The Effects of Toluene on the Ontogenetic Development of the Fish, Oryzias latipes, the Japanese Medaka

Abstract

The effects of toluene to the ontogenetic development of the Cyprinodontid fish, Oryzias latipes, the Japanese Medaka was established. By the use of static bioassays, the median tolerance limits (TL 50 values) were calculated with their respective 95% confidence limits for different stages of embryonic development exposed to the chemical for periods of 24-hrs, 48-hrs, and 96-hrs. The TL 50 values were also obtained for embryos at the time of hatching of the eggs and at the time of the absorption of the yolk’s oil droplet, one week after hatching. The mortality effects of toluene to newly hatched fry were determined. Again TL50 values were obtained at 24-hrs, 48-hrs, 96-hrs, and 168-hrs exposure to toluene solutions. The effects of the chemical to the hatchability of the eggs was noted. The induction of gross anatomical deformities was examined. The results indicated that newly hatched fry, the earlier stages of development (before the hardendening of the chorion), and the later stages of development (prior to hatching) were t he more sensitive periods to the action of the toluene. The 96-hr TL50 values of these groups ranged from 20-30 mg/l toluene. Factors influencing mortalities were: (1) the stage of embryonic development at which the embryo was initially introduced to the toluene solutions, (2) the concentration of toluene in which the embryo was introduced, and (3) the duration of exposure to which the embryo was subjected. The induction of embryonic deformities was influenced by: (1) the degree of cellular organization at the time the embryo was initially introduced to the toluene, and (2) the concentration of toluene to which the embryo was treated. Deformities were restricted to those embryos treated with toluene before stage 28 (74 hrs). The more predominant deformities were: (1) disruptions of the cleaving blastomeres, (2) malformation of the heart and vitelline circulatory systems, (3) deformation of the eyes, (4) malformation of the tail musculature as indicated by a bending of the tail, and (5) a failure of some of the visceral organs to develop properly. Tissue of a mesodermal origin in whole or in part appeared to be most sensitive to the teratogenic action of toluene. The differential susceptibility of the embryos and fry was discussed in relation to the extent of cellular organization present at the time when first introduced in to the toluene solutions. The use of fish embryos in bioassays was discussed. Fish embryos appear to be well suited for screening tests in the determination of the toxic effects of aquatic pollutants.