壳聚糖对泥鳅毒性及其引发急性死亡分析

Toxicity of Chitosan on Loach and Mechanism behind Its Acute Lethal Effect on Loach

壳聚糖对动物的安全性是公认的,但壳聚糖能造成泥鳅急性死亡,其死亡原因值得探索,因此本实验研究了不同种类、不同质量浓度的壳聚糖对泥鳅死亡的影响,并观察泥鳅死亡症状,测定半致死剂量(half lethal concentration,LC_(50))、呼吸强度、细胞膜透性、红细胞核异常情况等。结果发现不同壳聚糖均能引起泥鳅快速死亡,且质量浓度和温度越高,泥鳅死亡速度越快,壳聚糖对泥鳅的LC_(50)为16 mg/L。壳聚糖可引起泥鳅体表黏液大量脱落,导致液体浑浊;破坏泥鳅皮肤结构,影响鱼鳃呼吸;刺激泥鳅早期快速游动;显著增加泥鳅呼吸强度,导致水中溶解氧质量浓度低于极限值;使泥鳅耗尽自身糖原,导致后期无力浮出水面进行肠呼吸;促进泥鳅体内的氯、钠、钾离子和氨大量渗出,破坏细胞正常功能。壳聚糖引发泥鳅急性死亡主要与壳聚糖损害泥鳅呼吸系统有关,但壳聚糖一般不会进入人类呼吸系统,因此壳聚糖按照食品添加剂标准使用还是安全的。

It is well known that chitosan has no toxicity to animals. Surprisingly, however, chitosan has an acute lethal effect on loach (Misgurnus anguillicaudatus). The underlying mechanism deserves to be explored. In this study, we evaluated the effect of different types and concentrations of chitosan on the death of loach, and this study also observed symptoms during the dying process and measured half lethal concentration (LC 50), respiration rate, cell membrane permeability and erythrocyte cell nucleus abnormality. Results showed that all types of chitosan caused loach to rapidly die. Higher chitosan concentration or higher temperature accelerated the dying process. The LC 50 of chitosan for loach was determined as 16 mg/L. In the presence of chitosan, large quantities of mucilage fell off the surface of loach skin, thus making the water appear turbid. Moreover, chitosan destroyed the structure of loach skin, affected gill respiration, stimulated loach to rapidly swim at the early stage of the experiment, and significantly increase respiration rate, resulting in a dissolved oxygen concentration below the safe limit. After using up all the glycogen, loach could not come up to the water surface and have to respire through intestine at the later stage of the experiment. Chitosan also led to exudation of large amounts of chlorine, sodium, potassium ion and ammonium from loach and destroyed cell functions. In conclusion, chitosan exerts its lethal effect on loach mainly by destroying therespiratory system. Since chitosan normally does not enter the human respiratory system, it can be used safely as a food additive.