Effects Of Low-Dose Tetracycline Hydrochloride On Zebrafish Reproduction

Antibiotics are widely used in animal husbandry,among which tetracycline antibiotics（TCs）broad-spectrum antibiotics are the most used.Because the abuse of antibiotics in the aquaculture industry causes accumulation in animals,the drug progenitor is also excreted in the feces and enters the environment,causing serious environmental pollution.This experiment uses zebrafish as a model animal to evaluate the toxicity of low-dose Tetracycline hydrochloride（TCH）.Select4-month-old parents（F0 generation）15 female and male zebrafish,repeat 4 times.The zebrafish were treated with low-dose TCH(0.1μg·L^-1,1μg·L^-1,and 100μg·L^-1)for 30 days,and then mated to obtain the next generation of zebrafish（F1 generation）.Low-dose TCH exposure led to a significant reduction in the cumulative spawning rate of zebrafish.Compared with the control group,the 0.1,1 and 100μg·L^-1 TCH exposure groups（female and male fish exposed at the same time）decreased by25.57%,51.78%and 55.64%（P<0.05）,respectively.The overall quality of fish eggs also decreased significantly（P<0.05）.Histological examination revealed that ovarian development was delayed and mature follicles were reduced.Compared with the control group,the 1 and 100μg·L^-1 TCH exposure groups decreased by 32.13% and 48.39%,respectively,the development of the testis was also inhibited,and the percentage of mature sperm decreased by 12.96%and 39.25%（P<0.05）.Further detection by fluorescence quantitative PCR found that TCH significantly inhibited the expression of reproductive-related genes,such as cyp19a,vtg1 and vasa mRNA in the gonadal tissue,and was dose-dependent（P<0.05）.Compared with the control group,100μg·L^-1 TCH exposures caused a decrease in the expression of cyp19a1a and vtg1 mRNA in zebrafish ovarian tissue by 0.34 and 0.43 times,respectively,and a decrease in the expression of cyp19a1b mRNA in the brain tissue of zebrafish（female and male）by 0.62 and 0.75 times（P<0.05）.Although the F1 generation was not exposed to TCH,there were malformations such as pericardial edema,yolk edema,and notochordal curvature,and the total malformation rate was significantly increased（P<0.05）.Compared with the control group,1 and 100μg·L^-1 TCH exposure caused an increase in the length of the mandible and the length of the mandibular arch,and a decrease in the width of the mandible and the length of the hyoid angle in zebrafish juveniles.Further detection of genes associated with cartilage development,1 and 100μg·L^-1 TCH exposure inhibited the expression of runx1,sox9a,sox10,and col2α1a mRNA in F1 juveniles,respectively（P<0.05）.The above research results indicate that the residue and pollution caused by low-dose TCH may affect the reproductive function of adult zebrafish and the cartilage development of next-generation embryos.The experiment also provides important indicators for the safety assessment of TCs in the environment.