The View From the Inside

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Dr. William V. Raszka, our Associate Editor, offers the following insight into a current topic in the news:

For a number of years, our kids have had pet fish. The fish have been housed in aquariums of various sizes; from those that hold a gallon or so to those that hold 40 or more. We had never really paid too much attention to the size of the aquarium but did notice that many of our fish seemed more aggressive than expected. Moreover, the life expectancy of our fish population has been less than anticipated despite paying close attention to the water temperature, pH, and feeding practices.

According to an article in The New York Times (Science: December 26, 2011), part of the problem may be the size of the fish tanks. Evidently, freshwater fish kept in small tanks are substantially more aggressive than those kept in larger ones. Researchers studied young common freshwater fish in two experiments. In one, fish were added to a tank while in the other, three fish were placed in larger tanks with more complex ecosystems. The behaviors were recorded for two hours after feeding. The fish subject to overcrowding became aggressive while the fish placed in the larger tanks demonstrated far less aggressive behavior. Researchers suspect that in their natural environment, fish have places to hide and are not in constant contact with each other.

While other studies have confirmed that overcrowding changes animal behavior, fish owners are unlikely to purchase 100 gallon tanks to keep their fish content. According to the article, even the Humane Society opted not to wade into the issue. On a more practical aspect, overcrowding can affect the health of a fish population. This is most important for commercial fish farms. While some species can tolerate dense living conditions, most do not. Overcrowding can lead to poor fish health and the rapid spread of disease. In Scotland, the farmed salmon are so riddled with sea lice that the government may ban coastal farms. We are not planning to eat any of our pet fish. Still, we avoid buying too many and are content with only two fish for every 20 gallons of water.

Noted by WVR, MD

*This filler excerpt can be found in the April 2012 Pediatrics print journal p. 763, or via online here.