Light-dark transition releases locomotor response in catfish, Ictalurus sp.

R.C. Peters, B. Hoek and W.J.G. van den Loos

Department of Neuroethology, Utrecht University, Utrecht, The Netherlands

Catfish, Ictalurus nebulosus and Ictalurus melas, seek shelter when light levels go up; they leave their hiding place and start swimming around when light levels go down. For a long time we have been using this locomotor response to control behavior in two-alternatives forced-choice experiments, without knowing precisely at what light levels the locomotor responses occur. We investigated and report here how much darkening was needed to induce the swimming response, i.e. to make the fish leave their shelter.

 

Figure 1. Time between dimming the light and the moment a catfish leaves its shelter. The two sets of observations were made by lowering the light levels from 1820 and 5600 lux respectively to the values plotted on the X-axis in the graph above. It follows that the relative change in illumination controls the locomotor behavior.

A single catfish, I. melas, was kept in a circular inflatable plastic basin of 1.2 m diameter, water height 30 cm, with a shelter at the periphery. The arena was illuminated by a 100 W Philips Astralux bulb. We used two different initial light levels, namely 1800 and 5600 lux. Light levels were changed by reducing the power supply of the bulb. At this stage we accepted the change of spectral composition when the light level was changed. A Grundig FA851 infrared sensitive video camera together with a simple black and white TV monitor were used to inspect the behavior of the fish. We made 6 observations per day, 52 in all.

It proved that at both initial light levels the fish responded to a relative reduction of light level from 100 to 5% in 5 s by leaving its shelter in less than a minute (Figure 1). At smaller reductions the response took more than 5 minutes to occur.

This study will be continued by an analysis of the neural connections involved.


Poster presented at Measuring Behavior 2000, 3rd International Conference on Methods and Techniques in Behavioral Research, 15-18 August 2000, Nijmegen, The Netherlands

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