Early developmental responses to environmental stimuli in the fathead minnow, Pimephales promelas

59Aquatic organisms rely on multiple types of environmental sensory stimuli to detect and respond to challenges and opportunities. Although most research on the sensory ecology and development of behavior in fishes has focused on responses to these stimuli at adult and larval stages, emerging research suggests that embryos can also perceive and respond to these cues. This study aimed to i) determine the window(s) of development during which aquatic, oviparous embryos of a common freshwater fish species, fathead minnow (Pimephales promelas) first show behavioral responses to ecologically relevant chemical, photosensory, and mechanosensory stimuli; ii) evaluate whether embryos differentiate between chemical alarm cues generated from adults vs injured eggs; and iii) investigate the influence of the olfactory developmental environment on hatching, development, and post-hatch behavior. To determine the earliest onset of behavioral responses to external stimuli in alternative sensory modalities, the locomotor activity of embryos was measured in response to adult conspecific alarm cues, chemical cues from injured eggs, scent of a common piscivorous predator, an aversive light stimulus, and a vibrational/water displacement disturbance at 48, 72, 96, and 120 hours post-fertilization (hpf). To determine whether the information content of particular cues (i.e., those that indicate predation on eggs vs adults) influences the development or behavior of minnows, eggs were reared with daily exposure to adult alarm cues, egg alarm cues, or a control water treatment and evaluated for differences in morphology, hatching time, and post-hatch behavior. Responses to mechanosensory cues were first detected at 72 hpf, and responses to photosensory and olfactory cues were first detected at 96 hpf. Embryos showed observable changes in pre-hatch behavior in response to olfactory cues from injured eggs, but not to adult alarm cues or cues from a common predator. There were no significant differences in development or hatching time, or behavioral carryover effects in fishes that developed in the presence of either alarm cue compared to controls. Taken together, these results add to the growing body of literature on embryonic sensory ecology and development of behavior by providing evidence that embryos not only can detect and react to environmental cues in multiple sensory modalities, but that they may also discriminate between cues based on information content and show heightened sensitivity to cues associated with greater risk.