Nonnative grass carp Ctenopharyngodon idella have been used in the United States to control aquatic plants for approximately 42 years and are widely dispersed across 45 states, with reproduction occurring in 7 Mississippi River basin states. To prevent grass carp establishment and spread, a functionally sterile version—triploid grass carp—was produced in the early 1980s. However, there is uncertainty today regarding sterility and the efforts associated with triploid grass carp production and distribution. We reviewed relevant literature to summarize biological issues of interest to fishery managers: cell division for sexual reproduction, the induction of triploidy, sterility, reversion from the triploidy to diploidy, and pertinent aspects of the U.S. Fish and Wildlife Service's triploid grass carp certification program. Received December 13, 2010; accepted May 18, 2011

Amoebic gill disease (AGD), caused by the amoeba Neoparamoeba perurans, has led to considerable economic losses in every major Atlantic salmon producing country, and is increasing in frequency. The most serious infections occur during summer and autumn, when temperatures are high and poor dissolved oxygen (DO) conditions are most common. Here, we tested if exposure to cyclic hypoxia at DO saturations of 40–60% altered the course of infection with N. perurans compared to normoxic controls maintained at ≥90% DO saturation. Although hypoxia exposure did not increase initial susceptibility to N. perurans, it accelerated progression of the disease. By 7 days post-inoculation, amoeba counts estimated from qPCR analysis were 1.7 times higher in the hypoxic treatment than in normoxic controls, and cumulative mortalities were twice as high (16 ± 4% and 8 ± 2%), respectively. At 10 days post-inoculation, however, there were no differences between amoeba counts in the hypoxic and normoxic treatments, nor in the percentage of filaments with AGD lesions (control = 74 ± 2.8%, hypoxic = 69 ± 3.3%), or number of lamellae per lesion (control = 30 ± 0.9%, hypoxic = 27.9 ± 0.9%) as determined by histological examination. Cumulative mortalities at the termination of the experiment were similarly high in both treatments (hypoxic = 60 ± 2%, normoxic = 53 ± 11%). These results reveal that exposure to cyclic hypoxia in a diel pattern, equivalent to what salmon are exposed to in marine aquaculture cages, accelerated the progression of AGD in post-smolts.