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A common problem in marine fish hatcheries is the lack of functional embryonic parameters reliably predicting favorable larval outcomes. Embryos characterized as high-quality by typical assessment methods frequently result in weak larvae with high mortality during the endo-exotrophic transition. Thus, because there is no universal consensus on what parameters are most associated with successful larval survivability, this study aims to determine the most reliable, practical, and real-time predictor of vitality at the earliest developmental stage for first-feeding larvae of L. guttatus. From 18 mass volitional spawnings, the reproductive performance and quality of embryos and larvae were assessed by following quality parameters: total fecundity per spawning, percentage of floating eggs, fertilization rate, blastomere morphology score (at 8–32 cell stages), egg and oil globule volumes, coefficient of variation of eggs and oil globule diameters, percentage of poly-globular eggs, oil globule-to-egg volume percentage, morphological appearance and survival rates at 24 (hatching), 48 and 72 h post-spawning, larvae transition rate, and survival activity index (SAI). SAI was used as a larval vitality benchmark to determine the predictive capacity of the abovementioned parameters. Our results show that blastomere morphology score was the only parameter positively correlated with SAI. However, when examining each component of blastomere morphology to SAI prediction, only the presence of cell inclusions, but not size, symmetry, margins, or adhesions of blastomeres, predict the SAI. This reveals that embryos with defective blastomeres can develop into normal-appearing larvae but are weak to starvation. Therefore, cell inclusions are the best real-time, early, reliable, and functional predictor of first-feeding larvae vitality in L. guttatus.

Characteristics of the first blastomeres in fish have been evaluated in previous studies as a tool for predicting egg and larva quality. Nevertheless, there are still few studies of the presence of inclusions in fish blastodiscs or blastomeres. The object of the present study was to describe the relationship between cellular inclusions and some embryo quality parameters (symmetry, fertility rate, survival rate) in farmed coho salmon. Eggs from 261 females were fertilized with 400 × 103 spermatozoa/egg and incubated in the dark in separated flow-through incubators. Embryos at the four-cell stage were fixed in Stockard's solution and the blastodiscs were classified as: i) unfertilized, ii) fertilized with inclusion, and iii) without inclusion. The blastomere symmetry was also recorded. Embryos from 30 females (15 with and 15 without inclusions) were incubated until pigmented eye embryo stage to determine the survival rate. Cell inclusions were detected in 8.81 % of the females evaluated, with 24.1 ± 24.2 of the eggs from each of those females presenting inclusions. Egg samples with this abnormality showed significantly lower fertility, blastomere symmetry, and survival rate when compared with eggs without inclusions. • The term 'inclusion' is used to denote one or more holes of varying size and depth. • Inclusions can be found in the intracellular space of both blastomeres and blastodiscs. • Eggs with inclusions had low blastomere symmetry and survival rates. • As the percentage of inclusions increases, the fertility percentage decreases. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the efficacy of using different quality parameters to predict hatching percentage of fertilized eggs and early larval survival in a newly farmed species Polyprion oxygeneios (called ‘hapuku’ and ‘groper’ in New Zealand). Blastomere morphology was assessed for individual fertilized eggs, which were then incubated and monitored until hatch. Additionally, blastomere morphology, percentage of floating eggs, fertilization percentage and egg and lipid vesicle diameter were measured for multiple batches incubated during two consecutive captive hapuku spawning seasons in 2008 and 2009. The blastomere morphology score of individual fertilized eggs was significantly correlated with the percentage of individual fertilized eggs that hatched (R²=0.89, p <0.001). Furthermore, blastomere morphology score showed a significant correlation with the combined hatching percentage data from egg batches incubated in 2008 and 2009 (R²=0.32, p <0.001) and was also significantly correlated with larval survival to the post-yolk sac stage (R²=0.34, p =0.005). The percentage of floating eggs and fertilization percentage also significantly correlated with hatching success (R²=0.18 and 0.21 respectively, p<0.05) and with larval survival (R²=0.22 and 0.16 respectively, p <0.05). By comparison, egg diameter and lipid vesicle diameter showed no correlation with percentage hatch or with larval survival. We conclude that of all the egg quality parameters tested, the blastomere morphology score is the most useful and is an effective tool for assessing the quality of egg batches during hapuku hatchery management. [Copyright &y& Elsevier]

We investigated if simplified routines based on blastomere morphology and fertilization success can be used as predictors of egg and embryo viability in Atlantic cod, and abnormal blastomere morphology is related to juvenile deformities. Egg morphology data from 312 families that were produced by hand stripping of gametes were used. Fertilized eggs from all families were separately incubated in 25 L incubators. Blastomere morphology and fertilization success were assessed at 16-32 cell stage. Embryo mortality was measured until hatch. Fertilization success showed a significant positive correlation with the proportion of normal blastomere and 74% of the variation in the incidence of blastomere abnormality was explained by fertilization success. Juvenile deformities were positively correlated with blastomere abnormality and 8% of the variation in juvenile deformities was explained by incidences of blastomere abnormality. To our knowledge, this is the first direct evidence showing that incidences of blastomere abnormalities may be related to cod juvenile deformities. Our results suggest that fertilization success and the occurrence of blastomere abnormalities could be easily adopted by commercial cod hatcheries for the early determination of egg quality. [ABSTRACT FROM AUTHOR]