The neon tetra (Paracheirodon innesi) is a commercially important freshwater aquaculture species popular within the ornamental fish trade. Mortality during larval rearing of this species can limit domestic production, thus further research is needed to diminish bottlenecks and improve efficiency. Poor spawning and survival in early larval rearing of P. innesi may be attributed to suboptimal lighting conditions. This investigation aimed to advance our understanding of visual system ontogeny in larval P. innesi to help predict appropriate lighting and environmental protocols that would contribute to improved survival and growth.
Retinal ontogeny of P. innesi larvae was initially described using microspectrophotometry (MSP), a method which determines the spectral absorption properties of photoreceptor cells. In neon tetras, five cone opsins and one rod opsin were identified from sampling time points at 6-, 7-, 11-, 13-, and 21-days post hatch (DPH). Rods were present starting at 6 DPH and through all subsequent days sampled. Cone opsin expression changed over time: blue and violet pigments were present at 6–7 DPH, violet remained at 11 DPH alongside newly detected green and UV opsins, and numerous yellow opsins appeared from 13 DPH onward. While most opsins used A1 pigments, the green opsin consistently utilized A2 pigments. Results from MSP analysis were used to identify treatments in the subsequent spectrum experiment.
Applied experiments manipulating light intensity and spectrum were conducted from 1 – 20 DPH, with measured outcomes of survival, growth, and growth CV. The light intensity experiment compared five light levels (0, 7, 70, 270, 700 lux), with higher survival observed in the 700-lux treatment compared to all other treatments. The spectrum experiment compared four spectra (purple, blue, green, and yellow) to a white light control. The violet treatment resulted in significantly higher survival than in all other treatments, with a 44% increase relative to the white light (control, Figure 1). These results contribute to the development of revised commercial production techniques for P. innesi and provide important insights into improving larval rearing through retinal development.