Visual modelling supports the potential for prey detection by means of diurnal active photolocation in a small cryptobenthic fish

Active sensing has been well documented in animals that use echolocation and electrolocation. Active photolocation, or active sensing using light, has received much less attention, and only in bioluminescent nocturnal species. However, evidence has suggested the diurnal triplefin Tripterygion delaisi uses controlled iris radiance, termed ocular sparks, for prey detection. While this form of diurnal active photolocation was behaviourally described, a study exploring the physical process would provide compelling support for this mechanism. In this paper, we investigate the conditions under which diurnal active photolocation could assist T. delaisi in detecting potential prey. In the field, we sampled gammarids (genus Cheirocratus) and characterized the spectral properties of their eyes, which possess strong directional reflectors. In the laboratory, we quantified ocular sparks size and their angle-dependent radiance. Combined with environmental light measurements and known properties of the visual system of T. delaisi, we modeled diurnal active photolocation under various scenarios. Our results corroborate that diurnal active photolocation should help T. delaisi detect gammarids at distances relevant to foraging, 4.5 cm under favourable conditions and up to 2.5 cm under average conditions. To determine the prevalence of diurnal active photolocation for micro-prey, we encourage further theoretical and empirical work.

主动感知（active sensing）在利用回声定位（echolocation）与电感知（electrolocation）的动物中已有充分的研究记载。主动光定位（active photolocation），即依托光线开展的主动感知手段，相关研究却鲜少受到关注，且仅局限于生物发光的夜行性物种。不过已有研究证据显示，日行性的德氏三鳍鳚（Tripterygion delaisi）会通过受控的虹膜辐射行为——被命名为眼球闪光（ocular sparks）——来完成猎物探测。尽管该日行性主动光定位的行为模式已得到行为学层面的描述，但针对其物理过程的探索将为这一感知机制提供极具说服力的佐证。

在本研究中，我们旨在探究日行性主动光定位能够协助德氏三鳍鳚探测潜在猎物的具体条件。野外实验环节，我们采集了Cheirocratus属钩虾样本，并对其眼部的光谱特性进行了表征——该类动物的眼部具备强方向性反射结构。实验室环境下，我们量化了眼球闪光的尺寸及其角度依赖性辐射特性。结合环境光照测量数据以及德氏三鳍鳚视觉系统的已知特性，我们对多种场景下的日行性主动光定位过程进行了建模分析。

本研究结果证实，日行性主动光定位确实能够帮助德氏三鳍鳚在觅食相关的距离范围内探测到钩虾：有利条件下探测距离可达4.5厘米，普通条件下可达2.5厘米。为明确日行性主动光定位在微型猎物探测中的普及程度，我们呼吁学界开展更多相关的理论与实证研究。