Gilbert Beric M, Avenant-Oldewage Annemariè
Department of Zoology, University of Johannesburg, Johannesburg, South Africa.
Parasit Vectors. 2016 Jul 28;9(1):420. doi: 10.1186/s13071-016-1706-z.
Monogenea is a diverse group of ectoparasites showing great potential as sentinel organisms for monitoring environmental health. Exposure to metals negatively affects infrapopulations of monogeneans and exposure to aluminium has been found to negatively impact the survival of gyrodactylids.
Samples of infected host fish, the smallmouth yellowfish Labeobarbus aeneus (Cyprinidae), were collected from the Vaal Dam, South Africa and transported back to the laboratory in dark 160 l containers. Eggs of the monogenean Paradiplozoon ichthyoxanthon infecting L. aeneus were collected and exposed to varying concentrations of aluminium along with a control group in static tanks. The eggs were checked every 24 h and hatching commenced 13-14 days after exposure. Water samples were taken from exposure tanks and acidified for analysis of Al levels with inductively-coupled plasma mass spectrometry.
Hatching of eggs was variable between exposures, and in 30 μg Al/l and 60 μg Al/l was found to occur before eggs in control beakers, whereas, exposure to 120 μg Al/l delayed hatching and reduced hatchability. Survival of hatched oncomiracidia was concentration dependent and negatively correlated with aluminium concentrations. Lowest survival was recorded for 60 μg Al/l and 120 μg Al/l where all larvae died shortly after or during hatching. Normal development of embryos of P. ichthyoxanthon within eggs exposed to all doses of aluminium indicates that the egg shell is moderately impermeable to metals and inhibits movement of aluminium across the shell and interacting with developing embryos.
Higher larval mortality rate in 120 μg/l exposure can be related to aluminium crossing the egg shell in the late stages and causing death of unhatched yet fully developed embryos, possibly due to changes in the permeability of the egg shell as embryos neared developmental completion. Accelerated death of oncomiracidia after hatching indicates sensitivity toward high concentrations of aluminium.
单殖吸虫是一类多样的体外寄生虫，作为监测环境健康的指示生物具有巨大潜力。接触金属会对单殖吸虫的种群数量产生负面影响，并且已发现接触铝会对三代虫的生存产生负面影响。
从南非瓦尔大坝采集感染了宿主鱼类小口黄鲈（鲤科）的样本，并将其装在160升的深色容器中运回实验室。收集感染小口黄鲈的单殖吸虫黄斑副双身虫的卵，并将其与对照组一起置于静态水槽中，暴露于不同浓度的铝中。每24小时检查一次卵，暴露13 - 14天后开始孵化。从暴露水槽中采集水样并酸化，用感应耦合等离子体质谱法分析铝含量。
不同暴露组的卵孵化情况各不相同，在30μg Al/l和60μg Al/l浓度下，卵的孵化早于对照烧杯中的卵，而暴露于120μg Al/l会延迟孵化并降低孵化率。孵化出的纤毛幼虫的存活率与浓度有关，且与铝浓度呈负相关。在60μg Al/l和120μg Al/l浓度下记录到最低存活率，所有幼虫在孵化后不久或孵化期间死亡。暴露于所有铝剂量下的黄斑副双身虫胚胎在卵内正常发育，这表明卵壳对金属具有一定的不渗透性，可抑制铝穿过卵壳并与发育中的胚胎相互作用。
暴露于120μg/l时较高的幼虫死亡率可能与铝在后期穿过卵壳并导致未孵化但已完全发育的胚胎死亡有关，这可能是由于胚胎接近发育完成时卵壳通透性发生变化所致。孵化后纤毛幼虫的加速死亡表明其对高浓度铝敏感。
