blastodiscs: CB) and 100 random microphotographs from the whole group were classified as either symmetrical or asymmetrical according to their morphology and then compared with the CB. The length and width of each blastomere and the proportions of length and width were measured to determine symmetry in the embryos at the 4-cell stage. Seven categories were created to characterize the blastomeres: 38% normal (G1); 26% unequal (G2); 10% ‘pie-shaped’ (G3); 10% amorphous (G4); 8% with three equal and one unequal blastomere (G5); 6% ‘clover-shaped’ blastomeres (G7), and 3% with inclusions. The mean of the proportions of lengths and widths of the groups of blastomeres that were measured was 0.87 ± 0.08 and 0.85 ± 0.07, respectively. The morphometric results that were obtained in this investigation are compared with the results observed by other authors for teleostei and are discussed.

The growth response of diploid (2n) and thermally-induced triploid (3n) coho salmon to injected recombinant porcine somatotropin was examined over a 10 week period. All treatments were under-taken using replicate groups of 25 animals per group. Control 2n and 3n replicate groups grew at identical rates throughout the period of study, although 3n fish exhibited lower condition factors. Recombinant poreine somatotropin treated 2n and 3n fish responded positively to therapy and, by week 4 of the trial, expressed significantly greater increases in both weight and length (p < 0.01) when compared to controls. At the end of the study period, soinatotropin treated animals had gained approximately twice the amount of weight of controls. Food conversion efficiencies were greater in treated salmon, regardless of ploidy state. This relationship also extended to weight and length specific growth rates. The economic benefits of commercial application of recombinant porcine somatotropin therapy to triploid Pacific salmon culture are discussed.