This paper presents a test of time-place learning in fish. Convict cichlids, Cichlasoma nigrofasciatum, were offered food several times a day for 1 O-30 consecutive days. A signal was given 1 min before each food presentation. If the food was always delivered in the same corner of the aquarium, the fish spent 66% of their time in that corner after the signal was given. But if the food was given in different corners throughout the day, each corner being associated with a specific daily time, the fish failed to show preference for the target corner, even after 30 days. Instead they learned which corners yielded food at any time of the day and visited these corners successively after the feeding signal was given. Failure to associate time and place may have been caused by a low cost of travel between corners, a limited number of rewards each day, and/or interference from learning the signal-food association.
Reebs, Departement 3E9.
Reebs and Colgan, 1991).
cent lights. At one end of each aquarium there was a one-way mirror through which observations could be made (lights did not shine on the observer behind the one-way mirror). Lights came on at 0700 h and went off at ‘1900 h. All fish were fed four times a day, at 0830, 1130, 1430, and 1730 h (these times represent the mid-points of each of the 3-h periods that make up a 12-h day). At each feeding session the procedure was the same: first the observer noted which corner of the tank each fish was closest to; then the air supply to the filter was turned off as a signal to the fish that they were about to be fed; at 5-s intervals for the next 60 s, the nearest corner to the fish (or, in the case of groups, the majority of fish) was noted; food (4-5 mg/fish) was then dropped into the appropriate tube; and 2 min later the air pump was restarted.
each tank, this corner was initially chosen at random). This experiment did not test time-place learning per se; rather it tested whether fish could distinguish among corners, a necessary condition for time-place learning. This experiment lasted IO days. In experiment II, the morning (0830 and 1130 h) feeding sessions were both in the same corner (initially chosen at random for each tank, but thereafter remaining the same from day to day) and the afternoon (1430 and 1730 h) sessions were both in the diagonally opposed corner. In experiment III, each of the four feeding sessions was associated with a different corner (initially randomized for each tank), but the associations remained the same from day to day. Experiments II and III lasted 18 days each. The percentage of time spent in each corner was inferred from the scan sampling conducted between signal and food drop. (Scan sampling yields frequency data which can be used to estimate percentage of time spent in various activities or places; see Lehner 1979.) Throughout the paper, ‘target corner’ refers to the corner in which food was going to be dropped. To determine whether time-place learning had taken place, I defined the following criterion: after the feeding signal, a fish had to spend more time in the target corner than in any of the other corners, at all daily feeding times and for two consecutive days. The probability of this happening by chance during a 1 B-day experiment is 0.00026 if we assume a 25% chance of preferring a given corner, or 0.06 if we assume a 50% chance of preferring a given corner (see results of experiment II).
among days. NS = non-significant.
Headings and abbreviations are as in Table 1. Data show the total number of times a fish was found near each corner, added over the last four days of each experiment experiment.
independence among days.
always delivered in the same corner. Data points are the means of four solitary fish and four groups of five fish.
Fig. 2. Percentage of time spent by convict cichlids in the morning target corner (bottom part of each stack) and in the afternoon target corner (top part of each stack) of their aquarium during the min following a feeding signal, at four different times of day (panels) and on consecutive days, when food is always delivered in the same corner in the morning and in the diagonally opposed corner in the afternoon.
Hatched bars indicate the target corner for that particular time of day. Data are the means of four solitary fish and four groups of five fish.
for time-place learning. After the feeding signal was given the fish swam first to the middle of the tank near the filter, and then back and forth from one end of the tank to the other. They did not show a consistent tendency to first go to the target corner, nor did they spend consistently more time in the target half-tank during the minute that followed the feeding signal (Table 5).
periods of the experiments.
‘am’ and ‘pm’ refer to the morning and afternoon feeding session respectively.
learn spatio-temporal tasks. However, the results did not suggest this possibility. From the eighth day on, the percentage of time spent in each corner remained relatively stable; at the very least, there was no indication that it increased simultaneously at all target corners.
may have impeded time-place learning.
First, the ease with which fish could sample the different corners in succession may have made it unnecessary to associate a specific time with a specific corner, even in the distanced-corner experiment. There was little cost to not being in the right place at the right time, as a fish could quickly correct a mistake by swimming to the corner where food had arrived. The only possible cost was in the group situation, where a correctly positioned conspecific could eat most of the food before the other fish arrived. This potential cost was mitigated by the fact that groups tended to remain together during their movements from corner to corner. Second, the use of only four discrete feeding times each day may have unduly limited the number of rewards for the fish and the chances to associate time and place. Finally, the use of a feeding signal led to the formation of a signal-and-food association which may have interfered with the time-place learning task. The fish may have come to rely more on a signal-food association than on a time-place association to obtain food. To circumvent these problems, it would be appropriate to feed the fish more or less continuously for long daily periods, without feeding signals, and successively at places that are widely separated. Such an experiment is in progress. Choice of the study species may also be important. Convict cichlids appear to be omnivorous: in nature they feed on both animal and vegetable matter (Konings, 1989). Yet, because mobile animal prey are more likely to show daily spatio-temporal routines than more sedentary prey, one could expect time-place learning to evolve mostly in strictly carnivorous species feeding on wandering prey. Omnivorous species may simply switch prey rather than switch place when one type of food becomes less abundant geographically. Future studies of time-place learning could use fish species that are piscivorous or insectivorous and fairly specialized in their choice of prey species, as well as species that have to travel long distances during their foraging activities. In the present experiments, convict cichlids spent similar amounts of time in the corners that yielded food at any time of the day. This suggests that the fish adjusted their foraging behaviour to the daily, rather than time-specific, profitability of each corner. A test of this idea would require the use of feeding stations with various degrees of daily profitabilities. For example, one could feed fish twice in the morning in corner A, once in early afternoon in corner B, and once in late afternoon in corner C, and see whether the fish allocate their time between the corners in a 2 : 1 : 1 ratio at all feeding times.
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This paper presents a test of time-place learning in fish. Convict cichlids, Cichlasoma nigrofasciatum, were offered food several times a day for 10-3...