Abstract
Genetic (DNA) inactivation of fish sperm with ultraviolet irradiation is generally accompanied by a paradoxical effect on survival rates (Hertwig effect). In the present study, sperm samples from ten male bullseye puffer fish (Sphoeroides annulatus) were diluted 1:50 using Cortland's extender solution and used to test the effect of nine ultraviolet doses (0.2–1.0 J cm–2) on motility time in seconds, motility index, and embryo survival rate after fertilizing eggs from five bullseye puffer females. Motility time of sperm irradiated with 0.2–0.9 J cm–2 were not statistically different from the controls, but sperm irradiated with a dosage of 1.0 J cm–2 dosage had significant lower motility time. Motility indices (MI) allowed for the statistical differentiation of four groups in relation to their response to different radiation doses: the first had high MI, and included the controls and 0.2–0.3 J cm–2 treatments; the second had lower MI and included the 0.4–0.7 J cm–2 treatments; the third showed recovery of MI and included the 0.8–0.9 J cm–2 treatments; and the fourth showed the lowest MI with the 1.0 J cm–2 treatment. Embryo survival was highest for the controls and 0.2 J cm–2 treatment, decreasing in the 0.3–0.4 J cm–2 treatments, increasing again in the 0.5–0.8 J cm–2 treatments, until reaching lowest survival in the 0.9–1.0 J cm–2 treatments. These results indicate that the best ultraviolet dosage to achieve genetic inactivation of sperm of this species is close to 0.7 J cm–2, a dosage in which fish fry showed typical haploid syndrome characteristics.
Highlights
La fertilización externa en los peces facilita la manipulación de los gametos y las características genéticas que éstos portan (Purdom, 1983)
This study aims to determine the effect of nine doses of UV radiation on motility time and motility index of the spermatozoids of bullseye puffer, S. annulatus, and the survival rates of embryos at 24, 48 and 72 h of incubation, as a first step in establishing optimum conditions to produce genetically manipulated organisms
There were no significant differences between minimum and maximum motility time (MT) values (21.0 ± 0.0 and 40.0 ± 0.0 s, respectively) of control groups A and B; the values (25.6 ± 2.3 and 42.3 ± 4.0 s, respectively) for the C samples irradiated with 0.2–0.9 J cm–2 were high in relation to those of the control samples, though there was no significant difference
Summary
La fertilización externa en los peces facilita la manipulación de los gametos y las características genéticas que éstos portan (Purdom, 1983). Debido a que el empleo de radiaciones ionizantes como los rayos gamma y X generan individuos con características residuales de origen paterno (Chourrout, 1984), la inactivación completa del ADN de los espermatozoides se logra con luz UV (Jenneckens et al, 1999). Un fenómeno paradójico conocido en este tipo de experimentos es el llamado efecto de Hertwig, en el cual se observa que con ciertas dosis de radiación intermedia la supervivencia de los embriones muestra una ligera recuperación con respecto a dosis menores. Este fenómeno ha sido explicado por la supervivencia de espermatozoides cuyo ADN ha sido fragmentado por la radiación (y digerido por las nucleasas del huevo fertilizado), pero que conservan, no obstante, la motilidad necesaria para activar el desarrollo del huevo, que porta únicamente material genético de procedencia materna (Purdom, 1969, 1983)
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