Guiding the path of larvae: the potential of light traps in neotropical freshwater fish research

Light traps are devices utilized in biomonitoring studies across various aquatic environments. Although light traps are used globally, few studies report their efficacy in capturing fish larvae in the Neotropics. To address this gap, this study aimed to assess the efficacy of light traps in capturing larvae of six fish species commonly found in Neotropical rivers. Additionally, we aimed to evaluate the effect of light color on larval capture. To accomplish this, we selected larvae from six species: Cyprinus carpio, Ctenopharingodon idella, Piaractus mesopotamicus, Pimelodus maculatus, Prochilodus lineatus, and Rhamdia quelen. Each experiment lasted seven days, and six types of traps were tested, including those without light (control) and those with light (green, red, yellow, white, and blue), and installed in triplicate. A total of 18 traps were randomly positioned in earthen ponds containing the six species of interest. Each species was assessed separately in six experiments. Larvae were counted, measured, and identified daily according to their developmental stage. The light traps collected 30,498 larvae, whereas the control traps only collected 39 larvae by the end of the experiment. Larvae from species of the Cypriniformes order were the most captured, while those from the Siluriformes order were least captured. The light traps exhibited selectivity in capturing larvae at different developmental stages, which varied according to species. Traps installed with green lights captured a greater number of larvae and were more efficient at capturing larvae from a wider variety of species. In contrast, traps installed with red light led to the capture of fewer larvae. Therefore, by their ability to attract a greater number of larvae, compared to control, and selectively capture larvae at different developmental stages at variable rates, depending on light source, light traps can be a valuable tool in biomonitoring and managing fish larvae in Neotropical environments.