Singo Alukhethi, Myburgh Jan G, Laver Peter N, Venter Elizabeth A, Ferreira Gezina C H, Rösemann Gertruida M, Botha Christo J
Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, South Africa.
Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, South Africa.
Toxicon. 2017 Aug;134:50-56. doi: 10.1016/j.toxicon.2017.05.017. Epub 2017 May 19.
Cyanobacteria or blue green algae are known for their extensive and highly visible blooms in eutrophic, stagnant freshwater bodies. Climate change and global warming have also contributed to a rise in toxic cyanobacterial blooms. One of the most important cyanobacteria is Microcystis aeruginosa, which can synthesize various microcystins that can affect the health of terrestrial and aquatic animals. Commercial Nile crocodile (Crocodylus niloticus) farming in South Africa is based on keeping breeders (adult males and females) in big dams on farms (captive-bred approach). Unfortunately, cyanobacterial blooms in the breeder dams are a concern to farm owners, managers and veterinarians. The main objectives of this research project were to determine if microcystins were present in the contents of crocodile eggs and the liver and yolk of dead hatchlings, and to determine if the reduced hatchability on commercial farms might be caused by these toxins. Furthermore, the concentration of microcystins in the breeder dam was monitored on a monthly basis spanning the ovulation and egg laying period. During the hatching season microcystin concentrations in unfertilised eggs, egg shell membranes and in the yolk and liver of dead hatchlings were determined using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Microcystins were detected in Nile crocodile egg and hatchling samples. Microcystin (MC-LR, MC-RR, MC-YR) concentrations in the crocodile egg and hatchling samples collected from clutches with a good hatching rate (≥90%) ranged between 0 and 1.76 ng g, with the highest concentration in the egg shell membranes. Microcystin concentrations in samples collected from clutches with a bad hatching rate (≤10%) ranged from 0 - 1.63 ng g with the highest concentration detected in the hatchling yolk. However, the concentrations were probably underestimated as the percentage recovery from spiked samples was very low with the extraction method employed. Bayesian analysis suggests that the liver, yolk and unfertilised egg all have similar microcystin concentrations, while the membranes have (with moderate to high certainty) higher microcystin concentrations. There appears to be no difference in microcystin concentrations among good and bad clutches across all tissue types or within a specific tissue type, but due to the small sample size, it was not possible to determine whether microcystin affected the hatchability of Nile crocodile eggs. However, vertical transmission of microcystin variants to the Nile crocodile egg does occur and the possible implications for the survival of wild Nile crocodile populations should be ascertained.
蓝藻或蓝绿藻以在富营养化、停滞的淡水水体中大量繁殖且极易被看见而闻名。气候变化和全球变暖也导致了有毒蓝藻水华的增加。铜绿微囊藻是最重要的蓝藻之一，它能合成多种微囊藻毒素，这些毒素会影响陆生和水生动物的健康。南非的商业尼罗鳄（Crocodylus niloticus）养殖基于将种鳄（成年雌雄鳄）饲养在农场的大型水坝中（圈养繁殖方式）。不幸的是，种鳄水坝中的蓝藻水华令农场主、管理人员和兽医担忧。该研究项目的主要目标是确定尼罗鳄卵的内容物以及死亡幼鳄的肝脏和卵黄中是否存在微囊藻毒素，并确定商业农场孵化率降低是否可能由这些毒素引起。此外，在排卵和产卵期间，每月监测种鳄水坝中微囊藻毒素的浓度。在孵化季节，使用液相色谱 - 高分辨率质谱法（LC - HRMS）测定未受精卵、卵壳膜以及死亡幼鳄的卵黄和肝脏中的微囊藻毒素浓度。在尼罗鳄卵和幼鳄样本中检测到了微囊藻毒素。从孵化率良好（≥90%）的窝中收集的鳄鱼卵和幼鳄样本中的微囊藻毒素（MC - LR、MC - RR、MC - YR）浓度在0至1.76纳克/克之间，卵壳膜中的浓度最高。从孵化率差（≤10%）的窝中收集的样本中的微囊藻毒素浓度在0 - 1.63纳克/克之间，幼鳄卵黄中的浓度最高。然而，由于所采用的提取方法对加标样品的回收率非常低，这些浓度可能被低估了。贝叶斯分析表明，肝脏、卵黄和未受精卵中的微囊藻毒素浓度相似，而膜中的微囊藻毒素浓度（具有中等至高确定性）更高。在所有组织类型中，孵化率良好和差的窝之间或特定组织类型内，微囊藻毒素浓度似乎没有差异，但由于样本量小，无法确定微囊藻毒素是否影响尼罗鳄卵的孵化率。然而，微囊藻毒素变体确实会垂直传播到尼罗鳄卵中，应确定其对野生尼罗鳄种群生存的可能影响。
