We suggest helminthological investigations of cod as a supplement to traditional biological and hydrographical methods for elucidation of ecological changes in the Baltic Sea. It is under discussion if oxygen deficit or seal abundance should explain the present critical situation of Baltic cod. A comparative investigation of endoparasitic helminths in Baltic cod (Gadus morhua), captured in the same marine habitat with an interval of 35 years (1983/2018) recorded 11 species of helminths comprising trematodes (Hemiurus luehei, Podocotyle atomon, Lepidapedon elongatum), nematodes (Contracaecum osculatum, Hysterothylacium aduncum, Capillaria gracilis, Cucullanus cirratus), cestodes (Bothriocephalus sp.) and acanthocephalans (Echinorhynchus gadi, Pomphorhynchus laevis, Corynosoma semerme). Significant prevalence and intensity increases were recorded for third-stage larvae of the nematode C. osculatum (liver location) and larvae of C. semerme (encapsulated in viscera). Both parasite species use grey seal as their final host, indicating the recent expansion of the Baltic seal population. A lower E. gadi intensity and an increased prevalence of L. elongatum of small cod (31–40 cm body length) suggest a lowered intake of amphipods (intermediate host) and elevated ingestion of polychaetes, respectively, but no significant changes were seen for other helminths.

中文翻译：

---

波罗的海鳕鱼内寄生虫反映了最近的生态变化

我们建议对鳕鱼进行蠕虫学研究，作为传统生物和水文方法的补充，以阐明波罗的海生态变化。目前正在讨论氧气不足或海豹丰度是否应该解释波罗的海鳕鱼目前的危急情况。波罗的海鳕鱼体内寄生蠕虫的比较调查（虎杖)，在同一海洋栖息地捕获，间隔 35 年 (1983/2018) 记录了 11 种蠕虫，包括吸虫 (半鹌鹑,足叶原子,细长鳞甲鱼), 线虫 (盲肠盲肠,鲢鱼,纤细毛细血管,卷须葫芦), 绦虫 (头螟sp.) 和棘头动物 (刺鳐,绒毛龙,棒状体）。线虫第三阶段幼虫的流行率和强度显着增加C. osculatum（肝脏位置）和幼虫C. semerme（包裹在内脏中）。两种寄生虫都使用灰海豹作为最终宿主，这表明波罗的海海豹种群最近有所扩张。一个较低的E.加迪强度和患病率增加细长乳杆菌小鳕鱼（体长 31-40 厘米）分别表明片脚类动物（中间宿主）的摄入量减少和多毛类动物的摄入量增加，但其他蠕虫没有观察到显着变化。