Effect of nonylphenol on giant freshwater prawn (Macrobrachium rosenbergii) via oral treatment: Toxicity and messenger RNA expression of hemocyte genes

A previous in vitro study has indicated that two alkylphenol ethoxylates (APEs) could potentially damage hemocytes and influence cellular immunity of prawns (Macrobrachium rosenbergii). The aim of this study was to investigate the effects of nonylphenol (NP) on susceptibility to a pathogen and on the mRNA expression of hemocyte genes, including four immune-related genes. NP at different concentrations was fed continuously to prawn (M. rosenbergii) for 1, 3, 6, and 9 days. Challenging prawns with Lactobacillus garvieae resulted in 44-50%, 20-24% and 10-12% mortality were detected after prawns were fed with 100, 10 and 1 μg of NP/prawn for 6 days, respectively. In comparison with control prawns fed with phosphate-buffered solution (PBS), the increase of mRNA levels of four immune-related genes, alpha-2 microglobulin (α-2m), antimicrobial peptides (amp), peroxinectin (pon), and prophenoloxidase (propo), was detected on days 1, 3 and 6 after feeding with 100 μg/prawn; on day 9, only the mRNA level of amp of the NP-treated group was significantly increased, while that of the remaining groups was not different from that of the control. In addition, two other hemocyte genes were also studied, including a respiration-related gene, cytochrome oxidase subunit (cos), and an unknown gene, L12X3. The mRNA level of cos was elevated during the experimental period, but an increase of L12X3 expression was detected only on day 1 after treatment. Regarding sensitivity of these genes to NP, the results from NP-treated prawns on day 1 after treatment revealed (1) that mRNA expression of the six genes in the 100-μg-NP-treated group was significantly different from that of control group, (2) that the mRNA levels of three immune-related genes (amp, pon and propo) in 10-μg-treated group were significantly higher than that of control group, and (3) that a significant change of propo was detected in 1-μg-treated group. These results suggest that NP may enhance the immune response of prawns, but the effect created by a high concentration of NP may damage prawns, and then increase the susceptibility to pathogen.