Nov 10, 2015

Fish Behavior

in the Aquarium and in the Wild
by Stephan Reebs

Fish aren't stupid. It's difficult for us to understand how they really perceive their world, and from that guess what their thinking process might be. But experiments have been made exploring their sensory and cognitive abilities. This information, as the author points out, is usually presented in scientific literature and not often read by the general public. Here the author has taken the trouble to summarize numerous of these experiments (using many different species, both fresh- and saltwater) and presents the findings together, along with his take on their implications. This book demonstrates how much fish can discern, judge risks and rewards and make decisions, even compromises. It starts by detailing what fish can sense of their surroundings and how they do it- using sound, smell, chemical signals (pheromones) and things beyond our normal ken as humans: electricity, magnetism and pressure via the lateral line. Fish can tell time, not just using daylight hours or sun position but an internal clock. They can anticipate a regular feeding time, or in the case of parental cichlids, start gathering up young fry for safekeeping before nightfall (even recognizing the difference between true approaching nightfall and someone turning off the lights at random during the day). Some species can sense the earth's magnetism and use it to navigate. They can judge another fish's size compared to their own and assess the risk of taking on a newcomer in a fight, verses a prior rival with whom they've already settled differences. They can learn things from other fish- where to find food or safety, how to recognize predators. Using the alarm substance of their kin combined with the scent of a predator, hatchery-raised salmon can be taught what dangers to avoid before they are released into the wild. And so on. Most of the experiments described were conducted in enclosed environments and can even be replicated in a home aquarium, but a lot were also done in open rivers, streams, lakes, and even the ocean. It's all really interesting to read about.

Two of my favorite parts of the book: one described the discovery of a fish in San Francisco that is so noisy during the mating season (males calling to attract females) that houseboat residents complained of the buzzing sound. Most were convinced it was mechanical in origin, they couldn't imagine a fish producing such noise. And this passage about a fish that has demonstrated spatial memory is so intriguing I quote it in full:

Spatial memory comes in handy for the small frillfin goby. At low tide, these fish seem to be prisoners of their home tide pool, but when they are chased by mad scientists, they can jump out of their pool and "land" with amazing accuracy in adjacent pools rather than on rocks. Sometimes they jump from pool to pool until they reach open water, a trip that may require up to six different jumps, not all of them in the same direction. This works only when the fish have had a chance to explore the whole area at high tide, when all pools are covered by water and swimming between them is possible. When introduced into an unfamiliar pool at low tide, gobies either refuse to jump or landed wrongly on the rocks. But after only one night of exploring the new pool at high tide, the jumping behavior became accurate again. The most likely hypothesis to explain this fantastic ability is that the shape of each pool is memorized and serves as the main cue for proper orientation toward the next landing place. Memory of such information is long lived: gobies tested in the same pools 40 days later still jumped in the right direction. These experiments came from Laster Aronson of the American Museum of Natural History in New York.

Reading about all these studies on fish reveals a lot about their behavior and preferences. What do fish care about when it comes to choosing a mate or a spawning site? At what point will they choose between food and safety? How do they decide who to hang out with (shoals usually contain fish all of the same size, but sometimes they are comprised of different species). I think anyone who keeps an aquarium should read this book, it sure gave me a lot to think about!

Found browsing at the public library.

Rating: 4/5       252 pages, 2001

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