Sex-dependent shifts in visual detection thresholds under turbid conditions in an African cichlid

Turbidity is increasing in freshwaters globally due to human activities
and is known to affect visually-mediated behaviors in fish. As
anthropogenic impacts continue to degrade aquatic environments, it is
critical to determine how sensory systems are affected and what this might
mean for population persistence. We investigated the effect of turbidity
on visual detection thresholds in an African cichlid fish
(Pseudocrenilabrus multicolor) that experiences environmental extremes
across its East African range. We tested the visual abilities of adult
wild-caught fish from two sites representing the extremes of turbidity and
oxygen (a high turbidity, high dissolved oxygen river and a low turbidity,
low dissolved oxygen swamp). Further, we reared offspring of wild-caught
parents from each population in a full-factorial high/low oxygen, high/low
turbidity design to tease apart the influence of each stressor on visual
detection thresholds. We used an optomotor response test to determine
detection thresholds under increasing levels of turbidity for both
wild-caught and lab-reared fish. Detection thresholds were higher in the
wild-caught river population compared to the swamp population, and there
was a strong sex difference, such that wild-caught males had higher
detection thresholds than females, regardless of population of origin. Our
results suggest that there are sex-based differences in contrast detection
abilities that could play a critical role in visual ecology for
populations experiencing divergent turbidity regimes. In the rearing
experiment, sex-based differences in detection thresholds were influenced
by different aspects of the rearing treatment. Detection threshold varied
significantly by oxygen rearing treatment for males and by the interactive
effects of oxygen and turbidity for females. This research improves our
understanding of the effect of elevated turbidity on African cichlid
vision and contributes to growing knowledge of how animals respond to
environmental change. Ethics statement:  All research was
approved by The Ohio State University Institutional Animal Care and Use
Committee (2014A00000055-R1). Permission was given by the Commissioner of
Fisheries Resources Management and Development, Uganda, for export of
fish, and from the Uganda National Council for Science and Technology for
permission to conduct research.