Atlantic haddock (Melanogrammus aeglefinus) is a commercially important species of gadoid fish. In the North Sea, their main spawning areas are located close to the northern continental slope. Eggs and larvae drift with the current across the North Sea. However, fish larvae of many taxa can orient at sea using multiple external cues, including the Earth's magnetic field. In this work, we investigated whether haddock larvae passively drift or orient using the Earth's magnetic field. We observed the behavior of 59 and 102 haddock larvae swimming in a behavioral chamber deployed in the Norwegian North Sea and in a magnetic laboratory, respectively. In both in situ and laboratory settings, where the magnetic field direction was modified, haddock larvae significantly oriented toward the northwest. We conclude that haddock larvae orientation at sea is guided by a magnetic compass mechanism. These results have implications for retention and dispersal of pelagic haddock larvae.

大西洋黑线鳕（Melanogrammus aeglefinus）是一种商业上重要的浮游鱼类。在北海，它们的主要产卵区位于北部大陆坡附近。卵和幼虫随洋流漂流到北海。但是，许多类群的鱼幼体可以使用多种外部线索（包括地球磁场）在海上定向。在这项工作中，我们研究了黑线鳕幼虫是利用地球磁场是被动漂移还是定向运动。我们观察到分别在挪威北海和磁性实验室中部署的行为室中59和102只黑线鳕幼体的游泳行为。在两个原位在实验室环境中，磁场方向发生了变化，黑线鳕幼虫明显朝向西北方向。我们得出的结论是，黑线鳕幼虫在海上的定向是由磁罗经机制引导的。这些结果对浮游黑线鳕幼虫的保留和扩散具有影响。