Differences in Optokinetic and Vestibular Ocular Reflex Performance in Teleosts and their Relationship to Different Life Styles

Abstract

Horizontal eye movements in response to vestibular and optokinetic stimulation were investigated in 20 species of marine and fresh water teleosts. Most species performed spontaneous saccadic eye movements in light and in darkness. Successive saccades occurred either at irregular intervals and in different directions (few species), or in bursts of smaller saccades in one direction followed by saccades in the opposite direction (majority of species). Thus, in the latter group the lines of sight shifted cyclically from one side to the other about every 10–15 s. Eye movement responses in goldfish and toadfish were prototypical for two major functional groups. Optokinetic and vestibular nystagmus in the goldfish were much more regular and attained significantly higher gains than in the oyster toadfish. Optokinetic afternystagmus (OKAN) and perVpostrotatory nystagmus lasted about 10–12 s in the goldfish, but only 2–3 s in the oyster toadfish. Bilateral labyrinthectomy in goldfish resulted in optokinetic gains and OKAN durations that were very close to those of intact toadfish. These results indicate the presence (in goldfish) and the absence (in toadfish) of a functioning velocity storage network, respectively. Other non-ostariophysan teleosts failed to show a ''goldfish-like'' response pattern as well. Ostariophysan species differed in their reflex performance as well. A ''gold-fish-like'' response pattern was observed in five of the seven cypriniform species and in two of the four characiform species but not in the four siluriform species. Positively correlated, combined response properties suggest that some species are better equipped for gaze stabilization at higher velocities than other species. These behavioral differences may parallel different specializations in locomotor pattern and mode of life. Absence of a functioning velocity storage network in bottom-dwelling teleosts (as in Amphibia) may be related to the sporadic, slow locomotion of these species and the resulting small requirements for continuous gaze stabilization during self-motion at higher velocities.

Sensitivity of the Goldfish Motion Detection System Revealed by Incoherent Random Dot Stimuli: Comparison of Behavioural and Neuronal Data

“…5A, B). Measured gains are comparable to gains which are reached with a planetarium projector or with a vertical black and white striped optokinetic drum [28]; [29]. When decreasing coherence by 10% steps gains significantly decreased (t-test, p≤0.001), independent from the presented direction.…”

“…Already Dieringer [28] and Easter [29] showed that gains ranged from 0.4 to 0.68 during binocular stimulation in the goldfish and our mean gains obtained by stimulation with 100% coherence are within this interval. Even gain values not very close to unity are sufficient to improve vision, as image drifts up to several degrees per second are tolerated by the visual system and do not lead to blurred vision [30].…”

It is not just size that matters: shark cruising speeds are species-specific

“…The stereo-BRUVS methodology does introduce the possibility that the bait used to lure sharks into the frame may alter the behaviour and therefore cruising speed (Dieringer et al 1992;Maioli 1988). Although bait was present during sampling, speeds were not measured whilst the sharks were feeding or interacting with the bait.…”

Differential central projections of physiologically characterized horizontal semicircular canal vestibular nerve afferents in the toadfish,Opsanus tau

“…The functional significance of keeping the eyes motionless is that the black pupil aperture is often the most conspicuous detail of a camouflaged benthic predator, and restricting eye movements limits the risk of visual detection by potential prey (Lythgoe, 1979). The physiological result is the absence of spontaneous saccades and a resultant weak optokinetic and vestibulo- ocular reflex (VOR) compared with visually active predators (Dieringer et al, 1992). Although it is not certain to what extent all or some of the reflex ocular and skeletomotor behaviors are determined by the pathways through the vestibular-related nuclei, it does provide a foundation on which to interpret the morphophysiology of the vestibular nerve afferents.…”