The key behavioural, physiological and anatomical components of a magnetite-based magnetic sense have been demonstrated in rainbow trout (Oncorhynchus mykiss). Candidate receptor cells located within a discrete sub-layer of the olfactory lamellae contained iron-rich crystals that were similar in size and shape to magnetite crystals extracted from salmon. Here we show that these crystals, which mapped to individual receptors using con-focal and atomic force microscopy, are magnetic, as they are uniquely associated with dipoles detected by magnetic force microscopy. Analysis of their magnetic properties identifies the crystals as single-domain magnetite. In addition, three-dimensional reconstruction of the candidate receptors using confocal and atomic force microscopy imaging confirm that several magnetic crystals are arranged in a chain of about 1 μm within the receptor, and that the receptor is a multi-lobed single cell. These results are consistent with a magnetite-based detection mechanism, as 1-μm chains of single-domain magnetite crystals are highly suitable for the behavioural and physiological responses to magnetic intensity previously reported in the trout.
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