[b:331fca0568]Can Fish Remember? [/b:331fca0568]

by Dr. Donald McCoy

One question I am routinely asked by professional and pleasure fisherman alike is "Can fish remember?" The answer is a resounding yes! And not only do they have memory, they have several types of memory. Perhaps the most obvious indication that fish possess the capacity to remember is the fact that they can learn! Memory is an important part of learning; without it learning would be impossible. Each "trial" or learning experience would be the same as the last and no improvement in behavior would ever occur. Many experiments have been conducted that prove fish can learn and that they possess both short- and long-term memory systems. Short-term memory is often called active, or working, memory. It pertains to information remembered to complete a particular task, or trial, and it is of limited duration (approximately 30 seconds). Long-term memory, or reference memory, has to do with the retention of information for longer lasting durations such as a day, month, or life time. Long-term memory systems in both humans and animals are not limited to temporal (time) relationships. They can also involve skill-based memories on how to do things (procedural memory). Moreover, memory systems can be based on objects, events, and episodes (episodic memory). Fish seem to remember experiences with predators and prey objects, (episodic memory). In addition, their foraging efficiency (i.e., their ability to catch and handle prey) also improves with practice, indicating the presence of procedural memory.

Many species of fish also have a well-developed memory for places (spatial memory). An amazing example of spatial memory involves several species of tidal water fish that jump from one tidal pool to another at low tide, even though they are unable to see the adjacent pools, and they rarely jump onto dry land. These fish apparently acquire a map of the bottom’s contours as they swim over the area at high tide. Fish also use spatial memory when learning to avoid areas where predators lie in waiting and in developing foraging strategies. Relatedly, bass use spatial memory when using migration routes. A migration route is the specific path fish take as they move from deep to shallow water or vice versa. These patterns seem to be fairly specific in the sense that they are structure-oriented and object-based. Moreover, they seem to persist over several years within an individual, suggesting the capacity for long-term spatial memory in this species.

What about memory for specific baits? Although fishermen are especially interested in this question, it is not a simple issue for several reasons. First, a bait can be both a prey and, if the fish has been hooked on it before, a predator. Second, it is well known that many baits seem to loose their effectiveness over time. This could be due to a "getting-used-to" process that psychologists call habituation. Habituation is a form of learning (i.e., learning to ignore) and, therefore, involves memory. It occurs if the memory of being hooked on a bait is sufficiently reinforced, in this case by repetition. What about examples of fish being hooked numerous times on the same bait? Does this indicate the absence of memory? Probably not. It more likely indicates the presence of other drives such as hunger and territoriality that are stronger than the aversion associated with the memory of the bait.