Visual acuity of snapper Pagrus auratus: effect of size and spectral composition

Abstract

Visual acuity of the commercially important sparid Pagrus auratus was tested using the optomotor response. Juvenile fish were categorized by size as group 1 (50 g), group 2 (100 g), group 3 (150 g), group 4 (300 g), group 5 (500 g) and group 6 (800 g). Group 3 fish demonstrated excellent visual acuity (minimum separable angle, M(SA), 1°), which was improved compared with the smaller fish groups (groups 1 and 2, M(SA), 2°). In the larger fish groups, however, a reduction in visual acuity was observed (groups 4, 5 and 6 M(SA), 4°). Group 2 (100 g) fish displayed positive optomotor responses in long wavelength light (red) but reduced responses in short wavelengths (blue). Red light sensitivity is beneficial for the estuarine lifestyle of these fish, where light is predominantly at long wavelengths. In contrast, group 6 (800 g) fish displayed improved acuity in blue and green light and reduced acuity in red light. Fish of this size move away from the estuary to open oceans, where light is predominantly in the shorter wavelengths (blue-green). These results support the sensitivity hypothesis for the relationship between fish visual systems and the light environment they inhabit.

The effect of motorboat sound on Australian snapper Pagrus auratus inside and outside a marine reserve

“…The waters in which the study was conducted were clear with sufficient light penetrating the water column that artificial lighting was not needed for video recording. However, the visual acuity of the adult snapper that dominated the BUV declines compared to juvenile estuarine fish, (Robinson, Jerrett, Black, & Davison, 2011) which would have lessened the distance that visual detection of the boat was possible. Additionally, on several occasions, the boat's shadow transited through the video recording frame with no startle response elicited by any of the fish, suggesting that visual cues were not precipitating behavior.…”

“…The waters in which the study was conducted were clear with sufficient light penetrating the water column that artificial lighting was not needed for video recording. However, the visual acuity of the adult snapper that dominated the BUV declines compared to juvenile estuarine fish, (Robinson, Jerrett, Black, & Davison, 2011) A range of stressors increasingly threatens reef ecosystems (Ferrari et al, 2015), yet reefs generate important revenue for many countries through tourism and provide food and livelihoods through fisheries. If sufficient resilience is to be retained for reef ecosystems to survive predicted global climate change, managing current, and local environmental stressors has been proposed as an essential goal.…”

Artificial Lighting at Night in Estuaries—Implications from Individuals to Ecosystems

“…Although there is inter-and intraspecific variability in diel foraging among estuarine fishes (Ramirez-Martinez et al 2016), many species (e.g., Lutjanidae) seek refuge in tidal mangroves during the day and migrate at night to feed in soft-bottom habitats. As another example, nocturnal foraging by reef-dwelling grunts (Haemulidae) is temporally partitioned; migration from resting to foraging habitats occurs chronologically for groups at different stages of ocular development (McFarland et al 1979, Robinson et al 2011. The spectral composition of light changes rapidly during dusk, requiring the eye to adjust to a blue-green dominated environment.…”