Blind Mexican cave fish lost their sight over time through lack of light in the water caves that they have inhabited. They rely on their very sensitive lateral line.
Their wonderful memories allow them to map their environment so that they can move around it safely. In this laboratory experiment in Oxford, plastic bricks were placed in a tank. The fish were quickly able to learn the layout, and then re-learn after it was later changed.
LATERAL LINE DETECTS OBJECTS
"As blind Mexican cave fish swim, they create a near-field particle displacement wave ahead of them which is distorted by physical structures in the fish’s path. The resulting change in the flow field around the fish is detected by superficial lateral line neuromasts."
"The cave fish respond to perceived changes in their environment by temporarily accelerating which extends the bow wave and hence the near-field range of the lateral line system. They eventually habituate to the change and reduce their swimming speed as they become familiar with their environment."
ORDER OF LANDMARKS CHANGED IN EXPERIMENTS
"By allowing the fish to learn an array before changing the order of the landmarks, it is possible to test whether order is encoded in the fish’s spatial map."
"Between each trial the landmarks were raised out of the water to control for experimental manipulation. The sequence remained the same during each set of training trials but was varied at random between fish and treatments."
"The fish become familiar with an artificial landmark array of four weighted plastic bricks (2 cm x 1.5 cm) after 6–8 trials."
FISH WERE QUICKLY ABLE TO MEMORISE A CHANGED MAP OF THEIR SURROUNDINGS
"The fishes demonstrated unequivocally that they had perceived the change ... showing that they do have an internal representation of order."
"The results of this study show that the order of the sequence of places could be learnt and stored as an internal representation of space. The fish would be able to orient efficiently by sensing its surroundings using the lateral line system to identify its current location, and then remember the place that follows. The spatial map would therefore be based upon ordered lists of learnt places through which the fish could pilot."