Study of the first blastomeres in Coho salmon (Oncorhynchus kisutch)

Abstract

Summary 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.

Morphometric of blastomeres in Salmo salar

“…For this study in S. salar , a morphometrical criterion was used for the first time to evaluate these asymmetries, an approach similar to that considered in Oncorhynchus kisutch by Effer et al . (2012). For this criterion, the ratio of all lengths and widths of blastomeres incubated (BC, 20 and 24 h groups), was close to 1 (Fig.…”

“…1) following the criteria proposed by Effer et al . (2012). For the morphometric description of the blastodisc with four blastomeres, we proceeded in the same way for each blastodisc and evaluated symmetry by comparison of the ratios of the length (L1/L2, L1/L3, L1/L4, L2/L3, L2/L4, L3/L4) and width (W1/W2, W1/W3, W1/W4, W2/W3, W2/W4, W3/W4; Fig.…”

“…‘Before’ fertilization, there are mechanism that are responsible for initiation of sperm motility, and also the morphology and quality of the plasmatic membrane of spermatozoa; the physical and chemical parameters of ovary or coelomic fluid, and the appearance of the oocyte during its first stages of development (Kjørsvik et al ., 1990; Bromage et al ., 1994; Penney et al ., 2006; Pavlov & Emel′yanova, 2008); the volume of the egg and the lipid drop of species such as Seriola lalandi (Moran et al ., 2007); and the composition of lipids and fatty acids in fish eggs and semen of species such as Oncorhynchus mykiss (Vassallo-Agius et al ., 2001), Dexten dexten (Giménez et al ., 2006) and Ictalurus punctatus (Sink & Lochmann, 2008). ‘During’ embryonic development, the characteristics and abnormalities of the blastomeres have been used as criteria to discriminate between good and bad quality embryos (Kjørsvik et al ., 1990, 2003; Bromage et al ., 1994; Shields et al ., 1997; Penney et al ., 2006; Pavlov & Emel′yanova, 2008; Avery et al ., 2009; Bobe & Labbé, 2010; Vásquez et al ., 2010; Effer et al ., 2012; Valdebenito et al ., 2012), whereas in Hippoglossus hippoglossus different characteristics of the blastomeres (symmetry, cell size, adhesion between blastomeres, margins and inclusions) are correlated positively with the percentage of hatched larvae (Shields et al ., 1997). In Scophthalmus maximus the symmetry of blastomeres is correlated positively with hatching rates, larval tolerance towards stress and larval survivability, metamorphosis and pigmentation (Kjørsvik et al ., 2003).…”

“…(2012) and Effer et al . (2012) have detailed for the first time morphometric aspects of blastomeres in rainbow trout and Atlantic salmon, respectively. In Atlantic salmon, Gorodilov (1996) characterized embryonic development and observed the first cleavage after 19 h of incubation at 5 °C, but this study lacked information on the morphometrics of the first blastomeres.…”

“…The first characterizations of blastomeres was made for brown trout (Salmo trutta fario) using drawings (Kopsch, 1911 in Kunz, 2004) or entirely with microphotography using embryonic discs (Killeen et al, 1999), in the same manner as for rainbow trout (Salmo gairdneri) by Ballard (1973Ballard ( , 1985. More resent studies by Valdebenito et al (2012) and Effer et al (2012) have detailed for the first time morphometric aspects of blastomeres in rainbow trout and Atlantic salmon, respectively. In Atlantic salmon, Gorodilov (1996) characterized embryonic development and observed the first cleavage after 19 h of incubation at 5 • C, but this study lacked information on the morphometrics of the first blastomeres.…”