The Effects of Increased Temperature on Fish Reproduction
Today, many factors can contribute to an unexpected increase in temperature in streams, ponds, lakes and even oceans. One of the many factors which may cause this is a nuclear power plant. Although many might think that nuclear power is a source of many pollutants, this has been proven not to be so (1). In fact, nuclear power plants only cause one pollutant to the nearby water bodies, increased temperature. Usually this increase in temperature is approximately ten degrees above normal (2). However, this main study is to look at any effects that fish may have because of this increase in temperature. Several studies have been performed in this area, on several different species of fish.
Although most fish respond in the same way, Eurasian Perch, for example, showed interesting side effects. By having an experimental group, which is placed into waters at a temperature of about ten degrees higher than the natural temperature, it is easy to compare to the control group, what physiological problems had occured. During the winter months, fish seek cooler water to perform gametogenesis, that is, sperm and eggs begin to form through meiosis. When spring arrives, these fish head back towards warmer water to spawn (3).
What if the temperature is kept at a constant higher than the control group? One could say that this might cause the fish to think it is in the spawning season. By giving the fish a constant spawning season, the fish's reproductive cycle is knocked out of sequence. For example, suppose a fish normally lives in cold water during the winter months. If the fish is suddenly exposed to warm water during this time period, it may cause problems by changing the season the fish is expecting to have. Can this change to a fish's cycle be harmful?
An experiment performed in 1997 was conducted near a power plant on this issue. Again, power plants are only one of the many factors which can contribute to an unexpected increase in temperature. The main fish tested, Eurasian Perch (Perca Flaveseens), was used to test near the power plant, where the temperature was increased by ten degrees. The control group was kept in the laboratory and kept at the natural temperature the fish would usually experience throughout the year. During the experiment, fish were examined from both groups to see if anything did happen as a result of the different environments (4).
Amazingly, physiological defects in both the fish, and their eggs were found. Although the control group continued to thrive, the experimental group's egg survival rate was very low. Of those that did survive, hatchlings turned out to be much smaller in size. Last of all the most interesting side effect was observed in the female fish of the experimental group. They had developed ovaries at a faster rate than the fish at a natural temperature (5). Perhaps this can also be explained by the same...