Shallow-water zooplanktivorous fish rely on their vision for foraging. In shallow water, feeding efficiency decreases in dim light and thus the fish cease foraging at crepuscular hours. Creatures living in the lower parts of their depth ranges are expected to be exposed to limited light levels for longer hours. However, observations of the zooplanktivore Dascyllus marginatus showed little change in foraging duration down to 40. m deep. We asked whether the visual system's functionality changes with depth along the depth range of this damselfish; we examined eye and retina anatomy for changes in visual acuity and light sensitivity and used the optomotor response to test for spatial and temporal light summation. We found only minor changes in the anatomy of the eye that are not expected to affect visual sensitivity or acuity. However, behavioural experiments showed that the deeper water fish's test performance exceeded those of fish in shallow water under lower light levels. We found that deeper water fish responded to the optomotor test at lower light levels and also had more discriminating visual acuity in low light, which can increase their potential reactive distance. The plastic adaptive ability of the visual system to low light levels may explain the fish's ability to inhabit deeper reef habitats and thus expand their depth range limits.
|Number of pages||9|
|Journal||Physiology and Behavior|
|State||Published - Nov 2010|
Bibliographical noteFunding Information:
We thank the Israel Nature and Park Authority for their cooperation, and the Israel Oceanographic and Limnological Research Centre for their help with fish histology. We express our gratitude to R. Kröger for some insightful discussions, A. Alamaru for comments on the manuscript, Naomi Paz for editing and O. Polak for use of his D. marginatus photo. E. Zarafti and M. Ohavia built and helped maintain the optomotor system. Deep dives were accomplished with the aid of O. Ben-Shaprut, O. Ben-Tzvi, S. Einbinder, O. Polak and D. Tobias from the Marine Twilight-zone Research and Exploration (MTRX) centre. We acknowledge NATO 's grant SfP 981883 given to D. Iluz and G. Dishon. This research was supported by the Israel Science Foundation (grant no. 740/04 to SK).
- Gulf of Aqaba
- Spatial summation
- Technical diving
- Temporal summation
- Visual acuity