Influence of magnetic field on zebrafish activity and orientation in a plus maze.

We describe an impact of the geomagnetic field (GMF) and its modification on zebrafish's orientation and locomotor activity in a plus maze with four arms oriented to the north, east, south and west. Zebrafish's directional preferences were bimodal in GMF: they visited two arms oriented in opposed directions (east-west) most frequently. This bimodal preference remained stable for same individuals across experiments divided by several days. When the horizontal GMF component was turned 90° clockwise, the preference accordingly shifted by 90° to arms oriented to the north and south. Other modifications of GMF (reversal of both vertical and horizontal GMF components; reversal of vertical component only; and reversal of horizontal component only) did not exert any discernible effect on the orientation of zebrafish. The 90° turn of horizontal component also resulted in a significant increase of fish's locomotor activity in comparison with the natural GMF. This increase became even more pronounced when the horizontal component was repeatedly turned by 90° and back with 1min interval between turns. Our results show that GMF and its variations should be taken into account when interpreting zebrafish's directional preferences and locomotor activity in mazes and other experimental devices.

Lateralisation of rotational swimming but not fast escape response in the juvenile sterlet sturgeon, Acipenser ruthenus (Chondrostei: Acipenseridae).

For the first time, behavioural lateralisation was shown in a chondrostean fish (sterlet sturgeon Acipenser ruthenus). A significant directional bias was found in young A. ruthenus swimming along a circular swimway. This laterality manifested itself as an individual preference for a certain movement direction (either clockwise or counterclockwise) which was consistent at the retest 10 days later. On the other hand, no significant rotational bias was observed at the population level. The same sterlet individuals displayed the C-start (the first stage of escape response) elicited by sudden low-frequency sound vibrations (50 Hz). However, the experiments failed to reveal either individual or population laterality of this response: the frequencies of leftward and rightward bends in startled fish were virtually equal. These results demonstrate that the two types of laterality can be independent in fish.

Individual-level consistency of different laterality measures in the goldbelly topminnow.

In humans, hemispheric language dominance is, to some degree, associated with handedness. Significant associations have been reported between several other lateralized functions. Much less is known about the organization of cerebral asymmetries in nonhuman species and, in particular, whether the presence of reversed asymmetry of one function is associated with a reversal of other lateralized functions or, instead, if cognitive functions lateralize independently. In this study, we compare four measures of sensory and motor laterality in the same individuals in a sample of goldbelly topminnows. A significant association was found between two measures of eye preference and two measures of motor laterality, but sensory and motor asymmetries were uncorrelated. We found interesting that individuals preferring to examine a predator with the right eye tended to use the left eye to look at a shoal mate and the reverse was true for fish that monitored predators with the left eye. This complementarity of functions could be adaptively advantageous for a small social fish, because it allows an individual to monitor the movements of its shoal mates with one eye as the other eye remains free to scan the surroundings for the presence of predators.