Can chemical cues act as landmarks in the orientation of the cave fish Phreatichthys andruzzii?

In the constant darkness of cave environments fish locomotion has to be directed by nonvisual spatial information. Four series of tests were done to determine the ability of the hypogean cyprinid Phreatichthys andruzzii Vinciguerra, 1924 to memorize a synthetic chemical cue (morpholine, C(4)H(9)NO), to associate it with an area, to utilize such information for direct locomotory activity, and to determine how long that association is retained in fish memory. Although morpholine acts as neutral stimulus for P. andruzzii, after acclimation in morpholine-scented areas devoid of food resources specimens showed a clear tendency to avoid waters characterized by the odour of that chemical. We hypothesize that an association between odours and trophic characteristics of an area allows the fish to optimize their exploratory activity, as it allows them to recognize areas already experienced to be devoid of trophic resources and to avoid these as unprofitable places. The above association seems to be memorized for a short time; the behavioural response vanishing between 6 and 18 h after the end of the acclimation period. After a certain time has elapsed, it could be profitable to visit the same areas again to verify the incidental availability of new food sources.